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NAME
xv - interactive image display for the X Window System
SYNTAX
xv [options] [filename [filename...]]
NOTE
This man page is merely the text portion of the (PostScript) xv docs,
without the figures, and without the appendicies. As such, it is
highly recommended that you get your hands on the *real*
documentation.
DESCRIPTION
xv is an X11 program that displays images in the GIF, PBM, PGM, PPM,
X11 bitmap, JPEG, Sun Rastefile, and PM formats on 1-, 4-, 6-, 8-,
16-, 24-, and 32-bit X displays. xv will also read compress-ed
versions of these files.
SECTION 1: OVERVIEW
xv lets you do a large number of things (many of them actually
useful), including, but not limited to, the following:
o+ display an image in a window on the screen
o+ display an image on the root window, in a variety of styles
o+ arbitrarily stretch or compress the image
o+ rotate the image in 90-degree steps
o+ flip the image around the horizontal or vertical axes
o+ crop a rectangular portion of the image
o+ magnify any portion of the image by any amount, up to the size of
the screen
o+ determine pixel values and x,y coordinates in the image
o+ adjust image brightness and contrast with a gamma correction
function
o+ apply different gamma functions to the Red, Green, and Blue color
components, to correct for non-linear color response
o+ adjust global image saturation
o+ perform global hue remapping
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o+ edit an image's colormap
o+ reduce the number of colors in an image
o+ dither in color and b&w
o+ smooth an image
o+ crop off solid borders automatically
o+ convert image formats
o+ generate Encapsulated PostScript Unfortunately the Automatic
Checkbook Balancing Module still isn't completely debugged, and is
not included in this distribution.
SECTION 2: STARTING XV
Note: unless explicitly stated otherwise, the term click means "click
with the Left mouse button."
Start the program up by typing 'xv'. After a short delay, a window
will appear with the default image (the xv logo, credits and revision
date) displayed in it. If you change the size of the window (using
whatever method your window manager provides), the image will be
automatically stretched to fit the window.
Section 2.1: Displaying Pixel Values
Clicking (and optionally dragging) the Left mouse button inside this
window will display pixel information in the following format:
196, 137 = 191,121,209 (287 42 81 HSV) The first pair of numbers
(196,137) are the x and y positions of the cursor, in image
coordinates. These numbers remain the same regardless of any
image resizing, or cropping. For example, if you click on the
eye of the fish on the right side of the default image, you'll
get (approximately) 251,129 regardless of the size of the
displayed image. This allows you to zoom in for precise
measurements.
The first triplet of numbers (191,121,209) are the RGB values of
the selected pixel. The components will have integer values in
the range 0-255. The values displayed are prior to any HSV/RGB
modification, but after any colormap changes. See "Section 5:
The Color Editor" for details.
The second triplet of numbers (287 42 81) are the HSV values of
the selected pixel. The first component will have integer values
in the range 0-359, and the second and third components will have
integer values in the range 0-100. The values displayed are
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prior to any HSV/RGB modification, but after any colormap
changes. See "Section 5: The Color Editor" for details. Also,
see "Appendix D: RGB and HSV Colorspaces" for more information
about what these numbers mean.
Note: If you actually want to measure some pixels, it will
probably help to crop to a small region of your image, and expand
that region to the point where you can see the individual pixels.
This string is automatically copied to your X server's cut buffer
whenever you measure pixel values. This lets you easily feed
this information to another program, useful if you're doing
manual feature extraction, or something. Try it: measure a
pixel's value, and then go click your Middle mouse button in an
xterm window.
Section 2.2: Cropping
Bring up the xv controls window by typing the '?' key or clicking the
Right mouse button inside the image window.
Clicking and dragging the Middle button of the mouse inside the image
window will allow you to draw a cropping rectangle on the image. If
you're unhappy with the one you've drawn, simply click the Middle
button and draw another. If you'd like the rectangle to go away
altogether, click the Middle button and release it without moving the
mouse.
You can determine how large the cropping rectangle is (in image
coordinates) by bringing up the xv info window. Do this by clicking
the Info button in the xv controls window or by typing the 'i' key
into any open xv window.
The xv info window will display, among other things, the current size
and position of the cropping rectangle in terms of image coordinates.
For example, if it says:
114x77 rectangle starting at 119,58 that would mean that the
current cropping rectangle is 114 image pixels wide, 77 image
pixels high, and its top-left corner is located 119 image pixels
in from the left edge of the image, and 58 image pixels in from
the top edge. These values will be updated as you drag the
cropping rectangle around.
If you want to set the size or position of the cropping rectangle
precisely, you can use the arrow keys on your keyboard. First,
make the xv info window visible as described above (if it's not
already visible). Second, use the mouse to draw a rough
approximation of the cropping rectangle that you want. You can
now use the arrow keys to move the cropping rectangle around the
image. Once you've gotten the top and left sides of the cropping
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rectangle precisely where you want them, you can move the
bottom-right corner of the cropping rectangle (only) by holding
the <shift> key down while using the arrow keys. Pressing the up
arrow will make the rectangle shorter, and pressing the down
arrow will make the rectangle taller.
Once you have a cropping rectangle that you can live with, you
can proceed with the actual cropping operation. Click the Crop
button in the xv controls window, or type the 'c' key in any open
xv window. The image window will shrink to show only portions of
the image that were inside the cropping rectangle.
Note: if you are running a window manager such as mwm, which
decorates windows with a title bar, resizing regions, and such,
it is quite possible that the aspect ratio of the cropped image
will get screwed up. This is because certain window managers
enforce a minimum window size. If you try to crop to a rectangle
that is too small, the window manager will create the smallest
window it can, and the image will be stretched to fit this
window. If this happens, you can press the Aspect button in the
xv controls window, or type the 'a' key in any open xv window.
This will expand the image so that it has the correct aspect
ratio again.
You can crop a cropped image by repeating the same steps (drawing
a new cropping rectangle and issuing the Crop command), ad
infinitum.
You can return to the original, uncropped image by using the
UnCrop command. Simply click the UnCrop button or type the 'u'
key in any open xv window.
Note that if you try to make the cropping rectangle too small in
either width or height (under 5 screen pixels), it'll just turn
itself off. If you want to crop a very small portion of an
image, you'll probably have to do it in two passes. First, crop
to a small (but large enough to still be enabled) rectangle,
expand that region, then crop again.
SECTION 3: THE CONTROL WINDOW
The xv controls window is the central point of control for the
program, hence the name. It provides controls to resize the current
image, flip and rotate it, load and save different files, and bring up
the other xv windows. It can be brought up by clicking the Right
mouse button in the image window, or by typing the '?' key inside any
open xv window. Doing either of these things while the xv controls
window is visible will hide it.
All of the following commands may be executed by either clicking the
appropriate command button, or typing the keyboard equivalent (where
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given) into any open xv window.
Section 3.1: Resizing Commands
Note that none of the 'resizing' commands modify the image in any way.
They only affect how the image is displayed. The image remains at its
original size. This allows you to arbitrarily stretch and compact the
image without compounding error caused by earlier resizing. In each
case, the displayed image is recomputed from the original internal
image.
Normal (Keyboard equivalent 'n')
Attempts to return the image to its normal size, where one image
pixel maps to one screen pixel. For example, if the image (or
the current cropped portion of the image) has a size of 320x200,
this command will attempt to make the image window be 320 screen
pixels wide by 200 screen pixels high.
This command may fail in two cases. If you're running a window
manager (such as mwm) that enforces a minimum window size, and
the 'normal' size is too small, the image may get distorted. See
the note in "Section 2.2: Cropping" for more information.
Also, if the image is larger than the size of your screen, it
will be 'halved' until it fits on the screen. For example, if
you try to display a 1400x900 image on a 1280x1024 screen, the
Normal command will display a 700x450 image.
Max Size (Keyboard equivalent 'm')
This command will make the displayed image be the same size as
the screen. If you are running a window manager that puts up a
titlebar, you'll find that the titlebar is now off the top of the
screen. To get the titlebar back, simply shrink the image to
anything smaller than the size of the screen. The window will be
moved so that the titlebar is once again visible.
Maxpect (Keyboard equivalent 'M')
Makes the image as large as possible, while preserving the aspect
ratio. This avoids the generally unwanted image distortion that
Max Size is capable of generating. For example, if you have a
320x200 image, and an 1280x1024 screen, doing the Maxpect command
will result in an image that is 1280x800. Max Size, on the other
hand, would've generated an image of size 1280x1024, which would
be appear 'stretched' vertically.
Dbl Size (Keyboard equivalent '>')
Doubles the current size of the image, with the constraint that
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neither axis is allowed to be larger than the screen. For
example, given a 320x200 image and a 1280x1024 screen, the image
can be doubled once (to 640x400), a second time (to 1280x800),
but a third time would make the image 1280x1024. You'll note
that on the third time, the width didn't change at all, since it
was already at its maximum value. Also note that the height
wasn't allowed to double (from 800 to 1600), but was truncated at
its maximum value (1024).
Half Size (Keyboard equivalent '<')
Halves the current size of the image, with the constraint that
neither axis is allowed to have a size less than 1 pixel. Also,
you may run into 'minimum size' problems with your window
manager. See the note in "Section 2.2: Cropping" for more
information.
Note that the window size is maintained as a pair of integers.
As a result you may see some integer round-off problems. For
example, if you halve a 265x185 image, you'll get a 132x92 image,
which is just fine. However, if you Dbl Size this image, you'll
get a 264x184 image, not the 265x185 image you might have
expected.
+10% (Keyboard equivalent '.')
Increases the current size of the image by 10%, subject to the
constraint that the image cannot be made larger than the screen
size (in either axis). For example, issuing this command on a
320x200 image will result in a 352x220 image.
-10% (Keyboard equivalent ',')
Decreases the current size of the image by 10%. Neither axis of
the image is allowed to shrink below 1 pixel. Also, you run the
risk of running into 'minimum window size' problems with your
window manager.
It should be noted that the +10% and -10% commands have no
concept of an 'original size'. They simply increase or decrease
the current image size by 10%. As a result, they do not undo
each other. For example, take a 320x200 image. Do a +10% and
the image will be 352x220. If you issue the -10% command now,
the image will be made (352 - 35.2)x(220 - 22), or 316x198.
4x3 (Keyboard equivalent '4')
Attempts to resize the image so that the ratio of width to height
is equal to 4 to 3. (e.g., 320x240, 400x300, etc.) This is
useful because many images were meant to fill the screen of
whatever system they were generated on, and nearly all video
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tubes have an aspect ratio of 4:3. This command will stretch the
image so that things will probably look right on your X display
(nearly all of which, thankfully, have square pixels). This
command is particularly useful for images which have really
bizarre sizes (such as the 600x200 images presumably meant for
CGA, and the 640x350 16-color EGA images).
Aspect (Keyboard equivalent 'a')
Applies the 'default aspect ratio' to the image. This is done
automatically when the image is first loaded. Normally, the
default aspect ratio is '1:1', but certain GIF files may have an
aspect ratio encoded in them. You can also set the default
aspect ratio via a command-line argument or an X resource. See
'Section 9: Modifying XV Behavior' for more info. The idea
behind this command is that you'd stretch the image manually (via
your window manager) to roughly the size you'd like, and then use
the Aspect command to fix up the proportions.
Normally Aspect expands one axis of the image to correct the
aspect ratio. If this would result in an image that is larger
than the screen, the Aspect command will instead shrink one of
the axes to correct the aspect ratio.
Section 3.2: Rotate/Flip Commands
Turn CW (Keyboard equivalent 't')
Rotates the image 90 degrees clockwise.
Turn CCW (Keyboard equivalent 'T')
Rotates the image 90 degrees counter-clockwise.
Flip H (Keyboard equivalent 'h')
Flips the image horizontally (around the vertical center-line of
the image).
Flip V (Keyboard equivalent 'v')
Flips the image vertically (around the horizontal center-line of
the image).
Section 3.3: Smoothing Commands
Raw (Keyboard equivalent 'r')
Returns the displayed image to its 'raw' state (where each pixel
in the displayed image is as close as possible to the
corresponding pixel in the internal image). In short, it turns
off any dithering or smoothing. When dithering or smoothing
haven't been done, this command is disabled.
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Dither (Keyboard equivalent 'd')
Regenerates the displayed image by dithering with the available
colors in an attempt to approximate the original image. This is
only relevant if the color allocation code failed to get all the
colors it wanted. If it did get all the desired colors, the
Dither command will just generate the same display image as the
Raw command. On the other hand, if you didn't get all the
desired colors, the Dither command will try to approximate the
missing colors by dithering with the colors that were obtained.
If you're running xv on a 1-bit display the Dither command will
be disabled, as the image will always be dithered for display.
Smooth (Keyboard equivalent 's')
Smooths out distortion caused by integer round-off when an image
is expanded or shrunk. This is generally a desirable effect,
however it is fairly time-consuming on large images on most
current workstations. As such, by default, it is not done
automatically. See "Section 9: Modifying XV Behavior" for more
details.
Section 3.4: Cropping Commands
Crop (Keyboard equivalent 'c')
Crops the image to the current cropping rectangle. This command
is only available when a cropping rectangle has been drawn on the
image. See "Section 2.2: Cropping" for further information.
UnCrop (Keyboard equivalent 'u')
Returns the image to its normal, uncropped state. This command
is only available after the image has been cropped. See "Section
2.2: Cropping" for further information.
AutoCrop (Keyboard equivalent 'A')
Crops off any constant borders that exist in the image. It will
crop to the smallest rectangle that encloses the 'interesting'
section of the image. It may not always appear to work because
of minor invisible color changes in the image. As such, it works
best on computer-generated images, and not as well on scanned
images.
Section 3.5: The Display Modes Menu
In addition to displaying an image in a window, xv can also display
images on the root (background) window of your X display. There are a
variety of ways that xv can display an image on the root window. The
Display Modes popup menu lets you select where (and how) xv will
display the image.
- 8 - Formatted: September 27, 1994
Click on the Display Modes button in the xv controls window, and hold
the mouse button down. This will cause the Display Modes menu to pop
up. The current display mode will be shown with a check mark next to
it. To select a new mode, drag the mouse down to the desired mode,
and release the mouse button.
It is not possible for xv to receive button presses or keyboard
presses in the root window. As such, there are several functions that
cannot be used while in a 'root' mode, such as pixel tracking and
image cropping. If you want to do such things, you'll have to
temporarily return to 'window' mode, and return to 'root' mode when
you're finished. Also, when you are in a 'root' mode, you will not be
able to get rid of the xv controls window. At best you can iconify it
(using your window manager). (The reason for this is that if you ever
got rid of it there'd be no way to get it back.)
Window
Displays the image in a window. If you were previously in a
'root' mode, the root window will also be cleared.
Root: Tiled
The image is displayed in the root window. One image is
displayed aligned with the top-left corner of the screen. The
image is then duplicated towards the bottom and right edges of
the screen, as many times as necessary to fill the screen.
Root: Integer Tiled
that the image is first shrunk so that its width and height are
integer divisors of the screen's width and height. This keeps
the images along the bottom and right edges of the screen from
being Normal, Dbl Size, etc.) will lose the 'integer'-ness of the
image.
Root: Mirrored
Tiles the original image with versions that have been
horizontally flipped, vertically flipped, and both horizontally
and vertically flipped. This gets rid of the sharp dividing
lines where tiled images meet. The effect is quite interesting.
Root: Integer Mirrored
Like Root: Mirrored, but also does the integer-ization described
under the Root: Integer Tiled entry.
Root: Center Tiled
Like Root: Tiled, but it positions the images so that one of them
- 9 - Formatted: September 27, 1994
is centered on the screen, and the rest are tiled off in all
directions. Visually pleasing without the image size distortion
associated with Root: Integer Tiled.
Root: Centered
Displays a single image centered in the root window, surrounded
by black.
Root: Centered, Warp
Displays a single image centered in the root window, surrounded
by a black and white 'warp' pattern, which produces some mildly
visually pleasing Moire effects.
Root: Centered, Brick
Displays a single image centered in the root window, surrounded
by a black and white 'brick' pattern.
Note: The three 'centered' modes (Root: Centered, Root: Centered,
Warp, and Root: Centered, Brick, but not Root: Center Tiled)
require the creation of a Pixmap the size of the screen. This
can be a fairly large request for resources, and will fail on a
color X terminal with insufficient memory. They can also require
the transmission of considerably more data than the other 'root'
modes. If you're on a brain-damaged X terminal hanging off a
slow network, you should probably go somewhere else. Barring
that, you should certainly avoid the 'centered' modes.
Also note: If you quit xv while displaying an image on the root
window, the image will remain in the root window, and the colors
used by the image will remain allocated. This is generally
regarded as correct behavior. If you decide you want to get rid
of the root image to free up resources, or simply because you're
sick of seeing it, the quickest route is to use run 'xv -clear',
which will clear the root window, release any allocated colors,
and exit. Alternately, xsetroot and any other X program that
puts things in the root window should be able to do the trick as
well.
Section 3.6: Working With Multiple Files
xv provides a a set of controls that let you conveniently operate on a
list of images. To use the following commands, you'll have to start
up xv with a list of filenames. For example, you could type 'xv
*.gif' (assuming, of course, that you have a bunch of files that end
with the suffix '.gif' in the current directory).
The filenames are listed in a scrollable window. The current
selection is shown in reverse video. If there are more names than
- 10 - Formatted: September 27, 1994
will fit in the window, the scrollbar will be enabled.
Section 3.6.1: Operating a List Window
The scrollbar operates as follows:
o+ clicking in the top or bottom arrow of the scrollbar scrolls the
list by one line in the appropriate direction. It will continue to
scroll the list as long as you hold the mouse down.
o+ The thumb (the small white rectangle in the middle of the
scrollbar) shows roughly where in the list you are. You can change
your position in the list by clicking and dragging the thumb to
another position in the scrollbar.
o+ You can scroll the list up or down a page at a time by clicking in
the grey region between the thumb and the top or bottom arrows. If
you click on a name in the list, that name will become highlighted.
You can drag the highlight bar up and down, and the list will
scroll appropriately.
It is also possible to control the list window from the keyboard.
In all cases, you must make sure that the window sees the keypress.
Generally, this means you have to have the cursor inside the
window, though your window manager may also require you to click
inside the window first.
o+ The up and down arrow keys move the highlight bar up and down. If
the bar is at the top or bottom of the window, the list will scroll
one line.
o+ The page up and page down keys scroll the list up or down a page at
a time.
o+ Pressing the home key will jump to the beginning of the list.
Pressing the end key will jump to the bottom of the list.
Section 3.6.2: The File Commands
You can directly view any image in the list by double-clicking on its
filename. If xv is unable to load the file (for any of a variety of
reasons), it'll display an error message and put up the default image,
the xv logo.
Next (Keyboard equivalent <space>)
Attempts to load the next file in the list. If it is unable to
load the next file, it will continue down the list until it
successfully loads a file. If it gets to the bottom of the list
without successfully loading a file, it will put up the default
image.
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Previous (Keyboard equivalent <backspace>)
Attempts to load the previous file in the list. If it is unable
to load the previous file, it will continue up the list until it
successfully loads a file. If it gets to the top of the list
without successfully loading a file, it will put up the default
image.
Delete (Keyboard equivalent <ctrl-D>)
This command lets delete the currently selected file from the
list (and optionally delete the associated disk file). Note that
the currently selected file is the one with the highlight bar on
it. While this is generally the same as the currently displayed
image, it doesn't have to be.
The Delete command will pop-up a window asking you what you want
to delete. Your choices are:
o+ List Entry, which will remove the highlighted name from the
list. (Keyboard equivalent: the enter key)
o+ Disk File, which will remove the highlighted name from the
list and also delete the associated disk file. This removes
unwanted images, just like manually typing 'rm <filename>' in
another window. (Keyboard equivalent: <ctrl-D>)
o+ Cancel, which lets you get out of the Delete command without
actually deleting anything. (Keyboard equivalent: the esc
key)
Section 3.7: Other Commands
Info (Keyboard equivalent 'i')
Opens and closes the xv info window. See "Section 4: The Info
Window" for more details.
ColEdit (Keyboard equivalent 'e')
Opens and closes the xv color editor window. See "Section 5: The
Color Editor" for more details.
Load (Keyboard equivalent <ctrl-L>)
Opens the xv load window. See "Section 6: The Load Window" for
more details.
Save (Keyboard equivalent <ctrl-S>)
Opens the xv save window. See "Section 7: The Save Window" for
more details.
- 12 - Formatted: September 27, 1994
Quit (Keyboard equivalent 'q')
Quits out of the program.
SECTION 4: THE INFO WINDOW
Section 4.1: Overview
xv provides a window to display information about the current image,
color allocation, expansion, cropping, and any error messages. This
window can be opened by issuing the Info command. (Click on the Info
button in the xv controls window, or type 'i' in any open xv window.)
You can close the window by using the Info command while the window is
open. You can also close the window by clicking anywhere inside it.
The top portion of the window displays the program name, revision
date, and patchlevel. It also shows the University of Pennsylvania
shield, the GRASP Lab logo, the copyright notice, and of course, the
author's name.
Section 4.2: The Fields
The "Filename" field displays the name of the currently loaded file.
The name is displayed without any leading pathname. If there is no
currently loaded image (you're looking at the default image) this
field will display "<none>".
The "Format" field displays information describing what image format
the file is stored in, and how large the file is (in bytes).
The "Resolution" field shows the width and height (in image pixels) of
the loaded image. Note that this does not necessarily have anything
to do with the size of the image currently displayed on your screen.
These numbers do not change as you modify the display image.
The "Cropping" field displays the current state of any cropping
activity. If you are looking at the entire (uncropped) image, and
there is no cropping rectangle drawn, this field will show "<none>".
If you draw a cropping rectangle, or if you are viewing cropped
portion of image, this field will display something like "247x128
rectangle starting at 132,421". See "Section 2.2: Cropping" for more
details.
The "Expansion" field gives you information about how the image is
displayed. It will display something like "1.58 x 1.37 (505 x 273)".
This tells you that the current displayed image is 505 pixels wide and
273 pixels high, and that it is 1.58 times wider and 1.37 times higher
than the internal image (which, in this case, had a size of 320x200).
The "Colors" field gives you detailed information on how well (or
poorly) color allocation went. If everything went reasonably well it
will display something like:
- 13 - Formatted: September 27, 1994
Got all 67 desired colors. (66 unique) This means that 67
entries in the image's colormap were used in the image, but that
only 66 of these colors were different, as far as the X server
was concerned.
See "Appendix E: Color Allocation" for a complete discussion of
how colors are allocated, and what the "Colors" field can tell
you.
Note that the fields are filled in as information becomes
available. As such, they can be used as a rough 'progress
indicator' when loading images. When you begin loading, all the
fields are cleared. Once the image has been successfully loaded,
the top three fields (Filename, Format, Resolution) are filled
in. Once the colors have been allocated, and the display image
generated, the bottom three fields are shown (Cropping,
Expansion, and Colors).
Section 4.3: Status Lines
The bottom two lines in the info window display various error
messages, warnings, and status information. These two lines are also
duplicated in the xv controls window.
The upper line is the more commonly used. It normally displays a
one-line summary of the current image and color allocation success.
If an error occurs, it will be displayed on this line as well.
The lower line is used to display warning messages.
SECTION 5: THE COLOR EDITOR
Section 5.1: Overview
The xv color editor provides a powerful system for manipulating color
images. Since there are many different reasons why a person would
want to modify an image's colors, and many different types of images
that may need modification, there is no one color manipulation tool
that would be 'best' for all purposes. Because of this problem, xv
gives the user three different color tools, all of which can be used
simultaneously.
o+ Colormap Editing: This tool lets you arbitrarily modify individual
colormap entries. Useful for modifying the color of captions or
other things that have been added to images. Also works well on
images that have a small number of colors, such as images generated
by 'drawing' or CAD programs. It's also an easy way to spiff up
boring 1-bit black and white images.
o+ HSV Modification: This tool lets you alter the image globally in
the HSV colorspace. (See "Appendix D: RGB and HSV Colorspaces" for
more info.) Here are examples of the sort of things you can do
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with this tool:
o+ turn all the blues in an image into reds
o+ change the tint of an image
o+ change a greyscale image into a mauve-scale image
o+ increase or decrease the amount of color saturation in an image
o+ change the overall brightness of an image
o+ change the overall contrast of an image
o+ RGB Modification: This tool lets you route the red, green, and blue
color components of an image through independent mapping functions.
The functions can either be the standard gamma function, or any
arbitrary function that can be drawn with straight line segments or
a cubic spline. See "Section 5.3.4: The Intensity Graph" for more
info about graph functions. The major use of the RGB Modification
tool is to correct for the differing color response curves of
various color monitors, printers, and scanners. This is the tool
to use when "the image is too red", for instance.
These three tools are tied together in a fixed order. The Colormap
Editing tool operates on the original colors in the image. The
output of this tool is piped into the HSV Modification tool. Its
output is piped into the RGB Modification tool. The output from
the RGB Modification tool is what actually gets displayed.
In addition there is a collection of buttons that control the xv
color editor as a whole (more or less).
Don't Panic! It's not as complicated as it looks.
Section 5.2: The Colormap Editing Tool
The top portion of this window shows the colormap of the current
image. There are 16 cells across, and up to 16 rows down, for a
maximum of 256 color cells. Only cells actually used somewhere in the
image are shown in this array.
The currently selected color cell is shown with a thick border. You
can change the selection by clicking anywhere in the array. If you
drag the mouse through this area, you'll see the dials at the bottom
change to track the current pixel values.
You can also select a color cell by clicking anywhere in the image
window. Whichever pixel value you were on when you let go of the
mouse will become the new selected color cell.
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Since certain images will have many colors that are the same, or
nearly the same, it is sometimes convenient to group color cells
together. Grouped color cells all take on the same color, and
changing any one of them affects all of the other colors in the group.
To group color cells together, do the following:
o+ Hold down the <shift> key.
o+ Left click on one color cell that you would like to be in the group
o+ Right click on other color cells that you wish to be in this group.
(Right clicking on cells that are already selected will de-select
them.)
o+ Release the <shift> key when you're done. You can create as many
groups as you like.
You can use this grouping/ungrouping technique to copy colors from
one color cell to another. Left click on the source color cell,
Right click on the destination color cell, and Right click on the
destination color cell again (to ungroup it).
Section 5.2.1: Using the Dial Controls
At the bottom the Colormap Editing tool are three dials that let you
set the color of the current color cell (or group of cells). By
default, the dials control the Red, Green, and Blue components of the
RGB colorspace, but they can also control the Hue, Saturation, and
Value components of the HSV colorspace. (The RGB/HSV button controls
this.)
Regardless of what they control, all dials in xv work the same way.
Clicking on the single arrows increase/decrease the value by 1.
Clicking on the double arrows increase/decrease the value by a larger
amount (16 in this case). If you click on one of the arrows, and hold
the mouse button down, the increase/decrease will repeat until you
release the mouse button.
You can also click in the general area of the pointer and simply drag
it to the position you want. The further your mouse cursor is from
the center of the dial, the more precise the control will be. While
dragging, you do not have to keep the cursor inside the dial window.
Section 5.2.2: Colormap Editing Commands
ColUndo
Undoes the last change made to the colormap that resulted in a
color cell changing value. This includes grouping and ungrouping
color cells, and changing any of the dials.
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Revert
Undoes all color changes. Returns the colormap to its original
state. Destroys any groups that you may have created.
RGB/HSV
Toggles the Colormap Editing dials between editing colors in
terms of Red, Green, and Blue, and editing colors in terms of
Hue, Saturation, and Value.
Grey Turns color images into greyscale images by changing the
colormap. This replaces each color cell with a greyscale
representation of itself. Use the Revert command to restore the
colors.
RevVid
This command behaves differently, depending on the setting of the
RGB/HSV mode. (You can tell which mode you're in by the titles
on the dials.)
In RGB mode, each color component is separately 'inverted'. For
example, Yellow (which is composed of full red, full green, and
no blue) would turn to Blue (no red, no green, full blue).
In HSV mode, only the Value (intensity) component is 'inverted'.
The Hue and Saturation components remain the same. In this mode,
bright colors turn to dark versions of the same color. For
example, a Yellow would turn Brown.
Random
Generates a random colormap. This is of questionable usefulness,
but it will occasionally come up with pleasing color combinations
that you never would've come up with yourself. So it stays in.
It works best on images with a small number of colors. Note that
it respects cell groupings, so if your image has a lot of colors,
you can create a few large groups and then use the Random
command.
Note: It is HIGHLY RECOMMENDED that if you're using the Colormap
Editing tool, you do NOT use the HSV Modification tool or the RGB
Modification tool as well. If you do, the results can be quite
confusing. For example, you might edit a color cell, and set its
color values to produce a purple. However, because of HSV/RGB
Modification further down the line, the actual color displayed on
the image (and in the color cell) is yellow. Very confusing,
indeed.
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Section 5.3: The HSV Modification Tool
There are four separate controls in the HSV Modification tool. At the
top of the window are a pair of circular controls that handle hue
remapping. Lower down is a circular control that maps 'white' (and
greys) to a specified color. There is a dial control that lets you
saturate/desaturate the colors of the current information. Finally,
at the bottom there is a graph window that lets you modify intensity
values via an arbitrary remapping function.
Section 5.3.1: Hue Remapping Controls
These two dials are used to define a source and a destination range of
hue values. Every hue in the source range (defined in the From dial)
gets mapped to the value of the corresponding point in the destination
range (defined in the To dial).
Each dial has a pair of radial lines with handles at their ends.
Between the two lines an arc is drawn with an arrow at one end. The
wedge drawn by these lines and the arc defines a range of values (in
degrees). The direction of the arc (clockwise, or counter-clockwise)
determines the direction of this range of values (increasing or
decreasing).
Distributed around the dial are tick marks and the letters 'R', 'Y',
'G', 'C', 'B', and 'M'. These letters stand for the colors Red,
Yellow, Green, Cyan, Blue, and Magenta, and they show where these
colors appear on the circle.
The range is shown numerically below the control. By default the
range is '330, 30 CW'. This means that a range of values [330, 331,
332, ... 359, 0, 1, ... 28, 29, 30] has been defined. Note that
(being a circle) it wraps back to 0 after 359.
The range can be changed in many different ways. You can click on the
'handles' at the end of the radial lines and move them around. If you
click inside the dial, but not on one of the handles, you'll be able
to drag the range around as a single object. There are also 5 buttons
below the dial that let you rotate the range, flip the direction of
the range, and increase/decrease the size of the range while keeping
it centered around the same value.
In its default state, the To dial is set to the same range as the From
dial. When the two dials are set to the same range, they are
effectively 'turned off', and ignored.
An example of hue remapping:
o+ As a simple example of the sort of things you can do with the hue
remapping control, we'll change the background color of the default
(xv logo) image without changing any other colors in the image.
Since the background is composed of a gradient of 64 colors, you
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would not want to do this with the Colormap Editing tool. It would
take forever.
o+ First, get the default image up on the screen by running 'xv'
without giving any filenames. Open up the xv color editor window
via the ColEdit command.
o+ Next, click the mouse in the image window and drag it around.
You'll see that all the background pixels have the same Hue
component value (240).
o+ To remap this hue, simply adjust the From dial so that its range
includes this Hue value. The background should change from 'blue'
to a reddish color, assuming the To dial is still set to its
default range (centered around 'R'). If more than the background
changed color, you can shrink the From range so that it covers
fewer colors. In fact, it's possible to shrink the range to the
point where it only covers only a single value. Note that the
values printed when you are tracking pixel values in the image are
the values before the HSV Modification tool is applied. For
example, the background of the default image will still claim to be
blue, regardless of what color you may have changed it to. This is
so that you know what Hue value you will need to remap if you want
to change its color again.
If you press the Reset button that is located near the hue
remapping controls, it will effectively disable the hue remapping
by setting the To range equal to the From range.
Below the hue remapping controls are a group of 'radio buttons'.
You can have up to six different hue remappings happening
simultaneously. Higher numbered mappings take precedence over
lower number mappings.
An example of multiple hue remappings:
o+ Draw a From range that is a complete circle. The easiest way to do
this is to draw a range that is nearly a full circle, then click
and hold down the 'increase range' button located below the From
range dial until the range stops getting bigger.
o+ Copy this range to the To range by pressing the Reset button.
o+ Rotate the To range slightly, by either clicking and dragging
anywhere in the To range dial, or by using the 'rotate clockwise'
and 'rotate counter-clockwise' buttons located below the To range.
o+ You've just built yourself what is effectively a tint control.
o+ Now, suppose, you'd like to adjust the background color of your
(tint-modified) image, without affecting anything else. Clicking
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on the background in the image window reveals that the background
still has an (original) hue of 240. To modify this hue without
affecting anything else, we'll need a second hue remapping.
o+ Click on the 2 radio button. The dials will change to some other
default setting. As before, set the From range to encompass the
value 240, preferably as 'tightly' as possible, and set the To
range to produce the desired background color. Note that the six
hue remappings are not 'cascaded'. The output of one remapping is
not fed as input into any of the other hue remappings. The hue
remappings always operate on the hue values in the original image.
In this example, if remapping #1 adds 32 to all hue values, thereby
mapping the blue background (value 240) into a purple-blue (value
272), remapping #2 still sees the background at 240, and can remap
it to anything it likes. Similarly, in the same example, if
remapping #1 has mapped a green-blue color (value 208) into blue
(value 240), remapping #2 will not map this into another color. As
far as remapping #2 is concerned, that green-blue is still green-
blue.
If it seems complicated, I'm sorry. It is.
Section 5.3.2: The White Remapping Control
In the HSV colorspace, 'white' (including black, and all the greys in
between) has no Hue or Saturation components. As such, it is not
possible to use the hue remapping controls to change the color of
white pixels in the image, since they have no 'color' to change.
The white remapping control provides a way to add Hue and Saturation
components to all the whites in the image. It consists of a movable
point in a color dial. The angle of the dot from the center of the
dial determines the Hue component. The distance of the dot from the
center of the dial determines the Saturation component. The further
the dot is from the center of the dial, the more saturated the color
will be.
You can control the white remapping control in several ways. You can
click on the handle and drag it around with the mouse. There are also
four buttons provided under the dial. One pair allows you to rotate
the handle clockwise and counter-clockwise without changing its
distance from the center. The other pair of buttons lets you change
the distance between the handle and the center without changing the
angle.
The current Hue and Saturation values provided by the control is
displayed below the dial. The first number is the Hue component, in
degrees, and the second is the Saturation component, as a percentage.
There is also a checkbox that will let you turn off the white
remapping control. This lets you quickly compare your modified
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'white' with the original white. You can also effectively disable the
white remapping control by putting the handle back in the center of
the control. The easiest way to do this is to click and hold the
'move towards center' button until the saturation gets down to 0%.
Example:
o+ Press the Grey control in the Colormap Editing tool. This turns
all the colors in the image into shades of grey.
o+ Drag the handle in the white remapping control halfway down towards
the 'R' mark. The Hue and Saturation values should be roughly 0-
degrees and 50%. The image should now be displayed in shades of
pink.
Section 5.3.3: The Saturation Control
The saturation control lets you globally increase or decrease the
color saturation of the image. In effect, it is much like the 'color'
control on most color televisions.
The saturation control is a dial that operates exactly like the dials
described in "Section 5.2.1 Using the Dial Controls". In short, you
can click and hold down any of the four buttons in the bottom of the
control to increase or decrease the control's value. You can also
click on the dial itself and move the pointer around directly.
The saturation control has values that range from '-100%' to '+100%'.
At its default setting of '0%', the saturation control has no effect
on the image. As the values increase, the colors become more
saturated, up to '+100%' where every color is fully saturated.
Likewise, as values decrease, the colors become desaturated. At '-
100%', every color will become a completely desaturated (i.e., a shade
of grey). Note that this control is applied after the the White
Remapping control, so if you 'greyify' the image by completely
desaturating it, you will not be able to color it using the White
Remapping control.
Unless you're trying for some special effects, the useful range of
this control is probably '+/-20%'. Also note that the control will
have no effect on shades of grey, as they have no color to saturate.
Section 5.3.4: The Intensity Graph
The intensity graph allows you to change the brightness of the image,
change the contrast of the image, and get some unique effects.
The intensity graph is a function that lets you remap intensity values
(the Value component in HSV Colorspace) into other intensity values.
The input and output values of this function both range from 0 to 255.
The input values range along the x axis of this graph (the
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horizontal). For every input value (point along the x axis) there is
a unique output value determined by the height of the graph at that
point. In the graph's default state, the function is a straight line
from bottom-left to top-right. In this case, each input value
produces an equivalent output value, and the graph has no effect.
There are a number of 'handles' along the graph. These provide your
major means of interacting with the graph. You can move them around
arbitrarily, subject to these two constraints: the handles at the far
left and far right of the graph can only be moved vertically, and
handles must remain between their neighboring handles for the graph to
remain a proper function.
The handles are normally connected by a spline curve. To see this,
move one of the handles by clicking and dragging it. The function
will remain a smoothly curved line that passes through all the
handles. You can change this behavior by putting the function into
'lines' mode. Press the 'lines' button (the second button down from
the top). The function will change to a series of line segments that
connect the handles. Press the 'spline' button (the top button) to go
back to 'spline' mode.
The next two buttons let you add or delete handles. The 'add handle'
button will insert a handle into the largest 'gap' in the function.
The 'delete handle' button will remove a handle from the smallest
'gap' in the function. You can have as little as 2 handles, or as
many as 16. Note that as the number of handles gets large, the spline
will start getting out of control. You may wish to switch to 'lines'
mode in this case.
The 'Reset' button puts everything back on a straight line connecting
bottom-left to top-right (a 1:1 function). It does not change the
number of handles, nor does it change the x-positions of the handles.
The 'Gam' button lets you set the function curve by entering a single
number. The function is set equal to the gamma function:
Y = 255 * (I/255) ^ (1/g) where I is the input value (0-255), g
is the gamma value, and Y is the computed result.
Gamma values (for our purposes) can range between 0 and 10000,
non-inclusive.
o+ A gamma value of '1.00' results in the normal 1:1 straight line.
o+ Gamma values of less than 1.00 but greater than 0.00 result in
'exponential' curves, which will dim the image.
o+ Gamma values greater than 1.00 result in 'logarithmic' curves,
which will brighten the image. Try it and see. There is a
shortcut for the 'Gam' button. Type 'g' while the mouse is inside
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the graph window.
Also, touching any of the handles after a 'Gam' command will put
the graph back into its 'normal' mode. (Either 'spline' or 'lines'
depending on which of the top two buttons is turned on.)
Generally, whenever you move a graph handle and let go of it, the
image will be redrawn to show you the effects of what you've done.
This can be time-consuming if you intend to move many points
around. You can temporarily prevent the redisplay of the image by
holding down a <shift> key. Continue to hold the <shift> key down
while you move the handles to the new position. Release the
<shift> key when you're done, and the image will be redisplayed.
Section 5.4: The RGB Modification Tool
The RGB Modification tool is a collection of three graph windows, each
of which operate on one of the components of the RGB colorspace. This
tool lets you perform global color-correction on the image by boosting
or cutting the values of one or more of the RGB color components. You
can use this to correct for color screens that are 'too blue', or for
color printers that produce 'brownish' output, or whatever.
The graphs work exactly as explained in "Section 5.3.4: The Intensity
Graph".
Neat Trick: In addition to color-correction, you can use the RGB
modification tool to add color to images that didn't have color to
begin with. For instance, you can 'pseudo-color' a greyscale image.
An example of pseudo-coloring:
o+ Adjust the Red graph so that there is a strong red presence on the
right side of the graph, and none on the left, or in the middle.
o+ Adjust the Green graph so that there is a strong green presence in
the middle of the graph, and none on the left or right.
o+ Adjust the Blue graph so that there is a strong blue presence on
the left side of the graph, and none on the left, or in the middle.
You now have a transformation that will take greyscale images and
display them in pseudo-color, using a 'temperature' color scheme.
Neato!
Section 5.5: The Color Editor Controls
These buttons provide general control over the whole xv color editor
window. You can display the image with or without color modification,
save and recall presets, and undo/redo changes. Also, convenience
controls are given for performing some of the most common operations
on the Intensity graph.
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Apply (Keyboard equivalent 'p')
Displays the image using the current HSV and RGB Modifications.
Also turns the 'Display with HSV/RGB mods' checkbox on. (See
below.)
This is only useful when the 'Auto-apply HSV/RGB mods' checkbox
is off.
NoMod
Displays the image without any HSV or RGB Modifications. Also
turns the 'Display with HSV/RGB mods' checkbox off.
Reset (Keyboard equivalent 'R')
Resets all HSV and RGB controls to their default settings.
Doesn't affect the Colormap Editing tool.
Undo Undoes the last change to the HSV or RGB controls.
It may be helpful to think of xv as maintaining a series of 32
'snapshots' of the HSV and RGB controls. You are normally
looking at the last frame in this series. The Undo control moves
you backwards in the series.
Redo Only available after you've hit Undo. Moves you forward in the
'snapshot' series described above. Note that if you have hit
Undo a few times (i.e., you're now looking at some frame in the
middle of the series), and you change an HSV or RGB control, all
subsequent frames in the series are thrown away, and the current
state becomes that last frame in the series.
1,2,3,4
Pressing any of these buttons recalls a preset (a complete set of
values for the HSV and RGB controls).
Set Used in conjunction with the 1,2,3,4 buttons to store the current
settings of the HSV and RGB controls into a preset. To do so,
press the Set button, and then press one of the 1,2,3,4 buttons.
The current HSV and RGB control settings will be stored in that
preset, as long as xv continues running. The values will be lost
when the program exits. It is also possible to save these values
permanently. See the Cut Resources button (below) and "Section
9: Modifying XV Behavior" for more details.
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Cut Resources
Copies the current settings of the HSV and RGB controls, as text,
into the X server's cut buffer. You can then use a text editor
to paste these values into your '.Xdefaults' (or '.Xresources')
file. This lets you save the current settings 'permanently'.
See "Section 9: Modifying XV Behavior" for more details.
Close
This button closes the xv color editor window.
Brite
Brightens the image by moving all the handles in the Intensity
graph up by a constant amount.
Dim Darkens the image by moving all the handles in the Intensity
graph down by a constant amount.
Sharp
Increases the contrast of the image by moving handles on the left
side of the Intensity graph down, and handles on the right side
up.
Dull Decreases the contrast of the image by moving handles on the left
side of the Intensity graph up, and handles on the right side
down.
MaxCn (Keyboard equivalent 'C')
Automatically maximizes the contrast of an image by finding the
second-brightest and second-darkest colors in the image, making
those full-bright and full-dark respectively, effectively
expanding the dynamic range of the image. All in-between colors
are remapped accordingly. The image must have at least four
colors for this control to have any effect. The 'Display with
HSV/RGB mods' checkbox tells you whether or you're looking at a
modified image (checked) or the 'raw', unmodified image
(unchecked). The Apply and NoMod buttons change the setting of
this checkbox, and you can also change the checkbox directly by
clicking on it.
The 'Auto-apply HSV/RGB mods' checkbox controls whether or not
the program regenerates and redisplays the image after each
change to an HSV or RGB control. By default, this checkbox is
turned on, so that you can easily see the results of your
modifications. However, in the case that you want to make a
large number of changes at once, it might be preferable to turn
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automatic redisplay off for a while, to speed things up.
The 'Auto-reset on new image' checkbox controls whether or not
the HSV and RGB controls are Reset back to their default values
whenever a new image is loaded up. By default, this is also
turned on, as when you're playing with the HSV/RGB controls, you
probably only want to affect the current image, and not all
subsequently loaded images as well.
SECTION 6: THE LOAD WINDOW
The xv load window lets you load and view images interactively,
without specifying them on the command line when you start xv.
The load window shows the contents of the current directory in a
scrolling window. The files will be sorted alphabetically, with all
the directories (and symbolic links to directories, if your operating
system supports them) displayed first.
This list window operates in the same way that the one in the xv
controls window works. (See "Section 3.6.1: Operating a List Window"
for details.) In short, you can operate the scroll bar, drag the
highlight bar around the window, and use the up-arrow, down-arrow,
Home, End, Page Up, and Page Down keys on your keyboard.
Whenever you click on a name in the list (or otherwise change the
position of the highlight bar), the name of the highlighted file is
copied to the "Load file" text entry region, located below the list
window. Pressing the Ok button (or typing <return>) will cause the
program to attempt to load the specified file. If the load attempt is
successful, the load window will disappear, and the new image will be
displayed. Otherwise, an error message will be displayed, and the
load window will remain visible.
If the image is successfully loaded, its name will be added to the xv
controls window list. This will let you quickly reload it later
without have to go through the xv load window again.
You can also load a file by double-clicking on its name in the file
list.
If the specified file is a directory, xv will figure that out and
(instead of loading it) will 'cd' to that directory, and display its
contents in the list window.
Above the list window is a pop-up menu button, much like the Display
Modes button in the xv controls window. It normally displays the name
of the current directory. If you click this button, and hold the
mouse down, the complete path will be shown, one directory per line.
You can go 'up' the directory tree any number of levels, all the way
up to the root directory, by simply selecting a directory name in this
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list.
For those who prefer the direct approach, you can simply type file or
directory names in the "Load file" text entry region. If you type a
directory name and hit <return>, xv will 'cd' to that directory and
display its contents in the list window. If you type a file name and
hit <return>, xv will attempt to load the file. You can enter
relative paths (relative to the currently displayed directory),
absolute paths, and even paths that begin with a '~'.
The "Load file" text entry region supports a number of emacs-like
editing keys.
Ctrl-F moves the cursor forward one character
Ctrl-B moves the cursor backward one character
Ctrl-A moves the cursor to the beginning of the line
Ctrl-E moves the cursor to the end of the line
Ctrl-D deletes the character to the right of the cursor
Ctrl-U clears the entire line
Ctrl-K clears from the cursor position to the end of the line.
If the filename is so long that it cannot be completely displayed
in the text entry region, a thick line will appear on the left or
right side (or both sides) of the region to show that "there's
more over this way".
SECTION 7: THE SAVE WINDOW
The xv save window lets you write images back to disk, presumably
after you've modified them. You can write images back many different
formats, not just the original format.
For the most part, the xv save window operates exactly like the xv
load window. (See "Section 6: The Load Window" for details.) Only
the differences are listed here.
When the window is opened, it should have the filename of the
currently loaded file already entered into the text entry region. If
you change directories, or click on a file name in the list window,
this name will be cleared and replaced with the new name.
At the bottom of the window are a list of possible formats in which
you can save the file. If you click on one of these formats, and your
filename has a recognized suffix (i.e., '.gif', '.GIF', '.pbm', etc.),
the suffix portion of your filename will be replaced with the new,
appropriate suffix for the selected format.
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You can pipe output from xv to other programs by using the xv save
window. A fine use for this feature is directly printing images to a
PostScript printer by selecting 'PostScript' in the formats list, and
typing something like "| lpr" as the filename. In this case, xv will
create a temporary file, write the PostScript to that file, and cat
the contents of that file to the entered command. XV will wait for
the command to complete. If the command completed successfully, the
xv save window will disappear. If the command was unsuccessful, the
window will remain visible. In any event, the temporary file will be
deleted.
At the bottom right side of the window there is a list of possible
'Color' variations to save. Most file formats support different
'sub-formats' for 24-bit color, 8-bit greyscale, 1-bit B/W stippled,
etc. Not all of them do. Likewise, not all 'Color' choices are
available in all formats.
In general, the 'Color' choices do the following:
Full Color
Saves the image as currently shown with all color modifications,
cropping, rotation, flipping, resizing, and smoothing. The image
will be saved with all of its colors, even if you weren't able to
display them all on your screen. For example, you can load a
color image on a 1-bit B/W display, modify it, and write it back.
The saved image will still be full color, even though all you
could see on your screen was some B/W-dithered nightmare.
Greyscale
Like Full Color, but saves the image in a greyscale format.
B/W Dithered
Like Full Color, but before saving the image xv generates a 1-
bit-per-pixel, black-and-white dithered version of the image, and
saves that, instead.
Reduced Color
Saves the image as currently shown, with all color modifications,
cropping, rotation, flipping, resizing, and smoothing. The image
will be saved as shown on the screen, with as many or few colors
as xv was able to use on the display. The major purpose of this
is to allow special effects (color reduction) to be saved, in
conjunction with the '-ncols' command line option. You will
probably never need to use this. Format notes:
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GIF While xv can read both the GIF87a and GIF89a formats, it will
only write GIF87a. This is in keeping with the GIF89
specification, which states that if you don't need any of the
features added in GIF89 (which xv doesn't), you should continue
to write GIF87, for greater compatibility with old GIF87-only
readers.
Since GIF only supports one format (up to 8 bits per pixel, with
a colormap), there will be no size difference between a Full
Color and a Greyscale image. A B/W Dithered image, on the other
hand, will be considerably smaller.
PM Full Color images are saved in the 3-plane, 1-band, PM_C format.
Greyscale and B/W Dithered images are both saved in the 1-plane,
1-band, PM_C format. As such, there is no size advantage to
saving in the B/W Dithered format.
PBM (raw)
Full Color images are saved in PPM format. Greyscale images are
saved in PGM format. B/W Dithered images are saved in PBM
format. Each of these formats are tailored to the data that they
save, so PPM images are larger than PGM images, which are in turn
larger than PBM images.
In the raw variation of the PBM formats, the header information
is written in plain ASCII text, and the image data is written as
binary data. This is the more popular of the two dialects of
PBM.
PBM (ascii)
Like PBM (raw), only the image data is written as ASCII text. As
such, images written in this format will be several times larger
than images written in PBM (raw). This is a pretty good format
for interchange between systems because it is easy to parse.
Also, since they are pure, printable ASCII text, images saved in
this format can be mailed, without going through a uuencode-like
program.
Note that xv-produced PBM files may break some PBM readers that
do not correctly parse comments. If your PBM reader cannot parse
comments, you can easily edit the PBM file and remove the comment
lines. A comment is everything from a "#" character to the end
of the line.
X11 Bitmap
Saves files in the format used by the bitmap program, which is
part of the standard X11 distribution. Since bitmap files are
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inherently 1-bit per pixel, you can only select the B/W Dithered
option for this format.
Sun Rasterfile
Full/Reduced Color images are stored in a 24-bit RGB format,
Greyscale images are stored in an 8-bit greyscale format, and B/W
Dithered images are stored in a 1-bit B/W format.
PostScript
Full/Reduced Color images are stored in a 24-bit RGB format,
Greyscale images are stored in an 8-bit greyscale format, and B/W
Dithered images are stored in a 1-bit B/W format.
XV writes Encapsulated PostScript, so you can incorporate xv-
generated PostScript into many desktop-publishing programs. XV
also prepends some color-to-greyscale code, so even if your
printer doesn't support color, you can still print 'color'
PostScript images. These images will be three times larger (in
file size) than their greyscale counterparts, so it's a good idea
to save Greyscale PostScript, unless you know you may be printing
the file on a color printer at some point.
Also, you should probably never need to generate B/W Dithered
PostScript, as every PostScript printer I've ever heard of can
print greyscale images. The only valid cases I can think of are:
A) doing it for a special effect, and B) doing it to generate a
much smaller (roughly 1/8th the size) PostScript file.
Note: When you try to save a PostScript file, the xv postscript
window will pop up to let you specify how you want the image
printed. (See "Section 8: The PostScript Window", for details.)
JPEG XV writes files in the JFIF format created by the Independent
JPEG Group. Full/Reduced Color images are written in a 24-bit
RGB format, and Greyscale images are written in an 8-bit
greyscale format. B/W Dithered images should not be used, as
they will probably wind up being larger than Greyscale versions
of the same images, due to the way JPEG works.
When you save in the JPEG format, a dialog box will pop up and
ask you for a quality setting. '75%' is the default value, and
really, it's a fine value. You shouldn't have to change it
unless you're specifically trying to trade off quality for
compression, or vice versa. The useful range of values is 5%-
95%.
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SECTION 8: THE POSTSCRIPT WINDOW
The xv postscript window lets you describe how your image should look
when printed. You can set the paper size and the image size, position
the image on the paper, and print in 'portrait' or 'landscape' mode.
The majority of the xv postscript window is taken up by a window that
shows a white rectangle (the page) with a black rectangle (the image)
positioned on it. You can position the image rectangle anywhere on
the page. The only constraint is that the center of the image (where
the two diagonal lines meet) must remain on the page. Only the
portion of the image that is on the page will actually be printed.
The image can be (roughly) positioned on the page by clicking in the
image rectangle and dragging it around. As you move the image, the
"Top" and "Left" position displays will show the size of the top and
left margins (the distance between the top-left corner of the page and
the top-left corner of the image).
You'll note that you have limited placement resolution with the mouse.
If you want to fine-position the image, you can use the arrow keys to
move the image around. The arrow keys will move the image in .001"
increments. You can hold them down, and they will auto-repeat. You
can also hold a <shift> key down while using the arrow keys. This
will move the image in .01" increments.
You can change the size of the printed image by adjusting the "Width"
or "Height" dials. Normally, the dials are locked together, to keep
the aspect ratio of the image constant. You can unlock the dials by
turning the off the checkbox located below the dials. As you change
the dials, the size of the image (when printed) is displayed below, in
inches and in millimeters. The current resolution of the image is
also displayed below. The "Resolution" numbers tell you how many
image pixels will be printed per inch.
Located below the 'page' rectangle are a set of radio buttons that let
you specify the current paper size (8.5" x 11", 8.5" x 14", 11" x 17",
A4, and B5), and orientation (Portrait and Landscape).
The Center button will center the image on the page. The Maxpect
button will make the image as large as possible (maintaining half-inch
margins on all sides) without changing the aspect ratio.
There are a pair of small buttons located next to the "Left" and "Top"
displays. Clicking the "Left" one will cycle between displaying the
"Left" margin, the "Right" margin, and the "Center X" position (the
distance from the left edge of the paper to the center of the image).
Clicking the "Top" display's button will cycle between displaying the
size of the "Top" margin, the size of the "Bottom" margin, and the
"Center Y" position (the distance from the top edge of the paper to
the center of the image).
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Click the "Ok" button when you're finished with the xv postscript
window. If everything is successful, the xv postscript and the xv
save window will both close. If xv was unable to write the PostScript
file, the xv postscript window will close, but the xv save window will
remain open, to give you a chance to enter a different filename.
SECTION 9: MODIFYING XV BEHAVIOR
XV supports literally dozens of command line options and X11
resources. Fortunately, it is doubtful that you'll ever need to use
more than a small few. The rest are provided mainly for that 'one
special case' application of xv...
Section 9.1: Command Line Options Overview
If you start xv with the command 'xv -help', the current list of
options will be displayed:
xv [-] [-2xlimit] [-aspect w:h] [-bg color] [-black color]
[-bw width] [-cegeometry geom] [-cemap] [-cgeometry geom]
[-clear] [-cmap] [-cursor char#] [-DEBUG level]
[-display disp] [-dither] [-expand exp] [-fg color]
[-fixed] [-geometry geom] [-help] [-hi color] [-hsv]
[-igeometry geom] [-imap] [-keeparound] [-lo color] [-max]
[-maxpect] [-mono] [-ncols nc] [-nglobal] [-ninstall]
[-nopos] [-noqcheck] [-owncmap] [-perfect] [-quit] [-rbg color]
[-rfg color] [-rgb] [-rmode mode] [-root] [-rw] [-slow24]
[-smooth] [-visual type] [-wait seconds] [-white color]
[-wloop] [filename ...]
Section 9.2: General Options
-help
Print usage instructions, listing the current available command-
line options. Any unrecognized option will do this as well.
-display disp
Specifies the display that xv should attempt to connect to. If
you don't specify a display, xv will use the environment variable
$DISPLAY.
-fg color (Resource name: foreground string)
Sets the foreground color used by the windows.
-bg color (Resource name: background string)
Sets the background color used by the windows.
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-hi color (Resource name: highlight string)
Sets the highlight color used for the top-left edges of the
control buttons.
-lo color (Resource name: lowlight string)
Sets the lowlight color used for the bottom-right edges of the
control buttons, and also the background of some windows.
-bw bwidth (Resource name: borderWidth integer)
Sets the width of the border on the windows. Your window manager
may choose to ignore this, however.
Section 9.3: Image Sizing Options
-geometry geom (Resource name: geometry string)
Lets you specify the size and placement of the 'image' window.
It's most useful when you only specify a position, and let xv
choose the size. If you specify a size as well, xv will create a
window of that size, unless -fixed is specified. The geom
argument is in the form of a normal X geometry string (e.g.
"300x240" or "+10+10" or "400x300+10+10").
-fixed (Resource name: fixed boolean)
Only used in conjunction with the -geometry option. If you
specify a window size with the -geometry option, xv will normally
stretch the picture to exactly that size. This is not always
desirable, as it may seriously distort the aspect ratio of the
picture. Specifying the -fixed option corrects this behavior by
instructing xv to use the specified geometry size as a maximum
window size. It will, however, preserve the original aspect
ratio of the picture.
For example, if you give a rectangular geometry of '320x240', and
you try to display a square picture with a size of '256x256', the
window opened will actually be '240x240', which is the largest
square that still fits in the '320x240' rectangle that was
specified.
-expand exp (Resource name: expand floating-point)
Lets you specify an initial expansion or compression factor for
the picture. You can specify floating-point values. Values
larger than zero multiply the picture's dimensions by the given
factor. (i.e., an expand factor of '3' will make a 320x200 image
display as 960x600).
Factors less than zero are treated as reciprocals. (i.e., an
expand factor of '-4' makes the picture 1/4th its normal size.).
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'0' is not a valid expansion factor.
-aspect w:h (Resource name: aspect string)
Lets you set an initial aspect ratio, and also sets the value
used by the Aspect control. The aspect ratio of nearly every X
display (and, in fact, any civilized graphics display) is 1:1.
What this means is that pixels appear to be 'square'. A 100
pixel wide by 100 pixel high box will appear on the screen as a
square. Unfortunately, this is not the case with some screens
and digitizers. The -aspect option lets you stretch the picture
so that the picture appears correctly on your display. Unlike
the other size-related options, this one doesn't care what the
size of the overall picture is. It operates on a pixel-by-pixel
basis, stretching each image pixel slightly, in either width or
height, depending on the ratio.
Aspect ratios greater than '1:1' (e.g., '4:3') make the picture
wider than normal. Aspect ratios less than '1:1' (e.g. '2:3')
make the picture taller than normal. (Useful aspect ratio: A
512x480 image that was supposed to fill a standard 4x3 video
screen (produced by many video digitizers) should be displayed
with an aspect ratio of '5:4')
Section 9.4: Color Allocation Options
-ncols nc (Resource name: ncols integer)
Sets the maximum number of colors that xv will use. Normally,
this is set to 'as many as it can get'. However, you can set
this to smaller values for interesting effect. Most notably, if
you set it to '0', it will display the picture by dithering with
'black' and 'white'. (The actual colors used can be set by the
-black and -white options, below.)
-nglobal (Resource name: nglobal boolean)
Adjusts the way the program behaves when it is unable to get all
the colors it requested. Normally, it will search the display's
default colormap, and 'borrow' any colors it deems appropriate.
These borrowed colors are, however, not owned by xv, and as such,
can changed without xv's permission, or knowledge. If this
happens, the displayed picture will change, in a less-than-
desirable direction. If you specify the -nglobal option, xv will
not use 'global' colors. It will only use colors that it
successfully allocated, which makes it immune to any color
changes.
It should be noted that 'use global colors' is the default
because color changes aren't generally a problem if you are only
using xv to display a picture for a short time. Color changes
only really become a problem if you use xv to display a picture
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that you will be keeping around for a while, while you go and do
some other work (such as using xv to display a background). In
such cases you will want to specify -nglobal. Note: using the
-ncols or -root options automatically turn on -nglobal.
-rw (Resource name: rwColor boolean)
Tells xv to use read/write color cells. Normally, xv allocates
colors read-only, which allows it to share colors with other
programs. If you use read/write color cells, no other program
can use the colors that xv is using, and vice-versa. The only
reason you'd do such a thing is that using read/write color cells
allows the Apply function in the xv color editor window to
operate much faster.
-perfect (Resource name: perfect boolean)
Makes xv try 'extra hard' to get all the colors it wants. In
particular, when -perfect is specified, xv will allocate and
install its own colormap if (and only if) it was unable to
allocate all the desired colors. This option is not allowed in
conjunction with the -root option.
-owncmap (Resource name: ownCmap boolean)
Like '-perfect', only this option forces xv to always allocate
and install its own colormap, thereby leaving the default
colormap untouched.
-ninstall (Resource name: ninstall boolean)
Prevents xv from 'installing' its own colormap, when the -perfect
or -owncmap options are in effect. Instead of installing the
colormap, it will merely 'ask the window manager, nicely' to take
care of it. This is the correct way to install a colormap (i.e.,
ask the WM to do it), unfortunately, it doesn't actually seem to
work in many window managers, so the default behavior is for xv
to handle installation itself. However, this has been seen to
annoy one window manager (dxwm), so this option is provided if
your WM doesn't like programs installing their own colormaps.
Section 9.5: 24-bit Conversion Options
The following options only come into play if you are using xv to
display 24-bit RGB data (PPM files, color PM files, JPEG files, and
the output of bggen). They have no effect whatsoever on how GIF
pictures or 8-bit greyscale images are displayed.
-slow24 (Resource name: slow24 boolean)
Specifies that the 'alternate' 24-bit to 8-bit conversion
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algorithm is to be used by the program. The default algorithm
dithers the picture using a fixed set of colors that roughly
approximate all displayable colors. The -slow24 algorithm picks
the 'best' colors on a per-image basis, and dithers with those.
Advantages: The -slow24 algorithm often produces better looking
pictures.
Disadvantages: The -slow24 algorithm is about half the speed of
the default algorithm. Also, since the colors are chosen on a
per-image basis, it can't be used to display multiple images
simultaneously, as each image will almost certainly want a
different set of 256 colors. The default algorithm, however,
uses the same exact colors for all images, so it can display many
images simultaneously, without running out of colors. Also, the
-slow24 algorithm occasionally produces worse-looking pictures
than the default algorithm, particularly on displays with very
few colors. The default algorithm produces nice, dependably
'okay' pictures.
-noqcheck (Resource name: noqcheck boolean)
Turns off a 'quick check' that is normally made. Normally,
before running either of the 24-bit to 8-bit conversion
algorithms, xv determines whether the picture to be displayed has
more than 256 unique colors in it. If the picture doesn't, it
will treat the picture as an 8-bit colormapped image (i.e., GIF),
and won't run either of the conversion algorithms.
Advantages: The pictures will be displayed 'perfectly', whereas
if they went through either of the conversion algorithms, they'd
be dithered.
Disadvantages: Often uses a lot of colors, which limits the
ability to view multiple images at once. (See the -slow24 option
above for further info about color sharing.)
Section 9.6: Root Window Options
xv has the ability to display images on the root window of an X
display, rather than opening its own window (the default behavior).
When using the root window, the program is somewhat limited, because
the program cannot receive input events (key press and mouse clicks)
from the root window. As a result, you cannot track pixel values, or
crop, nor can you use keyboard commands while the mouse is in the root
window.
-root (Resource name: <none>)
Directs xv to display images in the root window, instead of
opening its own window. Exactly how the images will be displayed
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in the root window is determined by the setting of the -rmode
option.
-rmode mode (Resource name: rootMode integer)
Determines how images are to be displayed on the root window,
when -root has been specified. You can find the current list of
'modes' by using a mode value of '-1'. XV will complain, and
show a list of valid modes. The current list at of the time of
this writing is:
0: tiling
1: integer tiling
2: mirrored tiling
3: integer mirrored tiling
4: centered tiling
5: centered on a solid background
6: centered on a 'warp' background
7: centered on a 'brick' background
The default mode is '0'. See "Section 3.5: The Display Modes
Menu" for a description of the different display modes.
-rfg color (Resource name: rootForeground string)
Sets the 'foreground' color used in some of the root display
modes.
-rbg color (Resource name: rootBackground string)
Sets the 'background' color used in some of the root display
modes.
-max (Resource name: <none>)
Makes xv automatically stretch the image to the full size of the
screen. This is mostly useful when you want xv to display a
background. While you could just as well specify the dimensions
of your display ('-geom 1152x900' for example), the -max option
is display-independent. If you suddenly decide to start working
on a 1280x1024 display (ferinstance) the same command will still
work. Note: If you specify -max when you aren't using -root, the
behavior is slightly different. The image will be made as large
as possible while still preserving the normal aspect ratio.
-maxpect (Resource name: <none>)
Makes the image as large as possible while preserving the aspect
ratio.
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-quit (Resource name: <none>)
Makes xv display the (first) specified file and exit, without any
user intervention. Since images displayed on the root window
remain there until explicitly cleared, this is very useful for
having xv display background images on the root window in some
sort of start-up script. Needless to say, this is only useful if
you are using -root.
-clear (Resource name: <none>)
Clears the root window of any extraneous xv images. Note: it is
not necessary to do an 'xv -clear' before displaying another
picture in the root window. xv will detect that there's an old
image in the root window and automatically clear it out (and free
the associated colors).
Section 9.7: Window Options
XV currently consists of three main windows, plus one window for the
actual image. These three windows (the xv controls window, the xv
info window, and the xv color editor window) may be automatically
mapped and positioned when the program starts.
-cmap (Resource name: ctrlMap boolean)
Maps the xv controls window.
-cgeom geom (Resource name: ctrlGeometry string)
Sets the initial geometry of the xv controls window. Note: only
the position information is used. The window is of fixed size.
-imap (Resource name: infoMap boolean)
Maps the xv info window.
-igeom geom (Resource name: infoGeometry string)
Sets the initial geometry of the xv info window. Note: only the
position information is used. The window is of fixed size.
-cemap (Resource name: ceditMap boolean)
Maps the xv color editor window.
-cegeom geom (Resource name: ceditGeometry string)
Sets the initial geometry of the xv color editor window. Note:
only the position information is used. The window is of fixed
size.
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-nopos (Resource name: nopos boolean)
Turns off the 'default' positioning of the various xv windows.
Every time you open a window, you will be asked to position it.
(Assuming your window manager asks you such things. mwm, for
instance doesn't seem to ask)
Section 9.8: Miscellaneous Options
-mono (Resource name: mono boolean)
Forces the image to be displayed as a greyscale. This is most
useful when you are using certain greyscale X displays. While xv
attempts to determine if it's running on a greyscale display,
many X displays lie, and claim to be able to do color. (This is
often because they have color graphics boards hooked up to b/w
monitors. The computer, of course, has no way of knowing what
type of monitor is attached.) On these displays, if you don't
specify -mono, what you will see is a greyscale representation of
one of the RGB outputs of the system. (For example, you'll see
the 'red' output on our greyscale Sun 3/60s.) The -mono option
corrects this behavior.
-white color (Resource name: white string)
Specifies the 'white' color used when the picture is b/w
stippled. (When '-ncols 0' has been specified.)
-black color (Resource name: black string)
Specifies the 'black' color used when the picture is b/w
stippled. (When '-ncols 0' has been specified.)
Try something like: 'xv -ncols 0 -bl red -wh yellow <filename>'
for some interesting, late-'60s-style psychodelia effects.
-wait secs (Resource name: <none>)
Turns on a 'slide-show' feature. Normally, if you specify
multiple input files, xv will display the first one, and wait for
you to give the Next command (or whatever). The -wait option
makes xv wait the specified number of seconds, and then go on to
the next picture, without any user intervention. The program
still accepts commands, so it's possible to 'abort' the current
picture without waiting the full specified time by using the Next
command.
-wloop (Resource name: <none>)
Normally, when running a slide-show with the -wait option, xv
will terminate after displaying the last image. If you also
specify the -wloop option, the program will loop back to the
first image and continue the slide-show until the user issues the
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Quit command.
-rgb (Resource name: hsvMode boolean)
Specifies that, by default, the colormap editing dials in the xv
color editor window should be in RGB mode. This is the normal
default behavior.
-hsv (Resource name: hsvMode boolean)
Specifies that, by default, the colormap editing dials in the xv
color editor window should be in HSV mode.
-dither (Resouce name: autoDither boolean)
When specified, tells xv to automatically issue a Dither command
whenever an image is first displayed. Useful on displays with
limited color capabilities (4-bit and 6-bit displays.)
-smooth (Resource name: autoSmooth boolean)
When specified, tells xv to automatically issue a Smooth command
whenever an image is first displayed. This is useful when you
are using one of the image sizing options (such as '-expand' or
'-max').
-visual vistype (Resource name: visual string)
Normally, xv uses the default visual model provided by your X
server. You can override this by explicitly selecting a visual
to use. Valid types are StaticGray, StaticColor, TrueColor,
GrayScale, PseudoColor,
and DirectColor. Not all of these are necessarily provided on
any given X display. Run xdpyinfo on your display to find out
what visual types are supported.
-cursor curs (Resource name: cursor integer)
Specifies an alternate cursor to use in the image window (instead
of the normal 'cross' cursor). curs values are obtained by
finding the character number of a cursor you like in the 'cursor'
font. (Run 'xfd -fn cursor' to display the cursor font.) For
example, a curs value of '56' corresponds to the (singularly
useless) 'Gumby' cursor.
-keeparound (Resource name: keepAround boolean)
By default if you Delete the last file in the xv controls list,
the program will automatically exit, as a convenience. If you
find this an inconvenience, the -keeparound option inhibits this
behavior.
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-2xlimit (Resource name: 2xlimit boolean)
By default, xv prevents the image window from ever getting larger
than the screen. Unfortunately, because of this, if you load an
image that is larger than your screen, the image will be shrunk
until it fits on your screen. Some folks find this undesirable
behavior. Specifying the -2xlimit option doubles the size
limitations. The image window will be kept from getting larger
than 2x the width and height of your screen.
Just in case you're wondering why there's any size limitations:
it's fairly easy to accidentally ask for a huge image to be
generated. Simply crop a section of the image, zoom so you can
see the individual pixels, and uncrop. If there were no size
limitations, the (expanded many times) image could be huge, and
might crash your X server. At the very least, it would take a
long period of time, and freeze your X server during part of it.
Generally undesirable behavior.
-DEBUG level (Resource name: <none>)
Turns on some debugging information. You shouldn't need this.
If everything worked perfectly, I wouldn't need this either.
- Specifying '-' all by itself tells xv to take its input from
stdin, rather then from a file. This lets you put xv on the end
of a Un*x pipe.
Section 9.9: Color Editor Resources
You can set default values for all of the HSV and RGB modification
controls in the xv color editor window via X resources. The easiest
way to explain this is with an example.
o+ Start xv and put it in the background by typing 'xv &'.
o+ Type the command 'cat >foo' in an active xterm window
o+ Bring the xv color editor window up.
o+ Issue the Cut Resources command.
o+ Click your Middle mouse button in the xterm window. A set of
resource lines describing the current state of the xv color editor
controls will be 'pasted' into the window.
o+ You could type '<ctrl-D>' in the xterm to complete the cat command,
edit this file, and put it in your .Xdefaults/.Xresources file.
The lines generated by Cut Resources will look like the following:
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xv.default.huemap1: 330 30 CW 330 30 CW
xv.default.huemap2: 30 90 CW 30 90 CW
xv.default.huemap3: 90 150 CW 90 150 CW
xv.default.huemap4: 150 210 CW 150 210 CW
xv.default.huemap5: 210 270 CW 210 270 CW
xv.default.huemap6: 270 330 CW 270 330 CW
xv.default.whtmap: 0 0 1
xv.default.satval: 0
xv.default.igraf: S 4 : 0,0 : 64,64 : 192,192 : 254,254
xv.default.rgraf: S 4 : 0,0 : 64,64 : 192,192 : 254,254
xv.default.ggraf: S 4 : 0,0 : 64,64 : 192,192 : 254,254
xv.default.bgraf: S 4 : 0,0 : 64,64 : 192,192 : 254,254 These lines
completely describe one state of the xv color editor controls.
There are five different states that you can specify via X
resources. The 'default' state (as shown) holds the settings used
whenever the program is first started, and whenever the Reset
command is used. You can also store settings in one of the four xv
presets (accessed via the '1'-'4' buttons in the xv color editor)
by changing the string 'default' in the above lines to 'preset1',
'preset2', 'preset3', or 'preset4' respectively.
There are four types of resource described in these lines: huemap,
whtmap, satval, and graf.
Section 9.9.1: Huemap Resources
The huemap resources describe the state of the hue remapping dials.
There are six huemap resources per state of the xv color editor.
These huemap resources are numbered 'huemap1', 'huemap2', ...
'huemap6', and correspond to the '1'-'6' radio buttons under the hue
remapping dials.
Each huemap resources takes six parameters:
1. The 'starting' angle of the From range, in degrees (integer).
2. The 'ending' angle of the From range, in degrees (integer).
3. The direction of the From range. Either 'cw' (clockwise) or 'ccw'
(counter-clockwise).
4. The 'starting' angle of the To range, in degrees (integer).
5. The 'ending' angle of the To range, in degrees (integer).
6. The direction of the To range. Either 'cw' or 'ccw'.
Section 9.9.2: Whtmap Resources
The whtmap resource describes the state of the white remapping
control. There is one whtmap resource per state of the xv color
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editor controls. The whtmap resource takes three parameters:
1. The hue to remap 'white' to, in degrees (integer).
2. The saturation to give to the remapped 'white', in percent
(integer).
3. A boolean specifying whether the white remapping control is
enabled. If '1', the control is enabled. If '0', the control is
disabled.
Section 9.9.3: Satval Resource
The satval resource describes the value of the Saturation dial. There
is one satval resource per state. The satval resource takes a single
integer value, in the range +/-100, which specifies how much to add or
subtract to overall image color saturation.
Section 9.9.4: Graf Resources
The graf resources describe the state of the four 'graph' windows in
the xv color editor window (Intensity, Red, Green, and Blue). The
graf resources can be in one of two formats, 'gamma' and
'spline/line'. In 'gamma' format, the graf resource takes two
parameters:
1. The letter 'G', specifying 'gamma' mode
2. A single floating point number specifying the gamma value.
In 'spline/line' mode, the graf resource takes a variable number of
parameters:
1. The letter 'S' specifying 'spline' mode, or the letter 'L'
specifying 'line' mode.
2. An integer number indicating the number of handles (control points)
that this graph window will have. (Must be in the range 2-16,
inclusive.)
3. For each handle, there will be a ':', and the x and y positions of
the handle, separated by a comma. The x and y positions can be in
the range 0-255 inclusive.
LIMITATIONS
xv will NOT work on displays that aren't 1-, 4-, 6-, 8-, 16- 24-, or
32-bits deep. Luckily, that should still cover nearly every display
out there. It may not work on certain 6- or 24-bit displays.
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It also only displays the first image in GIF files that have multiple
images in them.
As for PM pictures, this program only displays 1-plane PM_I pictures,
or 1-, 3-, or 4-plane PM_C pictures.
PM FORMAT
The PM format is a file format that we use at the GRASP Lab for our
image processing work. If you aren't at Penn, you are unlikely to
ever run into a PM-format file, so don't worry about it. Please
ignore all references to PM.
The 4-, 6-, 16-, 24-, and 32-bit code has not been extensively tested.
(A 4-bit MicroVax GPX system, a 6-bit HP 9000/320, a 16-bit Sony 3710,
and a 24-bit HP 9000/350, respectively. The 32-bit code hasn't
actually been tested at all.) You won't be able to do '-ncols 0' on a
6-, 16-, 24-, or 32-bit display, not that you should want to.
AUTHORS
John Bradley - bradley@cis.upenn.edu
GIF reading code based on gif2ras.c, by Patrick J. Naughton
(naughton@wind.sun.com)
GIF writing code essentially unchanged from code written by Michael
Maudlin (mlm@cs.cmu.edu).
SUN Rasterfile i/o code written by Dave Heath (heath@cs.jhu.edu)
JPEG interface code written by Markus Baur (s_baur@iravcl.ira.uka.de)
JPEG i/o code provided by the Independent JPEG Group.
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