Acorn User: China/Acorn User China CD-ROM (UK) (Disc A)/Acorn User China CD-ROM (UK) (Disc A).bin/HENSA/CONVERTER/ARC-JPEG.ARC/!ArcJPEG_!Help

Text File | 1993-11-30 | 17.3 KB | 425 lines

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*    The copyright notice and credits are at the end of this file     *
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Contents:
---------
Aims
Features
Compatibility
About JPEG
Operation
Menus
Options Windows : To JPEG window, From JPEG window
Hints
Known Bugs
Solid Drags in RiscOS3
Author's address
New features since last release
Copyright notice and credits



Aims:
-----

The !ArcJPEG application provides a desktop front-end for the fourth release
of the Independent JPEG Group's free JPEG software, the command-line
programs "cjpeg" and "djpeg", which implement JPEG image compression and
decompression.
It will convert JPEG images (filetype &C85) to either PBMPlus (&69E), Targa
(&69D) or GIF (&695) file formats and also the reverse process, creation of
a JPEG file from the above.
Can be used in conjunction with either !Translator or !ChangeFSI to display
JPEG files.

Features include:
-----------------

* Full control of all features provided by version four of and djpeg and
  most of cjpeg.
* Destination file hotlinks
* Application hotlinks
* Multitasking file conversion (see compatibility note below)
* Quick opening of options and file information windows by clicking on
  iconbar icon with select and adjust (configurable)
* Uses new features in RiscOS3, such as solid icon drags (when selected in
  CMOS ram, see note at end of file), but still remaining compatible with
  RiscOS2 (see compatibility note below)

Compatibility:
--------------

To work under RiscOS2 it needs the Interface Manager by Simon Huntington and
the CLib and FPEmulator modules, which should be located in the
!System.Modules directory.
For multitasking file conversions to work under RiscOS2 you need at least
version 0.29 of the taskwindow module which is supplied with Desktop C and
Desktop Assembler. If you don't have the taskwindow module then the program
will still work, but without that feature.
When running under RiscOS3 the interface module is not needed and the other
modules, including the taskwindow module are present in ROM.

About JPEG:
-----------

JPEG (pronounced "jay-peg") is a standardized compression method for
full-colour and gray-scale images. JPEG is designed to handle "real-world"
scenes, for example scanned photographs. Cartoons, line drawings, and other
non-realistic images are not JPEG's strong suit; on this sort of material
you may get poor image quality and/or little compression.
JPEG is lossy, meaning that the output image is not necessarily identical to
the input image. Hence you should not use JPEG if you have to have identical
output bits. However, on typical real-world images, very good compression
levels can be obtained with no visible change, and amazingly high
compression is possible if you can tolerate a low-quality image.

Operation:
----------

The !ArcJPEG application starts up when you double-click on its filer icon
or on a JPEG file and installs itself on the icon bar.
JPEG files can be loaded by either double-clicking on its filer icon or
dragging the icon onto the iconbar. PBMPlus, Targa, and Gif files can only
be loaded by dragging onto the icon. This is so that !ArcJPEG can coexist
with programs like !Translator or !ChangeFSI.

Menus:
------

Icon bar menu:
--------------

-------------
|  ArcJPEG  |
|-----------|
| Info     ⇨| ⇨ Opens "About this program" window
| Open Win ⇨| ⇨ Opens Open Win submenu (see below)
| Hotlink  ⇨| ⇨ Opens Hotlink submenu (see below)
| Options  ⇨| ⇨ Opens Options submenu (see below)
| Quit      |   Quits program
-------------

Open Win submenu:
-----------------

-------------
| Open Win  |
|-----------|
| File Info |   Opens window showing input/output filenames and process time
| To JPEG   |   Opens options window for creation of jpeg files
| From JPEG |   Opens options window for decompaction of jpeg files
-------------

Hotlink submenu:
----------------

-----------------
|  Hotlink      |
|---------------|
|€ Save Box     |  Selects normal save box to appear when saving
|  hotlink 1   ⇨|  \  Selects file hotlinks
|  hotlink 2   ⇨|   | Subwindows also allow hotlink filename to be set by
|  hotlink 3   ⇨|  /  dragging icon to a filer window or by typing the name
|---------------|
|  Application ⇨|  Subwindow allows application hotlinks to be set
|  ChangeFSI    |  Example of application hotlink
-----------------

When savebox is selected a savebox appears in the normal way when a file is
saved.

When any of the hotfile options is selected the filename in the hotfile
subwindow is used for the output file. This filename can be changed or set
by either typing it into the writable box in the subwindow (pressing return
or clicking on OK closes the menu but is not needed to make the change
permanent) or dragging the icon onto a filer window. Either of these
operations results in that particular option being selected.

The Application subwindow is used to set up application hotlinks. This can
be done in two ways, either by dragging the icon from the application
subwindow to an icon on the icon bar or by selecting the application option
which results in the same window as before popping up when a file is loaded.
When the icon is dragged from the menu window the menu is removed from the
screen so that any obscured icons on the iconbar are revealed. When an
application hotlink is setup, the application name appears on the bottom of
the menu, the hotlink is always selected after creation. Once set then can
be selected by simply clicking on the application name required. Since the
hotlink is invalid when the application has quitted, even if it is reloaded,
entries are removed when the application quits. For this reason these
options are not saved, if an application hotlink was selected when the
options were saved than the application item is selected when they are
loaded up.

Options submenu:
----------------

---------------
|  Options    |
|-------------|
|  Multitask  |    Selects Multitasking file conversion
|€ Fast Mode  |    Selects "Fast Mode" (single tasking file conversion only)
|  Program   ⇨|    Subwindow allows DJPEG or CJPEG to be held in ram
|  Icon Bar  ⇨|    Subwindow allows selection of effect of clicking on
|-------------|    iconbar icon
|  Save       |    Saves options and file hotlink filenames
|  Load       |    Loads saved options and clears application hotlinks
|  Default    |    Sets default options and clears application hotlinks
---------------

This allows the options to be saved, reloaded or set to the defaults. The
default or load options remove all the application hotlinks from the list.
The last saved options are always loaded up when the program is started.
Selecting Mulititask selects multitasking file conversions and greys out the
Fast Mode option as it is invalid for these operations.
Selecting Fast Mode speeds up single tasking file conversion by turning off
the screen display when processing the file.
The Program subwindow sets whether DJPEG and CJPEG are loaded from disc
for each file conversion or kept in ram. Keeping the program(s) in ram
saves disc swaping if running off a floppy disc at the expence of ram,
about 50K for each program, not realy any use if it is installed on a
hard disc.
The Icon Bar subwindow sets which window gets opened when the select and
adjust buttons of the mouse are clicked on the iconbar icon.

Window menu:
------------

This is opened when the menu button is pressed over any of the options
windows and the file information window. It is the same as the iconbar menu
except as shown below

-------------
|  ArcJPEG  |
|-----------|
| Reprocess |---Clicking on Reprocess will reprocess the last file that was
| Open Win ⇨|   converted. Useful when seeing the effect of changing the
| Hotlink  ⇨|   options on the resulting image where the same file is loaded
| Options  ⇨|   every time.
-------------

Note, no quit option.

Options Windows:
----------------

To JPEG window:
---------------

This controls the cjpeg program which creates JPEG files from the various
input formats.

Optimise:
When selected optimization of the entropy encoding parameters is performed.
Without this, default encoding parameters are used. Optimize usually makes
the JPEG file a little smaller, but cjpeg runs somewhat slower and needs
much more memory. Image quality and speed of decompression are unaffected by
Optimize.

Quality:
Selecting this means the number in the writable box below is used for the
quality value rather than the default value of 75.
This value adjusts the scale quantization tables which adjust the image
quality. The value is 0 (worst) to 100 (best). This allows you to trade off
compressed file size against quality of the reconstructed image: the higher
the quality setting, the larger the JPEG file, and the closer the output
image will be to the original input. Normally you want to use the lowest
quality setting (smallest file) that decompresses into something visually
indistinguishable from the original image. For this purpose the quality
setting should be between 50 and 95; the default of 75 is often about right.
If you see defects at 75, then go up 5 or 10 counts at a time until you are
happy with the output image. (The optimal setting will vary from one image
to another.)
A quality value of 100 will generate a quantization table of all 1's,
eliminating loss in the quantization step (but there is still information
loss in subsampling, as well as roundoff error).  This setting is mainly of
interest for experimental purposes. Quality values above about 95 are NOT
recommended for normal use; the compressed file size goes up dramatically
for hardly any gain in output image quality.
In the other direction, quality values below 50 will produce very small
files of low image quality. Settings around 5 to 10 might be useful in
preparing an index of a large image library, for example. Try 2 (or so) for
some amusing Cubist effects. (Note: quality values below about 25 generate
2-byte quantization tables, which are considered optional in the JPEG
standard.

Colour-Grey Scale:
These select whether the output image will be in colour or grey scale.
Be sure to select Grey Scale when compressing a grayscale GIF file, because
cjpeg isn't bright enough to notice whether a GIF file uses only shades of
gray. By selecting Grey Scale, you'll get a smaller JPEG file that takes
less time to process.

Restart:
This option when selected includes markers in the JPEG file every N rows,
where N is the number in the writeable box below. This allow a JPEG decoder
to resynchronize after a transmission error. Without restart markers, any
damage to a compressed file will usually ruin the image from the point of
the error to the end of the image; with restart markers, the damage is
usually confined to the portion of the image up to the next restart marker.
Of course, the restart markers occupy extra space. We recommend a value of
1 for images that will be transmitted across unreliable networks such as
Usenet.

Smooth:
When selected the input file is filtered  to eliminate fine-scale noise.
This is often useful when converting GIF files to JPEG: a moderate smoothing
factor of 10 to 50 gets rid of dithering patterns in the input file,
resulting in a smaller JPEG file and a better-looking image. Too large a
smoothing factor will visibly blur the image, however.

From JPEG window:
-----------------

This controls the djpeg program which creates PBMPlus, Targa or Gif files
from JPEG files.

PBMPlus-Targa-Gif:
These allows the output file format to be selected.
Changing this when a save box is on screen does have an affect and even
changes the icon in the save box when it is open.
Selecting Gif file output means that colours are by default quantised at
256, unless the Force Colours option is selected.
Selecting Gif ungreys the options that correspond to the quantisation of
colours, when a 24 bit format is then selected the quantisaton options
are greyed out unless the Force Colours option in the is selected.

Colour-Grey Scale:
When Colour is selected then the output file will be in colour (if the
original image was colour), selecting Grey Scale will result in the output
image being in black and white.

Force Colours:
When Force Colours is selected this sets the number of colours for
quantisation to the number in the writable icon and ungreys out the colour
quantisation options. The maximum number of colours in a Gif file is 256. If
Gif is selected then the quantisation options are also ungreyed out.

One Pass-Two Pass:
When One Pass (quantisation) is selected this rather than the normal Two
Pass quantisation is used. The one-pass method is faster and needs less
memory, but it produces a lower-quality image.

FSI Dither:
This option selects whether FSI dithering is used when quantising colours.
This is selected by default when quantisation is selected.

Cross Block:
When selected, Cross Block smoothing is used when quantising colours. This
is quite memory-intensive and only seems to improve the image at very low
quality settings (10 to 20 or so). At normal quality settings it may make
things worse.

Hints:
------

Colour GIF files are not the ideal input for JPEG; JPEG is really intended
for compressing full-colour (24-bit) images. In particular, don't try to
convert cartoons, line drawings, and other images that have only a few
distinct colours. GIF works great on these, JPEG does not. If you want to
convert a GIF to JPEG, you should experiment with cjpeg's quality and
smooth options to get a satisfactory conversion. A smooth value of 10 or so
is often helpful.
Avoid running an image through a series of JPEG compression/decompression
cycles. Image quality loss will accumulate; after ten or so cycles the image
may be noticeably worse than it was after one cycle. It's best to use a
lossless format while manipulating an image, then convert to JPEG format
when you are ready to file the image away.
The optimize option to cjpeg is worth using when you are making a "final"
version for posting or archiving. It's also a win when you are using low
quality settings to make very small JPEG files; the percentage improvement
is often a lot more than it is on larger files.
When making images to be posted on Usenet, we recommend using cjpeg's option
restart with a value of 1. This option limits the damage done to a
compressed image by netnews transmission errors.
The <Wimp$ScrapDir> directory is used for tempory files if there is not
enough RAM available.
The <Wimp$Scrap> file is used for application hotlinks.
The WimpSlot value given to the process can be changed in the !Run file.
360K is the default value.

Known Bugs:
-----------

When dragging the application icon off the window when setting the
applicaton hotlink, the icons on the icon bar are sometimes not redrawn
correctly when the window disapears.

Solid Drags in RiscOS3:
-----------------------

If you have RiscOS 3 then you can have solid drags when dragging the icon
out of the saveboxes. A solid drag is when the file icon (rather than a
dashed box) is used when dragging. This feature is also used by the
applications present in ROM, such as !Edit, but not the filer.
Cut out the simple basic program below (sourced from usenet), load it into
!Edit and save it as BASIC. When run it will toggle the solid drag option in
the CMOS RAM.

   10REM Toggle state of DragASprite bit in CMOS
   20REM Read byte
   30SYS "OS_Byte",161,&1C TO ,,byte%
   40REM EOR byte with mask for bit 1
   50byte% = byte% EOR 1<<1
   60REM Write byte back again
   70SYS "OS_Byte",162,&1C,byte%
   80END

Author's address:
-----------------

I, Andrew Sellors, can be contacted either at
   57 Boundaries Road
   Feltham
   Middlesex
   TW13 5DR

Or via Internet email at
   [e-mail]

New features since last release
-------------------------------

Added to v1.13
    : Holding of DJPEG and CJPEG in ram (configurable)

Added to v1.14
    : Improved Wimp Polling (doesn't eat nulls now)
    : Improved error handling during loading/saving
    : Ability to change WimpSlot given to process in !Run file


Copyright notice and credits:
-----------------------------

!ArcJPEG is FreeWare. This means that you may freely copy and distribute it,
provided that it is complete with all original files, and that you do not
sell it. PD libraries may charge a nominal fee for the cost of duplication,
postage etc.
In no circumstances shall the author be liable for any damage, loss of
profits, time or data or any indirect or consequential loss rising out of
the use of this software or inability to use this software.

!ArcJPEG was written with the help of !BlibII ,Copyright 1992 Ian Palmer,
a BASIC program library linker and the associated libraries shown below.
  Event    - © Ian Palmer, 1st March 1993
  Icon     - © Ian Palmer & Tom Hughes, 1st March 1993
  Memory   - © Ian Palmer, 1st March 1993
  Menu     - © Ian Palmer, 1st March 1993
  OS       - © Ian Palmer, 1st March 1993
  Sprite   - © Tom Hughes 1st March 1993
  Template - © Ian Palmer & Tom Hughes, 2nd March 1993
  WIMP     - © Ian Palmer & Tom Hughes, 1st March 1993
  Window   - © Ian Palmer & Tom Hughes, 1st March 1993
  as well as my own libraries © Andrew Sellors 1993

The Interface Manager module is © Simon Huntington

!ArcJPEG was beta-tested by Dominic Thomas, and who suggested the previous
name needed changing, if you think it is bad now you should have seen it
before.

The programs djpeg and cjpeg were ported to the Archimedes by Tom Crossland.
The JPEG sources are written by the people of 'The Independent JPEG Group'.