You can access the program’s general preferences dialog box by selecting “General preferences” from the Options menu, or pressing Command-K.
Black borders
When this option is unchecked, GIF Slideshow automatically draws a coloured border around pictures which do not fully fill your screen. The colour of the border is selected for each picture at random. If you prefer to always have a black border check the “Black borders” option. Sometimes pictures will seem to be off-centre or still have a black border. This is because the black border is part of the picture, and is therefore drawn on the screen before the coloured border is added.
Dither if monitor less than 256 colours
When this option is checked, GIF Slideshow automatically dithers pictures when your monitor is set to less than 256 colours. The dithering process approximates colours by blending available colours to simulate other colours. This process slows down the drawing of the picture.
Dither if scaled to other than 100%
When this option is checked, GIF Slideshow automatically dithers pictures when they are being scaled up or down (enlarged or reduced). The dithering process can make scaled pictures look more natural by reducing “banding” (vertical or horizontal lines), particularly when pictures are being scaled down (reduced). This process slows down the drawing of the picture. We suggest that unless you have a very fast Mac (or don’t mind waiting about twice as long for each picture) that you leave this option unchecked.
Ignore single errors
Out of a collection of a few thousand GIF or TIFF pictures there will usually be a couple that cannot be displayed either because:
• The picture was incorrectly saved and cannot be processed; or
• The picture uses a GIF or TIFF file format the GIF Slideshow does not recognise.
If the “Ignore single errors” option is checked then non-consecutive errors will be quietly ignored.
If however there are multiple consecutive errors (because, for example there is not enough memory to display pictures) then an error alert will appear.
This is particularly useful for running unattended displays of many GIF pictures.
Note that GIF Slideshow has been tested with thousands of commercially available GIF pictures with only very occasional errors.
Minimum free memory
Selecting this option displays an alert box showing the smallest amount of memory that GIF Slideshow had free in the current session. You can use this to “tune” the amount of memory that it needs to display a particular series of pictures. For example, if you had 6000K allocated to GIF Slideshow, and after displaying an entire CDROM the minimum free memory available was 1500K, then you can probably safely allocate only 4500K to GIF Slideshow next time you want to display that CDROM. You would be advised to allow a “safety margin” of, say, 200K to be added to any figure obtained by the above method.
Mouse click advances
If this option is checked then clicking the mouse when viewing a picture advances to the next picture.
If the option is not checked then the mouse automatically becomes a “grabber hand” when clicked while viewing a picture that is larger than the screen.
Warn if screen not 256 colours
Because GIF Slideshow displays pictures most efficiently (quickly) when your screen is set to 256 colours, it automatically warns you if your screen is set to some other number of colours when the application starts up (providing your screen supports 256 colour mode). You can disable this warning message if you find it annoying by unchecking this option.
Slideshow control options
You can access the program’s slideshow options dialog box by selecting “Slideshow options” from the Options menu, or pressing Command-J. The first three options (automatic advance, random sequencing and looping) are also directly available from the menu bar under the “Slideshow” menu, however it is sometimes helpful to be able to see all of the program options at once (i.e. to see if they are on or off), and in those cases using this dialog box is more useful.
Automatic advance
If this option is checked then the program automatically advances to the next picture in the current sequence after the time delay specified by the “Delay between pictures” dialog box (you can access that dialog box by pressing Command-D). If the option is not checked then you must manually advance to the next picture by:
 • Clicking the mouse; or
 • Pressing the “return” or “enter” keys; or
 • Pressing the space bar; or
 • Pressing a key in the range “A” to “Z”
The “automatic advance” option can also be toggled (turned on and off) by pressing Command-A.
The “automatic advance” option can also be turned off by pressing F5, if you have an extended keyboard.
The “automatic advance” option can also be turned on by pressing F6, if you have an extended keyboard.
Random sequencing
If this option is checked then pictures are displayed in random sequence from the current picture list. If the option is unchecked then pictures are displayed sequentially.
The “random” option can also be toggled (turned on and off) by pressing Command-R.
The “random” option can also be turned off by pressing F7, if you have an extended keyboard.
The “random” option can also be turned on by pressing F8, if you have an extended keyboard.
Loop at end of picture list
If this option is checked then when the entire list of pictures has been displayed the program starts displaying them again from the start. If the option is unchecked then pictures are only displayed once.
The “loop” option can also be toggled (turned on and off) by pressing Command-L.
Shrink pictures which are larger than the screen
When this option is checked, GIF Slideshow automatically scales down (reduces) pictures which are smaller than the screen. This makes the picture fit on the screen, but at the sacrifice of losing some picture detail. If you prefer large pictures to be shown at their actual size un-check this option. When a picture that is too large to fit is being drawn on the screen GIF Slideshow automatically draws a 3D-style border around the picture as a visual indication that there is more of the picture available. You can scroll around and see the rest of the picture by option-clicking with the mouse (the mouse pointer will turn into a “grabber hand”), and then — whilst holding the mouse down — moving the mouse around to see the rest of the picture. Alternatively, you can use the arrow keys on the keyboard, or the “page up”, “page down”, “home” and “end” keys.
The “shrink large pictures” option can also be turned off by pressing F9, if you have an extended keyboard.
The “shrink large pictures” option can also be turned on by pressing F10, if you have an extended keyboard.
Enlarge pictures which are smaller than the screen
When this option is checked, GIF Slideshow automatically scales up (enlarges) pictures which are smaller than the screen. This makes the picture bigger, but at the sacrifice of looking more “chunky”. If you prefer smaller pictures to be shown at their actual size and centred on the screen, un-check this option.
Replace black pixels with best guess
When this option is checked, GIF Slideshow automatically replaces black pixels in the picture with its best guess about what colour should be there instead.
Experience has shown that a small percentage of GIF pictures (about 1%) have been erroneously saved with the colour black in their colour palettes where a non-black colour should have been (this is a fault in the GIF picture file, not GIF Slideshow). This is probably because the Mac’s “Palette Manager” insists on the colours black and white being present in each palette.
In order to fix black pixels, the program scans the entire picture, counting the number of instances of each colour that is adjacent to black pixels. It then chooses the second-most popular one, and then replaces each black pixel in the picture with this colour.
In about 70% of pictures which have unsightly black pixels in the middle of them, this technique improves the picture considerably.
However, unless the picture you are viewing has a “black pixel” problem, we suggest leaving this option unchecked, because:
  • The black pixels may be correct (i.e. genuine black areas); and
  • Sometimes the guess gives a completely incorrect colour, which makes the picture worse; and
  • The process described above takes time, because of the calculations involved
Information options
You can access the program’s information options dialog box by selecting “Information” from the Options menu, or pressing Command-I.
The options that you last had selected are remembered by GIF Slideshow at the end of each session so that the same options will apply when you start your next session.
Name of current picture
The file name of the GIF picture being currently displayed can be shown by checking the “Name of current picture” option. If you have an extended keyboard you can toggle showing the current picture name by pressing function key F12.
Amount of memory currently free
The amount of free memory currently available to GIF Slideshow can be shown by checking the “Amount of memory currently free” option.
Information about picture size and dimensions
General information about the picture is displayed if the “Information about picture size and dimensions” option is checked. This includes:
• Size of picture on disk
• Size of picture in memory once decoded
• Width of picture in pixels
• Depth of picture in pixels
• Number of colours used in the picture
Percentage picture is scaled
The amount that the current picture is scaled (shrunk or expanded) can be shown by checking the “Percentage picture is scaled” option. If the percentage is 100% then the picture is being shown full size. If it is 200% then it is being shown at double size.
Depending on settings in the preferences dialog box, GIF Slideshow will attempt to scale each picture so that it fits into the current screen, so that you do not need to “scroll” around to see the whole picture.
Scaling a picture takes longer than displaying it at full size, so that a picture shown at 150% will be drawn more slowly than one drawn at 100%.
Also, the scaling is always carried out so that the picture keeps its original proportions, so that a rectangular picture may have blank areas on the sides, or above and below. In this case, the picture is centred so that the blank parts are evenly on each side of the picture.
Sometimes a picture will appear to be “off-centre”. This is not a bug in GIF Slideshow, it is simply that the black areas on the side of the picture are part of the original picture.
In order to allow for users who may be using very large screens, GIF Slideshow sets a maximum scaling factor of 400%. Pictures scaled larger than that would not only take a long time to draw, but would look “chunky”. Correspondence will be entered into if any users would like this limit changed.
For technical reasons, interlaced pictures are always scaled by an integral amount (i.e. 100%, 200%, 300% or 400%).
If you do not want small pictures scaled up (enlarged), un-check the “Enlarge pictures which are smaller than the screen” option in the Preferences dialog box.
If you do not want large pictures scaled down (shrunk), un-check the “Shrink pictures which are larger than the screen” option in the Preferences dialog box.
Progress through current sequence of pictures
The progress through the current list of pictures can be shown by checking the “Progress through current sequence of pictures” option. The display appears in the format, “File 45 of 3421”, indicating that you are viewing file number 45 out of a list of 3421 files.
This number can be entered into the “Go to picture number” dialogue box available under the “Slideshow” menu so that you can reposition to a given point in a sequence of pictures.
If the files are being shown in random order then the number shows how far you are through the random sequence, not which file number in the list you are currently viewing.
If you switch from Random to Sequential mode or vice-versa the progress number will change from “how many pictures you have seen” to “how far through the picture list you are”.
If the “loop” option is active then the file number will reset to 1 when the sequence restarts.
If you have an extended keyboard you can toggle showing the picture number by pressing function key F11.
Show when next ready
The moment that the next GIF picture is ready for viewing can be shown by checking the “Show when next ready” option. This displays a small white box on the bottom right-hand corner of the screen.
This is useful in conjunction with manual advancing of frames, or when you are manually scrolling pictures which are larger than the screen. Until the white box appears, pressing “space”, “enter”, “return” (or clicking) to advance to the next frame will not have an immediate effect, because GIF Slideshow is still decoding the next picture while you are viewing the current one. Once the box appears you know that attempting to advance or scroll will result in immediate action.
File type recognition options
You can access the program’s file type recognition options dialog box by selecting “File type recognition” from the Options menu, or pressing Command-U.
The file type recognition options affect what sort of pictures are considered for displaying when you scan a folder or volume (i.e. disk or CDROM). Once you have saved a series of file names in a tag file, changing the file type recognition options will not affect whether or not pictures in the tag file are displayed.
GIF pictures
If you wish to scan for GIF pictures, check this option.
Autodesk Animator movies
GIF Slideshow has some rudimentary support for Autodesk Animator “.FLI” files. If you have a “.FLI” file on disk you may find that GIF Slideshow attempts to process it and display it in animated form. This display routine is still under development, and the displays therefore may not be correct, or at the correct speed. If you wish to scan for Autodesk Animator movies, check this option.
TIFF pictures
GIF Slideshow now supports some TIFF file formats. If you wish to scan for TIFF pictures, check this option.
MacPaint pictures
GIF Slideshow now supports MacPaint pictures. If you wish to scan for MacPaint pictures, check this option.
PICT pictures
GIF Slideshow now supports PICT files (under System 7, if you capture the screen by pressing Shift-Command-3 the file which is created, called “Picture 0”, is a PICT file). If you wish to scan for PICT files, check this option.
