These options determine how PMView saves GIF files.
Always Write GIF89a Format If set, the file will always be written in the newer GIF89a format. If not set, the file will be written in GIF87a format, unless the Transparent Color Index option is used. The GIF89a format has a new color table flag that specifies whether the color table is sorted or not. If you know that the target application can take advantage of this information, you may turn on this option and the sort flag will be set (PMView always keeps the palette sorted). The flag will not be set for GIF87a files in order to preserve compatibility with older applications that (erroneously) will not accept GIF87a files with the sort flag set.
Interlace If set, the image will be saved using 4-pass interlacing. If not set, the image will be saved sequentially in one pass. Using interlacing only makes sense with programs that progressively update the display while loading. For instance, when loading an interlaced GIF file the image will gradually be displayed during four passes. At the end of the first pass each eighth row of the image is visible. Already at this point of loading you'll probably see what the image looks like. With each pass the image quality will gradually improve as missing lines are added.
Transparent Color Index If set, transparency information will be written to the GIF file. Use this option if you would like one of the colors in your image to be transparent with the background. Typically you'll need this if you make images for WWW-browsers. Note that transparency information requires the newer GIF-variant; GIF89a. Thus, if this option is on, the file will be written in the GIF89a format instead of GIF87a. Note that PMView will not use transparency information when loading GIF files.
Background Color Index If set, the specified background color index will be written to the GIF file. Use this option if the target application fills unused space with the color specified in the GIF file. Typically may need this if you make images for WWW-browsers. If not set, index zero (0) will be written to the file (in PMView index zero will always correspond to the most used color in the image). Note that PMView will not use this information when loading GIF files.
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