Appendix C
GIF Save File Format

Since version 5.0, Fractint has had the [S]ave-to-disk command, which stores screen images in the extremely compact, flexible .GIF (Graphics Interchange Format) widely supported on CompuServe. Version 7.0 added the [R]estore-from-disk capability.

Until version 14, Fractint saved images as .FRA files, which were a non- standard extension of the then-current GIF87a specification. The reason was that GIF87a did not offer a place to store the extra information needed by Fractint to implement the [R] feature -- i.e., the parameters that let you keep zooming, etc. as if the restored file had just been created in this session. The .FRA format worked with all of the popular GIF decoders that we tested, but these were not true GIF files. For one thing, information after the GIF terminator (which is where we put the extra info) has the potential to confuse the online GIF viewers used on CompuServe. For another, it is the opinion of some GIF developers that the addition of this extra information violates the GIF87a spec. That's why we used the default filetype .FRA instead.

Since version 14, Fractint has used a genuine .GIF format, using the GIF89a spec - an upwardly compatible extension of GIF87a, released by CompuServe on August 1 1990. This new spec allows the placement of application data within "extension blocks". In version 14 we changed our default savename extension from .FRA to .GIF.

There is one significant advantage to the new GIF89a format compared to the old GIF87a-based .FRA format for Fractint purposes: the new .GIF files may be uploaded to the CompuServe graphics forums fractal information intact. Therefore anyone downloading a Fractint image from CompuServe will also be downloading all the information needed to regenerate the image.

Fractint can still read .FRA files generated by earlier versions. If for some reason you wish to save files in the older GIF87a format, for example because your favorite GIF decoder has not yet been upgraded to GIF89a, use the command-line parameter "GIF87a=yes". Then any saved files will use the original GIF87a format without any application- specific information.

An easy way to convert an older .FRA file into true .GIF format suitable for uploading is something like this at the DOS prompt:

      FRACTINT MYFILE.FRA SAVENAME=MYFILE.GIF BATCH=YES

Fractint will load MYFILE.FRA, save it in true .GIF format as MYFILE.GIF, and return to DOS.

GIF and "Graphics Interchange Format" are trademarks of CompuServe Incorporated, an H&R Block Company.


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Noel Giffin,
noel@triumf.ca