ColoRIX

ColoRIX, or RIX, is a raster image file format associated with the EGA Paint and ColoRIX VGA Paint applications for MS-DOS, developed by RIX SoftWorks. There are at least two versions of it.

Format details
The "new" format (with "RIX3" signature) has a 10-byte header, then an optional and rare "extension block", then a color palette, then the image data. If the image is compressed, the high bit of the byte at offset 9 is set.

The "old" format lacks the header. If the image is compressed, the high bit of the first byte of the file is set. The low 6 bits of the first 16 bytes are an EGA-style color palette. The image data starts at offset 16.

Both old and new ColoRIX files may optionally be compressed, using a fairly complex compression scheme. The compression scheme starts by splitting the image data into one or more segments. For 256-color images only, an XOR filter is applied. Then comes run-length encoding, followed by Huffman coding. It is vaguely similar to Squeeze, though the details are different.

Identifiers
Many filename extensions have been reported or observed. Most are listed below. Extensions beginning with "SC" are generally used for full-screen images, with the third letter a code for the screen mode.

Identification
New (VGA Paint) format: Files begin with ASCII characters "".

Note that the VGA Paint distribution includes other files, in other formats, that also begin with "", but have a different fourth byte.

Uncompressed old format: There's no robust way to identify the format, though you could check the file size (exactly 112016 bytes for SCR format), and validate the palette.

Compressed old format: There's no easy way to identify the format, though it is possible to identify it by reading the file and checking for errors.

Specifications

 * , from the Encyclopedia of Graphics File Formats
 * RIX image File Format
 * Picture format docs (of a number of formats including this one)
 * Fallout 2 RIX File Format

Software

 * ColoRIX VGA Paint 1.36 (at Internet Archive)
 * ColoRIX VGA Paint - Various versions at old-dos.ru
 * RIXLATE.EXE - Format conversion utility for DOS, included with, e.g., ColoRIX VGA Paint 1.36
 * Konvertor
 * XnView
 * GrafX2

Sample files

 * → *.SCI
 * https://telparia.com/fileFormatSamples/image/rix/
 * SCF Samples
 * SDN¹ Plus → demos/colorix.zip → *.SCF
 * Shareware Grab Bag → 008/egaslide.arc - EGA Slide, a component of EGA Paint (?). Includes some .SCR files in an old version of the format.

The Rolex demo
Apparently, RIX SoftWorks released a "Rolex" clock demo app that loads and displays an included (old-format) RIX file.
 * MS-DOS Shareware: ROLEX

And some people modified it to display a custom image. A few of these mods may be found by searching the Internet Archive Software Collection for "rix softworks" (some may be NSFW).
 * Other examples (compressed):, , , ,
 * Other examples (uncompressed):, , , ,

Links

 * EGA Paint ad in PC Magazine, Mar 10, 1987, p. 287