The Sun Rasterfile Format

Jamie Zawinski,, 15 Nov 89
... the manpage for rasterfile(5) doesn't say anything about the format of byte-encoded images, or about plane/scanline ordering in multi-plane images. Pretty cool, yes? Anyway, I have the firmly held belief that this information shouldn't be as hard to come by as it was for me. So in the interest of spreading the data far and wide, here is what I know about the sun rasterfile format.

The first thing in the file is

    struct rasterfile {
	int ras_magic;
	int ras_width;
	int ras_height;
	int ras_depth;
	int ras_length;
	int ras_type;
	int ras_maptype;
	int ras_maplength;
The ras_magic field always contains the following constant:
    #define RAS_MAGIC 0x59a66a95
The ras_length field is the length of the image data (which is the length of the file minus the length of the header and colormap). Catch: this is sometimes zero instead, so you can't really depend on it.

The ras_type field is ras_old=0, ras_standard=1, ras_byte_encoded=2, or ras_experimental=FFFF. There doesn't seem to be any difference between OLD and STANDARD except that the ras_length field is always 0 in OLD.

I didn't deal with cmaps, so from the man page: "The ras_maptype and ras_maplength fields contain the type and length in bytes of the colormap values, respectively. If ras_maptype is not RMT_NONE and the ras_maplength is not 0, then the colormap values are the ras_maplength bytes immediately after the header. These values are either uninterpreted bytes (usually with the ras_maptype set to RMT_RAW) or the equal length red, green and blue vectors, in that order (when the ras_maptype is RMT_EQUAL_RGB). In the latter case, the ras_maplength must be three times the size in bytes of any one of the vectors."

Regardless of width, the stored scanlines are rounded up to multiples of 16 bits.

I found the following description of byte-length encoding in Sun-Spots Digest, Volume 6, Issue 84, by Pat McGee:

The format is composed of many sequences of variable length records. Each record may be 1, 2, or 3 bytes long. A run is not terminated at the end of a scan line. So, if there are three lines of red in a picture 100 pixels wide, the first run will be 0x80 0xff 0x<red>, and the second will be 0x80 0x2b 0x<red>.