Inside SUN Rasterfile Jamie Zawinski jwz@teak.berkeley.edu 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. 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: > From: jpm%green@lanl.gov (Pat McGee) > Subject: Re: Format for byte encoded rasterfiles (1) > > The format is composed of many sequences of variable length records. > Each record may be 1, 2, or 3 bytes long. > > o If the first byte is not 0x80, the record is one byte long, and > contains a pixel value. Output 1 pixel of that value. > o If the first byte is 0x80 and the second byte is zero, the record > is two bytes long. Output 1 pixel with value 0x80. > o If the first byte is 0x80, and the second byte is not zero, the > record is three bytes long. The second byte is a count and the > third byte is a value. Output (count+1) pixels of that value. > > 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, and the second will be 0x80 0x2b 0x. > > Pat McGee, jpm@lanl.gov