Calamus Raster Graphic
Calamus Raster Graphic (CRG) is a graphics format associated with the Calamus desktop publishing software by invers Software. At least some CRG images are compressed using a simple run-length encoding scheme.
Refer to Calamus for more information about the software, and related formats.
Contents |
Identification
CRG files apparently begin with the ASCII signature "CALAMUSCRG".
Format details
[Partial decoding, based on analysis of a small number of CRG files. This may be incorrect.]
Multi-byte integers are big-endian.
| Offset | Length | Field | Observed values | Details |
|---|---|---|---|---|
| 0 | 10 | signature | "CALAMUSCRG" |
|
| 10 | 2 | 03 e8 |
Unknown. By analogy to CVG, maybe a code for the format version. | |
| 12 | 2 | 00 02 |
Unknown. By analogy to CVG, maybe a code for the page size. | |
| 14 | 4 | (file size, minus 24) | ||
| 18 | 2 | 00 80 |
Unknown | |
| 20 | 4 | width | Image width in pixels | |
| 24 | 4 | height | Image height in pixels | |
| 28 | 4 | (various) | Unknown | |
| 32 | 1 | 01 |
Unknown | |
| 33 | 1 | 00 |
Unknown | |
| 34 | 4 | ff ff ff ff |
Unknown | |
| 38 | 4 | cmpr_size | Size of compressed image data, in bytes | |
| 42 | cmpr_size | cmpr_image_data | Compressed image data (see below) |
RLE compression
The compressed data consists of a code byte, followed by one or more data bytes, followed by another code byte, and so on. To decompress:
| Code byte (N) | Instructions |
|---|---|
| N ≤ 127 | Emit the next N+1 bytes literally. |
| N ≥ 128 | Emit the next byte N−127 times. |
(This is essentially the same algorithm as in TGA, but byte-oriented instead of pixel-oriented.)
After decompression, pixels are in left-to-right, top-to-bottom order. The format is 8 pixels per byte, most significant bit first, white is 0. Rows are padded to the next byte boundary.
