Difference between revisions of "Image file"

Revision as of 21:54, 21 November 2007

Team17's image files (typically with an .img file extension) are usually compressed palleted images.

File format

• 4-byte signature - "IMG\x1A"
• complete file length (4 bytes)
• optionally, a null-terminated string describing the image (present only in some Worms 2 images)
• the number of bits per pixel in the image (usually 8) (1 byte)
• image flags (1 byte)
• if the image has a palette (highest flag bit is set):
  • the number of colours in the image palette, excluding black^[1] (2 bytes)
  • the image palette, excluding black^[1] ((3 × number of colours) bytes)
• the image width (2 bytes)
• the image height (2 bytes)
• the image data. If the data is compressed (the corresponding image flag is set), see Team17 compression for the decompression routine; otherwise, it's just an array (Width × Height).

Flags

The flag byte is a bit field of the following values:

• 0x40 (01000000) - set if the image data is compressed
• 0x80 (10000000) - the image has a palette

Notes

1. ↑ ^{1.0 1.1} The black colour isn't listed in the image palette, nor counted in the "number of colours" word. It is counted as the colour 0, so the palette stored in the file should be loaded starting from colour 1.