nx_tga_decode.nx

nx_tga_decode.nx -- Truevision TGA reader (the DOS/Amiga-era workhorse). Types handled: 1/9 colour-mapped (8-bit index), 2/10 truecolour (16/24/32), 3/11 grayscale (8) -- the 9/10/11 variants being the RLE forms of the same pixel layouts, which is why the RLE unpack sits BEFORE the pixel decode and both paths share it. Refused: types 32/33 (Huffman+delta), colour maps whose entry size is not 15/16/24/32. THE ORIGIN BIT IS NOT DECORATION. Bit 5 of the image descriptor selects top-left vs bottom-left row order. A reader that ignores it returns a vertically MIRRORED image that is otherwise perfectly valid-looking -- the single most common TGA defect, and invisible to any check that only compares dimensions or means. 16-bit is A1R5G5B5 with 5-bit channels replicated to 8 (v<<3|v>>2), NOT shifted-and-zero-filled: the latter loses white (31 -> 248, never 255). genealogy_id: tga_spec_2_0 lineage_id: nx_tga_v1 license_tier: ORIGINAL