CTAB — colour tables

Implemented in colwin/palette.py. 43 resources, all in COLDATA8.DLL, ids 111, 210–215, 220–223 and 260–291.

Exactly 4 + 3 × 97 = 295 bytes. A table whose last entries are black ends short once the resource’s NUL padding is trimmed; that is not corruption, and a decoder that treats it as such will reject real data.

Not a reading of the bytes

The field meanings come from the loader. 1068:0180 matches the literal 'CTAB' in DGROUP, takes the WORD at 0 as start, the WORD at 2 as count, and calls 1068:083b(port, start, count, data + 4) — which walks a packed 3-byte RGB array with stride 3 and ends in SetPaletteEntries.

So a CTAB is exactly the argument list of the routine that writes ranges into the runtime palette. That these blobs are one of its payloads is established.

What is not established

Which table a sprite is drawn under. 1068:0180’s only caller, 1050:1d16, computes the CTAB id from game state at four sites, from base constants 111, 210, 220 and 260 — exactly the four id groups that ship. No sprite id is involved anywhere in the program.

Sprite id nevertheless predicts colour well, because art and its colour tables were numbered together during authoring: for sprites with enough pixels in the CTAB window, the best-fitting table carries the sprite’s own id in 36 of 57 cases, against 1.0 by chance, from a scorer that never sees an id. colwin uses that as a rendering heuristic and labels it a reconstruction. See Palettes.

Why there are 43 variants of one 97-entry range — colour cycling, per-nation recolouring, per-context palettes — is open.

The reserved teal

(0,173,173) appears exactly once in 42 of the 43 tables; table 222 is the sole exception and has none. The index it occupies is not fixed: 18 distinct indices over 209–233, one per table.

Sprites drawn through such a table use that index at a median 8.5% of their pixels and up to 41%, in long contiguous runs — mean run 15.3 px against 4.0 for a frequency-matched control index in the same sprite, longer in 33 of 33 sprites measured. One reserved colour per palette, at a palette-specific index, filling solid regions of the art is what a colour key or backdrop looks like.

It is not established as one, and colwin does not treat it as one. No code has been shown keying that colour out, and because the index differs per table a blitter could not test for it with a constant index. It is recorded per sprite in the manifest and rendered as ordinary colour — which is why extracted portraits show a teal backdrop.

One entry is constant across all 43 tables: index 142, the first of the range, is pure white in every one.