SCUMM: DIG: Gray artifacts/pixels in ending video (SQ19A.SAN)

[ATMcashpoint]

In some shots in SMUSH cutscene videos in The Dig, the proper color depth as seen on DOS is crushed down severely for some reason. A good example is the shot of the shuttle taking off from the landing pad in the intro.

Other SMUSH cutscenes appear to have artifacting that isn't present on DOS. For instance, in the shot in the ending where the crystal spaceship takes off from Cocytus, random gray pixel artifacts are visible on the ocean surface that shouldn't be there.

There may well be more instances of such issues. I only watched the first part of the intro cutscene and the very last shot of the ending because I was taking screenshots of the fonts in the credits for another bug report.

These errors are present in the current daily build of ScummVM (March 17, 2024) for Windows 64-bit.

[AndywinXp]

In 9b0c049e:

SCUMM: SMUSH: Fix color banding issues

Fixes the main issue of #15026:
"SCUMM: DIG: Color depth issues & artifacting
in some shots in SMUSH videos".

Verified from FT, DIG and COMI disassemblies.

[AndywinXp]

I fixed the main issue, if you don't mind I'm renaming the ticket so the remaining issue gets some visibility.

[AndywinXp]

There, the gray pixel issues in the final SMUSH video persists. I couldn't find the root cause of that one, but hopefully time will tell...

[eriktorbjorn]

The ending video we're talking about is sq19b.san, right?

[eriktorbjorn]

The artifacts seem to all be palette color 236, though the palette is probably not to blame since it's also used for some other parts of the image.

[eriktorbjorn]

I could be wrong, but I think it's case 0xFE (LITERAL_4X1) in proc3WithFDFE() that draws the bad pixels. But if so, I still have no idea why or how.

[AndywinXp]

In c7ed01fc:

SCUMM: DIG: Fix SMUSH codec edge case

From disasm; this fixes #15026:
"SCUMM: DIG: Gray artifacts/pixels in ending video (SQ19A.SAN)"