Truecolor questions

[markanini]

I'm trying to better understand the mechanics. Given that the games use 8 bit palette indexes, how are they mapped into 24 bit color from the original 256 color output?
What makes the colors appear different in true color mode? Could this suggest the colors have been hacked to replace 8 bit indexes with 24 bit colors?

[Phredreeke]

Each color in the palette has its own RGB values. At some point the color indices have to be translated back to RGB values. On vintage hardware that was done on the graphics card itself. When using hardware rendering without palette emulation the translation happens as the texture is loaded. When using palette emulation I believe it occurs right after the texture is drawn. When using software rendering it occurs after the whole image finishes rendering

The colors are different without palette emulation because shading is done by multiplying with the shade level, while with palette emulation or using the software rendering shading is done using a look up table (for each of the 256 possible colors in the texture you have 32 or 64 entries, these entries are limited to the same 256 colors)

[Graf Zahl]

... and those color deviations come from these lookup tables being "optimized" (meaning they do not fade linearly - or at least as linearly as the palette allows - their makers took some creative licenses, which is the reason why some colors are visibly off at lower light levels - the most obvious examples are the sandy pathways in RR which are a lot more red in software, or the strong reddish tint throughout SW or as a particularly strange example, the house to the right of the starting point in World Tour's E5L1.

[markanini]

The colors are different without palette emulation because shading is done by multiplying with the shade level, while with palette emulation or using the software rendering shading is done using a look up table (for each of the 256 possible colors in the texture you have 32 or 64 entries, these entries are limited to the same 256 colors)

How does the shade level work?

[Graf Zahl]

Quite simple: Shade 0 is fullbright, shade 31/63 is black, i.e. it's an inverse light scale.

[Phredreeke]

How does this translate into a multiplier though? Something like 1 - (shade/max shades)?

[Graf Zahl]

1- shade/(maxshades-1), to be precise. If you got 32 shades, 31 is the darkest one.
That is, if the ramp was truly linear. None of Build's shade tables are truly linear so they need a small fudging factor. Some of Exhumed's even have a totally different falloff where this factor needs to be quite different.