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Revert "More accurate 8-bit <=> 5-bit RGB color conversion (#1827)"

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This reverts commit 223b3d1921.
This commit is contained in:
Rangi42
2025-10-24 13:32:59 -04:00
parent 8bedd710d7
commit ca383c91ca
20 changed files with 15 additions and 31 deletions
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18
man/rgbasm-old.5
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@@ -461,24 +461,6 @@ Previously we had
.Pp
Instead, now we have
.Ql p ** q ** r == p ** (q ** r) .
.Ss 8-bit and 5-bit color conversion
Changed in 1.0.0.
.Pp
RGBGFX takes 8-bit RGB colors as its PNG input, and outputs 5-bit GBC colors.
Its
.Ql -r/--reverse
mode does the opposite 5-bit to 8-bit conversion.
Instead of the previous inaccurate conversions, we now do accurate rounding to the nearest equivalent.
.Pp
Previously to convert an 8-bit color channel to 5-bit, we truncated it as
.Ql c >> 3 ;
and to reverse a 5-bit color channel to 8-bit, we extended it as
.Ql (c << 3) | (c >> 2) .
.Pp
Instead, now we round 8-bit to 5-bit as
.Ql (c * 31 + 127) / 255 ,
and round 5-bit to 8-bit as
.Ql (c * 255 + 15) / 31 .
.Sh BUGS
These are misfeatures that may have been possible by mistake.
They do not get deprecated, just fixed.