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Decode canonical RGB values for indexed palette colors #121

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Decode canonical RGB values for indexed palette colors #121

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8 changes: 8 additions & 0 deletions convert.go
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Original file line number Diff line number Diff line change
Expand Up @@ -612,6 +612,14 @@ func RgbTo256(r, g, b uint8) uint8 {

// C256ToRgb convert an 256 color code to RGB numbers
func C256ToRgb(val uint8) (rgb []uint8) {
if val >= 232 {
level := uint8(8 + 10*int(val-232))
return []uint8{level, level, level}
}
if val >= 16 {
index := val - 16
return []uint8{incs[index/36], incs[index/6%6], incs[index%6]}
}
hex := c256ToHexMap[val]
// convert to rgb code
rgbInts := Hex2rgb(hex)
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18 changes: 17 additions & 1 deletion convert_test.go
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Expand Up @@ -155,4 +155,20 @@ func TestRgbHsvConv(t *testing.T) {
assert.StrEq(t, "(0.00, 0.00, 1.00)", "(%.2f, %.2f, %.2f)", h, s, v)
r, g, b = HSVToRGB(h, s, v)
assert.StrEq(t, "(255, 255, 255)", "(%d, %d, %d)", r, g, b)
}
}

func TestC256ToRgbPalette(t *testing.T) {
levels := []uint8{0, 95, 135, 175, 215, 255}
for r, red := range levels {
for g, green := range levels {
for b, blue := range levels {
index := uint8(16 + 36*r + 6*g + b)
assert.Equal(t, []uint8{red, green, blue}, C256ToRgb(index), index)
}
}
}
for i := 0; i < 24; i++ {
level := uint8(8 + 10*i)
assert.Equal(t, []uint8{level, level, level}, C256ToRgb(uint8(232+i)))
}
}