I'm not working on directly with the Gimp source, but I did fix the
bug with Preserve Luminosity. The offending code in color-balance.c
lines 182-187:
if (cb->preserve_luminosity)
{
gimp_rgb_to_hsl_int (&r_n, &g_n, &b_n);
b_n = gimp_rgb_to_l_int (r, g, b);
gimp_hsl_to_rgb_int (&r_n, &g_n, &b_n);
}
I'm working in Objective-C, so my code isn't copy paste ready.
Basically, if cb-> preserve_luminosity, re-scale the slider values so
that the lightness of R1+G1+B1 = the lightness of the base pixel
R+G+B, now use these modified slider values when changing the pixel
values:
-(NSBitmapImageRep *)colorAdjustedImage:(NSBitmapImageRep *)baseImageRep
preserveLumenance:(BOOL)preserveLumenance
colorTone:(LSColorTone)colorTone
{
int w,h,x,y = 0;
unsigned char *srcData, *p1;
int n, red, green, blue;
double shadowScale, midScale, highlightScale;
shadowScale = midScale = highlightScale = 1.0;
if (preserveLumenance == YES) {
shadowScale = 1.0 / ( ([_shadowToneRed doubleValue] / 100.0)
+
([_shadowToneGreen doubleValue] / 100.0) + ([_shadowToneBlue
doubleValue] / 100.0) );
midScale = 1.0 / ( ( [_midToneRed doubleValue] / 100.0)
+ (
[_midToneGreen doubleValue] / 100.0) + ( [_midToneBlue doubleValue]
/ 100.0) );
highlightScale = 1.0 / ( ( [_highToneRed doubleValue] / 100.0)
+ (
[_highToneGreen doubleValue] / 100.0) + ( [_highToneBlue doubleValue]
/ 100.0) );
shadowScale = shadowScale < -1/3 ? -1/3 : shadowScale;
shadowScale = shadowScale > 1/3 ? 1/3 : shadowScale;
shadowScale = shadowScale == 0 ? 1.0 : shadowScale;
midScale = midScale < -1/3 ? -1/3 : midScale;
midScale = midScale > 1/3 ? 1/3 : midScale;
midScale = midScale == 0 ? 1.0 : midScale;
highlightScale = highlightScale < -1/3 ? -1/3 : highlightScale;
highlightScale = highlightScale > 1/3 ? 1/3 : highlightScale;
highlightScale = highlightScale == 0 ? 1.0 : highlightScale;
}
// update the tonal range values from any changes in the UI
[self applyToneToColorAdjustment:colorToneMatrix];
// now set the slider values for the different tonal ranges
cyan_red[LSColorToneShadow] = shadowScale * [_shadowToneRed
doubleValue];
magenta_green[LSColorToneShadow] = shadowScale * [_shadowToneGreen
doubleValue];
yellow_blue[LSColorToneShadow] = shadowScale * [_shadowToneBlue
doubleValue];
cyan_red[LSColorToneMidtone] = midScale * [_midToneRed doubleValue];
magenta_green[LSColorToneMidtone] = midScale * [_midToneGreen doubleValue];
yellow_blue[LSColorToneMidtone] = midScale * [_midToneBlue doubleValue];
cyan_red[LSColorToneHighlights] = highlightScale *
[_highToneRed doubleValue];
magenta_green[LSColorToneHighlights] = highlightScale *
[_highToneGreen doubleValue];
yellow_blue[LSColorToneHighlights] = highlightScale *
[_highToneBlue doubleValue];
// create the color lookup tables for the current slider values
and tonal ranges
[self color_balance_create_lookup_tables];
// change the pixels
w = [baseImageRep pixelsWide];
h = [baseImageRep pixelsHigh];
srcData = [baseImageRep bitmapData];
n = [baseImageRep bitsPerPixel] / 8;
for ( y = 0 ; y < h ; y++) {
for ( x = 0 ; x < w ; x++) {
int r, g, b = 0;
p1 = srcData + n * (y * w + x);
// get the pixels color components
r = p1[0];
g = p1[1];
b = p1[2];
// lookup the new color values in the LUTS contructed from
slider values and tonal selections
red = r_lookup[r];
green = g_lookup[g];
blue = b_lookup[b];
// preserve lumenance if requested to do so
// original code from adapted from the Gimp, which does
not work correctly.
// if (preserveLumenance == YES) {
// gimp_rgb_to_hsl_int (&red, &green, &blue); // red
becomes hue, green becomes saturation, blue becomes lightness
// blue = gimp_rgb_to_l_int (r, g, b); // get the
lightness, set it
// gimp_hsl_to_rgb_int (&red, &green, &blue);
// }
// stomp the pixel component values
p1[0] = red;
p1[1] = green;
p1[2] = blue;
}
}
return baseImageRep;
}
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