I'm struggling with setting color in a NSBitmapImageRep. I'm computing
the components of a NSColor according to a numeric value; its basically
a linear interpolation between all components of two NSColors. I've got
a function which is computing the new NSColor based on a given value. If
I call this function repeatedly using the same value and setting the
color using NSBitmapImageRep setColor:atX:y:, I expect to have a uniform
image if applying to all pixels. But this is not the case...! What am I
missing ?
As I'm probably a little bit confusing, here the code producing my
strange image :
// Creating two colors which define a gradient. The color for our image
// will be computed using this gradient.
NSColor *lightYellow =
[NSColor colorWithCalibratedRed:0.97 green:0.93 blue:0.65
alpha:1.0];
NSColor *darkRed =
[NSColor colorWithCalibratedRed:0.69 green:0.09 blue:0.11
alpha:1.0];
// Creating an empty image with the same color space.
NSBitmapImageRep *img = [[NSBitmapImageRep alloc]
initWithBitmapDataPlanes:NULL
pixelsWide:10
pixelsHigh:10
bitsPerSample:8
samplesPerPixel:3
hasAlpha:NO
isPlanar:YES
colorSpaceName:[lightYellow colorSpaceName]
bitmapFormat:0
bytesPerRow:0
bitsPerPixel:0];
// Assigning the same (???) color to all pixels.
int x, y;
for (y = 0; y < 10; y++)
{
for (x = 0; x < 10; x++)
{
NSColor *imgColor = [GradientColor gradientColorWithValue:40.0
minColor:lightYellow maxColor:darkRed
minValue:30.0 maxValue:60.0];
[img setColor:imgColor atX:x y:y];
}
}
[[img TIFFRepresentation]
writeToFile:@"/Users/chkaiser/Desktop/img.tif" atomically:YES];
And the function computing the gradient color based on our values:
+(NSColor*)gradientColorWithValue:(double)value minColor:(NSColor*)c1
maxColor:(NSColor*)c2 minValue:(double)v1 maxValue:(double)v2
{
// Color components.
CGFloat comps1[5];
[c1 getComponents:comps1];
CGFloat comps2[5];
[c2 getComponents:comps2];
// Compute the multiplication factor for the value. This factor has
// a value between 0 and 1.
double factor = (value - v1) / (v2 - v1);
// Compute the new components.
int i;
CGFloat newComps[5];
for (i = 0; i < [c1 numberOfComponents]; i++)
{
newComps[i] =
(factor * (comps2[i] - comps1[i])) +
comps1[i];
}
// Create the new color with the computed components.
NSColor *newColor = [NSColor colorWithColorSpace:[c1 colorSpace]
components:newComps count:[c1 numberOfComponents]];
return newColor;
}
What is going wrong here ?
I have not found any similar topic on this list until now, even if it
seems to me quite strange. Is there something obvious I am missing ?
--Christian Kaiser
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