I have 3 files, one with only a red channel, one with only a green channel, one with only a blue channel. Now i want to combine those 3 images to one, where every image is one color-channel in the finished image.
How can i do this with cocoa? I have a solution that is working but is too slow:
NSBitmapImageRep *rRep = [[rImage representations] objectAtIndex: 0];
NSBitmapImageRep *gRep = [[gImage representations] objectAtIndex: 0];
NSBitmapImageRep *bRep = [[bImage representations] objectAtIndex: 0];
NSBitmapImageRep *finalRep = [rRep copy];
for (NSUInteger i = 0; i < [rRep pixelsWide]; i++) {
for (NSUInteger j = 0; j < [rRep pixelsHigh]; j++) {
CGFloat r = [[rRep colorAtX:i y:j] redComponent];
CGFloat g = [[gRep colorAtX:i y:j] greenComponent];
CGFloat b = [[bRep colorAtX:i y:j] blueComponent];
[finalRep setColor:[NSColor colorWithCalibratedRed:r green:g blue:b alpha:1.0] atX:i y:j];
}
}
NSData *data = [finalRep representationUsingType:NSJPEGFileType properties:[NSDictionary dictionaryWithObject:[NSNumber numberWithDouble:0.7] forKey:NSImageCompressionFactor]];
[data writeToURL:[panel URL] atomically:YES];
The Accelerate.framework provides a function to combine 3 planar images into one destination: vImageConvert_Planar8toRGB888.
I haven't tried your approach but the vImage based method below is quite fast.
I was able to combine three (R,G,B) planes of a 1680x1050 image in ~0.1s on my Mac. The actual conversion takes ~1/3 of that time - The rest is setup & file IO.