Get the color a pixel on the screen in objective-c cocoa app

Question

I am trying to create a color picker cocoa app in objective-c so I can get the color of any pixel on my screen. Is there a way to get the color a certain screen pixel in objective-c?

Answer 1

You can use CGDisplayCreateImageForRect to get a CGImageRef that encompasses the point you're interested in. Once you have a CGImage, you can get a color value out of it by rendering the image into custom buffer, or by using NSBitmapImageRep's initWithCGImage and then colorAtX:y:. The "written in stack overflow code window" code for the NSBitmapImageRep method would look something like:

NSColor *MyColorAtScreenCoordinate(CGDirectDisplayID displayID, NSInteger x, NSInteger y) {
    CGImageRef image = CGDisplayCreateImageForRect(displayID, CGRectMake(x, y, 1, 1));
    NSBitmapImageRep *bitmap = [[NSBitmapImageRep alloc] initWithCGImage:image];
    CGImageRelease(image);
    NSColor *color = [bitmap colorAtX:0 y:0];
    [bitmap release];
}

That will probably return the color in device color space. It might be useful to return the color in calibrated RBG color space instead.