Is it possible to isolate a single color in an UIImage/CGImageRef - iphone

Question

Wondering if there is a way to isolate a single color in an image either using masks or perhaps even a custom color space. I'm ultimately looking for a fast way to isolate 14 colors out of an image - figured if there was a masking method it might may be faster than walking through the pixels.
Any help is appreciated!

Answer 1

You could use a custom color space (documentation here) and then substitute it for "CGColorSpaceCreateDeviceGray()" in the following code:
- (UIImage *)convertImageToGrayScale:(UIImage *)image
{
// Create image rectangle with current image width/height
CGRect imageRect = CGRectMake(0, 0, image.size.width, image.size.height);
// Grayscale color space
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceGray(); // <- SUBSTITUTE HERE
// Create bitmap content with current image size and grayscale colorspace
CGContextRef context = CGBitmapContextCreate(nil, image.size.width, image.size.height, 8, 0, colorSpace, kCGImageAlphaNone);
// Draw image into current context, with specified rectangle
// using previously defined context (with grayscale colorspace)
CGContextDrawImage(context, imageRect, [image CGImage]);
// Create bitmap image info from pixel data in current context
CGImageRef imageRef = CGBitmapContextCreateImage(context);
// Create a new UIImage object
UIImage *newImage = [UIImage imageWithCGImage:imageRef];
// Release colorspace, context and bitmap information
CGColorSpaceRelease(colorSpace);
CGContextRelease(context);
CFRelease(imageRef);
// Return the new grayscale image
return newImage;
}
This code is from this blog which is worth a look at for removing colors from images.