Get all colors from an image

Question

I have a posterized image with CIColorPosterize CIFilter. The image contains a few number of colors. At this point I would like to extract an UIColor's array with the n-colors from this image. There is a function that does something like this? Otherwise, which could be an effective approach to realize this?

Thank you experts!

Answer 1

You can try this..

CGImageRef imageRef = [yourImage CGImage];
NSUInteger width = CGImageGetWidth(imageRef);
NSUInteger height = CGImageGetHeight(imageRef);
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
unsigned char *rawData = (unsigned char*) calloc(height * width * 4, sizeof(unsigned char));

// Now your rawData contains the image data in the RGBA8888 pixel format.
int byteIndex = (bytesPerRow * yy) + xx * bytesPerPixel;
for (int i = 0 ; i < count ; byteIndex += 4,++i)
{
    CGFloat red   = (rawData[byteIndex]     * 1.0) / 255.0;
    CGFloat green = (rawData[byteIndex + 1] * 1.0) / 255.0;
    CGFloat blue  = (rawData[byteIndex + 2] * 1.0) / 255.0;
    CGFloat alpha = (rawData[byteIndex + 3] * 1.0) / 255.0;    
    UIColor *acolor = [UIColor colorWithRed:red green:green blue:blue alpha:alpha];
    [result addObject:acolor];
}

free(rawData);
NSLog(@"Extracted colors count %d",result.count);