ImageExtractor.m

// Turn an image into an array of UIColors.
+ (NSArray *)pixelsForImage:(UIImage *)image {
  NSUInteger width = [image size].width;
  NSUInteger height = [image size].height;
  NSUInteger count = width * height;
  NSMutableArray *result = [NSMutableArray arrayWithCapacity:count];

  CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();

  // Add 1 for the alpha channel
  size_t numberOfComponents = CGColorSpaceGetNumberOfComponents(colorSpace) + 1;
  size_t bitsPerComponent = 8;
  size_t bytesPerPixel = (bitsPerComponent * numberOfComponents) / 8;
  size_t bytesPerRow = bytesPerPixel * width;

  uint8_t *rawData = (uint8_t*)calloc(count * numberOfComponents, sizeof(uint8_t));

  CGContextRef context = CGBitmapContextCreate(rawData,
                                               width,
                                               height,
                                               bitsPerComponent,
                                               bytesPerRow,
                                               colorSpace,
                                               (CGBitmapInfo) kCGImageAlphaPremultipliedLast);

  CGColorSpaceRelease(colorSpace);

  CGImageRef cgImage = [image CGImage];
  CGContextDrawImage(context, CGRectMake(0, 0, width, height), cgImage);

  int byteIndex = 0;
  for (int i = 0 ; i < count ; ++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;
    byteIndex += 4;

    UIColor *color = [UIColor colorWithRed:red green:green blue:blue alpha:alpha];
    [result addObject:color];
  }

  CGContextRelease(context);
  free(rawData);

  return result;
}