Objective-C change image color performance - ios

Question

I am currently using the function below to change png image color, the color is set through a color slider, so while sliding through colors everything works fine and get the resulted image colored correspondingly, I am only having issue with slider performance while sliding, it keeps lagging as well as for the image color update, need help to make the process smooth.
- (UIImage*)imageWithImage:(UIImage *)sourceImage fixedHue:(CGFloat)hue saturation:(CGFloat)saturation brightness:(CGFloat)brightness alpha:(CGFloat)alpha{
CGSize imageSize = [sourceImage size];
UIGraphicsBeginImageContext(imageSize);
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextTranslateCTM(context, 0, sourceImage.size.height);
CGContextScaleCTM(context, 1.0, -1.0);
CGRect rect = CGRectMake(0, 0, sourceImage.size.width, sourceImage.size.height);
CGContextSetBlendMode(context, kCGBlendModeNormal);
CGContextDrawImage(context, rect, sourceImage.CGImage);
CGContextSetBlendMode(context, kCGBlendModeColor);
[[UIColor colorWithHue:hue saturation:saturation brightness:brightness alpha:alpha] setFill];
CGContextFillRect(context, rect);
CGContextSetBlendMode(context, kCGBlendModeDestinationIn);
CGContextDrawImage(context, rect, sourceImage.CGImage);
CGContextFlush(context);
UIImage *editedImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return editedImage;
}

Answer 1

Make an async version of your function as follows...
- (void)imageWithImage:(UIImage *)sourceImage
fixedHue:(CGFloat)hue
saturation:(CGFloat)saturation
brightness:(CGFloat)brightness
alpha:(CGFloat)alpha
completion:(void (^)(UIImage *))completion {
dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
dispatch_async(queue, ^{
// call your original function. Use this to create the context...
UIGraphicsBeginImageContextWithOptions(imageSize, YES, 0.0 );
// don't call CGContextFillRect, call...
UIRectFill(rect);
// don't call CGContextDrawImage, call...
[sourceImage drawInRect:rect]
// don't call CGContextFlush, don't need to replace that
UIImage *image = [self imageWithImage:sourceImage fixedHue:hue saturation:saturation brightness:brightness alpha:alpha];
dispatch_async(dispatch_get_main_queue(), ^{
completion(image);
});
});
}
Use it like this:
- (IBAction)sliderValueChanged:(UISlider *)sender {
[self imageWithImage:sourceImage
fixedHue:hue
saturation:saturation
brightness:brightness
alpha:alpha
completion:^(UIImage *image) {
// update the UI here with image
}];
}