How to change hue of UIIMAGE having transparent area?

Question

I am currently using following code for hue change:

  CGSize imageSize = [imageView.image size];
  CGRect imageExtent = CGRectMake(0,0,imageSize.width,imageSize.height);

  // Create a context containing the image.
  UIGraphicsBeginImageContext(imageSize);
  CGContextRef context = UIGraphicsGetCurrentContext();
  [imageView.image drawAtPoint:CGPointMake(0, 0)];

  // Draw the hue on top of the image.
  CGContextSetBlendMode(context, kCGBlendModeHue);
  [color set];

  UIBezierPath *imagePath = [UIBezierPath bezierPathWithRect:imageExtent];
  [imagePath fill];

  // Retrieve the new image.
  UIImage *result = UIGraphicsGetImageFromCurrentImageContext();
  imageView.image= result;

  UIGraphicsEndImageContext();

This code is working fine, only issue is it also sets the colour of transparent portions. Can I avoid applying the hue to that transparent area of the UIImage?

Attached following two images for reference:

Thanks in advance?

Output

Answer 1

Apply a mask from the image before adding the color.

CGSize imageSize = [imageView.image size];
CGRect imageExtent = CGRectMake(0,0,imageSize.width,imageSize.height);

// Create a context containing the image.
UIGraphicsBeginImageContext(imageSize);
CGContextRef context = UIGraphicsGetCurrentContext();
[imageView.image drawAtPoint:CGPointMake(0, 0)];

// Setup a clip region using the image
CGContextSaveGState(context);
CGContextClipToMask(context, imageExtent, imageView.image.CGImage);

[color set];
CGContextFillRect(context, imageExtent);

// Draw the hue on top of the image.
CGContextSetBlendMode(context, kCGBlendModeHue);
[color set];

UIBezierPath *imagePath = [UIBezierPath bezierPathWithRect:imageExtent];
[imagePath fill];

CGContextRestoreGState(context); // remove clip region

// Retrieve the new image.
UIImage *result = UIGraphicsGetImageFromCurrentImageContext();
imageView.image= result;

UIGraphicsEndImageContext();