Masking changes colors of UIImage- iOS - ios

Question

Here is what I am doing to mask a UIImage dynamically. It is working but for some reason the colors of output image is not the same as original one. What would be causing this? Thanks..
- (void) setClippingPath:(UIBezierPath *)clippingPath : (UIImageView *)imgView {
CAShapeLayer *maskLayer = [CAShapeLayer layer];
maskLayer.frame = self.imgView.frame;
maskLayer.path = [clippingPath CGPath];
maskLayer.fillColor = [[UIColor whiteColor] CGColor];
maskLayer.backgroundColor = [[UIColor clearColor] CGColor];
self.imgView.image = [self maskImage:self.imgView.image withClippingMask:[self imageFromLayer:maskLayer]];
}
- (UIImage *)imageFromLayer:(CALayer *)layer
{
UIGraphicsBeginImageContext([layer frame].size);
[layer renderInContext:UIGraphicsGetCurrentContext()];
UIImage *outputImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return outputImage;
}
-(UIImage*)maskImage:(UIImage *)image withClippingMask:(UIImage *)maskImage
{
CGImageRef maskRef = image.CGImage;
CGImageRef mask = CGImageMaskCreate(CGImageGetWidth(maskRef),
CGImageGetHeight(maskRef),
CGImageGetBitsPerComponent(maskRef),
CGImageGetBitsPerPixel(maskRef),
CGImageGetBytesPerRow(maskRef),
CGImageGetDataProvider(maskRef), NULL, false);
CGImageRef maskedImageRef = CGImageCreateWithMask([maskImage CGImage], mask);
UIImage *maskedImage = [UIImage imageWithCGImage:maskedImageRef];
CGImageRelease(mask);
CGImageRelease(maskedImageRef);
// returns new image with mask applied
return maskedImage;
}
Original Image
Mask
Output Image

Answer 1

The documentation for CGImageMaskCreate mentions:
When you draw into a context with a bitmap image mask, Quartz uses the mask to determine where and how the current fill color is applied to the image rectangle.
So if you want to just replace the black with white then you should be able to set the context color before creating the mask:
-(UIImage*)maskImage:(UIImage *)image withClippingMask:(UIImage *)maskImage
{
CGImageRef maskRef = image.CGImage;
CGContextSetFillColorWithColor( UIGraphicsGetCurrentContext( ), [ UIColor whiteColor ] );
CGImageRef mask = CGImageMaskCreate(CGImageGetWidth(maskRef),
CGImageGetHeight(maskRef),
CGImageGetBitsPerComponent(maskRef),
CGImageGetBitsPerPixel(maskRef),
CGImageGetBytesPerRow(maskRef),
CGImageGetDataProvider(maskRef), NULL, false);
CGImageRef maskedImageRef = CGImageCreateWithMask([maskImage CGImage], mask);
UIImage *maskedImage = [UIImage imageWithCGImage:maskedImageRef];
CGImageRelease(mask);
CGImageRelease(maskedImageRef);
// returns new image with mask applied
return maskedImage;
}
You might also want to update your mask to a more basic, greyscale JPG, something like this: