CGImageCreateWithMask() not returning a masked image - ios

Question

I am trying to mask a UIImage with another UIImage. The image to be masked is generated from a gradient of colours, and the mask is a [UIImage systemImageNamed:]. The problem is that the resulting UIImage after masking looks like the gradient without the mask applied. I have provided the methods for creating the gradient and for masking it with the other image. Can anybody identify what is going wrong here? Thank you in advance!
// Creating the image
UIImage *mask = [UIImage systemImageNamed:#"person.crop.circle.fill.badge.plus"];
UIImage *gradient = [UIImage imageWithGradientColours:#[[UIColor redColor], [UIColor greenColor]] size:mask.size];
UIImage *masked = [gradient imageByApplyingMaskImage:mask];
UIImageView *imageView = [[UIImageView alloc] initWithImage:masked];
[self.view addSubview:imageView];
// UIImage+Gradient
// Generates a UIImage of the specified size with a gradient in the specified colours
+ (UIImage*)imageWithGradientColours:(NSArray*)colours size:(CGSize)size {
CAGradientLayer *gradientLayer = [CAGradientLayer layer];
gradientLayer.frame = CGRectMake(0, 0, size.width, size.height);
NSMutableArray *cgColours = [NSMutableArray array];
for (UIColor *colour in colours) {
[cgColours addObject:(id)colour.CGColor];
}
gradientLayer.colors = cgColours;
UIGraphicsBeginImageContext(size);
[gradientLayer renderInContext:UIGraphicsGetCurrentContext()];
UIImage *gradientImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return [gradientImage imageWithRenderingMode:UIImageRenderingModeAlwaysOriginal];
}
// UIImage+MaskWithImage
// Returns a UIImage with a mask applied using the provided mask image
- (UIImage *)imageByApplyingMaskImage:(UIImage *)maskImage {
CGImageRef maskRef = maskImage.CGImage;
CGImageRef mask = CGImageMaskCreate(CGImageGetWidth(maskRef),
CGImageGetHeight(maskRef),
CGImageGetBitsPerComponent(maskRef),
CGImageGetBitsPerPixel(maskRef),
CGImageGetBytesPerRow(maskRef),
CGImageGetDataProvider(maskRef), NULL, false);
CGImageRef maskedImageRef = CGImageCreateWithMask(self.CGImage, mask);
UIImage *maskedImage = [UIImage imageWithCGImage:maskedImageRef scale:[[UIScreen mainScreen] scale] orientation:UIImageOrientationUp];
CGImageRelease(mask);
CGImageRelease(maskedImageRef);
// returns new image with mask applied
return maskedImage;
}

Answer 1

Ah, I found the answer. I had to do some processing on the mask image before it would work properly as a mask:
- (UIImage *)imageAsMask {
//Ensure the image isn't rendered as template
//Tint the image with [UIColor blackColor]
UIImage *mask = [[self imageWithRenderingMode:UIImageRenderingModeAlwaysOriginal] imageWithTintColor:[UIColor blackColor]];
//Context for redrawing the mask
UIGraphicsBeginImageContextWithOptions(mask.size, YES, 1.0);
//Fill the mask with white background
[[UIColor whiteColor] setFill];
CGContextFillRect(UIGraphicsGetCurrentContext(), CGRectMake(0, 0, mask.size.width, mask.size.height));
//Draw the black mask on top of the white background
[mask drawAtPoint:CGPointZero];
//Get the image from the context and return
mask = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return mask;
}
And then to generate a masked image I just do:
UIImage *mask = [[UIImage systemImageNamed:#"person.crop.circle.fill.badge.plus"] imageAsMask];
UIImage *gradient = [UIImage imageWithGradientColours:#[[UIColor redColor], [UIColor greenColor]] size:mask.size];
UIImage *masked = [gradient imageByApplyingMaskImage:mask];