@interface UIImage (Mask)
- (UIImage *)imageWithMask:(UIImage *)maskImage;
@end

@implementation UIImage (Mask)

- (UIImage *)imageWithMask:(UIImage *)maskImage {
	CGImageRef maskRef = maskImage.CGImage;

	CGImageRef mask = CGImageMaskCreate(
        CGImageGetWidth(maskRef),
		CGImageGetHeight(maskRef),
		CGImageGetBitsPerComponent(maskRef),
		CGImageGetBitsPerPixel(maskRef),
		CGImageGetBytesPerRow(maskRef),
		CGImageGetDataProvider(maskRef), NULL, false
    );

    CGImageRef masked = CGImageCreateWithMask(self.CGImage, mask);
    CGImageRelease(mask);
	return [UIImage imageWithCGImage:masked];
}

@end

Enjoy!

David

Here is my code:

- (void)viewDidLoad
{
[super viewDidLoad];
UIImage *imageToMask = [UIImage imageNamed:@"koko.jpg"];
UIImageView *imageToMaskImgView = [[UIImageView alloc] initWithImage:imageToMask];
CGRect imgRect = CGRectMake(0, 0, imageToMaskImgView.frame.size.width, imageToMaskImgView.frame.size.height);
UIView *maskMaster = [[UIView alloc] initWithFrame:imgRect];
[maskMaster setBackgroundColor:[UIColor whiteColor]];
[maskMaster addSubview:imageToMaskImgView];
UIGraphicsBeginImageContext(maskMaster.bounds.size);
[maskMaster.layer renderInContext:UIGraphicsGetCurrentContext()];
UIImage *viewImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
NSLog(@”%@ is the view image”, viewImage);
UIImage *bFooImg = [UIImage imageNamed:@"blackapple.png"];
self.myPic.image = [self maskImage:bFooImg withMask:viewImage];
}

- (UIImage*) maskImage:(UIImage *)image withMask:(UIImage *)maskImage {

CGImageRef maskRef = maskImage.CGImage;

CGImageRef mask = CGImageMaskCreate(CGImageGetWidth(maskRef),
CGImageGetHeight(maskRef),
CGImageGetBitsPerComponent(maskRef),
CGImageGetBitsPerPixel(maskRef),
CGImageGetBytesPerRow(maskRef),
CGImageGetDataProvider(maskRef), NULL, false);

CGImageRef masked = CGImageCreateWithMask([image CGImage], mask);
//memman
CGImageRelease(mask);
CGImageRelease(maskRef);
return [UIImage imageWithCGImage:masked];

}

Thanks for the detailed code. However i tried the same snippet with in my project. It didn’t work for me Let me explain you the situation in more detailed way. I have one image of a fish which is the main image having a fish image in front but the background is white. I created another image which is a mask which is of the same size of the original image but is of color black. When i execute the following piece of code it gives me a transparent black.

[self maskImage:[UIImage imageNamed:@"MaskedBlack.png"] withMask:[UIImage imageNamed:@"Angel-fish-300x233.png"]];

With the following code i am getting the original image as it is. It does not give me the extracted image

[self maskImage:[UIImage imageNamed:@"Angel-fish-300x233.png"] withMask:[UIImage imageNamed:@"MaskedBlack.png"]]

Pl. let me know if there is any resolution to this.

Note: I want to extract the fish out of the image as it is without any white background.

Thanks
Harry

-(CGImageRef) CopyImageAndAddAlphaChannel :(CGImageRef) sourceImage
{
CGImageRef retVal = NULL;

size_t width = CGImageGetWidth(sourceImage);
size_t height = CGImageGetHeight(sourceImage);

CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();

CGContextRef offscreenContext = CGBitmapContextCreate(NULL, width, height,
8, 0, colorSpace, kCGImageAlphaPremultipliedFirst);

if (offscreenContext != NULL) {
CGContextDrawImage(offscreenContext, CGRectMake(0, 0, width, height), sourceImage);

retVal = CGBitmapContextCreateImage(offscreenContext);
CGContextRelease(offscreenContext);
}

CGColorSpaceRelease(colorSpace);

return retVal;
}

- (UIImage*)maskImage:(UIImage *)image withMask:(UIImage *)maskImage {
CGImageRef maskRef = maskImage.CGImage;
CGImageRef mask = CGImageMaskCreate(CGImageGetWidth(maskRef),
CGImageGetHeight(maskRef),
CGImageGetBitsPerComponent(maskRef),
CGImageGetBitsPerPixel(maskRef),
CGImageGetBytesPerRow(maskRef),
CGImageGetDataProvider(maskRef), NULL, false);

CGImageRef sourceImage = [image CGImage];
CGImageRef imageWithAlpha = sourceImage;
//add alpha channel for images that don’t have one (ie GIF, JPEG, etc…)
//this however has a computational cost
if (CGImageGetAlphaInfo(sourceImage) == kCGImageAlphaNone) {
imageWithAlpha = [self CopyImageAndAddAlphaChannel :sourceImage];
}

CGImageRef masked = CGImageCreateWithMask(imageWithAlpha, mask);
CGImageRelease(mask);

//release imageWithAlpha if it was created by CopyImageAndAddAlphaChannel
if (sourceImage != imageWithAlpha) {
CGImageRelease(imageWithAlpha);
}

UIImage* retImage = [UIImage imageWithCGImage:masked];
CGImageRelease(masked);

return retImage;
}

- (void)viewDidLoad
{
[super viewDidLoad];

imgView.image = [self maskImage :[UIImage imageNamed:@"input.png"] withMask:[UIImage imageNamed:@"mask.png"]];

// Do any additional setup after loading the view, typically from a nib.
}

I have an image with an white background. I want to extract that image portion of it. Can anybody help how to do this. I tried the above code it returning me an transparent image part of it.

I implemented this, but the mask image (logo) is always taking up the whole original image size. I just want to add a logo at the right bottom corner, but the logo takes up the whole image. How do we fix this? Is there a way to position the mask?

- (UIImage*) maskImage:(UIImage *)image withMask:(UIImage *)maskImage {

CGImageRef maskRef = maskImage.CGImage;

CGImageRef mask = CGImageMaskCreate(CGImageGetWidth(maskRef),
CGImageGetHeight(maskRef),
CGImageGetBitsPerComponent(maskRef),
CGImageGetBitsPerPixel(maskRef),
CGImageGetBytesPerRow(maskRef),
CGImageGetDataProvider(maskRef), NULL, false);

CGImageRef masked = CGImageCreateWithMask([image CGImage], mask);
UIImage *tempImage= [UIImage imageWithCGImage:masked];

NSData *imageData=UIImagePNGRepresentation(tempImage);

return ([UIImage imageWithData:imageData]);