http://d.asgeirsson.is/Vvpo <-inputs (PNG: 1.5m JPEG+Mask: ~100k)

uiimage+mask.mm

+ (NSString *)_pathForImageName:(NSString *)aFileName
{
    NSString * const extension = [aFileName pathExtension];
    if([extension length] == 0)
        return
            [self _pathForImageName:[aFileName stringByAppendingString:@".png"]]
         ?: [self _pathForImageName:[aFileName stringByAppendingString:@".jpeg"]]
         ?: [self _pathForImageName:[aFileName stringByAppendingString:@".jpg"]];
    else {
        aFileName = [aFileName stringByDeletingPathExtension];
        
        if([[UIScreen mainScreen] scale] == 2.0f)
            return [[NSBundle coineyKitBundle] pathForResource:[aFileName stringByAppendingString:@"@2x"]
                                                        ofType:extension]
                ?: [[NSBundle coineyKitBundle] pathForResource:aFileName ofType:extension];
        else
            return [[NSBundle coineyKitBundle] pathForResource:aFileName ofType:extension]
                ?: [[NSBundle coineyKitBundle] pathForResource:[aFileName stringByAppendingString:@"@2x"]
                                                        ofType:extension];
    }
}

+ (UIImage *)cy_imageNamed:(NSString * const)aName
{
    NSString * const path = [self _pathForImageName:aName];
    if(path) {
        UIImage * const image = [self imageWithContentsOfFile:path];
        
        NSString * const maskPath = [self _pathForImageName:[[aName stringByDeletingPathExtension] stringByAppendingString:@"Mask"]];
        if(maskPath)
            return [image cy_imageByApplyingMask:[self cy_imageWithContentsOfFile:maskPath]];
        else
            return image;
    } else
        return [self imageNamed:aName];
}

- (UIImage *)cy_imageByApplyingMask:(UIImage * const)aMaskImage
{
    if(!aMaskImage)
        return nil;
    
    CGImageRef const mask = CGImageMaskCreate(CGImageGetWidth(aMaskImage.CGImage), CGImageGetHeight(aMaskImage.CGImage),
                                              CGImageGetBitsPerComponent(aMaskImage.CGImage),
                                              CGImageGetBitsPerPixel(aMaskImage.CGImage),
                                              CGImageGetBytesPerRow(aMaskImage.CGImage),
                                              CGImageGetDataProvider(aMaskImage.CGImage),
                                              NULL, FALSE);
    
    CGImageRef const maskedCGImage = CGImageCreateWithMask(self.CGImage, mask);
    UIImage  * const maskedImage = [UIImage imageWithCGImage:maskedCGImage
                                                       scale:self.scale
                                                 orientation:self.imageOrientation];
    CGImageRelease(maskedCGImage);
    CGImageRelease(mask);
    
    return maskedImage;
    
}