UIImage category that adds a method to create a white image based on the source images alpha channel

UIImage+Alpha

@implementation UIImage (Alpha)

- (UIImage *)alphaImage{
    CGRect imageRect = CGRectMake(0, 0, self.size.width, self.size.height);
    CGColorSpaceRef rgbColorSpace = CGColorSpaceCreateDeviceRGB(); // create an RGB Color Space
    
    // create the context to do our drawing in
    CGContextRef context = CGBitmapContextCreate(NULL, imageRect.size.width, imageRect.size.height, 8, imageRect.size.width * 4, rgbColorSpace, kCGImageAlphaPremultipliedLast);
    // use the images alpha channel as a mask
    CGContextClipToMask(context, imageRect, self.CGImage);
    // set the fill color to be white
    CGContextSetRGBFillColor(context, 1.0, 1.0, 1.0, 1.0);
    // paint the image white w/ the mask
    CGContextFillRect(context, imageRect);
    
    // convert the context to a CGImage
    CGImageRef cgImage = CGBitmapContextCreateImage(context);
    // convert the CGImage into a UIImage
    UIImage *alphaImage = [UIImage imageWithCGImage:cgImage];
    
    // clean up
    CGContextRelease(context);
    CGColorSpaceRelease(rgbColorSpace);
    CGImageRelease(cgImage);
    
    // return the alpha image
    return alphaImage;
}

@end