How to make images transparent on the fly in an iPhone app?

Recently I had to clean-up images on the fly. I didn't find anything by googling. After trying out different things , I ended up with the following piece of code that removes the white background from any image on the fly and makes it totally transparent

-(UIImage *)createMask:(UIImage*)temp {
     size_t height = CGImageGetHeight(temp.CGImage);
     size_t width = CGImageGetWidth(temp.CGImage);
     UIGraphicsBeginImageContext(CGSizeMake(width, height));
     CGContextRef context = UIGraphicsGetCurrentContext();
     const float colorMasking[6] = { 255.0, 255.0, 255.0, 255.0, 255.0, 255.0};
     CGImageRef maskedImageRef = CGImageCreateWithMaskingColors(temp.CGImage, colorMasking);    
     CGContextDrawImage (context, CGRectMake(0, 0, width, height), maskedImageRef);
     UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
     UIGraphicsEndImageContext();
     return image;
}

Note that you can give a range of colors to CGImageCreateWithMaskingColors..