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

    CFDataRef dataRef = CGDataProviderCopyData(CGImageGetDataProvider(masked));
    UInt8 *pixelBuffer = (UInt8 *)CFDataGetBytePtr(dataRef);

    CGContextRef ctx = CGBitmapContextCreate(pixelBuffer,
                                             CGImageGetWidth(masked),
                                             CGImageGetHeight(masked),
                                             CGImageGetBitsPerComponent(maskRef),
                                             CGImageGetBytesPerRow(masked),
                                             CGImageGetColorSpace(masked),
                                             kCGImageAlphaPremultipliedFirst);

    CGImageRelease(masked);
    CGImageRef imageRef = CGBitmapContextCreateImage(ctx);
    UIImage *newImage = [UIImage imageWithCGImage:imageRef];
    CGContextRelease(ctx);
    return newImage;