test.m

    UIGraphicsBeginImageContextWithOptions(self.size, NO, [[UIScreen mainScreen] scale]);
    CGContextRef outputContext = UIGraphicsGetCurrentContext();
    CGContextScaleCTM(outputContext, 1.0, -1.0);
    CGContextTranslateCTM(outputContext, 0, -self.size.height);

    // draw base image
    CGContextDrawImage(outputContext, imageRect, self.CGImage);

    // draw effect image
    if (hasBlur) {
        CGContextSaveGState(outputContext);
        if (maskImage) {
            CGContextClipToMask(outputContext, imageRect, maskImage.CGImage);
        }
        CGContextDrawImage(outputContext, imageRect, effectImage.CGImage);
        CGContextRestoreGState(outputContext);
    }

    // output image is ready
    UIImage *outputImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();