CaveOps | Post: iOS: UIImage gauss blur

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为 UIImage 生成高斯模糊效果:
- (UIImage *)gaussBlurWithLevel:(CGFloat)blurLevel {
    blurLevel = MIN(1.0, MAX(0.0, blurLevel));

    int boxSize = (int)(blurLevel * 0.1 * MIN(self.size.width, self.size.height));
    boxSize = boxSize - (boxSize % 2) + 1;
    UIImage *decode = [UIImage decode:self];
    NSData *imageData = UIImageJPEGRepresentation((decode ? decode : self), 1);
    if (imageData == nil) {
        return self;
    }
    UIImage *tmpImage = [UIImage imageWithData:imageData];
    if (tmpImage == nil) {
        return self;
    }

    CGImageRef img = tmpImage.CGImage;
    vImage_Buffer inBuffer, outBuffer;
    vImage_Error error;
    void *pixelBuffer;

    //create vImage_Buffer with data from CGImageRef
    CGDataProviderRef inProvider = CGImageGetDataProvider(img);
    CFDataRef inBitmapData = CGDataProviderCopyData(inProvider);

    inBuffer.width = CGImageGetWidth(img);
    inBuffer.height = CGImageGetHeight(img);
    inBuffer.rowBytes = CGImageGetBytesPerRow(img);

    inBuffer.data = (void*)CFDataGetBytePtr(inBitmapData);

    //create vImage_Buffer for output
    pixelBuffer = malloc(CGImageGetBytesPerRow(img) * CGImageGetHeight(img));

    outBuffer.data = pixelBuffer;
    outBuffer.width = CGImageGetWidth(img);
    outBuffer.height = CGImageGetHeight(img);
    outBuffer.rowBytes = CGImageGetBytesPerRow(img);

    NSInteger windowR = boxSize/2;
    CGFloat sig2 = windowR / 3.0;
    if(windowR>0){ sig2 = -1/(2*sig2*sig2); }

    int16_t *kernel = (int16_t*)malloc(boxSize*sizeof(int16_t));
    int32_t  sum = 0;
    for(NSInteger i=0; i<boxSize; ++i){
        kernel[i] = 255*exp(sig2*(i-windowR)*(i-windowR));
        sum += kernel[i];
    }

    // convolution
    error = vImageConvolve_ARGB8888(&inBuffer, &outBuffer, NULL, 0, 0, kernel, boxSize, 1, sum, NULL, kvImageEdgeExtend)?:
    vImageConvolve_ARGB8888(&outBuffer, &inBuffer, NULL, 0, 0, kernel, 1, boxSize, sum, NULL, kvImageEdgeExtend);
    outBuffer = inBuffer;

    free(kernel);

    if (error) {
        MXLog(@"error from convolution %ld", error);
    }

    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
    CGContextRef ctx = CGBitmapContextCreate(outBuffer.data,
                                             outBuffer.width,
                                             outBuffer.height,
                                             8,
                                             outBuffer.rowBytes,
                                             colorSpace,
                                             kCGBitmapAlphaInfoMask & kCGImageAlphaNoneSkipLast);
    CGImageRef imageRef = CGBitmapContextCreateImage(ctx);
    UIImage *returnImage = [UIImage imageWithCGImage:imageRef];

    //clean up
    CGContextRelease(ctx);
    CGColorSpaceRelease(colorSpace);
    free(pixelBuffer);
    CFRelease(inBitmapData);
    CGImageRelease(imageRef);

    return returnImage;
}