自适应阈值 CIKernel/CIFilter iOS

为了找到一个在 iOS 上执行自适应阈值处理的内核，我进行了全面的研究。不幸的是我不理解内核语言或其背后的逻辑。下面，我找到了一个执行阈值处理的例程（https://gist.github.com/xhruso00/a3f8a9c8ae7e33b8b23d https://gist.github.com/xhruso00/a3f8a9c8ae7e33b8b23d)

static NSString * const kKernelSource = @"kernel vec4 thresholdKernel(sampler image)\n"
"{\n"
"  float inputThreshold = 0.05;\n"
"  float pass = 1.0;\n"
"  float fail = 0.0;\n"
"  const vec4   vec_Y = vec4( 0.299, 0.587, 0.114, 0.0 );\n"
"  vec4  src = unpremultiply( sample(image, samplerCoord(image)) );\n"
"  float Y = dot( src, vec_Y );\n"
"  src.rgb = vec3( compare( Y - inputThreshold, fail, pass));\n"
"  return premultiply(src);\n"
"}";

是否可以将其重写为自适应阈值内核？我提供给它的图像已变成黑白并且已经模糊。您可以向我指出任何资源吗？我想坚持使用 CoreImage，因为我的整个堆栈都是围绕它构建的。

编辑：我想要实现的最佳示例/参考已在 GPUImage 的 GPUImageAdaptiveThresholdFilter 中实现 -https://github.com/BradLarson/GPUImage/blob/c5f0914152419437869c35e29858773b1a06083c/framework/Source/GPUImageAdaptiveThresholdFilter.m https://github.com/BradLarson/GPUImage/blob/c5f0914152419437869c35e29858773b1a06083c/framework/Source/GPUImageAdaptiveThresholdFilter.m

看起来怎么样：我使用了 CoreImageCIBoxBlur（虽然专用的卷积滤波器may更快）并将其输出传递到我的现有阈值过滤器 https://github.com/FlexMonkey/Filterpedia/blob/master/Filterpedia/customFilters/CustomFilters.swift.

class AdaptiveThresholdFilter: CIFilter
{
    var inputImage : CIImage?


    var thresholdKernel =  CIColorKernel(string:
    "kernel vec4 thresholdFilter(__sample image, __sample threshold)" +
    "{" +
    "   float imageLuma = dot(image.rgb, vec3(0.2126, 0.7152, 0.0722));" +
    "   float thresholdLuma = dot(threshold.rgb, vec3(0.2126, 0.7152, 0.0722));" +

    "   return vec4(vec3(step(imageLuma, thresholdLuma)), 1.0);" +
    "}"
    )


    override var outputImage: CIImage!
    {
        guard let inputImage = inputImage,
            thresholdKernel = thresholdKernel else
        {
            return nil
        }

        let blurred = inputImage.imageByApplyingFilter("CIBoxBlur",
               withInputParameters: [kCIInputRadiusKey: 9])

        let extent = inputImage.extent
        let arguments = [inputImage, blurred]

        return thresholdKernel.applyWithExtent(extent, arguments: arguments)
    }
}

I found 这个图片 http://homepages.inf.ed.ac.uk/rbf/HIPR2/images/son1.gif阴影页面并使用以下代码：

let page = CIImage(image: UIImage(named: "son1.gif")!)

let filter = AdaptiveThresholdFilter()

filter.inputImage = page

let final = filter.outputImage

我得到这个结果：

Cheers!

Simon