Accord.Imaging.Filters.FastGuidedFilter.ProcessFilter C# (CSharp) Method

        protected override void ProcessFilter(UnmanagedImage image, UnmanagedImage overlay)
        {
            BaseResizeFilter resizer = new ResizeNearestNeighbor(
                (int)(image.Width * _subSamplingRatio),
                (int)(image.Height * _subSamplingRatio));

            UnmanagedImage imageSub = resizer.Apply(image);
            UnmanagedImage overlaySub = resizer.Apply(overlay);
            byte kernelSizeSub = (byte)(_kernelSize * _subSamplingRatio);

            UnmanagedImage imageBorder = new FastBoxBlur(kernelSizeSub, kernelSizeSub).Apply(
                GetFilledImage(imageSub.Width, imageSub.Height, imageSub.PixelFormat, Color.White));

            UnmanagedImage imageMean = new FastBoxBlur(kernelSizeSub, kernelSizeSub).Apply(imageSub);
            new Divide(imageBorder).ApplyInPlace(imageMean);

            UnmanagedImage overlayMean = new FastBoxBlur(kernelSizeSub, kernelSizeSub).Apply(overlaySub);
            new Divide(imageBorder).ApplyInPlace(overlayMean);

            UnmanagedImage mulMean = new Multiply(overlaySub).Apply(imageSub);
            overlaySub.Dispose();
            new FastBoxBlur(kernelSizeSub, kernelSizeSub).ApplyInPlace(mulMean);
            new Divide(imageBorder).ApplyInPlace(mulMean);

            //This is the covariance of (image, overlay) in each local patch.
            UnmanagedImage mulCov = new Subtract(new Multiply(overlayMean).Apply(imageMean)).Apply(mulMean);
            mulMean.Dispose();

            UnmanagedImage imageMean2 = new Multiply(imageSub).Apply(imageSub);
            imageSub.Dispose();
            new FastBoxBlur(kernelSizeSub, kernelSizeSub).ApplyInPlace(imageMean2);
            new Divide(imageBorder).ApplyInPlace(imageMean2);

            UnmanagedImage imageVar = new Subtract(new Multiply(imageMean).Apply(imageMean)).Apply(imageMean2);
            imageMean2.Dispose();

            byte cc = (byte)(255 * _epsilon);
            var imageEpsilon = GetFilledImage(
                imageVar.Width, imageVar.Height, imageVar.PixelFormat, Color.FromArgb(cc, cc, cc));

            new Add(imageEpsilon).ApplyInPlace(imageVar);
            imageEpsilon.Dispose();

            UnmanagedImage a = new Divide(imageVar).Apply(mulCov);
            imageVar.Dispose();
            mulCov.Dispose();

            UnmanagedImage b = new Subtract(new Multiply(imageMean).Apply(a)).Apply(overlayMean);
            imageMean.Dispose();
            overlayMean.Dispose();

            UnmanagedImage aMean = new Divide(imageBorder).Apply(new FastBoxBlur(kernelSizeSub, kernelSizeSub).Apply(a));
            UnmanagedImage bMean = new Divide(imageBorder).Apply(new FastBoxBlur(kernelSizeSub, kernelSizeSub).Apply(b));
            imageBorder.Dispose();
            a.Dispose();
            b.Dispose();

            resizer = new ResizeBilinear(image.Width, image.Height);

            aMean = resizer.Apply(aMean);
            bMean = resizer.Apply(bMean);

            new Multiply(aMean).ApplyInPlace(image);
            aMean.Dispose();
            new Add(bMean).ApplyInPlace(image);
            bMean.Dispose();
        }