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

        protected override unsafe void ProcessFilter(UnmanagedImage image, Rectangle rect)
        {
            // processing start and stop X,Y positions
            startX = rect.Left;
            startY = rect.Top;
            stopX = startX + rect.Width;
            stopY = startY + rect.Height;
            stride = image.Stride;

            int offset = stride - rect.Width;

            // pixel value and error value
            int v, error;

            // do the job
            byte* ptr = (byte*)image.ImageData.ToPointer();

            // allign pointer to the first pixel to process
            ptr += (startY * stride + startX);

            // for each line
            for (y = startY; y < stopY; y++)
            {
                // for each pixels
                for (x = startX; x < stopX; x++, ptr++)
                {
                    v = *ptr;

                    // fill the next destination pixel
                    if (v >= threshold)
                    {
                        *ptr = 255;
                        error = v - 255;
                    }
                    else
                    {
                        *ptr = 0;
                        error = v;
                    }

                    // do error diffusion
                    Diffuse(error, ptr);
                }
                ptr += offset;
            }
        }
    }