Accord.Vision.Motion.TwoFramesDifferenceDetector.ProcessFrame C# (CSharp) Method

        public void ProcessFrame(UnmanagedImage videoFrame)
        {
            lock (sync)
            {
                // check previous frame
                if (previousFrame == null)
                {
                    // save image dimension
                    width = videoFrame.Width;
                    height = videoFrame.Height;

                    // alocate memory for previous and current frames
                    previousFrame = UnmanagedImage.Create(width, height, PixelFormat.Format8bppIndexed);
                    motionFrame = UnmanagedImage.Create(width, height, PixelFormat.Format8bppIndexed);

                    frameSize = motionFrame.Stride * height;

                    // temporary buffer
                    if (suppressNoise)
                    {
                        tempFrame = UnmanagedImage.Create(width, height, PixelFormat.Format8bppIndexed);
                    }

                    // convert source frame to grayscale
                    Accord.Vision.Tools.ConvertToGrayscale(videoFrame, previousFrame);

                    return;
                }

                // check image dimension
                if ((videoFrame.Width != width) || (videoFrame.Height != height))
                    return;

                // convert current image to grayscale
                Accord.Vision.Tools.ConvertToGrayscale(videoFrame, motionFrame);

                unsafe
                {
                    // pointers to previous and current frames
                    byte* prevFrame = (byte*)previousFrame.ImageData.ToPointer();
                    byte* currFrame = (byte*)motionFrame.ImageData.ToPointer();
                    // difference value
                    int diff;

                    // 1 - get difference between frames
                    // 2 - threshold the difference
                    // 3 - copy current frame to previous frame
                    for (int i = 0; i < frameSize; i++, prevFrame++, currFrame++)
                    {
                        // difference
                        diff = (int)*currFrame - (int)*prevFrame;
                        // copy current frame to previous
                        *prevFrame = *currFrame;
                        // treshold
                        *currFrame = ((diff >= differenceThreshold) || (diff <= differenceThresholdNeg)) ? (byte)255 : (byte)0;
                    }

                    if (suppressNoise)
                    {
                        // suppress noise and calculate motion amount
                        Accord.SystemTools.CopyUnmanagedMemory(tempFrame.ImageData, motionFrame.ImageData, frameSize);
                        erosionFilter.Apply(tempFrame, motionFrame);
                    }

                    // calculate amount of motion pixels
                    pixelsChanged = 0;
                    byte* motion = (byte*)motionFrame.ImageData.ToPointer();

                    for (int i = 0; i < frameSize; i++, motion++)
                    {
                        pixelsChanged += (*motion & 1);
                    }
                }
            }
        }