AForge.Vision.Motion.CustomFrameDifferenceDetector.ProcessFrame C# (CSharp) Method

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

                    // alocate memory for background frame
                    backgroundFrame = UnmanagedImage.Create( width, height, PixelFormat.Format8bppIndexed );
                    frameSize = backgroundFrame.Stride * height;

                    // convert source frame to grayscale
                    Tools.ConvertToGrayscale( videoFrame, backgroundFrame );

                    return;
                }

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

                // check motion frame
                if ( motionFrame == null )
                {
                    motionFrame = UnmanagedImage.Create( width, height, PixelFormat.Format8bppIndexed );

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

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

                // pointers to background and current frames
                byte* backFrame;
                byte* currFrame;
                int diff;

                backFrame = (byte*) backgroundFrame.ImageData.ToPointer( );
                currFrame = (byte*) motionFrame.ImageData.ToPointer( );

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

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

                    if ( keepObjectEdges )
                    {
                        AForge.SystemTools.CopyUnmanagedMemory( tempFrame.ImageData, motionFrame.ImageData, frameSize );
                        dilatationFilter.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 );
                }
            }
        }