AForge.Imaging.UnmanagedImage.CollectActivePixels C# (CSharp) Method

        public List<IntPoint> CollectActivePixels( Rectangle rect )
        {
            List<IntPoint> pixels = new List<IntPoint>( );

            int pixelSize = Bitmap.GetPixelFormatSize( pixelFormat ) / 8;

            // correct rectangle
            rect.Intersect( new Rectangle( 0, 0, width, height ) );

            int startX = rect.X;
            int startY = rect.Y;
            int stopX  = rect.Right;
            int stopY  = rect.Bottom;

            unsafe
            {
                byte* basePtr = (byte*) imageData.ToPointer( );

                if ( ( pixelFormat == PixelFormat.Format16bppGrayScale ) || ( pixelSize > 4 ) )
                {
                    int pixelWords = pixelSize >> 1;

                    for ( int y = startY; y < stopY; y++ )
                    {
                        ushort* ptr = (ushort*) ( basePtr + y * stride + startX * pixelSize );

                        if ( pixelWords == 1 )
                        {
                            // grayscale images
                            for ( int x = startX; x < stopX; x++, ptr++ )
                            {
                                if ( *ptr != 0 )
                                {
                                    pixels.Add( new IntPoint( x, y ) );
                                }
                            }
                        }
                        else
                        {
                            // color images
                            for ( int x = startX; x < stopX; x++, ptr += pixelWords )
                            {
                                if ( ( ptr[RGB.R] != 0 ) || ( ptr[RGB.G] != 0 ) || ( ptr[RGB.B] != 0 ) )
                                {
                                    pixels.Add( new IntPoint( x, y ) );
                                }
                            }
                        }
                    }
                }
                else
                {
                    for ( int y = startY; y < stopY; y++ )
                    {
                        byte* ptr = basePtr + y * stride + startX * pixelSize;

                        if ( pixelSize == 1 )
                        {
                            // grayscale images
                            for ( int x = startX; x < stopX; x++, ptr++ )
                            {
                                if ( *ptr != 0 )
                                {
                                    pixels.Add( new IntPoint( x, y ) );
                                }
                            }
                        }
                        else
                        {
                            // color images
                            for ( int x = startX; x < stopX; x++, ptr += pixelSize )
                            {
                                if ( ( ptr[RGB.R] != 0 ) || ( ptr[RGB.G] != 0 ) || ( ptr[RGB.B] != 0 ) )
                                {
                                    pixels.Add( new IntPoint( x, y ) );
                                }
                            }
                        }
                    }
                }
            }

            return pixels;
        }