Image Filters

This is a continuation of the previous post at Handling Images in C#
A Grayscale Filter
To develop a Grayscale filter simply add up the red green and blue pixels and divide by 3. This averages out the values.

public static Bitmap GrayScaleFilter(Bitmap inputbitmap)
        {

            Bitmap outputbitmap = new Bitmap(inputbitmap.Width, inputbitmap.Height);

            BitmapData inputdata = inputbitmap.LockBits(new Rectangle(0, 0, inputbitmap.Width, inputbitmap.Height), ImageLockMode.ReadOnly, PixelFormat.Format24bppRgb);
            BitmapData outputdata = outputbitmap.LockBits(new Rectangle(0, 0, outputbitmap.Width, outputbitmap.Height), ImageLockMode.ReadWrite, PixelFormat.Format24bppRgb);

            int inputstride = inputdata.Stride;
            int outputstride = outputdata.Stride;

            System.IntPtr inputScan = inputdata.Scan0;
            System.IntPtr outputScan = outputdata.Scan0;
            unsafe
            {

                byte* newp1 = (byte*)(void*)inputScan;
                byte* newp2 = (byte*)(void*)outputScan;

                int newOffset1 = inputstride - inputbitmap.Width * 3;
                int newOffset2 = outputstride - outputdata.Width * 3;

                byte redvalue, greenvalue, bluevalue;
                byte newred, newgreen, newblue;
                for (int y = 0; y < inputbitmap.Height; ++y)
                {
                    for (int x = 0; x < inputbitmap.Width; ++x)
                    {


                        bluevalue = newp1[0];
                        greenvalue = newp1[1];
                        redvalue = newp1[2];
                        byte  grayscalevalue =(byte )( (redvalue + greenvalue + bluevalue) / 3.0);
                       

                        newp2[0] = grayscalevalue  ;
                        newp2[1] = grayscalevalue  ;
                        newp2[2] = grayscalevalue  ;
                        newp1 += 3;
                        newp2 += 3;
                    }

                    newp1 += newOffset1;
                    newp2 += newOffset2;
                }
            }


            inputbitmap.UnlockBits(inputdata );
            outputbitmap.UnlockBits(outputdata );
            return outputbitmap;



        }

A BlackAndWhite Filter

Simply take the averaged value from the previous filter. If the average is greater than 128 make it white 255 else make it black 255.


      public static Bitmap BlackAndWhiteFilter(Bitmap inputbitmap)
        {

            Bitmap outputbitmap = new Bitmap(inputbitmap.Width, inputbitmap.Height);

            BitmapData inputdata = inputbitmap.LockBits(new Rectangle(0, 0, inputbitmap.Width, inputbitmap.Height), ImageLockMode.ReadOnly, PixelFormat.Format24bppRgb);
            BitmapData outputdata = outputbitmap.LockBits(new Rectangle(0, 0, outputbitmap.Width, outputbitmap.Height), ImageLockMode.ReadWrite, PixelFormat.Format24bppRgb);

            int inputstride = inputdata.Stride;
            int outputstride = outputdata.Stride;

            System.IntPtr inputScan = inputdata.Scan0;
            System.IntPtr outputScan = outputdata.Scan0;
            unsafe
            {

                byte* newp1 = (byte*)(void*)inputScan;
                byte* newp2 = (byte*)(void*)outputScan;

                int newOffset1 = inputstride - inputbitmap.Width * 3;
                int newOffset2 = outputstride - outputdata.Width * 3;

                byte redvalue, greenvalue, bluevalue;
              
                for (int y = 0; y < inputbitmap.Height; ++y)
                {
                    for (int x = 0; x < inputbitmap.Width; ++x)
                    {


                        bluevalue = newp1[0];
                        greenvalue = newp1[1];
                        redvalue = newp1[2];
                        byte  avgvalue =(byte )( (redvalue + greenvalue + bluevalue) / 3.0);
                        if (avgvalue > 128)
                            avgvalue = 255;
                        else
                            avgvalue = 0;

                        newp2[0] = avgvalue   ;
                        newp2[1] = avgvalue   ;
                        newp2[2] = avgvalue   ;
                        newp1 += 3;
                        newp2 += 3;
                    }

                    newp1 += newOffset1;
                    newp2 += newOffset2;
                }
            }


            inputbitmap.UnlockBits(inputdata );
            outputbitmap.UnlockBits(outputdata );
            return outputbitmap;



        }

Next we shall develop edge detection filters.