Course IPCis: Image Processing with C# Chapter C3: Commented Code of the Filter Project Copyright © by V. Miszalok, last update: 2011-03-11

using System; //Home of the base class of all classes "System.Object" and of all primitive data types such as Int32, Int16, double, string.

using System.Drawing; //Home of the "Graphics" class and its drawing methods such as DrawStirng, DrawLine, DrawRectangle, FillClosedCurve etc.

using System.Drawing.Imaging; //Home of the Bitmap-class.

using System.Windows.Forms; //Home of the "Form" class (base class of our main window Form1) and its method Application.Run.

//We derive our window public class Form1 : Form, which the compiler automatically finds in the System.Windows.Forms namespace.

{ [STAThread] static void Main() { Application.Run( new Form1() ); } //Create a single thread instance of Form1 and ask the operating system to start it as main window of our program.

Brush bbrush = SystemBrushes.ControlText; //Create a reference to an already existing Brush object (just a programming shortcut).

Bitmap Original, Noise, Lowpass, HighVertical, HighHorizontal, HighGradient; //Six Bitmap-objects:
1. row: Original = original image, Noise = noisy image, Lowpass = blurred image
2. row: HighVertical = vertical highpass, HighHorizontal = horizontal highpass, HighGradient = SQRT(HighVertical² + HighVertical²).

Byte[,] grayarray; //Raster matrix containing Original as monochrome image. Any gray value is the average of its three correspondent Original-RGB-values:
grayarray[x,y] = ( Original[x,y].R + Original[x,y].G + Original[x,y].B ) / 3;

Int32 x, y, xSize, ySize, gray; //Some global integers.

MenuItem miRead = new MenuItem( "&Read", new EventHandler( MenuFileRead ) ); //Purpose: Open an image file.

MenuItem miExit = new MenuItem( "&Exit", new EventHandler( MenuFileExit ) ); //Purpose: Leave the program.

MenuItem miFile = new MenuItem( "&File", new MenuItem[] { miRead, miExit } ); //Complete menu with two entries.

Menu = new System.Windows.Forms.MainMenu( new MenuItem[] { miFile } ); //Attach the menu to Form1.

Text = "Filter1"; //Blue title bar.

SetStyle( ControlStyles.ResizeRedraw, true ); //Redirect the OnResize-event to the OnPaint event handler.

Width = 1024; //Initial window size.

Height = 800; //Initial window size. Raise the OnResize-event which calls protected override void OnPaint(...).

OpenFileDialog dlg = new OpenFileDialog(); //Call the standard modal OpenFileDialog-box.

dlg.Filter = "bmp files (*.bmp)|*.bmp|All files (*.*)|*.*" ; //Pre select *.bmp-files, but choice of any other file type remains possible.

if ( dlg.ShowDialog() != DialogResult.OK ) return; //Forget it, if there was no reasonable user reaction.

Original = (Bitmap)Image.FromFile( dlg.FileName ); //Read the image using the powerful Bitmap-class.

if ( Original == null ) return; //Forget it, when no image could be opened.

Cursor.Current = Cursors.WaitCursor; //Change the mouse cursor to hour-glass indicating that a time consuming process is going to run.

xSize = Original.Width; //Use the traditional xSize for image width = no. of columns.

ySize = Original.Height; //Use the traditional ySize for image height = no. of lines.

Noise = new Bitmap( xSize, ySize, PixelFormat.Format16bppRgb555 ); //Image with 16 bits per pixel.

Lowpass = new Bitmap( xSize, ySize, PixelFormat.Format24bppRgb ); //Image with 24 bits per pixel = best quality.

HighVertical = new Bitmap( xSize, ySize, PixelFormat.Format16bppRgb555 ); //Image with 16 bits per pixel.

HighHorizontal = new Bitmap( xSize, ySize, PixelFormat.Format16bppRgb555 ); //Image with 16 bits per pixel.

HighGradient = new Bitmap( xSize, ySize, PixelFormat.Format16bppRgb555 ); //Image with 16 bits per pixel.

grayarray = new Byte [xSize, ySize]; //Raster matrix containing Original as monochrome Byte-image.

for ( y=0; y < ySize; y++ ) //For any line

for ( x=0; x < xSize; x++ ) //For any column

Color color = Original.GetPixel( x, y ); //Read a pixel.

gray = ( color.R + color.G + color.B ) / 3; //Sum up the three colors and divide = averaging.

grayarray[x, y] = (Byte)gray; //Store the gray value.

Int32 amplitude = 256; //Maximal noise = additional random gray

Int32 half_amplitude = amplitude / 2; //Half noise = 128

Random random = new Random(); //Start the random no. generator

for ( y=0; y < ySize; y++ ) //For any line

for ( x=0; x < xSize; x++ ) //For any column

gray = grayarray[x, y]; //Read a pixel.

gray += random.Next(amplitude) - half_amplitude; //Add a random gray between -128 and +128

if (gray < 0) gray = 0; else if (gray > 255) gray = 255; //Clip the resulting value to minimum=0 and maximum=256.

Noise.SetPixel( x, y, Color.FromArgb( gray, gray, gray ) ); //Store the noisy pixel.

// Version 3: Lowpass without border handling //

Int32 LowpassSize = 11; //insert an odd size: 3, 5, 7, ..., 29. //Width and height of the filter

Int32 MidWeight = 1; //set a positive mid weight: 1, 2, 3, ..., 1000. //Mid of the filter has no special weight yet.

Int32 xx, yy, sum, d = LowpassSize/2; //Local indicees: xx, yy; local sum = sum; half width = half height = d;

float divisor = (2*d+1)*(2*d+1) + MidWeight - 1; //MidWeight == 1 means no weight. //Sum of all weights (normally 11*11 = 121 = no. of elements of this averaging lowpass filter).

for ( y=d; y < ySize-d; y++ ) //For any line except the upper (0 to d-1) and lower (ySize-d to ySize-1) rim = half size of the quadratic filter (normally = 5).

for ( x=d; x < xSize-d; x++ ) //For any column except the left (0 to d-1) and right (xSize-d to xSize-1) rim = half size of the quadratic filter (normally = 5).

sum = (MidWeight-1) * grayarray[x,y]; //extra mid weight //When there is no special MidWeight, sum starts with 0, otherwise it starts with the wéighted central gray value.

for ( yy=-d; yy <= d; yy++ ) //For any y-offset between -d and +d, where d is the rim = the half size of the quadratic filter (normally = 5).

for ( xx=-d; xx <= d; xx++ ) //For any x-offset between -d and +d, where d is the rim = half size of the quadratic filter (normally = 5).

sum += grayarray[x+xx,y+yy]; //Add up the gray values of the 11*11 neighbourhood.

gray = Convert.ToByte( (float)sum / divisor ); //Divide by the sum of weights and round to Byte.

Lowpass.SetPixel( x, y, Color.FromArgb( gray, gray, gray ) ); //Store the pixel.

Int32 sumleft, sumright, sumtop, sumbottom, diff;

, , ,

diff = Abs(sumleft-sumright) or diff = Abs(sumtop-sumbottom)

for ( y=1; y < ySize-1; y++ ) //For any line except the 1st and last ones.

for ( x=1; x < xSize-1; x++ ) //For any column except the 1st and last ones.

sumleft = grayarray[x-1,y] + grayarray[x-1,y-1] + grayarray[x-1,y+1]; //Add the 3 left neighbours.

sumright = grayarray[x+1,y] + grayarray[x+1,y-1] + grayarray[x+1,y+1]; //Add the 3 right neighbours.

sumtop = grayarray[x,y-1] + grayarray[x-1,y-1] + grayarray[x+1,y-1]; //Add the 3 upper neighbours.

sumbottom = grayarray[x,y+1] + grayarray[x-1,y+1] + grayarray[x+1,y+1]; //Add the 3 lower neighbours.

diff = Math.Abs( sumleft - sumright ); //Subtract left minus right, diff must be positive.

if ( diff > 255 ) HighHorizontal.SetPixel( x,y,Color.FromArgb( 255, 255, 255 ) ); //Max. allowed difference = 255.

else HighHorizontal.SetPixel( x,y,Color.FromArgb( diff, diff, diff ) ); //Store pixel.

diff = sumtop - sumbottom; if ( diff < 0 ) diff *= -1; //Subtract top minus bottom.

if ( diff > 255 ) HighVertical.SetPixel( x,y,Color.FromArgb( 255, 255, 255 ) ); //Max. allowed difference = 255.

else HighVertical.SetPixel( x,y,Color.FromArgb( diff, diff, diff ) ); //Store pixel.

Double diff_h = sumleft - sumright; //Convert difference to type Double as requested by Math.Sqrt.

Double diff_v = sumtop - sumbottom; //Convert difference to type Double as requested by Math.Sqrt.

diff = Comvert.ToInt32( Math.Sqrt( diff_h * diff_h + diff_v * diff_v ) ); //Pythagorean theorem and rounding.

if ( diff > 255 ) HighGradient.SetPixel( x,y,Color.FromArgb( 255, 255, 255 ) ); //Max. allowed gradient = 255.

else HighGradient.SetPixel( x,y,Color.FromArgb( diff, diff, diff ) ); //Store pixel.

Cursor.Current = Cursors.Arrow; //Restaore default mouse cursor.

Invalidate(); //Call protected override void OnPaint(...) and show the 6 images.

{ Application.Exit(); } //Kill the current instance of program filter1.

Graphics g = e.Graphics; //Get the current device context.

if ( Original == null ) { g.DrawString( "Open an Image File !", Font, bbrush, 0, 0 ); return; } //Inform the user what to do, if there is no image at all.

Rectangle cr = ClientRectangle; //Get the size of the whole client area.

g.DrawImage( Original      , 0             , 0          , cr.Width/3, cr.Height/2 ); //Upper left corner.
g.DrawImage( Noise         , cr.Width/3    , 0          , cr.Width/3, cr.Height/2 ); //In the mid of the upper row.
g.DrawImage( Lowpass       , (2*cr.Width)/3, 0          , cr.Width/3, cr.Height/2 ); //Upper right corner.
g.DrawImage( HighHorizontal, 0             , cr.Height/2, cr.Width/3, cr.Height/2 ); //Lower left corner.
g.DrawImage( HighVertical  , cr.Width/3    , cr.Height/2, cr.Width/3, cr.Height/2 ); //In the mid of the lower row.
g.DrawImage( HighGradient  , (2*cr.Width)/3, cr.Height/2, cr.Width/3, cr.Height/2 ); //Lower right corner.