Click here to Skip to main content
15,868,141 members
Articles / Programming Languages / C#
Article

Multiple Matrices With ColorMatrix in C#

Rate me:
Please Sign up or sign in to vote.
4.40/5 (10 votes)
29 Jul 2004 79.8K   1.6K   21   6
Using multiple matrices to manipulate an image.

Introduction

In my current job, I was creating a control that manipulated the brightness and contrast of an image. I didn't want to call Graphics.DrawImage more than once. The solution was to do a matrix multiply on the two matrices (brightness and contrast) before drawing the image. Just for fun, I included a picture of my daughter in the project...

The main part of the code I wanted to share was the matrices and the matrix multiplication.

C#
private void NewMatrices()
{
  // Initialize the matices;
  bm = new float[5][];
  cm = new float[5][];
  for (int i = 0; i < 5; i++)
  {
    bm[i] = new float[5];
    cm[i] = new float[5];
  }
  // Set the values of the brightness matrix
  float brightness = 0.2f;
  bm[0][0] = 1; bm[0][1] = 0; bm[0][2] = 0; bm[0][3] = 0; bm[0][4] = 0;
  bm[1][0] = 0; bm[1][1] = 1; bm[1][2] = 0; bm[1][3] = 0; bm[1][4] = 0;
  bm[2][0] = 0; bm[2][1] = 0; bm[2][2] = 1; bm[2][3] = 0; bm[2][4] = 0;
  bm[3][0] = 0; bm[3][1] = 0; bm[3][2] = 0; bm[3][3] = 1; bm[3][4] = 0;
  bm[4][0] = brightness; bm[4][1] = brightness;
  bm[4][2] = brightness; bm[4][3] = 1; bm[4][4] = 1;
  // Set the values of contrast matrix
  float contrast = 20f;
  float T = 0.5f * (1f - contrast);
  cm[0][0] = contrast; cm[0][1] = 0; cm[0][2] = 0; cm[0][3] = 0; cm[0][4] = 0;
  cm[1][0] = 0; cm[1][1] = contrast; cm[1][2] = 0; cm[1][3] = 0; cm[1][4] = 0;
  cm[2][0] = 0; cm[2][1] = 0; cm[2][2] = contrast; cm[2][3] = 0; cm[2][4] = 0;
  cm[3][0] = 0; cm[3][1] = 0; cm[3][2] = 0; cm[3][3] = 1; cm[3][4] = 0;
  cm[4][0] = T; cm[4][1] = T; cm[4][2] = T; cm[4][3] = 1; cm[4][4] = 1;
}

private float[][] Multiply(float[][] f1, float[][] f2)
{
  float[][] X = new float[5][];
  for (int d = 0; d < 5; d++)
    X[d] = new float[5];
  int size = 5;
  float[] column = new float[5];
  for (int j = 0; j < 5; j++)
  {
    for (int k = 0; k < 5; k++)
    {
      column[k] = f1[k][j];
    }
    for (int i = 0; i < 5; i++)
    {
      float[] row = f2[i];
      float s = 0;
      for (int k = 0; k < size; k++)
      {
        s += row[k] * column[k];
      }
      X[i][j] = s;
    } 
  }
  return X;
}

Another interesting part of the code is the DrawImage function. It takes in a matrix (i.e., float[][]) and draws an image with that matrix.

C#
private void DrawImage(float[][] Matrix)
{
  ColorMatrix m = new ColorMatrix(Matrix);
  ImageAttributes ia = new ImageAttributes();
  ia.SetColorMatrix(m);
  Rectangle rMy = new Rectangle(0,0,i.Width, i.Height);
  Bitmap bm = new Bitmap(i.Width, i.Height);
  Graphics g = Graphics.FromImage((Image)bm);
  g.Clear(Color.Black);
  g.DrawImage(i, rMy, 0, 0, i.Width, i.Height, 
                               GraphicsUnit.Pixel, ia);
  pictureBox1.Image = (Image)bm;
}

So now, we can call DrawImage with one of our matrices we created above, or use Multiply to combine them.

C#
DrawImage(cm);
DrawImage(bm);
DrawImage(Multiply(cm,bm);

License

This article has no explicit license attached to it but may contain usage terms in the article text or the download files themselves. If in doubt please contact the author via the discussion board below.

A list of licenses authors might use can be found here


Written By
Web Developer
United States United States
.Net wannabe

Comments and Discussions

 
GeneralMy vote of 5 Pin
Member 434321322-Mar-11 23:56
Member 434321322-Mar-11 23:56 

General General    News News    Suggestion Suggestion    Question Question    Bug Bug    Answer Answer    Joke Joke    Praise Praise    Rant Rant    Admin Admin   

Use Ctrl+Left/Right to switch messages, Ctrl+Up/Down to switch threads, Ctrl+Shift+Left/Right to switch pages.