ColorMatrix Class

The matrix coefficients constitute a 5 x 5 linear transformation that is used for transforming ARGB homogeneous values. For example, an ARGB vector is represented as red, green, blue, alpha and w, where w is always 1.

For example, suppose you want to start with the color (0.2, 0.0, 0.4, 1.0) and apply the following transformations:

1. Double the red component

2. Add 0.2 to the red, green, and blue components

The following matrix multiplication will perform the pair of transformations in the order listed.

The elements of a color matrix are indexed (zero-based) by row and then column. For example, the entry in the fifth row and third column of matrix M is denoted by M[4][2].

The 5×5 identity matrix (shown in the following illustration) has 1s on the diagonal and 0s everywhere else. If you multiply a color vector by the identity matrix, the color vector does not change. A convenient way to form the matrix of a color transformation is to start with the identity matrix and make a small change that produces the desired transformation.

For a more detailed discussion of matrices and transformations, see Coordinate Systems and Transformations.

The following example takes an image that is all one color (0.2, 0.0, 0.4, 1.0) and applies the transformation described in the preceding paragraphs.

The following illustration shows the original image on the left and the transformed image on the right.

The code in the following example uses the following steps to perform the recoloring:

1. Initialize a ColorMatrix object.

2. Create an ImageAttributes object and pass the ColorMatrix object to the SetColorMatrix method of the ImageAttributes object.

3. Pass the ImageAttributes object to the DrawImage method of a Graphics object.

The preceding example is designed for use with Windows Forms, and it requires PaintEventArgs e, which is a parameter of the Paint event handler

Image image = new Bitmap("InputColor.bmp");
ImageAttributes imageAttributes = new ImageAttributes();
int width = image.Width;
int height = image.Height;

float[][] colorMatrixElements = { 
   new float[] {2,  0,  0,  0, 0},        // red scaling factor of 2
   new float[] {0,  1,  0,  0, 0},        // green scaling factor of 1
   new float[] {0,  0,  1,  0, 0},        // blue scaling factor of 1
   new float[] {0,  0,  0,  1, 0},        // alpha scaling factor of 1
   new float[] {.2f, .2f, .2f, 0, 1}};    // three translations of 0.2

ColorMatrix colorMatrix = new ColorMatrix(colorMatrixElements);

imageAttributes.SetColorMatrix(
   colorMatrix,
   ColorMatrixFlag.Default,
   ColorAdjustType.Bitmap);

e.Graphics.DrawImage(image, 10, 10);

e.Graphics.DrawImage(
   image,
   new Rectangle(120, 10, width, height),  // destination rectangle 
   0, 0,        // upper-left corner of source rectangle 
   width,       // width of source rectangle
   height,      // height of source rectangle
   GraphicsUnit.Pixel,
   imageAttributes);

.NET Framework

.NET Framework Client Profile

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

Reference

Other Resources