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How to: Shear Colors

Shearing increases or decreases a color component by an amount proportional to another color component. For example, consider the transformation where the red component is increased by one half the value of the blue component. Under such a transformation, the color (0.2, 0.5, 1) would become (0.7, 0.5, 1). The new red component is 0.2 + (1/2)(1) = 0.7.

The following example constructs an Image object from the file ColorBars4.bmp. Then the code applies the shearing transformation described in the preceding paragraph to each pixel in the image.

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

Shear Colors

The following table lists the color vectors for the four bars before and after the shearing transformation.

Original

Sheared

(0, 0, 1, 1)

(0.5, 0, 1, 1)

(0.5, 1, 0.5, 1)

(0.75, 1, 0.5, 1)

(1, 1, 0, 1)

(1, 1, 0, 1)

(0.4, 0.4, 0.4, 1)

(0.6, 0.4, 0.4, 1)

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

float[][] colorMatrixElements = { 
        new float[] {1,  0,  0,  0, 0},
        new float[] {0,  1,  0,  0, 0},
        new float[] {0.5f,  0,  1,  0, 0},
        new float[] {0,  0,  0,  1, 0},
        new float[] {0, 0, 0, 0, 1}};

ColorMatrix colorMatrix = new ColorMatrix(colorMatrixElements);

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

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

e.Graphics.DrawImage(
   image,
   new Rectangle(150, 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);

The preceding example is designed for use with Windows Forms, and it requires PaintEventArgs e, which is a parameter of the Paint event handler. Replace ColorBars.bmp with an image name and path valid on your system.

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