How to: Translate Image Colors

 

A translation adds a value to one or more of the four color components. The color matrix entries that represent translations are given in the following table.

Component to be translatedMatrix entry
Red[4][0]
Green[4][1]
Blue[4][2]
Alpha[4][3]

The following example constructs an Image object from the file ColorBars.bmp. Then the code adds 0.75 to the red component of each pixel in the image. The original image is drawn alongside the transformed image.

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

Translate Colors

The following table lists the color vectors for the four bars before and after the red translation. Note that because the maximum value for a color component is 1, the red component in the second row does not change. (Similarly, the minimum value for a color component is 0.)

OriginalTranslated
Black (0, 0, 0, 1)(0.75, 0, 0, 1)
Red (1, 0, 0, 1)(1, 0, 0, 1)
Green (0, 1, 0, 1)(0.75, 1, 0, 1)
Blue (0, 0, 1, 1)(0.75, 0, 1, 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,  0,  1,  0, 0},
           new float[] {0,  0,  0,  1, 0},
           new float[] {.75f, 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 PaintEventArgse, which is a parameter of the Paint event handler. Replace ColorBars.bmp with an image file name and path that are valid on your system.

ColorMatrix
ImageAttributes
Graphics and Drawing in Windows Forms
Recoloring Images

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