ImageAttributes.SetColorKey Method (Color, Color, ColorAdjustType)


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Sets the color key (transparency range) for a specified category.

Namespace:   System.Drawing.Imaging
Assembly:  System.Drawing (in System.Drawing.dll)

public void SetColorKey(
	Color colorLow,
	Color colorHigh,
	ColorAdjustType type


Type: System.Drawing.Color

The low color-key value.

Type: System.Drawing.Color

The high color-key value.

Type: System.Drawing.Imaging.ColorAdjustType

An element of ColorAdjustType that specifies the category for which the color key is set.

This method sets the high and low color-key values so that a range of colors can be made transparent. Any color that has each of its three components (red, green, blue) between the corresponding components of the high and low color keys is made transparent.

An ImageAttributes object maintains color and grayscale settings for five adjustment categories: default, bitmap, brush, pen, and text. For example, you can specify a color key for the default category, a different color key for the bitmap category, and still a different color key for the pen category.

The default color-adjustment and grayscale-adjustment settings apply to all categories that do not have adjustment settings of their own. For example, if you never specify any adjustment settings for the pen category, the default settings apply to the pen category.

As soon as you specify a color-adjustment or grayscale-adjustment setting for a certain category, the default adjustment settings no longer apply to that category. For example, suppose you specify a collection of adjustment settings for the default category. If you set the color key for the pen category by passing Pen to the SetColorKey method, none of the default adjustment settings will apply to pens.

The following code example is designed for use with Windows Forms, and it requires PaintEventArgse, which is a parameter of the Paint event handler. The code performs the following actions:

  1. Opens an Image that uses the file Circle.bmp and draws it to the screen.

  2. Creates an ImageAttributes object and sets its color key by calling the SetColorKey method.

  3. Draws the image to the screen using the color key of the ImageAttributes object.

private void SetColorKeyExample(PaintEventArgs e)

    // Open an Image file and draw it to the screen.
    Image myImage = Image.FromFile("Circle.bmp");
    e.Graphics.DrawImage(myImage, 20, 20);

    // Create an ImageAttributes object and set the color key.
    Color lowerColor = Color.FromArgb(245,0,0);
    Color upperColor = Color.FromArgb(255,0,0);
    ImageAttributes imageAttr = new ImageAttributes();

    // Draw the image with the color key set.
    Rectangle rect = new Rectangle(150, 20, 100, 100);
    e.Graphics.DrawImage(myImage, rect, 0, 0, 100, 100, 
        GraphicsUnit.Pixel, imageAttr);      


.NET Framework
Available since 1.1
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