C# Programming > Drawing GDI+

C# Draw Translucent Image



GDI+ provides an automatic way to draw translucent image in C# without the need for more complicated image processing algorithms. A translucent image can be any image that has a lower opacity than 100%.

The key is to make use of the System.Drawing.Imaging namespace.

Translucent Drawing

First you must set up a Color Matrix that will apply the opacity when you draw translucent image:

ColorMatrix matrix = new ColorMatrix();
matrix.Matrix33 = 0.5f; //opacity 0 = completely transparent, 1 = completely opaque
ImageAttributes attributes = new ImageAttributes();
attributes.SetColorMatrix(matrix, ColorMatrixFlag.Default, ColorAdjustType.Bitmap);

Next, as you can see from the C# code above, the color matrix is applied to an ImageAttributes object which will tell GDI+ the color properites to following when drawing the image.

Finally to draw translucent image, use the usual Graphics GDI+ class, for example, something like this:

Graphics g = Graphics.FromImage(img);

             new Rectangle(1, 1, pictureBox1.Width - 2, pictureBox1.Height - 2),
             0, 0,
             pictureBox1.Width, pictureBox1.Height,

Using this method to draw translucent image is a lot simpler than having to manually draw each pixel in an image at the target opacity.

Back to C# Article List