Applying gamma correction to PictureBox.BackgroundImage in C#?

[mwin]

I've got a PictureBox, let's call it pictureBox1, and I want to load an image into it's BackgroundImage. That part is easy, but I want the image to appear "washed out". I figure somewhere around gamma .25-.5 would be about right. I'm having the damndest time trying to find how to apply this to an image in memory. The Graphics.DrawImage method is about the only thing I've found, but I don't think it'll work for me in this application. Anybody want to point me towards something that'll help?