Check out Joe Pardue's tutorial on alpha blending here http://www.codeproject.com/cs/media/CsTranspTutorial1.asp or Rakesh Rajan's article here http://www.codeproject.com/cs/media/alphafx.asp

This was very informative and interesting! However, I believe I might have expressed myself a tad unprecise. My question was rather how to enable the preview mode on a file type I create myself. And then, secondly, I suppose the continuation will be to get hold of some image, remove the file headers, and finally embed the image data at some address in the file. Maybe the trick is to make my own derived file class? - Peder -

Anyone knows how to preview a custom file format with a bitmap in windows explorer? For example, the 3D Studio file format (file.3ds) is not a gif or bmp or anything. However, if you select it windows explorer, an image preview of the file pops up on the left anyway just as if it were an image file. How is this done? - Peder -