I found an issue with encoding images that contains semi-transparency. The colors are off compared to the output from WriteableBitmap. If I add two images to the Silverlight Control, one with the data from WriteableBitmap, and the other with data from the
PngEncoder, this is what I get:
These are basically just semitransparent yellow and orange ellipses on a transparent background. Also note the issues with the outline around the red circles (they are red ellipses with a white outline).
As far as I can tell this is not specific to the PNG encoder. I was seeing the same thing with the JpgEncoder (although I really need to preserve the semi-transparency).