Imagefilter like sketch, emboss and RGB...

Hi Brad,

I realy love your GPUImage-Framework. I need some help with some Filters like sketch, RGB, Emboss...
If I try to manipulate an Image within these kind of filters, the alphachannel is got to be lost. My Images always having a transparent pixelzone. What can I do to keep it ? Can you implement a feature like this or do you have a tricky Idea for me for doing this by myself ? This would be realy great.

Best Regards
Hans