do you need to compute the alpha values from the rgb channels of the current image, or are you using a different image as a source?
I am somewhat basing it off the current image. I basically want to take the current image and then stretch the range of values to be full 0-255. That way a dark texture won't always fall below a light texture. The current best way for me seems to be to use paint.net to convert to greyscale, adjust the range manually based on the histogram, then save the greyscale image and import both into the directx texture tool.