I'm currently working on an App that uses filters and the Nokia Imaging SDK in a unique way, instead of applying filters effect to the full image it allows you to add filters as either different geometric shapes (circle, square, triangle, star, heart, etc) to the image (i.e. only a star part of the full image is effected with the filter and you select where to place this star,circle, etc. shape)
You can also use your finger to apply filter as the finger is dragged on the image (selecting the exact parts/pixel you want to apply the filters to).
I had also plan to write a wiki article for this app to compete in the wiki articles but could not complete the app in time.
Anyway the improvement I'm suggesting is to be able to add parameters to the different image source classes such as BitmapImageSource to allow passing geometric or shapes classes that be effected by the filter and leave the rest of the image intact, I think that applying the filter to the full image is just the private case of this methoc with the parameter of the geometric of the entire image.
because at the moment I'm force to sample the part of the image that the shape contains and make the pixels that are outside the geometric shape transparent and then apply the filter to that section and the blit it back to the full image with overwriting the target pixels.