Been quite a while. Still looking forward to seeing this image editor (especially RotKeks) in action.
I often wonder if RotKeks could be used in Texture Filtering for a 3D engine as well (I'm tired of low resolution textures in old games becoming a complete blurfest on newer hardware)... The memory requirements would likely be insane, though, as would the computational requirements. Like you said previously, it would probably be much better suited as an offline utility.
However, while it probably wouldn't save on memory all that much, one possible way to save on computational resources for use in real-time sprite rotation might be to store the initial upscaled image (before calculation) and all the final sprite rotations (as they are calculated) in a cache, and reusing them by calling upon that cache as demanded.
Be sure to read up on both Attentive Transmission and Array Set Addressing when you get the chance as well.
In a nutshell;
Attentive Transmission can potentially save on storage space of both high resolution images and animated sprites by generating what are essentially Mipmaps, and then storing the lowest-sized Mipmap of a single frame along with the differences in Laplacean between each larger image and between each frame of animation. Reconstruction is Lossless, but does have some computational overhead (however, it does claim it can also reduce computational costs when combined with other algorithms, but that would require further experimentation).
http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.33.2933&rep=rep1&type=pdf
Array Set Addressing on the other hand is handy for hexagonally sampled images. While that wouldn't improve performance in this particular field, it could probably see more benefit from rotation algorithms than the rectangularly sampled images that we are used to.
http://ufdcimages.uflib.ufl.edu/UF/E0/04/23/19/00001/rummelt_n.pdf
With regards;
- Amaroq.
P.S.: I hope I haven't come off as too pushy or demanding. Sometimes I just need to let what is on my mind be heard by others.