So...
Out of curiosity, and as a means of doing some seam overpaint to tweak a normal map (and some experimentation...), I sent my layers to Photoshop. Then, collapsed what was there into a single layer and saved it back out as jpg. When I imported that jpg into SP, it came in with this incredibly dark color shift, as though the program was reading the color space of the image wrong. I then tried it in different formats (psd, then tga), all with the same effect. The image is a normal map and looks fine in Photoshop, but every time I import any version of it into SP, there is a huge, darkening color shift. Any ideas on this? It makes some potentially powerful workflows rendered dead in their tracks.
