log2lin and lin2log in Photoshop; here's an excerpt:
"For the record, you're not crazy if your have a 32-bit linear workflow but want to paint in log space. For one thing, many of Photoshop's tools aren't available in 32-bit (hello, Curves?!?). And some of the tools that are in 32-bit have not been appropriately tweaked for linear (I'm looking at you, Levels). Finally, if you have some film preview profiles, Photoshop can't use them in 32-bit mode like After Effects can.
So by painting in Log, you 1) reclaim some of your favorite tools, 2) can use film preview profiles, and 3) can still paint overbrights because 100% white in log space maps to 13.52 in linear. But be careful! Realize that layers will composite in Log space differently than in linear space, especially if you have soft feathered edges or use transfer modes such as Screen. If you flatten your layers before converting to 32-bit this won't be a problem, but if you need the layers to be separate, make sure you test everything first."