This project scans images in full 24-bit colour (8 bits per channel), which results in nice smooth gradients. It's a bit slow though, it takes 30 seconds to scan, on my system. It works by using image effects to isolate a specific colour channel, and then doing a binary search. There are some slight discontinuities resulting in minor artefacts, it should be possible to correct these (without affecting performance), if I can be bothered.
