Magic Lantern, the folks behind the free EOS Camera Tool software for Canon DSLRs, have released a custom firmware hack for the Canon 5D Mark III and 7D. They call their latest release Dual ISO and claim that it expands the dynamic range of the 5D Mark III and EOS 7D by four stops, giving those cameras a total dynamic range of 14EV. Dual ISO can be applied to stills and video on the 5D Mark III but only still images on the 7D. The samples are interesting, and appear to back up the claims. Dual ISO works by splitting the sensor’s output into alternating horizontal rows. Half of the rows capture the image at a high ISO (for shadow detail) and half at a low ISO (to retain highlights). The data from the alternating rows are then combined and the missing data is interpolated. If it sounds a little like HDR, the idea is similar. But unlike HDR, which requires multiple images, Dual ISO uses just a single exposure, making it far more suitable for moving subjects.
To be very clear, this is absolutely NOT an official Canon firmware release. As you might expect, installing something like this in your camera doesn’t come without some downside. Most obvious is the reduction in resolution. Perhaps more importantly, there’s a chance that you may fry your sensor since you are making it do something that Canon did not design it to do. One should assume that warranty claims due to this sort of firmware hacking will not be looked upon too kindly by Canon.
More information is on the Magic Lantern website: http://www.magiclantern.fm/forum/index.php?topic=7139.0