Every day I get more and more excited about the possibilities of HDR video with Magic Lantern and Canon SLRs. I finally broke down and got a 5D Mark II as well as writing some optical flow algorithms. Obviously, the guys at RE:Vision Effects (Twixtor) and The Foundry (Kronos) have been working on optical flow for years and I’ve spent about 3 weeks, so I’ve got some catching up to do. That being said, there’s no “magic” behind optical flow and all the research is publicly available. The videos above use our custom optical flow solver. They are an encouraging start but there is still a long way to go. There are a lot of “standard” improvements that aren’t in this optical flow solution yet.
So will the results be good enough to actually use? As always, it depends. If nothing moves very fast, the optical flow solver is rock-solid. And so far the tests of pans look clean. But excessive motion causes the typical “warping” artifacts around fast moving objects. Over time it will get better but the problem will never completely go away.
In other words, I can’t tell you if the optical flow solver is “good enough” for your application. If you’re doing a documentary on something that doesn’t move very fast and has uncontrollable lighting (like ancient castles) then HDR is probably worth it. But it might not be the best solution if you’re shooting action shots on a handycam in studio lighting. HDR Video with Magic Lantern is great for some cases and useless in others.
One other interesting opportunity is with 720p video at 60FPS. If you are shooting video for the web then there is very little reason to shoot at 1080p. In these tests, both the underexposed track and the overexposed track were slowed down 2x with optical flow. But instead of thinking about HDR as an “overexposed” and an “underexposed” track, you can think about it as an “even” trackand a “really underexposed” track. By shooting at 60, you could then use the “even” track as-is at 30 and only synthesize the “really underexposed” track. That should give you much better image quality and I hope to have some tests up soon.