Friday, November 27, 2009
Temporal Fish Imagery 2
Another temporal underwater image generated from the Flip video taken at the Sydney aquarium in Darling Harbour. This is a slit scan generated using temporal image processing in Studio Artist 4.
If you look closely at the image you can see the horrendous Flip avi frame indexing bug associated with Quicktime and the avi compression codec that Flip uses for the video files the camera generates. When you use the Quicktime apis to index the frames sequentially the actual video frames you get back are sometimes not correct for a given frame time. The bug seems to position itself along with the mpeg key frame indexes, so you see it every 20 frames. As you sequentially access the frames in Quicktime one will jump ahead too far, then the next one jumps back in time, then they advance forward in time again. It doesn't appear to happen when you play the video in real time, just when you try to access individual frames, which is what you need to do during video processing.
I can't believe it took me this long to notice this bug associated with the Flip camera on the mac. Most of what i do is either temporal processing where the frame order being slightly offset would not be noticeable since you are processing a big chunk of frames, or the scan tracker where it's going to be less noticeable. But looking back through my old slit scans you can see this problem, i always thought i was shaking the camera. When i started in on writing an image stabilization algorithm for Studio Artist to smooth out shaky video shots the real problem because apparent.
I ordered the Kodak Zi8 high def pocket video camera the day after i figured out this Flip bug was there. The extra resolution will be greatly appreciated. I started a dialog with Flip and Apple to try and resolve this problem, but i don't expect anything to happen quickly.