DSLR Video and Aliasing Artifacts
V-DSLRs, OLPF, and hoity-toity French words
By Matthew Jeppsen | December 04, 2009
If you are shooting video with one of the hot new DSLRs, you are probably aware of the aliasing issues found in some of your footage. If not yet, you will at some point. Just keep shooting, it will show up. Fine detail aliasing has always been an issue for any camera system, but it's particularly prevalent in DSLRs as they lack an Optical Low Pass Filter (OLPF) that is specifically tuned for video. In the case of the 5D & 7D, engineers at Canon have also chosen to sample a limited number of lines from the image sensor to downsample to 1080p. This is quick solution, but not the highest quality way of doing things; it creates aliasing image artifacts, and reportedly limits the resolution of the cameras at around 720p. It's almost as if these tools were primarily designed as still cameras! How strange. At any rate, I've learned to warn my clients before interview shoots not to wear shirts with fine detail patterns, as they will moir© faster than you can say "how the hell do you pronounce that word?"
Funny side note...when written moire, it's pronounced "mwahr." Moir© with the French accent aigu mark is pronounced "mwahr-AY." The more you know, right? I personally prefer mwahr-AY. Sounds more like a real word. I like it so much that back on Oct 30 when Red did their traditional biennial Fall Scarlet schedule update, I wrote a little poem about DSLRs and aliasing...
"Compression is uglyAnd that's why I'll stick to writing about geeky video topics instead of prose. But I digress...what were we talking about?
My DSLR will moir©
If you logged on for Scarlet
You'll be dissappointed today."
Ah yes, moir© and DSLR video. So over at DVXuser Barry Green wrote a detailed article on moire and how it affects DSLR video. If you aren't familiar with the topic, it's a great article to get you up to speed. Stu Maschwitz also has a few words on the subject at ProLost, offering his perspective (which mirrors my own take on the subject). And finally, No Film School just posted a few thoughts as well, putting the issue in perspective similar to how Stu approaches it. So there you have it. A veritable roundup of moire info and opinions. Or moir©, if you drink your tea with a dainty pinky extended like I do.
So in conclusion, be aware of your gear's limitations and take steps to work around or avoid those issues. Just like you always have. Happy shooting!
UPDATE: I somehow missed this thread over at Reduser about 7D Zone Charts, and the comparison to Red One Zone Charts. There's a lot of insight into DSLR aliasing issues in that thread from imaging genius Graeme Nattress. A must read. Favorite quote from the thread: "When two sets of lines cross to form weird designs, That's a moir©." I was pleasantly surprised in reading the thread to see most Redheads actually putting the camera comparisons in proper perspective...understanding that the 5D/7D are flawed, yet still useful tools, and that they have a place in the market.
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