Aliasing and Moire
Another issue to be aware of before diving headfirst into the DSLR world is the problem of aliasing (moire is an offshoot of the same problem). Aliasing is a problem with DSLRs because the cameras were designed primarily to shoot still photos at much higher resolution than their video mode allows. So, in order to drop from 5616 x 3744 in still mode to 1920 x 1080, the camera skips lines. Ideally the camera would sample all of the pixels and average them out, giving you a smooth image (think about resizing an image in Photoshop and choosing Bilinear or Bicubic); instead, because DSLRs lack the processing power required to do this in real time, they just toss every other line or so (think about resizing an image in Photoshop and choosing “Nearest Neighbor”). What you’re left with are unseemly jaggies. The end result is most commonly seen on thin lines and patterns and ranges from overt to invisible. For an example, watch the gray rooftop here:
The first thing you should do when switching your DSLR from still to movie mode is to make sure the Sharpness setting is turned all the way down. This won’t come close to eliminating aliasing under all conditions but it should reduce your camera’s problems. As the chips inside these cameras get more powerful, we might see a HDSLR that does some in-camera image sampling; but to eliminate aliasing problems, the best solution might be to actually lower the camera’s resolution (this is one of the advantages of a 5-megapixel RED camera over a 21-megapixel DSLR).
For more on the technical reasons behind aliasing and moire, see Barry Green’s post at DVXuser and Stu Maschwitz’s follow-up (I commented on both as well). For an eyeful of ugliness you can also click on the image at top right, which was one of the first things I shot from my NYC rooftop on a 5D; that brick building is not ensconced by gray concentric circles.
17 COMMENTS
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jf jackson on 09.16.11 @ 1:47PM
who cares about the video quality – people need to stop getting hung up on DSLR + Video. If you want video get a good camcorder. The real issue is this…how to prevent the above mentioned issues such as moire and zipper effect/jaggies from getting processed in the camera firmware that is making its way into the final pics so you have to waste time in PP.
With that in mind, perhaps you should report on something THAT MATTERS – like picture quality and DSLR. There is a SERIOUS issue with DSLR NOT giving picture quality that it could these days because focus has fallen to unneeded video instead of true IQ from still pics. If manufacturers would drop the video and focus on IQ firmware, perhaps I would not be wasting my time on the net reading useless articles such as this. I am trying to find out performance of DSLR cams and if jagged edges are an issue for all DSLR cams. All I come across is “video video video”… who cares. It like trying to get a Ferrari to be able to pull a 10 ton yacht when it is made to drive fast and it has problems cornering. People are focused on pulling the yacht when that is not the purpose and the issue with poor steering is ignored!!!
Pay attention to what matters. Articles like this get back to the manufacturers then they focus more on bogus feature like video when still image quality is far from its potential…report on what matters!!!
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bitter? on 10.17.11 @ 12:22PM
@jfjackson
All I hear from your post is:
“I can’t do video and I’m scared.”
Time to change old man!
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wow, you sound like the guy that nobody remembers saying “who wants to hear the actors talk anyway”
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Yeah cos iphones should only be able to make calls and thats all…
I’m sorry youre having issues with your DSLR, just for taking pictures, probably you’re not finding much information about it cos it doesn’t happen to a lot of people and you’re probably doing something wrong, anyway.
And who cares about DSLR video? most people do nowadays. If you cant see the possibilities of having a DSLR shooting video and focusing on that spot of technology, then you must be kinda very old and closed minded.
Most DSLR already create amazing photographs, so concentrating on video is a step further.
Reporting on DSLR video is what matters, reporting on jagged edges is useless.
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D. A. Krolak on 09.30.12 @ 1:52PM
Did you know the video embedded in this has since been removed by the user? Just thought I would let you know.
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Hi
I wanne use the canon 7d with a sigma 50-500 4.5-6.3 DG OS. I tried last weekend to shoot in difuse light conditions to film skiers and snowboarders. I tried by aperture of 24 and more! I know that was a mistake. The result was that i had not even one sharp video but the photographs were pretty good.
Do you think i can get better sharpness when I use the pol and ND filter?
And who knows the different of the fade ND Filter AND the Fade ND Filter (ND 2-400) of lightwork?
Please help me to get sharp images!