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I think you're right. It's the only kink in an otherwise perfect article. I just linked to it on Twitter and have seen about fifty retweets.

Barry, I would humbly suggest removing the rolling shutter reference. The wagon wheel example is a better on-ramp into the discussion.

-Stu

How's this for moiré/aliasing?

http://www.vimeo.com/7590690

see my post here about it: http://www.dvxuser.com/V6/showthread...63#post1813563

Though it is clear that the limited read out speed of the sensor is the (main) cause for both problems.

from the article:

This brings us back to the wagon wheel - for "some reason", people have given aliasing a "pass" when it comes to 24fps for quite a while now. Actually, lately, not just given a pass but actively demanded 24fps despite the temporal aliasing. I would suspect it's the same reason the HDSLRs get a pass on their spatial aliasing - the overall aesthetic they produce is worth the trouble of shooting around (or simply accepting) the aliasing. The audience has been watching wagon wheels go backward for a lot of years without complaint - I suspect the the same will be true for the spatial aliasing of these cameras as long as your story is engaging.

I agree. 24fps is clearly not able to accurately resolve motion as well as 60fps, and the reason is the same -- lower sampling accuracy. 24 is less than 60, and 60 samples result in much more accurate motion rendition.

BUT -- we (the moviemaking/moviewatching public) LIKE the look of 24fps (in most things; it can get headache-inducing if movement isn't controlled). I don't think anyone actually likes the wagon wheel effect, but we put up with it for the rest of the benefits.

The higher the sampling accuracy, the more accurate the representation of the thing being sampled. But in film, that's pretty much what we don't want -- we like the "surreal" or "larger than life" or "dream state" look of 24fps motion, instead of the "hyper-reality" look of 60fps.

The DSLRs certainly use aliasing to "punch above their weight class", giving images that, in the right circumstances, look like they came from far more expensive cameras. Without the aliasing, they'd never create objectionable image artifacts, but they'd also be substantially lower "sharpness".*

It is a tradeoff that you need to know you're making when you get into the game. The aliased DSLR look is sometimes incredible, and sometimes it can cause distracting or even shot-ruining artifacts. But at the price point, I think it's probably the right compromise, as long as people know what the compromise is, know how it manifests itself, and are on the lookout for it.

*the "resolution" would stay exactly the same without the aliasing; aliasing isn't resolution, it's an artifact. What would disappear is the "false sharpness". Which is what gives the DSLRs their "punch".

Barry, your article is making it's way through the internet; ProLost, slashcam.de, canonrumors.com...it's becoming a reference

There are some thoughts running round my head, I'd be curious about your opinion.

There are common modifications for astronomy- and infra-red photography, where the original anti-aliasing glass in front of the DSLR sensor is removed and replaced by other (special) glasses for astronomy or IR, or just normal glass or UV-filter glass. All replacements result in much sharper images and higher light-sensibility of the sensor due to the lack of the anti-aliasing/lowpass-filter glass.

http://www.maxmax.com/hot_rod_visible.htm

http://www.baader-planetarium.de/sektion/s45/s45.htm

http://www.optik-makario.de/
(sorry, last 2 are german)


Now, the caprock anti-moire filter seems to work nice on the 7D,

http://www.dvxuser.com/V6/showthread...hlight=caprock

so I'm wondering if it would do the job on a modified 7D in video mode as well? I'm very insecure about the whole issue, so I could imagine any result from becoming absolutely useless for video to being "real" sharp with less moire if the caprock filter can deal with the new amount of aliasing. The modification seems to work great for stills photography but I understand video and the meaning of anti-aliasing for video is a whole different thing and I'm not sure what role the DSLR's software plays in this.

EDIT: I'm very sorry if this has been discussed here already, I didn't find anything yet though

But "much sharper" is due to the exact same problems we've been discussing in this article. Removing the anti-aliasing filter means that you're letting all the aliasing through, which means you'll have all the moire and jaggy line problems and false detail that we've been talking about.

So while it may appear to be sharper, it's due to cheating and fake detail. Whether you (or any viewer) prefers that look is, of course, a matter of personal preference. But it's not actually sharper and it's not actually recording any more accurate of a picture, it's actually recording spurious inaccurate detail and presenting it as if it's accurate.

The Caprock filters can certainly overcome all of the aliasing issues, turning the DSLRs into properly anti-aliased video cameras. But, as I said in the article, you'll also be giving up all the fake detail that makes the images look so "sharp" in the first place! You'll be left with a camera that delivers somewhere around a reasonable 720p image, because that's all that the current crop of DSLRs (5D/GH1/7D) can deliver. Anything beyond that, is aliased false detail. The caprock eliminates the aliasing, which means that the false detail goes, leaving only the actual resolved detail. On these SLRs, that means about 600 lines.

Now, that's not bad, and I'm actually looking at picking up some of those to really experiment with. It would remove any uncertainty about the SLR's image, any worries about moire or rainbow patterns, etc... and still deliver sharpness around HVX200 level. With shallow DOF. For a grand total of about $2500 (camera plus filters). That's not bad. The Caprock filters need to be tested in combination with the SLR and the lenses, because each focal length lens will need a different strength of anti-moire filter.

Of course, a much less expensive way to go, that would work with every focal length lens, would be to just de-focus very slightly.

Which I thought would be good when using the Caprock filter because:


By removing/replacing the A-A glass and using the Caprock filter instead the image should stay quite "sharp" (as there is no more additional blurring from A-A glass only softening from Caprock filter) but be less "faked" with less moire issues:


I might be really confused here though

Well... I can see where you're coming from, but I doubt you're going to see any benefit to removing the AA filter from the 7D. The 7D's AA filter is tuned for the stills, and its video resolution is already so low that I bet the 7D's AA filter really has little to no effect on the video footage at all. The Caprock would probably filter out any and all too-fine detail, leaving nothing for the 7D's AA filter to catch. So if you like the look of footage from a filterless camera for stills, but want AA for video, then that's a case where removing the 7D's filter might make sense (and compensating with the caprocks).

Thank you Barry!