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Canon XL and GL Series DV Camcorders
Canon XL2 / XL1S / XL1 and GL2 / XM2 / GL1 / XM1.


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Old March 28th, 2005, 08:09 PM   #1
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Aliasing issues on XL2

Is anyone else out there having aliasing issues with there XL2? Landscape and basically non-linear forms (I guess those items of a more "amorphous nature" ) come out very nicely, but items such as telephone wires, mini blinds, repeated patterns (like bricks on a wall) grillwork, etc.. all have the moire effect.
It does this in at any frame rate in any aspect ratio.
I shot some footage of specific objects in 30i that demonstrate this unwanted effect with the XL2 then repeated the same exact shot with my GL1.
The footage is obviously nicer (higer res, of course) from the XL2 but the GL1 does not demonstrate this aliasing even slightly. It is very smooth and clean.
I talked to Canon and the guy had absolutely no idea how to explain it other than to basically say "Uh, yeah..that's normal".
Randy at EVS here in Burbank was more helpful and suggested lowering the sharpness control (which I have yet to do).
Does anyone think adjusting the knee lower will help?
Any other suggestions at all would help.
I don't really care for the fact that my 3 year old GL1 can produce a superior image with this aliasing issue.
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Old March 29th, 2005, 07:26 AM   #2
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Eric,

Put the word 'moire' into the search and you will get all the information you want. There was a long thread about this when the XL2 first hit the market. And yes, it's because of the increased resolution of the Xl2. I see it all the time on broadcast tv.

There is NOTHING WRONG with your camera! You have to learn about these types of 'gothchas' and work around them.

That's why on camera people are not allowed to wear certain types of clothing pattterns that could easily induce moire. But, watch professional golf where the shirts sometimes have a small, tightly spaced stripe pattern and you will see moire but they can't control what the players wear.

Hope this helps,

-gb-
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Old March 29th, 2005, 09:06 AM   #3
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Eric,

Early in your post you say that the XL2 image is "obviously nicer (higher res, of course)" and later that the "GL1 can produce a superior image with this aliasing issue" and in so doing underline the dichotomy that has spawned pages and pages of discussion here. It's one or the other. Hi res (meaning an optical system with resolution equal to or better than that of the CCD) means susceptibility to moire (aliasing). Limit the resolution of the camera (through the use of an antialiasing filter) and moire goes away. Canon has made the decision for you in deciding to make the trade in the resolution direction and so has brought down upon themselves more than a few complaints. Interestingly enough they also elected to have the XL2 produce color more accurately with the same result.

The only solutions to moire are to arrange shots so that it is not visible or to blur the image on the CCD suface as by a softening (portrait) filter.

And no, adjusting the gamma (knee) won't help.
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Old March 29th, 2005, 12:40 PM   #4
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Eric,

In all likelyhood, the primary culprit in the moire/aliasing problem you are seeing is your output device (monitor) or as we just found (scroll down to the thread "sample video- need advice") the encoding scheme used by some editing systems. Higher resolution in itself doesn't necessarily mean more moire or aliasing, however playback of high resolution footage on lower resolution devices (480p on standard ntsc televisions, or the HD footage broadcast during the olympics viewed on NTSC sets) will most assuredly introduce this kind of patterning, even when the DV file contains no such problems. The suggestions above will help (although I'm curious -read suspicious- about the 24p solution).

Barry
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Old March 29th, 2005, 02:04 PM   #5
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Barry,

My post was misleading. I've edited it to (I hope) fix that.
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Old March 29th, 2005, 02:37 PM   #6
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Aliasing issues

Thanks everyone, this helps. I have adjusted the sharpness and this did knock a little of the edge off of it, less than I'd like, but it helped.
I'll experiment with the other suggestions as well.
Does anyone know if the DVX100A has this issue?
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Old March 29th, 2005, 03:18 PM   #7
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Eric

Yes the dvx100a will also show this issue, although in my experience, it would appear that either panasonic has used an anti-moire filter (or algorithm), or canon has applied more sharpening or that simply the panasonic lens isn't as sharp. Either way there is at least a suggestion in still frames of slightly less detail in the dvx image, which does lead to less of a problem with pattern artifacts like these. But I do remember the days back when the DVX100 came out, and there were many discussions over at 2-pop over exactly this issue. So, yes the problem does occur to some extent on that camera.

Barry
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Old March 30th, 2005, 01:06 AM   #8
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Aliasing

After reading through all of the reply posts and checking through other threads it is obvious this is the cost, as A. J. and others said, of dealing with a higher resolution camera.
Despite the inherent nature of DV to be prone to this sort of thing, hopefully a solution can be worked out in the near future to allow higher registration of detail without the aliasing issue.
As I say that, I hear many cinematographers screaming they already have a solution...
It's called FILM...
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Old March 30th, 2005, 01:44 AM   #9
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Well Eric, it seems that film isn't totally immune and can fall victim to moire as well. See this thread.

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Old March 30th, 2005, 09:54 AM   #10
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Eric

I think the most obvious solution is to play your 480p footage back on a 480p device. Many of the cheaper LCD and plasma televisions are exactly this kind of monitor. I play my footage back sony wega 34" hd crt and the footage looks incredible. I never see much in the way of the aliasing many report on from viewing on a standard 60i ntsc model. (beware of some of the lcd HD sets as they often have poor scaling that will make you problem worse)

Barry
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