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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 October 25th, 2004, 09:30 AM   #1
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Custom Presets Brain Teaser

I have the XL2 and I've written a little bit about the moire/aliasing that I've experieced with the camera. I shot 6 or 7 hours of video in mexico a few weeks ago, And I've had a few minutes to review some of the footage. One shot in particular was looking at a building, and you could see telephone/power lines hanging over the streets. The moire/aliasing was so bad that I almost started to cry. It was a beautiful shot. But 100% of my attention was drawn to the moire around the lines.

Is the Vertical Detail option in the custom presets supposed to minimize this problem? ...And do you have to activate the custom presets for the Vertical Detail settings to work? ...

And if you do have to activate the Custom Presets to see the Vertical Detail settings work ....Then what setting (Vertical detail) is the camera using when the Custom Presets ARENT activated?

Thanks,

j.
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Old October 25th, 2004, 10:26 AM   #2
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John

When the custom preset is turned off, the vertical detail is set to Normal...which is the equivalent of the "thin" setting on some other cameras. Yes, you do have to activate the custom preset to set it to the low setting. The vertical resolution "low" setting will help but may not completely resolve the issue. Thin, close-to-horizontal lines are the bane of all video cameras, and the higher the resolving power of the camera/ lens...the more the problem will show itself ---the problem is mostly caused by the combination of the subject matter,camera and viewing device--- but if the camera resolves more of this fine detail, then it will show up more on some monitors.

Some other things you can do

--Lower the sharpness setting on the camera (especially important in 4:3 mode).

--Add a diffusion filter-- start with the lightest level of diffusion you can.

--alter your framing--moires tend to show up at certain subject pattern frequencies...quite often zooming in or out will fix the problem (this is impossible to do without a field monitor as the moires seen in the viewfinder will not match those seen on a television (which won't match those seen on HD or a computer monitor).

remember that adjusting VD, sharpness or filtering will lower the resolution that we all love about this camera (it's why some people are noticing more moire in the first place)...so its best to identify problem subject matter in the field, and apply your custom preset accordingly.

Barry
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Old October 25th, 2004, 10:47 AM   #3
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Or... Maybe just fix it in post? :)

Wouldn't softening an aliasing shot in editing be the equivalent of setting the vertical resolution to low? If so, you wouldn't need to bother when shooting. Just leaving it at normal at all times and fixiing the problematic shots during editing.
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Old October 25th, 2004, 11:07 AM   #4
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you shot in mexico and you still have the cam? wow =).
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Old October 25th, 2004, 11:15 AM   #5
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That's not very nice Yi,

Many people find Mexico to be a great place to shoot movies, away from overregulation and Overtaxing rampant in the States.

Those comments are biased and ignorant. Most of us Mexicans are hardworking honest people and we don't need any more bad rap.
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Old October 25th, 2004, 12:19 PM   #6
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Aliasing is a fact of life whenever information is sampled unless the frequency content of the subject matter is less than half the sampling rate Nyquist frequency). The only way to insure this is to install an antialiasing filter in front of the CCD. Few manufacturers are willing to do this (Nikon is an exception and there may be others) because precious resolution is thrown away in situations where the material is intrinsically band limited (unfortunately "brick wall" filters, i.e. those that do not suppress right up to the Nyquist frequency but suppress a great detail just above it exist in theory only). I was in a high end consumer video shop yesterday looking at the $8000 HDTV sets and lo, aliasing aplenty was clearly to be seen.

A.J.
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Old October 25th, 2004, 12:28 PM   #7
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I also just returned from Mexico to which I took my XL2. While I found the people warm and friendly I also got nicked about 30 pesos at all museums and archeological sites and in many churches for the privilege of shooting video. I've been given the impression that if you show up with a tripod you will not only be charged a good deal more but that burdensome paperwork is also involved. I think the trigger is professional vs. amateur. With an XL2 you are likely to be thought professional - I got asked at least once.

A.J.
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Old October 25th, 2004, 12:43 PM   #8
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>>>Or... Maybe just fix it in post? :)

Wouldn't softening an aliasing shot in editing be the equivalent of setting the vertical resolution to low? If so, you wouldn't need to bother when shooting. Just leaving it at normal at all times and fixiing the problematic shots during editing.>>>>

David

I think the method you described is correct, as it will deal with the vast majority of issues regarding moire (and line twitter...which is how I describe Johns issue)--most of these issues are really caused by how the camera image is interpreted by the output monitor (ie viewing resolution)...in these cases your method is just as valid as the ones I listed (maybe more so).

In some situations, though, the camera is the culprit...the moire is in the actual image (and thus can't be dealt with by softening after the fact)...In this case, we need to look at a solution that affects the image before it is written to tape... and this would be most likely a diffusion filter (caprock makes a antimoire filter that was developed for television and the graphics industry in the 50's), or adjusting the input pattern's frequency (zooming or camera placement) and possibly also the vertical detail adjustment on the camera. The camera's sharpness control might also play a role here, as at default (especially in 4:3) the xl2 is not neutral...it is sharpening the image somewhat, and thus could be bring up a moire where none existed if the sharpness was set lower.

Barry
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