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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 January 25th, 2005, 03:16 PM   #1
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Question to those who know

i notice that when i take video . things like aircondtioner grills or edges with stright lines that go out or up and down tend to get wavy or flutter for lack of a better word . it seems to do it in any mode and its reel bad when zooming in or out . this effect can be seen in view finder on the monitor and in post .what cause this and how can i correct it . thanks in advance for any help. dp
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Old January 25th, 2005, 03:29 PM   #2
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The frequency of the near horizontal or near vertical lines is approaching the limit the camera can capture based on its limited resolution. You need to understand how your camera reacts to certain patterns (including fabrics, etc.) and work around bad situations. That means doing test shots. Also, turn down the sharpness control on your camera for a smoother image.
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Old January 25th, 2005, 04:25 PM   #3
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The technical term for it is moire, I think. If you run a search I am sure you will find valuable info about it and how to avoid it.
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Old January 25th, 2005, 04:44 PM   #4
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thanks for the help

i will play with it . dp
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Old January 26th, 2005, 04:04 AM   #5
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It may also change when switching modes (24p, 30p, 60i) or shutter
speeds. Experimenting is definitely key here!
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Old January 26th, 2005, 05:58 AM   #6
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There is also a setting for Vertical Detail (Normal or Low) in the custom presets. This will affect the effect (if you know what I mean).

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Old January 26th, 2005, 05:59 AM   #7
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thanks Mr Lohman

one question . whitch frame rate would be most effective in reducing this problem . thank you dp
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Old January 26th, 2005, 06:06 AM   #8
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thanks to you also Mr Hunter

i did notice the vertical detail adjustment .but the camera seems to handle stuff like buildings and poles quite well . yet my air conditioner looked alive at one point in some video i took in my home . i will play with this adjustment also thanks dp
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Old January 26th, 2005, 07:01 AM   #9
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Best is to simply play with this Donald. There is no one best setting,
what may work in one situation for someone may not work for
you. Simply trial and error should yield what looks best in this
specific scenario. It also depends on camera angles and so forth.
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Old January 26th, 2005, 07:44 AM   #10
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Ever since the Moire discussion began around the XL2, I've started paying closer attention while watching television. You really do see examples of it on the news, high end productions (NOVA last night), a HUGE example caught my eye the other day while watching "Trip to Mars" (Or whatever that awful sci-fi flick was with Gary Sinese and Tim Robbins in it)

Moire happens to pros in video and film situations... it's just a factor of the physics of optics. You deal with it as best you can.
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Old January 26th, 2005, 12:15 PM   #11
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Remember that moire depends on the pixel spacing in the CCD and in the device you view it on. It will, thus, be more readily apparent in the viewfinder than it will on a TV screen or computer monitor.
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Old January 26th, 2005, 04:18 PM   #12
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Had a couple shots with moire in it in my last production (both caused by tightly stripped fabric). I was able to rectify it in post with a light gaussian blur on the vertical axis. It softens a bit but not much.

The best rule of thumb I've found so far is to avoid any fine regular patterns. It can be fine lines, but it can also be small dots with regular spacing, or anything else of a repetitive nature. It's always best to go with something more irregular or organic (especially for fabric).

Also, you have to watch for it in the VF, because sometimes, a fine stripped shirt will look just fine in close-up and it starts to look like live water when you zoom out, since the lines become finer and more difficult to handle for the optic.

If you're doing fictional work, this is something that must be stressed (sometimes repeatedly based on my experience) with the artistic director. If they don't come from a video background, they will likely not be familiar with the moire and high contrast issues that must be worked around in video.
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Old January 27th, 2005, 01:33 AM   #13
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Re: thanks Mr Lohman

<<<-- Originally posted by Donald Pittelli : one question . whitch frame rate would be most effective in reducing this problem . thank you dp -->>>

Progressive gives better result then interlace when you have moire problems.
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Old January 27th, 2005, 04:52 AM   #14
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thanks to All

thanks for the tips . i found setting the vertical detail to low and turning down the sharpness to be very helpful . also a defuser seemed to help a bit .i have a dvc30 i took some of the same problem shots . the dvc 30 seems to handle theese thing better . but i also noticed the dvc 30 is not as detailed as the xl2 . especialy with the manual lens 14x .i mean you can read fine print writing on things from a good distance yet the dvc 30 is fussy on the real detailed stuff. the xl2 is very detailed so i was wondering can the sharpness of the xl2 add to the moire effect .thanks dp
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Old January 27th, 2005, 07:48 AM   #15
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Moire is caused when the image presented to the CCD has more resolution than the resolution of the CCD. The only way to prevent it is to limit the resolution of the image as by a diffusing/softening attachment or by using a lens whose MTF falls off at lower frequencies than the resolution limit of the CCD. Some manufacturers of still cameras incorporate a low pass filter as part of the CCD assembly. Some allow the user to install one where moire is a problem. Mamiya is an example of the latter. If you go to http://www.mamiya.com/cameras.asp?id=1&id2=2107 and then download the brochure you will see an illustration of their removeable filter.

If you look at the pictures starting at http://www.pbase.com/agamid/image/38413496 you'll see that no mode is more or less susceptible to moire than any other. It just that in the higher resolution modes the aliasing starts at higher spatial frequencies. The reason this is true in the XL series is that the resolution of the lenses (except when stopped down to their minimum apertures) have resolutions better than the CCD (as we would certainly hope!).

So since you can't install a low pass filter you will either have to put a diffusing filter on the lens at the cost of resolution or change the image size until the pattern in the subject is at a higher frequency than the lens can pass or avoid patterned subjects. "Jaggies" on near horizontal lines are a form of moire. The only way to beat them is with a diffusing filter.
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