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Canon GL Series DV Camcorders
Canon GL2, GL1 and PAL versions XM2, XM1.


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Old September 18th, 2004, 11:45 AM   #1
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shimmer sharpness white lines grain

This is my first post. I have had my GL2 for only a month and have been experimenting with all the different setting and have become comfortable with the camera. Something I've noticed in digital video that I don't like is that during motion even sometimes under good shooting conditions, there are little lines of over sharpness or ? I don't know how to explain it. Film as far as I can tell doesn't suffer from these types of problems. I have been experimenting with all different settings like turning down the sharpness and trying frame mode and have had some success. Could somebody give me some advice, does this problem have a name? I could use a little direction on where I can find some more discussion on this topic to help me learn how to shoot better video. I have been searching threads but don't have the words to search for. I am most interested in achieving very good video in terms of color and without areas of little digitalized over sharp parts that distract from the video.

Thanks.
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Old September 19th, 2004, 01:26 PM   #2
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Welcome Bradley,
Before anyone speculates, please tell us how you are viewing your footage as you observe this "problem".
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Old September 19th, 2004, 03:14 PM   #3
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Ken,

Thanks for responding. I am a novice to using online listserves but I have spent weeks doing research on this site and have found the threads very helpful.

I have been viewing the video on my computer monitor. I have also noticed similar types of distortion in movies like "Bowling for Columbine" where there are areas, usually edges, that distracted me from the movie. I guess I am looking for a website or an article that explains in detail the different types of dv distortion or artifacts and how to prevent them. I want to do some experiments to pin point the problem but need a little more guidance into what some of the typical problems are and some of the different things I could try.

Thank you.
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Old September 19th, 2004, 07:58 PM   #4
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I am not certain I know what problem you're describing. But I can offer two thoughts.

First, the primary designed viewing venue for all video cameras is a television. Computers mimic television images but they're, at best, a simulation often prone to introducing illusory issues of its own. That's why professional editing stations -always- use an accurate production monitor to facilitate judgment of picture attributes. If you don't have a production monitor a good consumer television set will serve the primary goal of showing your footage in its true characteristics.

Second, video is not film. We have an entire forum dedicated to the notion that this difference can be defeated but, in the end, video is still not film. It has its own motion signature and different color and exposure latitude characteristics. Making video look truly good requires skillful lighting and control of the image within video's limitations.

The GL2 is a terrific video camera. I have one myself. But it's just a 1/4" video camera, a far cry from a Panavision film rig and even a far cry from the 1/2" cameras that we've become accustomed to seeing used on local broadcasts. So, while the GL2 is capable of producing very good images, realize that it does have some severe limitations. Don't make yourself nuts out there! <g>
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Old September 20th, 2004, 12:19 AM   #5
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THanks Ken. I was beginning to feel a little bit nuts. I have really been pushing the limits on my camera figuring that for 2 grand it better pump out some good images. I guess my expectations were a little too high or I a little too poor. I have made videos in the past that were intended to be viewed on a computer. I have not ever owned a television set due to the fact that I have always been rather poor and am an avid reader. I suppose it is time to break down and get one. I am in the process of redoing the video for the non-profit I volunteer at. I am absolutely sure the gl2 packs more than enough imaging power to handle some interviews and program highlights.

Take care.
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Old September 20th, 2004, 04:03 AM   #6
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Hi Bradley,
I'm far from being an expert but i might have understood what you say.
Did you say that by turning the sharpness down it was kind of solved?
I think that your problem might be called "aliasing". I'll check again this post...
Pietro
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Old September 20th, 2004, 06:17 PM   #7
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Pietro,

I think the word aliasing might be what I have seen. I believe the problems with the GL2 is that it experiences a lot of aliasing in low light conditions with the sharpness turning up, especially with high contrast areas of moving objects. I would like to read up on exactly how a dv camecorder works to better understand some of its limitations. If you come by any good tech articles let me know.

Thanks.
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Old September 20th, 2004, 11:00 PM   #8
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Here is a link that to others seeking terminalogy for different types of artifacts.

http://www.adamwilt.com/DV-FAQ-tech.html

text below from site:

What are the DV artifacts I keep hearing about?
DV artifacts [Pix: Artifacts] come in three flavors: mosquito noise, quilting, and motion blocking. Other picture defects [Pix: Defects] encountered are dropouts and banding (a sign of tape damage or head clogging).
The most noticeable spatial artifact is mosquito noise around any sharp, contrasty edges. These are compression-induced errors usually seen around sharp-edged fine text, dense clusters of leaves, and the like; they show up as pixel noise within 8 pixels of the fine detail or edge causing them. The best place to look for them is in fine text superimposed on a non-black background. White on blue seems to show it off best. The magnitude of these errors and their location tends to be such that if you monitor the tape using a composite video connection, the artifacts will often be masked by dot-crawl and other composite artifacts.

A spatial quilting artifact can sometimes appear at the boundaries between 8x8 pixel blocks, most noticeable on shallow diagonals or on slightly-defocused backgrounds, typically when there is some motion in the scene to make the fixed "grid pattern" a bit more obvious. Some DV codecs seem to be much more prone to this than others, and with a few the quilting really starts to appear only after a few generations of rendering.

Motion blocking occurs when the two fields in a frame (or portions of the two fields) are too different for the DVC codec to compress them together. "Bit budget" must be expended on compressing them separately, and as a result some fine detail is lost, showing up as a slight blockiness or coarseness of the image when compared to the same scene with no motion. Motion blocking is best observed in a lockdown shot of a static scene through which objects are moving: in the immediate vicinity of the moving object (say, a car driving through the scene), some loss of detail may be seen. This loss of detail travels with the object, always bounded by DCT block boundaries. However, motion blur in the scene usually masks most of this artifact, making this sort of blocking almost impossible to see in most circumstances.

Finally, banding or striping of the image occurs when one head of the two on the scanner is clogged or otherwise unable to recover data. The image will show 10 horizontal bands (12 in PAL countries), with every other band showing a "live" picture and the alternate bands showing a freeze frame of a previous image or of no image at all (or, at least in the case of the JVC GR-DV1u, a black-and-white checkerboard, which the frame buffers appear to be initialized with). Most often this is due to a head clog, and cleaning the heads using a standard manufacturer's head cleaning tape is all that's required. It can also be caused by tape damage, or by a defective tape. If head cleaning and changing the tape used don't solve it, you may have a dead head or head preamp; service will be required.

This sort of banding dropout occurs fairly often; about once per DV tape in my experience. Usually it isn't even noticeable -- a single frame of banding due to a momentarily clogged head won't be visible unless there's motion in the scene to show off the frozen stripes. Have a look through your old tapes frame by frame (on a slow day, of course!) and you might be surprised how often you'll be able to find a single, subtly banded frame. For what it's worth, I've only rarely found such a banded frame on any DVCAM footage I've shot, which indicates to me that DV is right on the edge of reliability. DVCAM, with its 15 micron track width, or DVCPRO with its 18 micron track, are sufficiently on the safe side of the bleeding edge so that this sort of droput is much less likely to occur.

Bear in mind that analog BetaSP typically has several dropouts per minute; the last time I measured visible dropout rates on Hi8 and S-VHS I got numbers in the range of a dropout every 3-5 seconds (Hi8) and every 7-20 seconds (S-VHS). One visible dropout per hour-long tape, on average, is not something to get flustered about. But if it does bother you, shoot DVCAM or DVCPRO instead.
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