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High video level causing jitter
After editing a sequence for what seemed like quite a while with no problems, some of my clips began to jump and jitter vertically. Turned out it was the scenes that had a light fixture in the scene that was overexposed and hitting about 110 IRE on the analog waveform monitor. Color correcting the highlights down a notch fixed the problem. Of course, this is the whole reason for preventing out-of-spec video, but in the non-broadcast world, I occasionally let small areas go. This was a large fluorescent fixture, so it was more than a minor specular highlight. Nonetheless, I was taken aback at the LHe’s sensitivity to this and my impression that it got worse over time. Is this normal for the LHe?
PS-Turning on the “Limit to legal levels” switch also cleared up the problem. If the rest of my footage was within legal spec, would this be a recommended fix?
Final Cut Studio, FCP 5.1.2, After Effects 6.5 Pro, Quicktime 7.1.3, G5 Quad 2.5, Kona-LHe V3, 4.5GB RAM, Nvidia GeForce 7800-GT, G-RAID 2x1TB FW800.
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21 Replies
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110 normally doesn’t cause a jitter, but the flourescent light sure would. It has an inherrent flicker when viewed on a video monitor and anything above 100 would enhance that flicker. Depending on the monitor you’re using to actually view the output of your LHe, that would also determine how badly your image would be affected.
Walter Biscardi, Jr.
https://www.biscardicreative.com
HD Editorial & Animation for Food Network’s “Good Eats”
HD Editorial for “Assignment Earth”“I reject your reality and substitute my own!” – Adam Savage, Mythbusters
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I don’t mean a mere flicker of an element within the frame, but rather vertical instability of the whole frame. It jumps up and down about 10 lines worth.
Final Cut Studio, FCP 5.1.2, After Effects 6.5 Pro, Quicktime 7.1.3, G5 Quad 2.5, Kona-LHe V3, 4.5GB RAM, Nvidia GeForce 7800-GT, G-RAID 2x1TB FW800.
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[Tom Brooks] “I don’t mean a mere flicker of an element within the frame, but rather vertical instability of the whole frame. It jumps up and down about 10 lines worth.”
I’ve never seen anything like that here.
Walter Biscardi, Jr.
https://www.biscardicreative.com
HD Editorial & Animation for Food Network’s “Good Eats”
HD Editorial for “Assignment Earth”“I reject your reality and substitute my own!” – Adam Savage, Mythbusters
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Are you seeing this flicker only in FCP. Many VTR’s can’t handle hi video levels, and many TV monitors have clamping issues with illegal levels. If this signal looks ok directly out of the VTR into your TV, but only jitters when digitized into FCP, and then flickers – I would be very surprised. Digital capture cards simply clip the video.
Bob Zelin
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[Bob Zelin] “Are you seeing this flicker only in FCP.”
I captured straight FW into FCP, so I didn’t really analyze the video prior to that, but would have to answer, yes, it’s only coming out of FCP. It doesn’t jump in the Canvas either, only on the output from the Kona.
I tried a couple monitors (Sony PVM type) with identical results, so I can rule out a flaky monitor.
And, color correcting the highlights down OR using the Kona’s “limit to legal video levels” switch fixed the jumping. I think the hot spot from the light is actally spiking chroma down into the vertical sync area. I’ve just never seen this coming out of an NLE system before–they usually clip things to the point where this can’t happen. The levels might be illegal, but not to the point of causing sync problems.
Final Cut Studio, FCP 5.1.2, After Effects 6.5 Pro, Quicktime 7.1.3, G5 Quad 2.5, Kona-LHe V3, 4.5GB RAM, Nvidia GeForce 7800-GT, G-RAID 2x1TB FW800.
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I am having a problem in hot areas of video as well. I am working in 10 bit uncompressed. This only happens to me on clips that have been scaled and instead of a jitter I get a plaid pattern throughout all the hot highlights. SOmeone else noticed this exact problem on the FCP forum as well and has contacted AJA. THe pattern does not show up in any quicktime movie, only on external displays. The only way I can get rid of it is to render in 8 bit or correct all the highlights way down and then the pattern goes away. What codec are you working in?
Jeremy
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I’ve seen this as well with some consumer level DV imported into a DV 50 timeline using a Kona LHe. As it was an offline edit and there were only a few shots in the timeline from that source, a quick broadcast safe filter took care of the problem.
However, for final mastering it’s important to look at the offending clips on a scope and use colour correction filters to bring the levels down, don’t just rely on the broadcast safe filter.
Cheers
John Christie
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In my case, this happens with whites that are well within broadcast safe. I have to turn them near grey before the pattern goes away.
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My shot in question is plain old mini-DV shot on an HVX-200. Very much a run & gun type of shot. On the waveform outside of FCP, the light sources is hitting right at 110 IRE and it is just starting to clip at that point. If I color correct the highlights down, the problem gets better. If I go the other way and make it worse, what I see on the scope as the white clips, is sort of a phantom baseline below the 0 IRE line. When this happens the video starts really jumping. I guess the initial learning here is that the LHe is not very forgiving of clipped levels above 100 IRE. If you throw that kind of garbage into it, it throws something else back out at you. Thanks for your thoughts.
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Hmm, I’d put your call or email into AJA tech support.
For the record, my base levels are NOT above 100 ire and they are still busted.
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