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  #1  
02-21-2015, 03:56 PM
Prelude Prelude is offline
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Hi all,

As a follow up on my post How to determine what to improve on TV recordings I am trying to determine if the input chain I am using to capture video has any deficiencies. In my opinion calibrating the capture card to my TBC for example will leave me with at most color errors from the VCR itself, or it must be the tape/recording. The AVT-8710 defaults to colored bars when no input is present and I was wondering if they are any good as a reference?

To test I recorded a few second of color bars and opened this up in fcp. By using the RGB overlay I get a picture as shown in the "fcpcolorbars" attachment. When I compare the value's I read there with the ones I found here http://www.pembers.freeserve.co.uk/T...ical.html#Bars (scroll down to 75% PAL) then they seem to be in the right ballpark, but not quite.

I am not sure how much of a deviation is acceptable or to be expected? Also, I am not sure how to correct this problem. I have been playing around with the color correction in FCP but can't get the image to be as it should be.

Do I correct this in software after capture, during capture in virtualdub (proc amp settings), do I use the controls on the AVT or do I just leave it all alone

Thanks a bunch,

-P


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  #2  
02-23-2015, 06:39 PM
dpalomaki dpalomaki is offline
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http://en.wikipedia.org/wiki/SMPTE_color_bars
http://www.negativespaces.com/blog/2012/2/21/hd-monitor-calibration-smpte-arib-and-white-balance.html

Provide some information on color bars. FCP documentation may have information as well.

Whether or not the bars provided by the AVT are accurate I do not know, and aging could be an additional factor with gear, both on the output and capture sides. (I know of some gear that put put full height bars were not very accurate - they were more for show than actual use.)
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02-23-2015, 09:36 PM
sanlyn sanlyn is offline
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Well, prelude, here's what happens. If you calibrate your system to perfectly display and capture the AVT colorbars, or anyone else's colorbars, you'll get a near-perfect colorbars display and a perfect capture of the colorbars. Get yourself an off-color VHS tape that's darker than normal. Start the capture with the colorbars and then start the tape. What you'll see will be a very good display of the colorbars and a very good capture of the colorbars, and very off-color and dark copy of the tape. You're going about it backwards.

Second: to what standard are you calibrating the colorbars? What display standard are the colorbars designed for? Do you keep adjusting your monitor or some other device until you think the colorbars "look nice"? Problem is, they'll probably look different on a different monitor and graphics card.

Third: PC monitors and TV s don't display video the same way.

4: Use test graphs and measuring devices to calibrate everything in the capture and viewing chain to a known standard.

5: You don't change every piece of hardware and software every time your signal changes. Instead, you adjust incoming capture signals to match a known standard, using instruments like histograms during capture.
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