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Old February 16th, 2005, 01:30 PM   #1
 
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Computer RGB to Studio RGB

Here goes one of my perennial questions as I continue to try to get a grip on RGB color mapping processes:

In a recent 3 camera shoot, I discovered that the captured footage from all 3 cams looked fine on my computer monitor, but, way too hot on my NTSC monitor. Thru the application of NTSC color bars, I discovered that my captured footage was ~15% too hot (in luma). In other words, a reduction of 15% in luma signal was required to make the Vegas generated color bars look right on my NTSC monitor. With a 15% reduction in luma, they now look too dark on my calibrated computer monitor.

Now, I notice that there's a preset in the Vegas color corrector FX called "Computer RGB to Studio RGB". Application of this preset to my footage shows that it's giving me a luma setting of about 86%, very close to my 15% reduction described above(as well as a bias of +16 RGB). I note that (235-16)/255=.86

This prompts a question re: color mapping in DV and Vegas. I understand that DV is RGB16-235, by specification. Is this what all DV is recorded at? Bringing this footage into Vegas shows RGB 0-255, so, if DV is 16-235, Vegas must be remapping it to full scale RGB. Yes or no?

Therefore, and I'm getting to my real question, when I render out to an NTSC output, either DVD or VCR tape, do I need to apply this color correction "Computer RGB to Studio RGB"?

It would seem, from my measurements, that this is needed.

Thanx for anyone who can help my understand this perplexity.
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Old February 16th, 2005, 01:43 PM   #2
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If my understanding is correct (and I'll be happy to admit it if it's not since this is not my strongest area of knowledge):

1) MiniDV as recorded from the camera is 0-255

2) The Vegas codec is 0-255

3) When printing back to VHS/MiniDV, it is OK to use 0-255 UNLESS it is being broadcast. As soon as you're broadcasting, it needs to be dropped to 16-235 (or risk getting the buzzing noise TV's sometimes exhibit)

4) DVDs are ok at 0-255

5) Internet WMV and other formats are ok at 0-255
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Old February 16th, 2005, 02:02 PM   #3
 
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thanx, Edward, for your answer. I beleive, however, DV is mapped at 16-235. Adam Wilt, on his website, says the following:

"All 601-conforming digital formats record nominal black at a luma level of 16, and nominal white at a luma level of 235 (in a 0-255 range, using 8 bits: there are 10-bit versions, too, like D-5 and DigiBeta, where the range is 64-940, but the DV formats are all 8-bit formats so we'll stick with 16-235 for this discussion).

When played over FireWire or over SDI or over SDTI, that's what you get: blacks at 16, and whites at 235. When you interchange files digitally, whether as DV-format stream files or QuickTime or AVI with the appropriate DV codec, black is 16 and white is 235. The same numbers hold, by the way, if your computer file holds 601-format uncompressed data, or DVCPRO50 data, or HDCAM, or DVCPROHD, as long as it's stored as "YUV" (really YCrCb) and not transcoded to RGB (wherein a whole range of gain/offset problems can occur, and even a gamma change if you're using Final Cut Pro"

So, this sounds like the full range is there, however black is mapped to 16 RGB and white is mapped to 235 RGB. By looking at the various scopes in Vegas, I'm seeing color mapping from 0-255 RGB. So, unless Vegas remaps to 16-235 on rendered output, I would need to do that manually with the color corrector.

As a side note, I would mention the 7.5 IRE issue, but, that's a whole 'nother discussion that I'd rather not confuse with this issue.

By the way, by "broadcast" do you include display on a television monitor, or are you referring to real "broadcast" over the air.
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Old February 16th, 2005, 02:28 PM   #4
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I was referring to "real" broadcast (i.e. over the air/cable).

As I said, this is not my area of expertise. I do know that if you want to make sure your video falls within 16-235, you MUST apply the effect to do that. Maybe someone with more knowledge in this area can step in here.
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Old February 17th, 2005, 06:33 AM   #5
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god im glad im in PAL land..

u see we dont have this problem.. well not this the extent of NTSC broadcasting requirements..

one thing though, you wont ever get your computer monitor to calibrate your colour accurateyl. You prolly already know this but the gamma, refresh and resolution of ur pc monitor just wont get it right..

"In other words, a reduction of 15% in luma signal was required to make the Vegas generated color bars look right on my NTSC monitor. With a 15% reduction in luma, they now look too dark on my calibrated computer monitor."

computer monitor images will ALWAYS be darker than those seen on ur reference tube.. even a hardcore ATI card with its smartshader wont calibrate correctly.. (beleive me i tried) Smartshader is a SW addon to ATI cards which allows the calibration/manipulation of video overlay without affecting the windows environment. works ok... but not to a point where i would trust it for any delivery. then again, im a pedant.. so ...

stick with ru reference tube and check colours from there.. its the most accurate way to go..

also you mention that your computer monitor is calibrated?? I knwo Photoshop allows me to calibrate my monitor to my printer and scanner, but thats about it..
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Old February 17th, 2005, 07:49 AM   #6
 
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FYI...

I calibrate my monitor with a Gretag Macbeth spectrophotometer. This cal allows me to see, pretty exactly, a photoshop print on my screen just as it will be when I print it with my Epson 2200. It seems NLE makers have failed at underdstanding how to make these adjustments. I find it hard to beleive that it can't be done correctly with the appropriate color map.
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Old February 17th, 2005, 08:57 AM   #7
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I was just yesterday struggling with this issue. If I capture direct from my Panasonic camcorder (being used only as a mini-DV player for tapes shot on a pro Sony system) via firewire into Vegas the footage has that washed-out look of changed black levels (I'm monitoring on an external video monitor). I've tried using the Broadcast Colors filter to correct it to no avail.

I did a series of tests encoding with the Mainconcept mpeg encoder and burning to DVD as well as frameserving to the TMPGEnc encoder (both with 601 enabled and disabled) and the resulting DVD still looks washed out.

The only thing that works so far is to use a DVD to analog box and go through a Proc Amp to fix the black level before capturing.

Tony
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Old February 17th, 2005, 09:52 AM   #8
 
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Tony...

a couple of things occur to me re: your washed out video...
1-perhaps somewhere in your chain, you're applying an NTSC pedestal to the footage...you know that IRE 7.5 pedestal will cause the kind of problem you're describing. And fixing it with a proc amp is the right solution if you can't disable the setup, somewhere.
2-another solution is to use the Sony Black Restore FX
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Old February 17th, 2005, 10:07 AM   #9
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Thanks Bill. When I get the washed-out look I am going directly from the camcorder's firewire out to the PC's firewire in and the camcorder has no IRE controls. I'll try the Sony Black Restore FX. Thanks again.
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