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What Happens in Vegas...
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Old January 31st, 2011, 08:54 PM   #1
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Compositing, transisions, plugins and sRGB cRGB

I'm wondering how Vegas handles this. If your source files (avchd) on the timeline are sRGB, and you wish the final render to be sRGB, what is to stop transitions, plugins, and the various compositing modes from outputting values that reach into cRGB? That would result in an uneven colorspace between the untouched media, and the transition/compsiting areas. Is the only right way to do this properly by adding a sRGB to cRGB media level plugin to each file, and then a cRGB to sRGB plugin to video output fx? Basically I'm guessing that Vegas does not limit itself to the colorspace of the media that it is compositing/mixing/effecting.
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Old January 31st, 2011, 10:04 PM   #2
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If you give Vegas YUV footage and it interprets it as YUV (use scopes to confirm this), any filters used will treat the footage as YUV as well. However...

AVCHD may get interpreted as RGB if your project is set to 32-bit instead of 8-bit... or so I have read. I can't speak from experience on this. Go to the following link if you wanna read more (scroll half-way down)

Color spaces and levels in Sony Vegas 9 and 10


1) If you're adding RGB media (title cards, etc) and are intending the final output to be YUV, you should add a "Computer RGB to Studio RGB" filter to the RGB media so they match the colorspace of your YUV footage.

2) Adding "Studio RGB to Computer RGB" and vice-versa to each clip is probably not a good idea :)
If you need to monitor in RGB and your footage is YUV, add ONE "Studio RGB to Computer RGB" filter to the Preview monitor window, then kill it before rendering. Use scopes if you're suspicious something is going out-of-range when it shouldn't... scopes are a good way of staying sane while sorting this out.
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Old February 1st, 2011, 11:45 AM   #3
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Jeremy, there really isn't anything to stop the FX from exceeding the value ranges. I think there is a "Safe Levels" or some similarly named plug-in, I've not looked at it but it may help. But, generated media, titler et al will put out 0:0:0 for black and 255:255:255 for white by default. You can either adjust these to 16:16:16 and 235:235:235 yourself, or apply a cRGB->sRGB filter which will compress the range for you.

Viewing with Scopes if it's critical is the only way to numerically detect it, afaik.

However, if it does exceed sRGB levels, it will simply be clamped. Your best defence is to ensure you're viewing it properly, and make your subjective decision based on that. That means one of these:
1) Use a proper external video preview device (the best, but not many of us have 'em).
2) Have a second monitor, and under the Preview settings, check "Use Colour Management", and then check "Use Studio RGB Colour Space" (if your source is) and select the appropriate colour space for your preview device, if it's a computer monitor, then cRGB. But, this is ONLY applicable in full-screen mode. When the preview is in a window, it is not using the colour management.
3) As suggested, put a sRGB->cRGB output filter on. This is the only way if you're using the preview window as an actual window. However, it is an output filter, not a preview only filter, so it must, must be removed before encoding.

And spend much time around Glenn's article(s) (the link Rob provided), they're invaluable.

Hope this helps.
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Old February 3rd, 2011, 07:23 PM   #4
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Thanks for the input, I am aware of/understand everything you both discussed, I was just wondering how well Vegas does at policing it's own compositing engine, efx, and third party plugins with respect to color space.
Here's an analogy that led me to consider converting everything to cRGB first:
You give a kid named Vegas a box of crayons, put a sheet of paper(sRGB) on the table and tell him to draw a picture. Well, most of the picture ends up on the sheet of paper, but a good portion ends up on the table. However if you cut a sheet of paper that covers the entire tabletop(cRGB), all of the picture is going to end up on the paper.
If Vegas handles colorspace correctly based on the source media, then it's just a matter of knowing which source media file types are dislpayed as sRGB or cRGB in the various Vegas versions/8 vs 32 bit, and then converting the colorspace on the odd media files to match the rest.
Thanks again!!
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Old February 3rd, 2011, 08:48 PM   #5
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Glenn Chan article on what colorspace Vegas chooses depending on 8/32bit project settings vs format type (above) discusses this in fair detail tho some formats are not in there I think.

Usually I rely on Scopes and just assign a specific Track for each range: like YUV on Track 1, RGB on 2, half-YUV (016-255) on a third... then apply an appropriate StudioRGB > ComputerRGB filter or tweaked variation for whichever Track(s) needs shifting.

There may be another filter on the Preview window display depending on monitor hardware: most adjustments I'm making are matching/grading shots so I have scopes running to spot problems during import.

But the buck stops with us... it isn't really the software that's responsible. Vegas has a bunch of preferences (same as all NLE's & compositing apps), but we're the ones who have to make sure the footage is all good-to-go... usually it isn't a big problem.
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