I don't know if this is necessarily so. It would be interesting to see this process (RGB->709->RGB->709...) done in a loop for 100x. I am willing to be proven wrong about this.
I think that the remapping from the larger color space to the smaller color space IS destructive. I think that about 15% of the tonal values are compressed away (256 tones down to 219), and when the space is again spread back out, the "missing" values are simply re-created/interpolated (spread) mathematically. I don't believe that Avid "remembers" the original RGB color space and then just spits it back out again. But I am not sure. It would take someone who actually knows the color science that's happening inside of the Avid to say for sure.
If you choose to import an RGB file as 601/709, you can not broadcast that signal without doing quite a bit of color correction to it to make it "legal." I've never considered wanting to bring in an RGB file and ignoring the "legality" of the signal just so I could re-export another RGB QT file. The other thing to consider is that Avid PROJECTS have color spaces, so if you want to edit in RGB you should really create an RGB color space PROJECT...
I guess I'm the guy that should know this stuff, but everything I do is a 709 color space project and any RGB footage that I bring in to those projects, I convert on import, telling the Avid "This is RGB, please convert to 709."
RGB media takes up more storage and throughput than 709 footage. Look at the codecs available when you choose RGB over 709 and the file sizes.
Again, I am not the authority on the way Avid specifically deals with RGB color inside of a 709 project. My guess is that the data disappears because it would be the most economical and efficient way to do it.
Steve Hullfish
contributor: www.provideocoalition.com
author: "The Art and Technique of Digital Color Correction"
On Mar 17, 2013, at 9:04 PM, Mark Spano <cutandcover@gmail.com> wrote:
> No that's not necessarily true. Importing 0-255 as RGB into Avid tells Avid
> to scale the 0-255 levels to 16-235. Do a straight export of that out to an
> RGB QT and it will map your 16-235 back out to 0-255. So nothing's lost.
> You may find that depending on codecs used, some slight shifting takes
> place, but no highlight or black level detail should be lost.
>
> Now if you import 0-255 as 709 into Avid, keeping the levels 0-255, and
> then export as RGB, then yes, the export module will attempt to stretch
> your levels back out and you'll clip a lot of highs and lows.
>
>
> On Sun, Mar 17, 2013 at 9:44 PM, Dario Caamaño <dario.caamano@gmail.com>wrote:
>
>> **
>>
>>
>> So that means that importing as RGB and then exporting to RGB, in this
>> simple process, I lose colour data?
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