I shoot (mostly) with a Panasonic AVCHD camera. I've been told (by other users of my camera) to import the footage in the Computer RGB (0-255) color space, not YCbCr (16-235). However, I've been told (by other editors) to edit and export in YCbCr to avoid broadcast problems. My questions is if that sounds correct, and if so, how color correction will be affected if I'm editing in a CbCr project with RGB footage. Do I need to adjust the levels to make sure that the RGB clips don't overrun the YCbCr boundaries? Will CC do that automatically? I have observed a noticeable difference in contrast when importing the same footage as RGB vs. YCbCr, which tells me the color space import is working correctly, since I'd expect higher apparent contrast on the RGB import.

Okay, the answer is simple but not readily apparent of how to manage MC's handling of color mapping. If you want MC to not remap and use the entire 0 to 255 range, then you should choose 601/709. This must read like a typo to you, but it's not. RGB does not use the 0 to 255 range, 601/709 does.

How can that be? Well Avid and its nomenclature was made before digital video, Windows Movie Player, youtube, accurate LCD monitors, etc.. So Avid did not envisioned a need for finishing in the range that's used by computer displays, which is 0 to 255.

In the analogue broadcast world that Avid grew up in, 16 to 235 is legal (this is a simplification actually, there is more to what is legal for broadcast than that). So from that POV, if an image or footage is recorded 0 to 255, aka "RGB" in Avid import/export speak, its range is illegal and needs to be dealt with. So when you choose "RGB," Avid lowers the contrast range from what was full range to 16 to 235.

I imagine your camera records full range. Avid's monitor windows display full range. And anything you watch on your computer screen will be full range. Now if you want to adjust the range to 16 to 235 entirely depends on how you are delivering the material you're working on and how it will be viewed, Quicktime, WMV, DVD, broadcast, film print.

The final use should decide to color specs of your material. And, unfortunately, it can get very messy.

BTW, while MC and Symphony can now use true RGB (4:4:4) material, I believe that's only if you have Nitris DX box. Your camera and your workflow will always be YCbCr. RGB and YCbCr are different ways of encoding an image, the later almost always uses chroma sub-sampling, represented by three numbers separated by ":". I believe your camera does 4:2:0. Which means its luminance is full resolution, while its vertical and horizontal chroma resolutions are halved. This lowers bandwidth, but also removes picture info. Encoding method is one aspect of a colorspace, but it is not in and of itself a colorspace.

And the terms "RGB" and "601/709" as used in Avid are different as well, unless you're using a Nitris DX box (I believe) or Avid DS. No matter if you choose "RGB" or "601/709," your camera's footage will always be represented YCbCr. The only difference is the color mapping upon import/export, as explained above. But no YCbCr to RGB conversion takes place on your footage. It stays YCbCr.

I would recommend you import with the 601/709 option selected, then use color correction to bring everything back to legal video (16-235). In CC Mode, you can set one of your windows so show a Wafeform monitor, which gives you an idea of the levels.

Also, I wrote this PDF about RGB versus 601/709 when importing/exporting with Avid. Might help.

BobbyMurcerFan:

MC and Symphony can now use true RGB (4:4:4) material

Wow, thanks for all the info! With both color mapping and image resizing, I think the way the Import options are phrased is backwards. At any rate, I think I'll import and export YCbCr to retain original levels, and then make sure they're legal in CC. That way (if I understand correctly) Avid will never mess with the levels (outside of CC). Now that I think about it, when I tested RGB vs. YCbCr imports, the whites and blacks looked like they had bee clipped out. 

Yes, that's correct. But do realize that no matter if you choose "RGB" or "601/709" your image will still be stored as YCbCr. So to equate "601/709" to YCbCr and "RGB" to RGB is inaccurate, as odd as that sounds. I expalined this above, but it's kind of hard to realize in this context that what Avid calls "RGB" is not RGB.

But your methodology is sound. BTW, there are legalizer filters that you can just throw on to the top most video track if want to supply a 16 to 235 signal. It seems a lot easier than CCing to be legal.

Actually as they have little to do with "colorspace" at all, the tabs should be labelled as:

IMPORT settings
709/601 = no remap of levels.
RGB = remap fill range to broadcast levels.

EXPORT settings
709/601 = no remap of levels.
RGB = remap broadcast levels to full range.

A CC on the top layer with a nice curve that compresses the top to 235 and the bottom to 16 is my way of legaiizing.

Avid v5.5 did bring some changes in this area. And yes, we are talking levels, not color space in these scenarios. With the new release it is referred to as graphic levels (0-255), video levels (16-235) or "do nothing). This will be available on AMA and can be changed on the fly via source settings.

Michael

And here we thought that importing 601/709 did nothing? So now we'll have 3 options (as before) but it's still not clear what each setting does?

Import graphic levels (0-255) - Assumes the incoming media is 0-255 and maps this to 16-235?

Import video levels (16-235) - Assumes the incoming media is 16-235 so it leaves it alone (no mapping)

Do nothing - ??? (how is this different from Import video levels?)

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You wouldn't think this sort of thing would be so complicated. The problem is that this dialog mixes up actions with interpretations. So on the one hand, we have settings that interpret the incoming data (like matte or color level) and then we have settings that sound more like actions like resize the footage... I know they are all settings that affect what Media Composer will do with the media, but for some reason the dialog seems to be confusing (and I'm by no means the only one who believes this).

Cheers

I'm glad that will be changed, but unfortunately I'm not in a positions to upgrade at the moment.

Barkin, I don't think there are three choices, only two ("do nothing" is part of "video levels").

But I DO agree that the new labels are still confusing.

I think something like these three choices would be good:

"Do not remap levels."

"Remap full swing levels (0-255) to studio swing levels (16 to 235)."

"Remap studio swing levels (16-235) to full swing levels (0 to 255)."

Calling 16 to 235 "video levels" isn't really accurate. Rec709 allows for transient overruns and underruns. The only truly invalid values in Rec709 are 0 and 255. So the entire range of 1 to 254 can be used for video. I'm not saying it's necessarily legal for broadcast, but video can exist outside of 16 to 235.

BobbyMurcerFan:

{snip}

{snip}  BTW, there are legalizer filters that you can just throw on to the top most video track if want to supply a 16 to 235 signal. It seems a lot easier than CCing to be legal.

But... wouldn't these "legalizer" filters add to the render time... And, in many cases CC can do more to correct the colors than the legal color range filters alone.  But.. that is an interesting point you make... I am going to have to try the legalizing filters to see what kind of impact it would have on the color vs. it's rendering efficiency loss or gain with manual CC combo.  Maybe the question should be... are you trying to get legal color or get "better" color (that is legal)?

Joe,

That's exactly the reason why you can't fast import when when choosing "RGB," b/c Avid is remapping and it takes considerable time.

And, yes I think using a filter can be easier and give you more control. But a lot of people, esp. in broadcast, like to adjust the levels during import or export in one fell swoop.

The choices I proposed mostly just clarify what Avid can do right now upon import/export.

As for CC vs filter, I think it really depends. What you could do is add a CC effect and adjust the gain and setup so 0 luminance on the waveform monitor becomes 16 and 255 luminance on the waveform monitor becomes 235. But it seems like it could get tricky. BTW, individual colors are allowed to go up to 240.

Avid's illegal color warning message is great, but you have to be parked on a frame to get the info. Could you imagine stepping frame by frame through an entire timeline. I had made a suggestion that you should be able to run the color warning filter in one fell swoop over and In to Out range and have it add warnings in the timeline (similar to the dupe detection or performance warnings) that you could jump to. But I've pretty much given-up on Product Feature Requests.

HTH.

P.S. In truth if you need to provide TRULY broadcast legal material, you should not be relying solely on Avid or any other NLE. There is a lot to it and it requires a real vectorscope and waveform monitor and a lot of knowhow.

I like BobbyMurcerFan's wording, I will pass on to product management - In previous versions, 601/709 basically did nothing as it assumed the sources were correct for video. Now the "do nothing" behavior is more explicit and you get an additional control of expanding which you didn't have before.

Also note that the setitng used is propegated into a bin column so you will know what level mapping was used should questions arise downstream.

Michael

MichaelP:

Also note that the setitng used is propegated into a bin column so you will know what level mapping was used should questions arise downstream.

 Michael

 

So if you make the wrong choice on import the bin column will have the wrong information?

So the heading isn't the actual level mapping but what it expects it to be. Uhm tricky....