Ok here we go..... I received some good fodder from Luc A. in Product Design that should be considered an introduction to some of the things discussed in this thread. Knowing this group, I am sure many, including John Moore who started the thread, will have more specific questions that I can then ask him to tackle.
Now, RGB refers only as the color model used to store the information, not the signal level.
This is why it is seen in the project color space setting where you can pick from a combination of color models (YCbCr or RGB) and color spaces (like 709, Rec.2020, DCI P3).
Rec 709 and Rec.2020 by specifications are "video range" as signal levels. BOTH are video levels for 8 and 10 bits. UHDTV is the same video levels - RGB 4:4:4 and YCbCr 4:2:2, including the 12 bits mode. You can see the specifications here: Rec 709 specifications. This means for 8-bit media, black is 16 and white 235. For 10-bit media, black is 64 and white 940.
Media composer internally works at video level to match those specifications. This is why when importing media the (new) choices are clear the media will end-up being treated at video levels:
-Do not modify; treat as legal range
-Scale from full range to legal range
For linking, MC will try as much as possible to detect the levels based on the metadata and we automatically apply color transformations to match the project color space.
For example, when using graphics files, these are usually created on computer graphics systems for which black is 0 and white is 255 (referred as "Full Range" in our nomenclature). For most graphic formats (tiff, JPG…), Media Composer understands this is full range and will automatically apply a color transformation "Scale from full range to video levels". If for some reasons the metadata informing us about levels is missing or wrong, users can manually apply color transformations in the source settings to bring the media to video levels (black =16, white =235). Besides color levels, look-up tables and CDL values can also be applied as color transformations.
Note that internally, levels are normalized to values between 0 and 1. Black being 0 and white being 1. This normalization process makes it easy to handle media at 8, 10 12 or 16 bits. Our internal format supports normalized values from -2.0 to 2.0 so nothing gets lost when you apply color transformations. It might become out of the Legal range (0 to 1 in normalized values, 16-235 in 8 bit representation) but those values are still there. Values go negative below black point, and above 1.0 for levels above white.
When exporting to QuickTime, there are 2 areas where you can change the color levels. The first one is from the first export window that opens:
In this window, you assign the color levels being sent to the QuickTime encoder.
Users can select:
-Keep as Legal Range. (This means it won't apply any further color transformations)
-Scale from Legal to Full Range. (This means video black 16 will be remapped to 0 and white 235 be remapped to 255. If there was some information below 16 and above 235, it will be lost by the remapping)
The second area available to change levels is in the QuickTime encoder window and should basically never be used (except for some legacy workarounds with other applications).
The QuickTime encoder window
Here's why:
This second setting is found when using "custom" codecs then "format options".
This opens the QuickTime encoder settings. When clicking on "settings" for video, it opens yet another window where "color levels" can be picked. The possible choices are:
-709
-RGB levels
This is where it gets interesting. The QuickTime encoder expects legal range as input.
If you pick "709" it assumes the media is already in 709 and won't touch it. This is the default value and should basically never be modifed. If you send Full Range media (setting Scale to Full Range in the export setting) to the encoder… and let the encoder believe it is 709 media, you actually achieve an encode at Full Range (the encoder, just like Media Composer does not eliminate values below 16 and above 235). If you pick "RGB Levels", you are telling the encoder that Full range media is sent to the encoder… it will thus apply a scaling from Full range to Legal range! This result is the opposite of trying to export Full Range. This is why we usually don't change this setting.
In between older versions of Media Composer / After Effect / Premiere, there have been many changes on all sides on how to interpret metadata and color levels. This is not an easy task but we are working with partners to make this as transparent as possible.
I hope the images come through ( there are 2 ) but if not, email me directly and I will respond in kind and provide the doc Luc created via email. marianna.montage@avid.com
---In Avid-L2@yahoogroups.com, <marianna_montague@...> wrote :
Posted by: marianna_montague@avid.com
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