Colour correction parameters

[rtX]

v1.78.7

I have a ProRes 4444 file from which I am going to master a DCP for delivery to a UK distributor (first one to be so delivered!). In the release notes it says, "Colour conversion presets have changed in this version. As a result, if you load films created by previous versions of DCP-o-matic they are likely to display their colour conversion as “Custom” since the conversion no longer matches any preset. You are advised to reset your configuration (from the Edit menu on Windows/Linux or the Tools menu on OS X) so that the default colour conversion settings are updated to the new (correct) values."

I'm creating a new DCP and the Colour Conversion is showing as "Custom" (even though this is a new DCP). I'm told that the source file colour space is Rec.709. Should I set the colour conversion to Rec.709 or leave it as "Custom"? On previous test versions, I've not adjusted this setting but cannot recall what it defaulted to.

Thanks in advance.

[carl]

Firstly, if you have made a test for your film with a previous version of DCP-o-matic I would stick with that version, and not change it for your final master. The .7 at the end of 1.78.7 means it is a version under test (a "beta", if you will) so things may go wrong with it.

That being said, it's strange that you are seeing "Custom" for a new project.

Did you just do File -> New and add some content?

Have you reset your configuration (using the method described in the release notes)?

If you trust the new version, I would set the colour conversion in your new project to the "Rec. 709" preset (click Edit then choose Rec 709 from the list at the top).

[rtX]

Did you just do File -> New and add some content?

First I went Edit->Preferences->Colour Conversions->[Select]Rec.709
Even after doing this, Colour Conversion shows as 'Custom' when I do File->New and add content . Having added the content, if I go Edit->Preferences->Colour Conversions again, Rec.709 is not selected/highlighted until I re-select it. And then Colour Conversion remains "Custom" until I press the adjacent Edit button. I then select the "Use preset" check box and choose Rec.709, press Ok and Colour Conversion then shows as Rec.709 (not "Custom")

[carl]

Edit->Preferences->Colour Conversions is only needed if you want to add your own presets or modify the default ones that DCP-o-matic gives you. Otherwise you've no need to go in there: just add some content and set the required colour conversion for it. I'll see I can reproduce the 'Custom' thing: it shouldn't happen.

[Carsten]

Carl - for a fresh install or after preferences reset - is it true that there are two rec.709 presets now?
When I choose edit, I can see that with the new color conversion system, I can choose between Rec. 601 and Rec. 709 for YUV to RGB matrix. I understand that in general, Rec. 601 is for SD sources, while Rec. 709 is for HD sources - shouldn't these two rec.709 presets be named accordingly? I think it's irritating to have two presets with the same name, but with different parameters.

I would suggest that for a fresh installation or after preferences reset, to have one preset named 'Rec. 709 (SD)' using the Rec. 601 conversion, and the other 'Rec. 709 (HD)' for the rec. 709 YUV-RGB conversion being used. Or add '601' to the corresponding preset name - but I think using 'SD' and 'HD' would give most users a better chance to choose the right preset.

I think the difference between rec. 601 and rec.709 will hardly be visible, but it would still probably be the correct way to suggest rec. 709 (SD) for e.g. DVD source footage, and rec. 709 (HD) for BluRay or other HD footage?

- Carsten

[carl]

Carl - for a fresh install or after preferences reset - is it true that there are two rec.709 presets now?

Not really. There are several parts to the colour conversion:

1. Input gamma correction
2. YUV -> RGB. This needs to be done differently for Rec. 601 and Rec 709 sources, so there are two options for that particular conversion.
3. RGB -> XYZ. This is also different for 601/709 sources.
4. White point adjustment
5. Output gamma correction

Most people should ignore the configuration and just choose the Rec 601 preset or SD or the Rec 709 preset for HD. In fact it is quite tempting to remove the GUI preset configuration altogether and just hide it in an XML file somewhere to avoid confusion

So the two Rec. 709 things that you mention are different: one is a preset (containing parameters for all parts of the colour conversion) and one is just a setting for the YUV->RGB part.

Does that make things any clearer? Maybe I should add (SD) and (HD) to the preset names.

[Carsten]

Hmm, I have to create a fresh install to see what the default presets actually are now. After I reset my prefs in windows, it showed two color transformation presets, both with the same name - Rec. 709. Yes, maybe, with color transformation having developed mature and with good presets for most typical content, it could be wise to at least move that edit option into advanced prefs...or even further away

Also, maybe at some point we need to find ways to deal with different parts of prefs - color, general, and especially the cinema certificate database.

- Carsten

[carl]

There should only be 1 Rec.709 preset. I'll look into that...

[Carsten]

What I mean is this (1.78.7 Mac) - and I think it's the same in my current windows 1.78.7 installation.
Currently I have renamed them to Rec. 709 (SD) and Rec. 709(HD) there.

Screenshot 2015-05-04 22.42.48.jpg

Screenshot 2015-05-04 22.43.07.jpg

[carl]

That shouldn't happen. I think I might remove the preset configuration altogether (so there are a set of hard-wired presets that cannot be altered nor added to) and then you can just tinker per-project if you want to.