Re: OCIO Configuration Reference Values


Thomas Mansencal <thomas.m...@...>
 

Hi,

I came across this thread.

Quick question: assuming you had primaries / whitepoint stored on a per colourspace basis, wouldn't that be competing with the OCIO MatrixTransform if not metadata? I can see a danger of disconnection between the primaries / whitepoint fields and the MatrixTransform if both are present at same time, precision issues induced by the rounding would be enough to break that relationship for example.

You would also likely need to support a field for the chromatic adaptation transform being used to convert from the given colourspace to the reference colourspace.

Cheers,

Thomas

On Thursday, September 29, 2016 at 9:54:37 AM UTC+13, Malcolm Humphreys wrote:

I always thought this would be better as a 'chromaticities' field per colorspace. With one also being on the reference colorspace.

Question would be would this just be metadata or actually used to create extra ops.

What do you think?

.malcolm


On 28 Sep 2016 20:35, "Troy Sobotka" <troy...@...> wrote:
Greetings all.

Seeing as how development has appeared to have been kick-started again, I was wondering the feasibility of adding a much needed configuration element to OCIO?

Currently it is *exceptionally* difficult relying on OCIO to develop in-application UIs in terms of managing colour representation and more complex algorithms. The basic metadata of any given configuration's reference space is missing, and as a result, the following becomes extremely tricky to manage:

* Saturation UI elements. Incorrect Y weights for the various RGB primaries are impossible to glean from transforms.
* Greyscale conversions. Again, missing metadata on Y weights.
* Colour manage wheels and pickers. Missing primary chromaticities makes it impossible to properly correct wheels and pickers for any given display view.
* Formulas / functions / light math that might be required by shaders or algorithms that require known values for XYZ.

Given that Sony established the luma coefs metadata tag, which is largely unused, I was wondering if it might be feasible to add a similar, extremely bare-bones metadata tag for chromaticities for the reference space? Something similar such as:

reference_values: [R1, G1, B1, R2, G2, B2, R3, G3, B3, WR, WG, WB]

Where RGB 1-3 represent the reference space's transform to XYZ, and W RGB represents the white point as expressed in specifications. The need to reproduce the white point as per specifications might be required for algorithms or formulas that need to match values that may differ from the canonical Y positions in the RGB to XYZ matrix.

I've started a simple branch that does this basic feature, and am wondering about feedback from the big brains that lurk on this list. If this seems feasible, I'd be happy to flesh this out to include the matrix get / set and update the luma coefficients function to pull from the updated reference_values facet.


Feedback appreciated.

With respect,
TJS

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