Re: [ocio-dev] Converting Primaries

[Troy Sobotka]

Convert the xy coordinates to XYZ, with red being the first column, then green, then blue. That forms a 3x3 matrix for taking linearized RGB to the XYZ domain.

From there you would need to perform a chromatic adaptation via Bradford or CAT02 to the AP1 or AP0 white point required.

The final matrix would be from XYZ, achromatic point aligned, to AP1 or AP0 RGB, which are well documented.

With respect,

TJS

On Wed, Mar 7, 2018, 8:20 AM Markel <markel.j...@gmail.com> wrote:

Hello,

I just wanted to know if you would be able to help me convert these primaries into the proper matrix for use with ACES? They would be for an input. 

r: 0.6484 0.3309

g: 0.2302 0.7016

b: 0.1559 0.0661

w: 0.3217 0.3291

Thank You

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- Markel Gregory

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[Troy Sobotka]

Not sure if you got help here Markel.

I managed to craft up a spreadsheet that should work. Should being that it hasn't been tested extensively and that you'll need to manually make your OCIO stanzas from the provided entries. This isn't nearly as terrific as Colour, but I realize not everyone has Python handy, and a sort of "online calculator" probably couldn't hurt as I found myself doing the adaptation frequently.

https://docs.google.com/spreadsheets/d/1qB1YVuQFTlAKeRLyQXtOJalbZQv3V1vRPXBywqIGV_o/edit?usp=sharing

I've input the values you gave along with ACES AP0 primaries. The chromatic adaptation is the Bradford CAT. The OpenColorIO stanzas appear on the final three lines. Those should be suitable to copypasta into a configuration as part of a group transform. Note that your source buffer will need to be linearized however appropriate for your encoded image.

Let me know if anyone spots a mistake.

With respect,

TJS

[Jim Houston]

I checked for the first (to new primaries) and third (to ACES) Matrix Transforms and they match conversion of the colorspace to XYZ.  I did not check for the middle XYZ adaptation Matrix (my spreadsheet doesn’t include that.)

Jim

On Mar 25, 2018, at 7:23 PM, Troy Sobotka <troy.s...@gmail.com> wrote:

Let me know if anyone spots a mistake.

[Troy Sobotka]

On Mon, Mar 26, 2018, 9:22 AM Jim Houston, <jim.h...@mindspring.com> wrote:

I checked for the first (to new primaries) and third (to ACES) Matrix Transforms and they match conversion of the colorspace to XYZ.  I did not check for the middle XYZ adaptation Matrix (my spreadsheet doesn’t include that.)

Thanks so much for the check Jim!

With respect,

TJS

[Sean Cooper]

I'd also point you here:

http://colour-science.org/cgi-bin/rgb_colourspace_models_transformation_matrices.cgi

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[Breadbox]

Thank you all, after searching around I stumbled upon the site Sean mentioned and ended up using it. They were PCS-relative XYZ values for AdobeRGB in case anyone was wondering. Here's another site I also found that works for XY values. Not as sophisticated but it seems to work. 

On Monday, March 26, 2018 at 12:32:16 PM UTC-5, Sean Cooper wrote:

I'd also point you here:

http://colour-science.org/cgi-bin/rgb_colourspace_models_transformation_matrices.cgi

On Mon, Mar 26, 2018 at 5:34 PM, Troy Sobotka <troy.s...@gmail.com> wrote:

On Mon, Mar 26, 2018, 9:22 AM Jim Houston, <jim.h...@mindspring.com> wrote:

I checked for the first (to new primaries) and third (to ACES) Matrix Transforms and they match conversion of the colorspace to XYZ.  I did not check for the middle XYZ adaptation Matrix (my spreadsheet doesn’t include that.)

Thanks so much for the check Jim!

With respect,

TJS

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