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ColorChart colors conversion

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anon_user_09389530
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Hi,

I need to recreate a color chart in Houdini.
I'm using values from this table.
https://xritephoto.com/documents/literature/EN/ColorChecker24_After_Nov2014.zip [xritephoto.com]

And convert the values from that table like this in VEX.
v@colorChartValue_sRGB = ctransform("cspace:Lab", "cspace:rgb",  set(20.64,  0.07, -0.46));
And then convert that color to ACES
v@colorChartValue_ACES = ocio_transform("Utility - Linear - sRGB", "ACES - ACEScg", v@colorChartValue_sRGB);

Does this seem like the correct method or not?

Thanks
Edited by anon_user_09389530 - 2021年4月1日 21:21:38

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jsmack
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deviner
Does this seem like the correct method or not?

Perhaps, but I don't think cspace:rgb is sRGB. I think it's most likely NTSC, because of the legacy of Prisms.

The other complication is the rather aggressive tone curve built into the ACES RRTODT which will affect the result. To get the colors looking the same you would need to apply the inverse RRT as well, but this might result in impossibly bright colors.
Edited by jsmack - 2021年4月1日 22:39:53
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anon_user_09389530
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Ok, I replaced the LAB to sRGB conversion with just the sRGB values from this table [xritephoto.com].

At least I know that I use sRGB now

Thank you
Edited by anon_user_09389530 - 2021年4月2日 00:56:09
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