Converting hdr to ACES

Hi there, I’m back with another question :slight_smile: I wanted to convert a hdri from into the ACES primaries inside of nuke. I was hoping you could tell me if my workflow is correct or not?

First I bring my hdri and colorChecker into nuke and set the IDT to Utility-Linear-srgb

The colorChecker seemed over-exposed so I color picked the ground near to where I presume the colorChecker was taken in the hdri and use and exposure node to match the to values of the hdri.

Using the X-Rite ColorChecker 2005 - 2014 Classic - GretagMacbeth 2.0 I match the "mid gray"swatch of the photographed colorChecker using an exposure and grade node.

I then cope and paste these nodes onto the hdri and write it out as ACEScg 32bit exr and bring it into maya.

I dont need the HDRI to be super accurate but just need something to work with thats using the ACES primaries and is somewhat neutral.



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I don’t claim expertise in CGI and the use of HDRIs, but that looks reasonable to me, except for one thing. You have checked the write ACES compliant EXR box, but selected ACEScg as the colorspace. That check box is tagging the EXR as being ACES2065-1 (linear AP0) which it isn’t. It’s also forcing it to half-float.

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Agreed ! This looks reasonable. Do we know if HDRIs from hdrihaven are with sRGB primaries ?
That’s my only doubt…


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Thank you Nick! I will be sure to change that!

Yeah it was only a presumption that it was in the srgb primaries, I emailed the creator of the HDRI but unfortunately he didn’t understand the question :frowning: Thanks for your feedback Chris, I’m currently reading your book at the moment and learning a lot.


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The creator of the HDRI I’m using just replied with the following following

“SRGB photos are source material. This is the color profile of my camera. Following transformations are also carried out in the SRGB space.”

Hi, I also quickly download the HDRI and the Checkerboard as lin_sRGB.

When I balance the colorchecker down to the ACEScg 18% grey and overlay the values I get this result

The greyscale seems a bit off - and how am I suppose to compare this to the values in the actual HDRI? They are not the same exposure, that is strange.



I don’t understand what the colorchecker is supposed to do here too. Souldn’t the colorchecker being on the hdri to be used as calibration ?

Yes, this is a very dangerous option and you will eventually clip your HDRI!