Colour Picking from reference, ACES and .tx conversion

[paul.clements]

Hi there, 

I have some sky reference images from the internet. I would like to create environment maps by picking colours from the reference images and using these colours in a ramp. I would like to render these 360 degree images to use as HDRI environment maps in an ACES scene.

For the colour picker to work, I start in a standard scene (not aces), and create the ramps. Everything looks great in the IPR and I render out as 32bit .exr, everything looks as expected.

When I try to use these maps in an ACES scene, the colours seem off. I have tried setting the colour space on .tx conversion to many different profiles and nothing seems to yield the correct result.

Does anyone know what the correct workflow should be here?

Many thanks,

[peter_horvath]

You render out your texture to exr using the legacy color manager, right? So your texture is in linear sRGB space. Set this on the Arnold Sky in your ACES scene if you use the ext directly (I think that should be the default anyway). Or if you convert to tx, set this as the color space of the input exr and leave the color space on the Arnold Sky to auto.

I guess the difference is coming from the view color space actually. The default view color space is 'ACES 1.0 SDR-video (sRGB)' which is tone mapped. You might want to switch to 'Un-tone-mapped (sRGB)' to match your reference.

If that does not help, please show some images of the current and expected output.

[paul.clements]

Thanks Peter, that is helpful and gives good results. Please see attached images.

'MATCHING_GRADIENTS.png' looks accurate to the reference, then rendered as .exr

This is then converted to .tx with the colour space Utility - Linear - sRGB.

Added to a sky and rendered in an aces scene, gives the 'SKY_RENDER.png' result which looks pretty close to the original reference... ACES seems to alway bring the whites down which is not ideal for HDRIs.

I guess my question is, how would we retain the look of the colour ramp, and also have the HDRI throw out lots of light from the sun as a real photographic HDRI would do? Ramp colours do not exceed white, so would it have to be cheated in some way do you think?

[peter_horvath]

Color inputs on the UI are indeed limited to the 0 - 1 range. You can link a shader to a ramp color and so you can input a color with higher range. It might make the whole setup a bit complicated though.

[paul.clements]

Thanks Peter, I will give it a try! Much appreciated