Thoughts on making Cycles into a spectral renderer

[troy_s]

@kram1032

So this is the equivalent of “Non-Color”, then? Could you maybe name it the same as regular Blender if that’s the case? - Because right now I have to keep switching that option as I render the same scene in either version, since they mutually don’t know the other’s option.

I suppose this is a good opportunity to integrate OCIO’s filename detection.

Specifically, it is named float because data can transport in a number of different encodings according to OCIO. Given spectral is a seismic shift, I figured it would be fine starting from a clean base for the time being.

@kram1032

Is that what CCTF stands for? And would there be a way of figuring out for sure which version is correct for a given screen? (I fully expect that you’re right in assuming my screen isn’t high end enough, but, like, “just in case” )

It’s a good question.

First, CCTF stands for Colour Component Transfer Function. Second, there’s no easy way to determine what display type you have without a piece of hardware to measure the intensity of output. A light meter or colourimeter would be required I think. It’s plausible that a clever use of a DSLR with a raw encoding could work too I suppose.

@kram1032

Also, my primary goal was comparability. Is what regular Blender lists as sRGB the same as BT.709 2.2 CCTF Colourspace or is it sRGB Colourspace

The “Standard” is the sRGB inverse EOTF. Filmic on the other hand, went with the large numbers and is aimed at a pure 2.2, as most folks likely don’t have a higher end display.

@kram1032

(which, by the way, now that I read that, you went with British spelling which is inconsistent with Blender’s choices)

Yeah it’s habit, sorry. Given only two or three folks are using it, didn’t leap out as a huge thing. Queen’s English and all…

@kram1032

PS: Can’t wait for that Spectral Filmic you’ve been teasing~

If I weren’t such a meathead it would be done by now. I had to shift gears as the original effort it was based on was a fixed, wider gamut. Spectral makes the entire spectral locus the target, so I ended up having to rethink things, and that led to the shorter term goal of a reasonable set of wider-than-BT.709 RGB primaries to get up and running, that also play nicely with spectral effects. It’s a huge kettle of fish, given as you can see from your “WTF PURPLE?!?” tests, drills right into gamut mapping and all sorts of other problems.

As folks have also noticed, the Flying Spaghetti Monster UI isn’t managed. That means that even though the working reference is somewhat close to proper D65 BT.709, when you input values in the RGB picker, they go directly in as reference values. This means that on the way out, they are transformed from, without the to. Hence that numerical discrepancy.

TL;DR: The spectral effort puts the broken bits of Blender front and centre. I’m hoping some gradual development in Blender proper can be added to make this more easy.