Thanks Troy, that's helpful. I took a look at the parallel stanza in spi-anim config and see that it is called vd16.
I could not find any documentation of spi-anim, but assuming that its vd16 is the same as the spi-vfx vd16, I see here
that it says "The dynamic range of the vd is limited to around 2.5 stops above diffuse
white... The last part of the transformation is a matrix transformation
moves the whitepoint of film to look correct when displayed with a d65
I'm not sure I understand what that means exactly, but I think it may be something similar to the description for the srgb8 view transform where it says that the last step of the transform is that "the grey balance and white scaling compensation are applied." which I understand to mean that it is remapping the values to fit into the 0-1 sRGB display rather than clipping values over white like a traditional sRGB 2.2 transform would do.
One difference I did notice is that while it says that for the srgb8 "the lut is scaled so that at least one of the color channels on maximum white uses the display max" in contrast for vd16 it says "It is undesirable to map the vd max to the linear max. Such a conversion
results in linear values are almost never what an artist intended. The
rule of thumb is that, at the high end, single value deltas in an 8 bit
image should never create over a half stop of additional linear light.
The vd conversion curve is limited to prevent this case."
So does that mean that the vd16 would scale things always below white? I can see how it could be desirable for textures to sit above 0 and below 1, but not for the display transform of a render. Am I just misunderstanding standing what this means perhaps? In a test I did, it did look like the whites were being displayed below 1 for spi-anim, so I'm trying to figure out what may be going on. I'll post an image of this once I'm back at work.