Re: AllocationVars with GPU path and 1d LUT


Troy Sobotka <troy.s...@...>
 

It took me a bit of time mucking to get the allocation variables set properly.

If you set your allocation variables type to lg2, the math for the lower and
upper variable is the same as it is in an AllocationTransform, which is
log2(VALUE), which if you have stops as a reference is
log2(2^STOP_ADJUSTMENT * MIDDLE_GREY). For example, for
ten stops down with a middle grey peg at 0.18 it should be log2(2^-10 * 0.18).

For uniforms, it is value as-is, and they get normalized to and from including
negatives I believe, as per the example given in the documentation.

With respect,
TJS

On Fri, Nov 9, 2018 at 11:09 AM Simon Therriault <mos...@gmail.com> wrote:

Thanks for your answer Troy.

I started to play with the latest version with the revamped GPU path. I'll have to wait for the official release to integrate it though.

For now, I'll continue to see if I can get something out of the AllocationVars. From what I understand, the nuke default config is not necessarily the best to play with the GPU path. All the 1dLUT in play describes the to_reference transform. When I use them for inverse, the config as is clips the negative.



On Friday, November 9, 2018 at 1:42:14 PM UTC-5, Troy James Sobotka wrote:

There's two issues at work, both of which are important.

The first is the deeper GPU issue that the ever wise Mr. Hodoul has fixed with
the completely reworked GPU code path. That is a massive issue, and one that
is deeper than the simple allocation variables. This ends up in
potential posterization
in OCIOv1 given that the GPU transforms are collapsed into a single transform.

The allocation variables are important if you have a GPU path as well,
given that
the GPU path is a constricted set of values. As far as I have come to expect and
understand things, the allocation variables are required if _either side of the
transform has a scene referred range_. If your from_reference or to_reference
requires a transform into the scene referred domain, your allocation vars need
to be set according to the minimum and maximum values required, as per
type. If these aren't set correctly, the range you require may be
clipped off when
going to the GPU.

With respect,
TJS
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