Marco Dörner

I followed this site to generate a *.lut file: https://www.sidefx.com/docs/hdk/_h_d_k__i_o__l_u_t.html [www.sidefx.com]

The way I understand it is that a number gets mapped to an index: ( (number_in - lut_min) / range_of_lut ) * number_of_entries. The color at that index is then the output.
For a lut with a pre lut, the pre lut is applied first to the color and the output then is treated as the color_in for the 3D lut.

With that in mind I want to create my own LUT for HDR inputs from 0-10 (see below). However when I load it in Nuke or MPlay the colors are much too bright (in nuke it's 10x the input color). Where is my logic wrong?

I'm working in Solaris but I think my problem is present in other contexts as well:

If I am using a wrangle node to set parameters they always update right away. If I use a python node and change the code it updates, but then if the input changes the python node doesn't update until prompted again.

To be more specific: In this case I'm reading primvars off prims - and writing them to new primvars. When I execute the code it works. But when I then change the primvars before the python node and afterwards click on a node following the python node the primvars didn't update. Only if I go on the python node and modify the code, only then it updates.

Is there a way to have the node always cook - like a wrangle node?

Thanks. I checked out your scene, but I think it's a little bit different as you use duplicates, instead of instancing.
I added a scene to demonstrate what I am going for. On the left there is the Karma approach - however I wasn't able to get that to work at all.
On the right side there is redshift. Redshift needs a "user data" node in the shader to pick up the primvars on primitives (from the documentation it sounds like Karma does that without an extra node). This userdata is set to look for the primvar "color". The pointinstancer creates instances. Then with materialvariation4 a primvar "color" is written to all instances. When I render here I see all soccer balls turn yellow - success! Then I want to overwrite a specific one which I can do with (materialvariation5) - also that works, success!
However when I now extract this particular instance (5) all the user data set before is lost. The color primvar doesn't exist at all.

So my original question is - is there a way to extract an instance with all the data on it?

EDIT: figured out how to show the problem with Karma (left side): when rendering materialvariation7 the 5th instance is blue, but after it is extracted with extractInstances it becomes grey and the primvar "basecolor" is nowhere on the primitives.