Hi,

I'm struggling with understanding Houdini's LUT format and getting a LUT to display properly in MPLAY (and Houdini) with Houdini 13.5 in Sci6 Linux. (Ive been reading on http://www.sidefx.com/docs/hdk12.5/hdk_io_lut.html) [sidefx.com]

Our artists are viewing linearized EXR's that have been generated with Nuke's standard cineon conversion formula: (pow(10,(1023.0*x-685.0)/300.0)-0.0108)/(1.0-.0108).

Using the above formula, with x=0 and x=1 we get a range between -0.00565310520765 and 13.5217230294.

In Autodesk Maya, Tweak RV and Fundry Nuke we are using one and same .CSP LUT that gives us an identical looking image. This CSP LUT has a PreLUT that maps from the -0.00565310520765-13.5217230294 range to 0-1 and after that the 3D LUT part is applied.

How can I achive the same thing in Houdini with the ascii LUT format? From reading the documentation from the HDK it seems to indicate that the “From” start value have to be above 0, which seems a bit strange, but thats still fine if I can just get MPLAY to treat those values at 0 and make all postive values look correct. What should the From and To values be when working with cineon linearized exr footage with the “Sampling Log” header?

I've tried both generating a PreLUT and just setting the header to “Sampling Log” (see attached LUT file) but it's not looking correctly, attached LUT looks extremly washed out compared to applying it in Nuke or RV. (gamma and color adjustments in Mplay are set to not do anything, the look of the raw image matches when turning of the LUT in mplay and in Nuke)

Version 3
Format any
Type 3D
Sampling Log
From 0.00001 13.5217230294
To 0 1
Black 0
White 1
Length 32
LUT:
{
…
…
}

What am I doing wrong?

Cheers
Christoffer