How to create a LUT in Houdini?

[andreb]

Howdy,

I have been playing around with the Color Settings in the Edit menu in order to cater to a Linear Workflow (yes, I know I am a bit late to the party ).

There is one entry for a LUT file and the Houdini Help says about that that you can plug a LUT file in there that you create in Houdini itself by right clicking any Color COP node and choosing Save LUT... from there.

I am trying to create a simple 1D LUT following the well known sRGB formula (see end of message) and I tried laying together pow and other math nodes in a COP filter VOP context but then I saw you can't right click a non Color COP and save it's processing to a LUT - the Save LUT... command will fail saying it can't be done.

So how can I make an sRGB LUT from VOPs?

Thanks for reading!

André

sRGB response curve

if (in <= 0.00304)
{
    out = in*12.92;
}
else
{
    out = (1.055 * pow(in, (1.0/2.4)) - 0.055);
}

[andreb]

Ok, been playing around a bit more and this is what I got.

There is a Color COP node, LUT (doh), which lets you crossreference a CHOP node.

My guess is that I would be able to create a true sRGB response curve with CHOPs, then reference it with the LUT node, which I can right click and Save LUT...

Before I saw this, however, I simply exported Nuke's sRGB curve as ASCII, and pasted it's values in a Houdini .lut file I exported earlier.

In case anyone has a use for it, I'll attach it to this post.

FWIW, the LUT doesn't appear to work with the Render Region tool, but everywhere else it does.

[andreb]

Sorry for the double reply, forgot to press "Attach This File" and editing my previous post wouldn't let me attach the file again.

sRGB.lut.zip

[schnelli]

Sorry for the double reply, forgot to press "Attach This File" and editing my previous post wouldn't let me attach the file again.

sRGB.lut.zip

Hello André,

thanks a lot for sharing! I ran into the same problem few days ago while creating a sRGB LUT file from COP nodes or VOP's.

Didn't recognize that the LookupCOP can reference CHOP's. Great!

Christian