[Sidefx-houdini-list] Linear Workflow

François Duchesneau sidefx at trinix.ca
Thu Aug 26 08:27:06 EDT 2010

This subject confuses me.

I thought Houdini already worked in linear space?

I thought Photoshop only generated sRGB texture so we have to apply a 
lut (or a gamma correction to approximate it) when we read those 
textures in our shaders?

When I read a Houdini image in Nuke. I set the read to linear and my 
viewer color space to "none" and my image is exactly how I see it in 
Mantra. Nuke works in linear so the gamma correction should be at the 
end of it?

Why do we have to set the gamma correction to "Gamma 2.2" to match XSI 
linear space????

Thanks for help me understand.


Mario Marengo wrote:
> In the Mantra ROP, try setting "Color Space" (vm_colorspace) to "Gamma 2.2". 
> This parameter is now always exposed in H11. It should help with the bottom-
> end noisiness (it biases the sampling importance so the dark stuff gets some 
> extra love).
> On Wednesday 25 August 2010 02:52:54 pm Andy Nicholas wrote:
>> Hi guys,
>> We've just started a job in Houdini and we're trying to use a linear
>> colour workflow. With the test I'm doing at the moment, I don't have any
>> textures, it's all pure lighting and shader models. I've got the Color
>> Correction gamma setting at 2.2 which I believe is the correct setting as
>> it visually matches what we do in XSI when we enable colour management.
>> The problem is that we're having a few issues with generating glossy
>> reflections because noise that wasn't visible before, now shows up a
>> treat, even with a large number of samples.
>> This is partly because the objects I'm reflecting are quite small, so in a
>> way, I'm not surprised I'm getting some noise. The issue is that before
>> using colour management, this wouldn't have been visible. On a black
>> background typically some of the noisy pixel values are only at around
>> 0.0002, but they still show up as little grey splats on the image.
>> I've been doing a few tests, and while I get noisier results in mental ray
>> (using XSI with colour management enabled), it generally isn't as bad as
>> I'm seeing in Mantra.
>> So my simple question is, have any of you guys run into similar problems,
>> and if so, what strategies did you use to work around this issue? (or
>> alternatively, are we just doing something stupid?!)
>> Thanks,
>> Andy
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