[Sidefx-houdini-list] H13 Linear lighting/rendering

Jordi Bares jordibares at gmail.com
Fri Nov 22 06:46:14 EST 2013


On 22 Nov 2013, at 10:37, Dan Wills <gdanzo at gmail.com> wrote:

> Jordi, I'm not being harsh but you really shouldn't do gamma
> correction in a shader. This is because texture values are already
> filtered by the time they get there.

Opps.. didn't know that.. (no offence taken of course)

> It is important for pixel values to be linear during filtering. This
> means that you shouldn't filter values that are currently in sRGB (or
> any other non-linear color space) and then apply a gamma afterwards.
> If you don't pre-convert to linear, you get unpredictable levels,
> especially in filtering extremes (like zooming up on an object, or at
> horizons).
> This is one of those problems that is only really possible to
> understand by testing it directly, it is all too easy just to hook it
> up and go 'yep, looks about right', when in fact you are trading a
> small amount of pipeline complexity for a continuing difficulty to get
> predictable behaviour.

I certainly will try to have a look myself…

> I think it's a good change for Houdini to treat linear as the default.
> For those that don't want to treat linearization as a simple gamma,
> they have the option to disable the conversion and use whatever
> transformation they prefer.

True… thanks for the notes.. really interesting.
jb

> Have a good one! :)
> Dan
> 
> On Fri, Nov 22, 2013 at 8:52 PM, Jordi Bares <jordibares at gmail.com> wrote:
>> On those very strange cases, treat the texture as linear, do your special thing on the shader should work like a charm.
>> 
>> Jordi Bares
>> jordibares at gmail.com
>> 
>> On 22 Nov 2013, at 07:57, jason slabber <jason.slabber at gmail.com> wrote:
>> 
>>> Hey Peter
>>> 
>>> Have you brought this up with SESI?
>>> Just wondering cause we would also like to have our own control
>>> over texture colorspace. Not just auto and linear, seems a bit limiting...
>>> 
>>> J
>>> 
>>> 
>>> On Thu, Nov 21, 2013 at 7:32 PM, Peter Bowmar <pbowmar at gmail.com> wrote:
>>> 
>>>> Hi Craig,
>>>> 
>>>> Basically Houdini assumes non-8 bit file formats are encoded sRGB so
>>>> it linearizes them (gamma .4545) on ingestion via (for example) the
>>>> vex texture() call. It assumes 16/32 bit are linear (gamma 1 as you
>>>> say) and uses them straight up.
>>>> 
>>>> I think it's very useful for the home user or smaller studio but we
>>>> apply LUTs to everything and control via pipeline what textures are
>>>> encoded as (displacement for example might be 8 bit but linear, though
>>>> that's unusual) so SESI have added some env vars to turn it all off if
>>>> you want to manage it yourself.
>>>> 
>>>> However, in a nutshell, yes, leave your viewer at gamma 2.2 since
>>>> renders will be "linear" i.e. gamma 1.0 internally.
>>>> 
>>>> Cheers,
>>>> 
>>>> Peter B
>>>> 
>>>> On 21 November 2013 09:05, Craig Hoffman <craigleehoffman at aol.com> wrote:
>>>>> 
>>>>> I read this in the H13 docs:
>>>>> 
>>>>> Linear color workflow
>>>>> 
>>>>> 
>>>>> Houdini is now set up to work in a linear color space/gamma of 2.2 by
>>>> default.
>>>>> 
>>>>> VEX texture functions that work on 8-bit images will now convert the
>>>> images from sRGB colorspace to linear. You can override this with a
>>>> variadic argument.
>>>>> 
>>>>> 
>>>>> I am a little confused- isn't linear gamma '1.0'?...   Or is this saying
>>>> that it is converting everything to 1.0 internally for calculations and
>>>> then back to work properly with 2.2 screen gamma in GL Viewport and Render
>>>> View?
>>>>> 
>>>>> So should I leave my Render View at 2.2?  It seemed to look better at
>>>> 1.0 for my PBR renders...
>>>>> 
>>>>> Thanks,
>>>>> Craig
>>>>> 
>>>>> _______________________________________________
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>>>> 
>>>> 
>>>> 
>>>> --
>>>> Cheers,
>>>> 
>>>> Peter B
>>>> 
>>>> --No, I am not on Facebook.
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>>> 
>>> 
>>> 
>>> --
>>> .................................
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