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

Dan Wills gdanzo at gmail.com
Fri Nov 22 07:05:21 EST 2013


No worries Jordi, glad to have piqued your interest :)

On Fri, Nov 22, 2013 at 10:16 PM, Jordi Bares <jordibares at gmail.com> wrote:
>
> 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
>>>>>>
>>>>>> _______________________________________________
>>>>>> Sidefx-houdini-list mailing list
>>>>>> Sidefx-houdini-list at sidefx.com
>>>>>> https://lists.sidefx.com:443/mailman/listinfo/sidefx-houdini-list
>>>>>
>>>>>
>>>>>
>>>>> --
>>>>> Cheers,
>>>>>
>>>>> Peter B
>>>>>
>>>>> --No, I am not on Facebook.
>>>>> _______________________________________________
>>>>> Sidefx-houdini-list mailing list
>>>>> Sidefx-houdini-list at sidefx.com
>>>>> https://lists.sidefx.com:443/mailman/listinfo/sidefx-houdini-list
>>>>>
>>>>
>>>>
>>>>
>>>> --
>>>> .................................
>>>> //sim+light+render
>>>> // http://vimeo.com/user3404661/albums // http://vimeo.com/channels/naiad
>>>> _______________________________________________
>>>> Sidefx-houdini-list mailing list
>>>> Sidefx-houdini-list at sidefx.com
>>>> https://lists.sidefx.com:443/mailman/listinfo/sidefx-houdini-list
>>>
>>> _______________________________________________
>>> Sidefx-houdini-list mailing list
>>> Sidefx-houdini-list at sidefx.com
>>> https://lists.sidefx.com:443/mailman/listinfo/sidefx-houdini-list
>> _______________________________________________
>> Sidefx-houdini-list mailing list
>> Sidefx-houdini-list at sidefx.com
>> https://lists.sidefx.com:443/mailman/listinfo/sidefx-houdini-list
>
> _______________________________________________
> Sidefx-houdini-list mailing list
> Sidefx-houdini-list at sidefx.com
> https://lists.sidefx.com:443/mailman/listinfo/sidefx-houdini-list



More information about the Sidefx-houdini-list mailing list