[Sidefx-houdini-list] OT: sRGB to linear question

Sean Lewkiw Sean.Lewkiw at CIS-London.com
Tue Jul 8 09:51:32 EDT 2008

A question then... let's say I want an object that is a nice purply blue 
at the top and a greenish orange at the bottom.  In one render I achieve 
this using point colours.  In another I achieve exactly the same thing 
using an sRGB image I downloaded off the interweb.  How is the one 
derived from the sRGB image any worse or less accurate than the one 
derived from the point colours?  Both final renders are linear.

I'm not trying to be provocative, just trying to get an understanding of 
this whole thing. 


John Coldrick wrote:
> On Tuesday 08 July 2008 09:25, Sean Lewkiw wrote:
>> A question for everyone, not exactly SESI related....  When you use an
>> image downloaded from the internet as a texture, do you do a sRGB to
>> linear correction before using it to render with?
> 	Depends on your pipeline.  Strictly speaking, yes, you should.  If every 
> single point along the pipeline is all sRGB all the time, including where 
> you're rendering to and you don't have a problem lighting your renders in 
> sRGB, then you can simply pretend it's not there and do nothing.  However, 
> increasingly there's reasons to not do this, with PBR, physically accurate 
> lights, etc.  If you are even coming close to having something in your 
> pipeline that's not sRGB, then you should be converting everything to the 
> same space(linear).
> 	It took us a long time and lots of conversations with lots of people to 
> figure this out.  I've decided the problem is if you've ever done any film 
> work of any kind, your brain suddenly switches to a world that seems to have 
> a very difficult time explaining precisely *why* this is important to people 
> that have traditionally worked in video only(like for advertising).  I see a 
> lot of misinformation and extremely poorly explained posts all over the net 
> regarding this issue.  Most of the time, people just start pointing fingers 
> at others and accuse them of having incorrectly calibrated monitors(which 
> does happen of course, it's just become a catch-all explanation).
> 	Cheers,
> 	J.C.

Sean Lewkiw
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