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

Rangi Sutton rangi at kanuka.com.au
Wed Jul 9 22:12:26 EDT 2008


Sean Lewkiw wrote:
> Sorry to hog the list, but I'm still struggling a bit....
>   
>> 	It seems obvious, but where it gets tricky is that when you render that sRGB 
>> texture in mantra, what you're doing is rendering a texture map that has a 
>> gamma burned into it(sRGB) that is different than what the renderer is 
>> using(probably linear assuming you've changed nothing).  
>>     
> I don't understand this.  How is the texture that mantra is using to 
> render different from the texture from the original (sRGB) texture?  
> Isn't is the same, gamma-burnt-in image I've been happily viewing?  That 
> is, if I multiply Cf by my gamma encoded image's zero value, I get zero, 
> and similarly again for values between zero and a bajillion? 

All stuff that the renderer handles should be in linear light. The 
simplest way to describe this is:

surface_colour = diffuse() * texture()

The diffuse component is going to be in linear space, your texture map 
should be linear too!

In 3d we should work in linear because there's lots of maths and you 
expect that when you multiple something by 0.5 it's half as bright as it 
was.

But then.. if you don't care, no one else will.

r.




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