CG Sketchbook , notes and tutorials

Vray Blender LWF notes

I just found out i’ve been using LWF incorrectly until now ! but  i think  i just understood the correct usage.

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Vray Blender is possibly misleading if you’re used to Luxrender or Yafaray:

the simplest -yet correct – use of LWF  in render engines usually is done this way  :

Option 1 : input gamma : 2.2  (the gamma used in your textures and solid colors , most of the times it’s srgb – gamma 2.2)

Option 2 : output gamma : 2.2  (the gamma of your monitor , most of the times it’s srgb – gamma 2.2)

In between we could also put “render engine gamma :  1.0” .. but   this is not an option , all engines work with linear data internally  ..And that’s the reason for LWF : you have srgb source colors and textures , they need to be converted to linear for the engine , then back to srgb  for display.

Most render engines for blender have this implemented in the easiest, yet correct ,way :  “input 2.2 , output 2.2”

While Vray blender works like this , in color correction tab :

—-Gamma : the output gamma , works as expected . it’s the gamma of the output image .

—-Input Gamma : this only affects textures , not solid colors ! plus usually “input gamma”  means ” Gamma of input images” (2.2) while this here is “the gamma correction value to be applied” (so if you have gamma 2.2 textures you must set this to 0.4545)

—-LWF button :  this applies a gamma correction on input to both colors and textures , the value used is the inverse of “Gamma”

So , the correct setup is :

Gamma: 2.2

input gamma: 1.0

LWF: on.

Don’t use srgb button in VrayFrameBuffer ,  it would do output correction twice.

While these are wrong :

Gamma: 1.0

input gamma: 1.0

LWF: on.

………….Lwf button does nothing with gamma set to 1.

Gamma: 2.2

input gamma: 0.4545

LWF: off.

………….this way only textures get gamma correction , but also all solid colors you set in blender are srgb  so they need it too.

Gamma: 2.2

input gamma: 0.4545

LWF: on.

…………. this way textures get gamma correction twice ,wrong.


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