Linear, gamma and profiles (oh my!) Tweet

[gordonrobb]

I am a noob to the whole concept of linear versus non workflow. My experience up till now was to tuxture and light something in linear, and then just switch on sRGB in Lightwaves CS panel. That put everything in sRGB and my renders looked better (better lit and more realistic).

Sooooo.

My question is this. I know to put CS to linear or off in LW. But what about all the gammas and liners etc in all the nodes in octane. If i have imager to liner and use a colour profile, what should all the textures and environments be at. They all have their own gamma. I've been assuming that if I use a non corrected jpg for a surface, I should have it's gamma at 2.2, but is that right. Same question with the hdri textures I use for environments.

Can anyone point me in the direction of a discussion, a tutorial, or just plan give me their wisdom? I'd hate to think I was putting an input in wrong, and having to correct 2 things to make it look right.

Help!

[juanjgon]

To work with Octane you must disable LW color space functions and use the octane gamma and color mapping functions.

Hdri images are always linear, you dont need to correct them. The 8 bits maps can be corrected using the gamma option in the texture node.

The output gamma and tone mapping settings are in the imager node. You can set also the correction settings only for the IPR if you want.

-Juanjo

[gordonrobb]

I'm sure that should mean something to me and answer mu question, but it doesn't

Switch off stuff in LW I know about.

However, so I don't need to correct hdri images, what does that mean the gamma should be set to? I don't know if 1 is correcting it, or 2.2. For 8 bit images, same question?

My issue isn't wether to correct or not, it's how to, and what is corrected and what is not.

Hope these ramblings make sense.

[juanjgon]

AFAIK all HDRI images should be floating linear, so you must set the gamma to 1.0 when use this map files. The 8 bit images (like JPGs) files usually have a 2.2 gamma, so you must set this value in the texture node.

Anyway Octane doesn't have a function to detect and correct the gamma of the map files, you need to set the correct value for each map.

-Juanjo

[kostache]

Hi!

I don't know why, but if I set 2.2 gamma for sRGB image texture (png, for example), I'm getting wrong output color in the render (gamma in the imager=1). But if the gamma=1 everything looks fine. Seems to me it's wrong, isn't it? (lw 11.6, lastest plug-in, LW CS correction is disabled).

[OctaneWannabe]

This podcast should help explain 'why linear':
http://www.fxguide.com/quicktakes/linea ... iscussion/

A short tutorial on working in Linear with Octane would be very useful.

Here's a useful Octane link:

viewtopic.php?f=21&t=33214

[kostache]

thanks for the link — there everything is right.
here is an article excerption:
"For most low dynamic range images (PNG, JPG, etc.) this is 2.2.
For most alpha images this is 1.0.
HDR images typically have linear encoding → 1.0."
But why if I'm setting a gamma to 2.2 (like it described above)for 8bit PNG bitmaps in LW Octane plug-in I'm always getting wrong render output color? Only gamma 1.0 giving me right result.

[juanjgon]

thanks for the link — there everything is right.
here is an article excerption:
"For most low dynamic range images (PNG, JPG, etc.) this is 2.2.
For most alpha images this is 1.0.
HDR images typically have linear encoding → 1.0."
But why if I'm setting a gamma to 2.2 (like it described above)for 8bit PNG bitmaps in LW Octane plug-in I'm always getting wrong render output color? Only gamma 1.0 giving me right result.

Can you post any pic about this issue?

-Juanjo

[kostache]

Sure!

Embedded is an example.Here is a simple plain blue color PNG texture (above). Why if I set Gamma 2.2 for png pic I'm getting this dark result? Nothing else were changed.

[juanjgon]

Sure!

Embedded is an example.Here is a simple plain blue color PNG texture (above). Why if I set Gamma 2.2 for png pic I'm getting this dark result? Nothing else were changed.

What gamma are you using for rendering (the gamma in the imager camera node)? ... I think that if you work with textures using a 2.2 gamma and you want to match the color, you are going to need to render also using an output gamma of 2.2

The texture node with a 2.2 gamma uses this value to transform the texture to the linear space for rendering, internal rendering is always made in linear space. After rendering, if you want to get the same color as in the input texture, you need to display the rendered image again with a 2.2 gamma.

-Juanjo