Color Manipulation Invert Texture Problem

[DCHA34]

Hi,
isn't there a bug in the "Color Manipulation Invert Texture" function?

I attach an image, it will be easier.

[natalia.gruzdova]

Hello DCHA34,
Thank you for your test.

The difference in Inverted texture result in Photoshop compared to the V-Ray is due to the way different applications work with gamma correction. Photoshop (and other image editing programs) are editing image as it is, while V-Ray (and other 3d renderers like 3ds max renderer used in this test) are importing bitmaps with gamma correction 2.2 if not specified otherwise.

To achieve the same result as in Photoshop you need to specify Transfer Function > None in Bitmap options. You can read more about what it does in our documentation. And to compensate for Display Correction sRGB space you have to apply Gamma correction 0.4545 to the Inverted texture.




For example, if to the inverted image in Photoshop we add Gamma Correction 2.2 the result will be the same as default V-Ray Invert texture settings.




I am attaching a link to the folder with example scenes created in 3ds max and SketchUp if you want to try it by yourself.

Also, please share in what cases do you use this option Invert Texture and how it affects your workflow.
Thanks in advance.

[DCHA34]

Thank you for your answer.

Also, please share in what cases do you use this option Invert Texture and how it affects your workflow.

I am simply trying to create my own PBR materials following your logic for creating Cosmos materials.
And that's where I get into the question of texture inversion.

Below is a screenshot with the original CGAXIS files (top row) and the Cosmos files (bottom row).
What strikes the eye immediately is the difference in the reflection textures. The Cosmos one is an inversion of the original one.
That' s why I have the problem that you can see on the preview of the 3 spheres above: the texture inversion made directly in VRay does not match the preview of the Cosmos material.




Which brings me to another question: how do you know when you download a texture pack from a website, whether or not to reverse the reflection map ?

[natalia.gruzdova]

Hello DCHA34,
Cosmos materials are created in a way that while the result should be similar to the original, at the same time it should meet our internal requirements for Cosmos assets. Cosmos 3D artists inspect all data they get and some changes may be made to the original textures, materials and models while adjusting them before loading into the Cosmos Browser.
In this case for example, the reflection texture is different and it was not inverted actually, but gamma 2.2 was added twice in the image editing app, so that the final result is more eye-pleasing and realistic in terms of reflection.

As for the general advices and PBR workflow I hope that the answer from this post provides a detailed explanation and hope it will be useful to you.

[DCHA34]

What I understand is that there is nothing "Physical" in "PBR" since everyone does what he wants with the different textures delivered by the material creator.

Knowing that from one software to another the material parameters are different (Normal Map DirectX or OpenGL, for example), we are far from having found a standard.

[konstantin_chaos]

Hi DCHA34,

In some situations the texture creators are measuring the real-world materials and the textures are intended to be used in a particular way.
The simplest example I already described in another post is:

1. A material is measured to reflect 50% (this is simplified)
2. The reflection texture is then se to a 50% gray color (in Photoshop for example)
3. The texture is saved as an 8bit file (which has a sRGB gamma curve baked in for viewing on a regular monitor)
4. When it comes time for loading the texture in an engine you have to decide whether you want to linearize the map (remove the baked in sRGB gamma curve) or not.
   In this particular example you do not want to linearize the map since you want 50% color value to directly control the reflectance in V-Ray and hence the Transfer Function should be set to None.

But to be honest even though the texture sets out there are based on scanned data you can still make artistic decisions when making materials out of them.

Konstantin