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KaiserJohan

Mesh/Material color contribution to shading

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This is somewhat related to assimp but perhaps it could be asked in a broader context aswell.
I've noticed in the assimp docs each mesh can have its own vertex-color set and materials can also have their own diffuse color set (on top of the actual diffuse texture it points to).
These are then supposed to be blended with the diffuse texture during shading... not to mention the blend method can vary aswell.
 
Reference: 
 
Two questions:
  1. - Why do models bother with all these extra channels of color and not just bake all contributing color into the diffuse texture?
  2. - Is it safe to ignore the mesh/material color parameters and just use the diffuse texture for color input? 

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1. You should normally not use mesh colors in a lit environment (unless these colors are the material colors, which AFAIK never happen). You can use them in an unlit environment, like for example in a modeler, or a simple viewer. It's always good to provide them for displaying a model easily and quickly. Colors might also have another goal, for example for doing face selection.

 

2. Unless these textures are dealing about materials (mainly PBR oriented textures, that is BRDF and friends), you should not. You will generally blend the mesh diffuse material with the diffuse texture.

 

Most commonly, what you will find on the internet will not be physically oriented. That is, you will have to deal with ambient, diffuse, specular and shininess materials, and generally a single diffuse texture.

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1. You should normally not use mesh colors in a lit environment (unless these colors are the material colors, which AFAIK never happen). You can use them in an unlit environment, like for example in a modeler, or a simple viewer. It's always good to provide them for displaying a model easily and quickly. Colors might also have another goal, for example for doing face selection.

 

2. Unless these textures are dealing about materials (mainly PBR oriented textures, that is BRDF and friends), you should not. You will generally blend the mesh diffuse material with the diffuse texture.

 

Most commonly, what you will find on the internet will not be physically oriented. That is, you will have to deal with ambient, diffuse, specular and shininess materials, and generally a single diffuse texture.

 

When you speak of diffuse material vs diffuse texture, I suppose they are not interchangeable? What is the difference between them?

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A texture will give you details at a pixel level whereas materials won't. Textures give 'looking' detail whereas materials give light transfer information.

In the real world they are the same: how a surface is absorbing and reflecting light wavelengths gives its final appearance and looking. Unfortunately in CG we are still far from there.

Edited by _Silence_

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