[pbr] How to extract albedo map with krita/gimp

[pbr] How to extract albedo map with krita/gimp

Postby samuncle » 14 Jan 2018, 10:28

Hi everyone

Since we are switching to PBR, here is a quick tutorial on how to extract the Albedo map form an existing diffuse texture (or a photography).

First a quick recap of what's the albedo map
An albedo map defines the color of diffused light. One of the biggest differences between an albedo map in a PBR system and a traditional diffuse map is the lack of directional light or ambient occlusion. Directional light will look incorrect in certain lighting conditions, and ambient occlusion should be added in the separate AO slot.

From: Physically-Based Rendering, And You Can Too!

In the case of SuperTuxKart, we don't need an ambiant occlusion map nor shadows in your albedo since the engine will compute it for you. You just provide the pure color and then everything is computed automatically (kinda nice when you think about it).

Our goal is to extract the color information without any shadows or bright part. While this seems tricky it's in fact very easy to do.

First let's take this existing SuperTuxKart texture as an example.
pbr-diffuse.jpg


We can immediately see the texture has some very dark spot which would be bad for our render engine.
Open the picture in your favorite 2D software editor, duplicate the current layer and desaturate it.
pbr-desaturate.jpg


Invert the desaturated layer
pbr-inverted.jpg


We have a picture which is darker where bright spots are and brighter where dark spots are, which exactly what we wanted to remove the shadow and highlight information.
Now just blend the inverted layer with the original picture using soft light blending
pbr-softlight.jpg


And voila! We have extracted the albedo map from the original picture.
Some considerations:
* You might have to do minor adjustment to your final picture.
* You might have also to adjust the hue slightly, but in general this is good enough.

If you have any suggestions feel free to post them, so I can improve the tutorial and then post it on our website
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samuncle
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