Colour/Diffuse maps

Most commonly labelled as diffuse, this is the component of a shader that determines the overall perceived colour of the surface. Some applications have separate colour and diffuse mappable slots in their shaders – in this case, the colour refers literally to a colour map, while a diffuse map may work as a multiplier map, using a greyscale map to lighten or darken the colour when rendered, but these days diffuse generally refers simply to the colour component of the shader.

It’s important to note that when dealing with non-game texturing, you should avoid painting shadows or highlights into your colour maps. Unlike in the case of games where lighting details are often baked into the textures because of a lack of realtime lighting in the game engine, colour maps for other mediums (film, television, etc) should just contain the raw colour. To illustrate this, the following image shows a couple of old coins with a set of colour, specular and bump textures. Notice how there is lighting in the image which creates highlights and shadows on the coins.

However when we look at the raw colour map applied to the models (using a constant shader), you can clearly see what’s coming from the shading (ie the lighting and shadowing), and what’s in the texture itself. There’s some patchy detailing to create a range of light and dark tones in the metal, but no highlights or shadowing painted in.

If we look at a shot of the flat texture map itself, we can see it’s pretty straightforward. I simply took some photos, cleaned up the lighting quickly, and projected the image onto model. The following image shows the original photo, followed by the cleaned up version with the lighting removed.

This was a really quick example done using the clone tool in Photoshop, but there are a variety of better ways to remove lighting. While the clone tool is useful for small quick fixes here and there, it’s not really suitable to large areas as it tends to soften details in the image and create noticeable repetition if over-used. A better way to approach the removal of lighting and evening of tones for a colour map is to use adjustment layers like Levels, and mask them where appropriate to either lighten or darken areas. This is a far better approach but isn’t really all that useful for images you may find on the internet, as you ideally need 16-bit images for best results, since they have a broader colour range to work with.

Another important thing to note from this example is the range of colours in the texture map – the photograph I used provided a wide range of tones and details to work with, which I preserved as much as possible. The light areas around the characters on the coin aren’t from lighting but rather the way in which the coin has weathered over the years.

Colour maps are one of the most important texture maps for any model, so don’t rush them. Use plenty of references and always ensure that your map has a good range of colours in it, for realism. Real surfaces in the real world are never truly flat colours – there’s always variation in them, however subtle it may be. This once again underlines the importance of using photographs in your textures, as they provide these necessary variations.