Textures in general
General questions about textures.
Is there something I should be aware of when resizing texture maps?
Yes, actually there is. It can be crucial to choose the right filtering method when resizing effect maps - in particular bump maps. Most image processing software (e.g. Photoshop) by default use 'bicubic filtering' to re-sample pixel. Although in case of photos this method is a good compromise between computational effort and result sharpness, it is exactly the sharpening characteristic that causes artefacts in bump maps, which harm texture quality. Therefore it is important to switch to 'bilinear filtering' in those cases.
As an example, here is what happens to a bump map when shrunk to 50% using bicubic filtering (top left). Notice the bright edges that create unwanted ridges (bottom left). This does not happen with a biliniar filter (right side).
What's the best way to store textures to have them readily available?
Although this somewhat depends on how you use the textures, here a couple of general tips:
- Diskspace has become really cheap. So copy the textures to your harddrive or network storage to have them close at hand.
- To quickly find the texture you need, organise all your textures into a hierarchical directory structure, e.g. 'natural'->'grounds'->'sand' or 'man-made'->'materials'->'metal'->'surfaces'->'weathered'.
- For large textures (such as ours) you might want to consider creating several versions of every map with different resolution, e.g. full, half and quarter resolution. This way you have always the resolution available that matches the needs of your scene while saving memory.
Why should I buy textures if I can get them for free elsewhere on the web?
True, you can find a lot of sites which offer thousands of textures for free download. However, this so-called textures are mostly just simple photographs of surfaces or objects; often available only single-layered, non-seamless and in low resolution. Sometimes you may get some additional maps, such as bump or specular maps. But these maps often turn out to be just plain gray-scaled versions of the texture map with adjustments of brightness and contrast. That's usually what you can get for free. You will have to decide whether or not that is enough for your purposes.
What are textures and who needs them?
The visual appearance of things is given by their surfaces. How we see an object is, simply speaking, determined by its surface color and structure. Therefore, to make virtual things look as if they were real, a realistic imitation of real surfaces is essential. To reach this goal, textures are essential.
Basically, textures are (mostly photographic) pictures of materials. These images are projected onto a model of a virtual object to simulate the visual characteristics of the real material and thus, to help make it look real.
Wether architect, artist or designer - if you want to give the visualization of your ideas a more realistic look, you're dependent on high-quality textures.
What's the purpose of all the different map types?
Multi-layered textures usually come with several different maps, containing information to different aspects of a material.
A diffuse map contains the color information of the texture. It defines what original color the texture will have at a certain position.
Bump maps are used to apply the illusion of structure to a textured surface. Dark zones define deepened areas, bright zones heightened areas. The renderer shades the surface accordingly, thus creating a relief effect.
Similar to bump maps, displacement maps are also used to give a surface structure. But where bump mapping only creates the illusion of 3D structure, displacement mapping generates 'real' depth by adding geometry. Depending on the capabilities of the rendering software used, this is achieved for example via micro-triangle-displacement or other techniques.
Specularity is an important aspect of the surface characteristic of materials. A specularity map defines how strong the textured surface will 'shine' at a certain position. Most render engines use this information to define the appearance of specular highlights.
Transparency maps define how opaque a texture is at a certain position. Bright zones mean solid areas, dark zones transparent areas. Such maps can be used to realize partly transparent surfaces, e.g. meshes.
This not so common map type specifies a slightly less intuitive aspect of shiny surfaces: The angle (or direction) of anisotrop reflection.