Textures
NOTE: This section contains terms that are derived mainly from POV-Ray scene description language. I tried to keep the treatment of the subject as general as possible but some applications may use different terms for the same concepts, or may lack some features here explained.)
A texture is what stores all the information about the object appearance. It defines his color pattern, his surface smoothness...
There are two kind of textures:
Procedural textures
Image map textures
Procedural textures are based on mathematical defined (usually fractal) patterns that lay in 3D space. Procedural textures has usually some parameters that can be adjusted by the user to create new textures or modify existing ones.
Procedural texture has the advantage over image map textures to being 3D textures. This means, for example, that the veins of a wooden pigment will be realistic even in a complex shaped object. They are also the only choice to simulate materials like metal, glass, plastic...
Also known as Brush textures, Image map textures are bitmap images that are wrapped around objects like a sheet of paper. The most common ways to wrap the image are:planar, cylindrical, spherical. Some software allows to tile a bitmap to map large objects with little bitmaps. Floor tiles textures are usually made this way.
Crating a texture can be a complex task since the two techniques are often mixed up and multiple semi transparent textures can be layered to create complex patterns.
Let's explain a texture in more detail.
A texture, in his general form can be composed by the following elements:
Pigment
Surface normals
Surface finish
Pigment stores information about the color of the texture.
It is composed by:
If texture has no pattern, it his the solid color of the texture. If texture has a pattern think about color as the color of a transparent colored paint added over the pattern.
The color map is a set of colors, at least one, that are used for pigmenting the textures.
Patterns are mathematical descriptions of how the color map is warped in 3D space to simulate different materials. Typical patterns are: wood, marble, granite, plasma, checker, spots...
Several textures can be layered so, if they are semi transparent the whole composed texture so obtained presents several different patterns at the same time. If the texture must simulate a material that is completely opaque the lower layer must be opaque as well. Some software allows to layer only patterns, not entire textures. Others can't layer at all or has a limited number of layers.
Surface normals are vectors that start from the surface of the object and (usually) point out. Although a surface virtually has infinite surface normals, 3D programs only take care of some of them.
When the renderer examine the surface of the object to choose colors, it evaluate for every point the surface normal direction and it renders the surface in that point as it is normal to the vector. From here the name of these vectors. By perturbating the surface normal's directions we can fake surface appearance that is different from the "real" surface shape.
For example suppose to want to render a golf ball. It is possible to model it using CSG but it's really a tricky and boring process. If we perturbate the surface normals in order to obtain the characteristic holes on the surface, we can obtain near the same appearance with less work and maintaining the model much simpler.
Why I wrote "near the same"? Since the model shape remain unchanged using surface normal perturbation, the protuberances and the depressions on the surface obtained this way are faked and can be revealed by viewing the object boundaries. The borders will not present any height modification. Does follows that this technique provides good results as long as the deformations introduced are limited in the height amount.
Here there are some typical procedural perturbations:
The surface is bumped like it's been beaten with a mace.
The surface is rippled like drops of liquid fell onto it. It's good to simulate liquid surfaces.
The surface presents waves. It's good to simulate the sea surface.
Another way to perturbate surface normal is:
This technique is allowed by many 3D software and it consists in using a grayscale bitmap to perturbate surface normals. The bitmap is mapped onto the object the same way as image map textures. Unless displacement mapping and like other surface normal perturbations, bump mapping does not alter the shape of the object, only his appearance.
Some 3D apps allows to use different perturbations at once to create composed ones.
Surface finish defines the way the light is processed after hitting the surface of the object. An object's surface can be smooth, rough, reflective, refractive... All these parameters, and other ones, are controlled by Surface finish settings. The parameters depends also by the rendering algorithm used.
Texture Positioning
After creating a texture it mast be positioned on the model. This can be really a tricky step.
Well designed and well positioned textures dramatically improve image impact and can make a low quality or low detail model looks pretty good. In general procedural textures does not need precision positioning due to their volumetric nature. They require however a proper scaling and orientation. The orientation is particularly needed using patterns like wood whose veins are orientated along one axis.
Image map textures are much more
difficult to set up. One interesting technique is to render a reference texture (usually a grid) on the model and then paint the textures by looking at the rendered image to see where on the model will fall the paintings using the same mapping option (spherical, cylindrical...).
Jyrki Hokkanen has made an interesting tutorial to explain this with a T-rex.
Recently there are available, even for desktop computers, 3D painting programs where is possible to paint directly on a 3D model.
Some 3D painting applications are: Detailer , StudioPaint 3D, MeshPaint 3D, FLESH 3D Paint.
Go to Lights
Home > 3D Graphics > 3D Overview > Textures
This page hosted by
Get your own Free HomePage