Texture types
Albedo texture maps
Albedo texture maps contain the base colors of a material. Make sure albedo textures don’t contain any lighting or shadows, because Unity adds lighting based on the positions of the object and the lights.
Normal maps
Normal maps are used by normal mapA type of Bump Map texture that allows you to add surface detail such as bumps, grooves, and scratches to a model which catch the light as if they are represented by real geometry.
See in Glossary ShadersA program that runs on the GPU. More info
See in Glossary to make low-polygon models look as if they contain more detail. Unity uses normal maps encoded as RGB images. You also have the option to generate a normal map from a grayscale height map image.
Alpha maps
An alpha map is a Texture that contains only alpha information. You can use an alpha map to apply varying levels of transparency to a Material.
You can create an alpha map by creating a Texture with information in the alpha channel, or by creating a grayscale Texture and converting the grayscale values to alpha in Unity.
See the documentation on Texture Import Settings for more information.
Detail maps
If you want to make a TerrainThe landscape in your scene. A Terrain GameObject adds a large flat plane to your scene and you can use the Terrain’s Inspector window to create a detailed landscape. More info
See in Glossary, you normally use your main Texture to show areas of terrain such as grass, rocks and sand. If your terrain is large, it may end up very blurry. Detail Textures hide this fact by fading in small details as your main Texture gets closer.
When drawing Detail Textures, a neutral gray is invisible, white makes the main Texture twice as bright, and black makes the main Texture completely black.
See documentation on Secondary Maps (Detail Maps) for more information.
Terrain Heightmaps
Textures can even be used in cases where the image will never be viewed at all, at least not directly. In a greyscale image, each pixelThe smallest unit in a computer image. Pixel size depends on your screen resolution. Pixel lighting is calculated at every screen pixel. More info
See in Glossary value is simply a number corresponding to the shade of grey at that point in the image (this could be a value in the range 0..1 where zero is black and one is white, say). Although an image like this can be viewed, there is no reason why the numeric pixel values can’t be used for other purposes as well, and this is precisely what is done with Terrain Heightmaps.
A terrain is a meshThe main graphics primitive of Unity. Meshes make up a large part of your 3D worlds. Unity supports triangulated or Quadrangulated polygon meshes. Nurbs, Nurms, Subdiv surfaces must be converted to polygons. More info
See in Glossary representing an area of ground where each point on the ground has a particular height from a baseline. The heightmap for a terrain stores the numeric height samples at regular intervals as greyscale values in an image where each pixel corresponds to a grid coordinate on the ground. The values are not shown in the sceneA Scene contains the environments and menus of your game. Think of each unique Scene file as a unique level. In each Scene, you place your environments, obstacles, and decorations, essentially designing and building your game in pieces. More info
See in Glossary as an image but are converted to coordinates that are used to generate the terrain mesh.
Interestingly, even though a heightmapA greyscale Texture that stores height data for an object. Each pixel stores the height difference perpendicular to the face that pixel represents.
See in Glossary is not viewed directly as an image, there are still common image processing techniques that are useful when applied to the height data. For example, adding noise to a heightmap will create the impression of rocky terrain while blurring will smooth it out to produce a softer, rolling landscape.
More information about terrains in Unity can be found in this section of the manual.