In
computer graphics, a texel, texture element, or texture pixel is the fundamental unit of a
texture map. Textures are represented by
arrays of texels representing the
texture space, just as other
images are represented by arrays of
pixel
In digital imaging, a pixel (abbreviated px), pel, or picture element is the smallest addressable element in a Raster graphics, raster image, or the smallest addressable element in a dot matrix display device. In most digital display devices, p ...
s.
Texels can also be described by
image regions that are obtained through simple procedures such as
thresholding.
Voronoi tesselation can be used to define their spatial relationships—divisions are made at the
midpoint
In geometry, the midpoint is the middle point of a line segment. It is equidistant from both endpoints, and it is the centroid both of the segment and of the endpoints. It bisects the segment.
Formula
The midpoint of a segment in ''n''-dim ...
s between the
centroid
In mathematics and physics, the centroid, also known as geometric center or center of figure, of a plane figure or solid figure is the arithmetic mean position of all the points in the figure. The same definition extends to any object in n-d ...
s of each texel and the centroids of every surrounding texel for the entire texture. This results in each texel centroid having a
Voronoi polygon surrounding it, which consists of all points that are closer to its own texel centroid than any other centroid.
Rendering
When texturing a 3D surface or surfaces (a process known as
texture mapping), the
renderer maps texels to appropriate pixels in the geometric fragment (typically a triangle) in the output picture. On modern computers, this operation is accomplished on the
graphics processing unit
A graphics processing unit (GPU) is a specialized electronic circuit designed for digital image processing and to accelerate computer graphics, being present either as a discrete video card or embedded on motherboards, mobile phones, personal ...
.
The texturing process starts with a location in space. The location can be in world space, but typically it is local to a model space so that the texture moves with the model. A projector function is applied to the location to change the location from a three-element vector (
) to a two-element (
) vector with values ranging from zero to one (
uv).
[Tomas Akenine-Moller, Eric Haines, and Naty Hoffman, ''Real-Time Rendering'', Wellesley: A K Peters, 2008. .] These values are multiplied by the resolution of the texture to obtain the location of the texel. When a texel is requested that is not on an
integer
An integer is the number zero (0), a positive natural number (1, 2, 3, ...), or the negation of a positive natural number (−1, −2, −3, ...). The negations or additive inverses of the positive natural numbers are referred to as negative in ...
position,
texture filtering is applied.
When a texel is requested that is outside of the texture, one of two techniques is used: clamping or wrapping.
Clamping limits the texel to the texture size, moving it to the nearest edge if it is more than the texture size.
Wrapping moves the texel in increments of the texture's size to bring it back into the texture. Wrapping causes a texture to be repeated; clamping causes it to be in one spot only.
See also
*
Pixel
In digital imaging, a pixel (abbreviated px), pel, or picture element is the smallest addressable element in a Raster graphics, raster image, or the smallest addressable element in a dot matrix display device. In most digital display devices, p ...
*
Resel
*
Voxel
References
3D rendering
Texture mapping
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