JG82852GMSL7VP Datasheet, PDF (129/176 Pages) Intel Corporation – Intel® 852GM/852GMV Chipset Intel® 852GM/852GMV Chipset Hub (GMCH)

Functional Description
R
5.4.2.10.
Texture Chromakey
Chromakey is a method for removing a specific color or range of colors from a texture map before it is
applied to an object. For “nearest” texture filter modes, removing a color simply makes those portions of
the object transparent (the previous contents of the back buffer show through). For “linear “ texture
filtering modes, the texture filter is modified if only the non-nearest neighbor texels match the key
(range).
Chromakeying can be performed for both paletted and non-paletted textures, and removes texels that fall
within a specified color range. The Chromakey mode refers to testing the ARGB or YUV components
to see if they fall between high and low state variable values. If the color of a texel contribution is in this
range and chromakey is enabled, then this contribution is removed from the resulting pixel color.
5.4.2.11.
Anti-Aliasing
Aliasing is one of the artifacts that degrade image quality. In its simplest manifestation, aliasing causes
the jagged staircase effects on sloped lines and polygon edges. Another artifact is the moiré patterns,
which occur as a result of the fact that there is very small number of pixels available on screen to contain
the data of a high-resolution texture map.
Full Scene Anti-Aliasing uses super-sampling, which means that the image is rendered internally at a
higher resolution than it is displayed on screen. The GMCH can render internally at 1600x1200 and then
this image is down-sampled (via a Bilinear filter) to the screen resolution of 640x480 and 800x600. Full
Scene Anti-aliasing removes jaggies at the edges as well as moiré patterns. The GMCH renders the
super-sampled image up to 2K x 2K pixel dimensions. The GMCH then reads it as a texture and bilinear
filters it to the final resolution.
5.4.2.12.
Texture Map Filtering
Many texture-mapping modes are supported. Perspective correct mapping is always performed. As the
map is fitted across the polygon, the map can be tiled, mirrored in either the U or V directions, or
mapped up to the end of the texture and no longer placed on the object (this is known as clamp mode).
The way a texture is combined with other object attributes is also definable.
The GMCH supports up to 12 Levels-of-Detail (LODs) ranging in size from 2048x2048 to 1x1 texels.
(A texel is defined as a texture map element.) Included in the texture processor is a texture cache, which
provides efficient MIP-mapping.
The GMCH supports 7 types of texture filtering:
Nearest (also known as Point Filtering): Texel with coordinates nearest to the desired pixel is
used. (This is used if only one LOD is present.)
Linear (also known as Bilinear Filtering): A weighted average of a 2x2 area of texels surrounding
the desired pixel is used. (This is used if only one LOD is present.)
Nearest MIP Nearest (also known as Point Filtering): This is used if many LODs are present. The
nearest LOD is chosen and the texel with coordinates nearest to the desired pixel are used.
Linear MIP Nearest (Bilinear MIP Mapping): This is used if many LODs are present. The nearest
LOD is chosen and a weighted average of a 2x2 area of texels surrounding the desired pixel is
used (four texels). This is also referred to as Bilinear MIP Mapping.
Nearest MIP Linear (Point MIP Mapping): This is used if many LODs are present. Two
appropriate LODs are selected and within each LOD the texel with coordinates nearest to the
desired pixel are selected. The Final texture value is generated by linear interpolation between the
two texels selected from each of the MIP Maps.
Intel^® 852GM/852GMV Chipset GMCH Datasheet
129