Mipmap

Mip mapping is an anti -aliasing technique for textures. It is used in modern 3D graphics chips to improve image quality, but also the speed.

Problems with the texture scale

The problem with texture mapping of objects is that you can view it from far and near to. Correlative to the appearance of the object so the texture must change their shape and size:

• Magnification - the texture needs to be greatly increased in order to cover the object when it is close to the viewer.
• Minification - the texture must be greatly reduced, if the object is very far away from the viewer (in the extreme case, the object then only exactly 1 pixel in size )

If no countermeasures are taken, occur in these scales on aliasing effects that are very disturbing as artifacts, especially with patterns with oblique or rounded lines, as distortions or fibrillation ( moiré ).

MIP Map

MIP is an abbreviation for multum in parvo, which means how much in a small space. A MIP maps ( also image pyramid ) is a sequence of raster images of the same scene, but with decreasing resolution. The edge length of each image is exactly half as large as that of the previous image. The smallest picture depending on the implementation size of 1 × 1 or 2 × 2 pixels. It follows that all images must be square and as edge length have a power of two. One speaks in this stage also of Level of Detail ( LOD).

Memory Requirements

MIP maps have a higher maximum of 1/3 memory than the largest file alone:

The exact number required by the images bytes of memory is calculated as:

With

N: = edge length of the image ( assumed square)

C: = byte per color channel (1: grayscale image with 256 gray levels; 3: RGB image with 8- bits per color channel )

Calculation

MIP maps can be easily calculated by taking the average of the four corresponding pixels of the output image is calculated for each pixel of the scaled image. This is recursively carried out for all other stages. This method is often implicitly used by the graphics hardware in texture loading in order to save memory bandwidth. A more complex but leading to better image quality method for MIP -map calculation provides the Fourier synthesis.

MIP- mapping and texture filtering

In minification of the texture mapping textures that of LOD is selected, in which a texel is large enough to completely cover one pixel.

In this way it is ensured that each texel of the texture origin has an impact on the compressed texture and thus no abtastbedingten aliasing occur. Especially the jumps between the LODs lead to discontinuities which are clearly visible as lines between the MIP- bands. Each of these bands has a severity level, which is very different from the neighboring bands. In addition, with each compression, which is not equivalent to a power of two, and also for anisotropic distortions always lead to excessive loss of sharpness.