Mipmap

This page describes mipmaps.

A mipmap is a technique of applying a low-resolution texture prepared ahead of time when displaying a texture at a reduced size.

For details on mipmaps, see the separate document Introduction to CTR Graphics.

Note: Use the Photoshop Plug-in to create the mipmap texture.
For details on the Photoshop Plug-in, see the following documentation:
%NW4C_ROOT%/documents/DccPlugin/Photoshop/PhotoshopPlugin.html

Creating a Mipmapped Texture

You must create a mipmapped texture from a square image whose dimensions are powers of two.

Figure 1 Mipmap Texture

Creating a Mipmapped Texture

The figure above depicts an example of a four-level mipmap with a maximum texture size of 128 x 128.

In this case, we create a texture that leaves the right-most unused portion empty, and specify the number of mipmap levels in the plug-in settings when outputting the texture data.

Mipmap Level

Mipmapped textures have levels. Level 0 is the original image at the original size. Each successive level is then the preceding level image cut to half the length and width.

A mipmap with up to eight levels can be used before reaching the smallest image size for both vertical and horizontal measurements.

Figure 2 Relationship Between Mipmap Levels and Resolution

Mipmap Level

The mipmap level or resolution used is determined by the mipmap level of detail (LOD).

LOD bias

Mipmap LOD bias refers to a feature that adjusts the mipmap level that is applied by shifting the mipmap LOD level when the a level with something other than the desired resolution is referenced.

Figure 3 Example of Adjusting LOD Bias

Mipmap LOD Bias

Mipmap Characteristics

This section describes the characteristics of using mipmaps.

Processor Load Reduction

When using mipmaps, textures are displayed at the resolution best suited for the area displayed on the screen.

The load from the texel process can be reduced by applying a large size texture to a small area screen.

Note: There is still a load incurred even when using mipmaps when the mipmap level filtering method is configured for smooth interpolation.

Moiré Reduction

You can reduce visual artifacts caused by moiré patterns when using mipmaps.

Figure 4 Comparison Using Mipmaps

Comparing Mipmapped Textures With and Without Moiré Reduction

Moiré patterns are interference patterns that occur when regular patterns are reduced in size.
Moiré patterns occur when a texture with relatively high resolution is mapped to an on-screen area with relatively low resolution, causing the texture not to fit neatly within a single pixel. This causes the texture to appear to flicker.


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