Level Of Detail
The Level Of Detail section displays mip and LOD settings.
Mip-map generation happens during importing of the Texture and creates a mip-map chain for the Texture. The mip-map chain consists of multiple levels of the sample image, each half the resolution of the level before. That data allows the graphic card to render faster when using the lower mips (less memory bandwidth) and also reduces the Texture aliasing (shimmering) that becomes visible when having detailed Texture in certain distances. The setting has no performance impact at runtime as it only affects the mip-map generation (during importing or when changing the setting).
In the Mip Gen Settings drop-down box, the SimpleAverage setting uses a 2x2 kernel size, and all Sharpen settings use a 8x8 kernel and some negative weights to sharpen. Sharpen0 is not sharpening, but it still uses the quality down-sampling filter all Sharpen settings use (4x4 Gaussian kernel). Compared to SimpleAverage, it appears blurrier but higher quality.
When you are using color content, the sharpening is not processing the color channels independently. Then luminance is done as defined and the chrominance (color) information is down-sampled without sharpening (currently 2x2 but 4x4 Gaussian would be possible as well). This avoids a color shift in some extreme cases. Sharpening also helps to improve the DXT compressor as the compression of subtle color shades is limited.
Mip Gen Settings
This option allows you to customize how the content of the mip-map chain looks. Note that the usage of mip-maps can reduce Texture details. In order to counteract the blurring the mip-mapping introduces, it is possible to sharpen the image during down-sampling to restore some of the information loss. Using a limited amount of sharpening (values up to 4 or 5) can help to increase the image quality without performance loss or memory cost. Using strong sharpening (values bigger than 6) can result in dark or bright borders around the image content, but this might be acceptable in certain situations (depending of art style and Texture content).
The number of miplevels to drop before uploading the Texture. This value can be negative to compensate for the LODGroup's LOD bias for a particular Texture. The LODBias, the LODGroup's LOD bias and the NumCinematicMipLevels are all added together to form a final LOD bias value for the Texture. Mip-levels that cannot be reached in-game because of its LOD bias are removed from the cooked data on disk by Unreal Frontend to save disk space.
The Texture group this Texture belongs to for LOD bias.
Global Force Resident Mip Levels
Global and serialized version of ForceMiplevelsToBeResident.
When true, the Texture's border will be preserved during mipmap generation.
Num Cinematic Mip Levels
Specifies how many of the highest-resolution mip levels should be reserved for cinematic usage - when the Texture is forcibly streamed in with cinematic quality. While the game is running normally, this property behaves just like a regular LOD bias: A value of 1 reduces the Texture's in-game resolution by one mip-level. However, when the corresponding Texture group is set to cinematic quality, the cinematic high-resolution mip levels are streamed in.
It is a good idea to have have some mip sharpening (for example, Sharpen4) defined for all color Textures. Normal maps or other Textures not storing colors might also get more detail on the first sight, but it actually might get worse (e.g. distorted surface normals, aliasing speculars).