What is bilinear filtering?
Bilinear filtering is a method of texture filtering used in computer graphic design to smooth out textures when the objects displayed on the screen are larger or smaller than they actually are in texture memory. Structured shapes drawn either smaller or larger than they should be on the screen often become distorted. Regular Texture mapping will make the image look pixelated or blocky. Bilinear filtering prevents this by interpolating the points between texels (texture elements) and assuming that they are points in the middle of their respective cells. These points are used to perform bilinear interpolation, a mathematical process, between the four closest texels to the point that a given pixel represents in order to make a relatively accurate estimate of the pixel color to be added.
When an object is scaled larger or smaller on the screen, it will become blocky and pixelated if not properly filtered. The bilinear filtering makes the object look good until it becomes smaller than half or larger than twice the original size of the texture. For example, if you have a 64 × 64 texture, it will look good when it is scaled down to 32 × 32 or upscaled to 128 × 128 - beyond those numbers it will lose quality.
MIP mapping is often used in conjunction with bilinear filtering to reduce quality issues. However, the transition between MIP cards of different sizes can be recognized very abruptly and very easily. In such cases, trilinear filtering can improve this, while using anisotropic filtering can improve it by eliminating Aliasing- could completely eliminate effects.