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Why is the image clarity at various angles so different? Delve deeper into the mystery of anisotropic filtering technology!
In the field of three-dimensional computer graphics, Anisotropic Filtering is a technology that improves texture image quality. It is mainly used to improve image clarity under oblique viewing angles. This technology does not work equally in all directions, but rather in the direction in which the texture is observed, through targeted filtering to reduce blur and preserve detail, especially at extreme viewing angles.
Anisotropic filtering preserves the "sharpness" of textures and avoids the loss of image detail using ordinary mipmap techniques.
Traditional isotropic filtering reduces the resolution of both the x and y axes at each level, so when rendering on a plane tilted relative to the camera, the vertical axis frequency will The reduction results in insufficient horizontal resolution. This will cause aliasing in other directions to be avoided, but textures in other directions may become blurry.
In contrast, anisotropic filtering allows textures to be filtered at different aspect ratios. For example, when the texture resolution is 256px × 256px, this filtering technology can reduce it to 128px × 128px, and further reduce it to non-square resolutions such as 256px × 128px and 32px × 128px. Not only does this improve texture detail at bevel angles, it also maintains clarity in other directions when aliasing must be avoided.
Different filtering levels
In practical applications, different anisotropic filtering degrees can be adjusted through developed settings. This ratio is the maximum anisotropy ratio supported by the filtering process. For example, a 4:1 anisotropic filter will produce a clearer effect on bevel textures than a 2:1 filter. This means that in the case of highly skewed textures, 4:1 filtering will show higher detail than 2:1 filtering. However, most scenes do not require such high precision and will only show specific differences in large numbers of particles that are affected by distance.
Modern graphics hardware places an upper limit on this level of filtering to avoid overly complex hardware designs and diminishing visual returns.
Implementation method
True anisotropic filtering is typically performed on a per-pixel basis on the fly. In rendering hardware, when a texture is anisotropically sampled, multiple samples are taken around it based on the projected shape of that pixel. Some of the original software approaches used summed-area tables, and each sampling pass might itself be a filtered mipmap instance, aggravating the sampling process. For example, if 16 triple linear samples are required, 128 samples may need to be taken from the stored texture, because triple linear mipmap filtering requires four samples as the basis for each mipmap. This complexity is This may not be necessary in some cases.
Performance and Optimization
The number of samples for anisotropic filtering can result in extremely high bandwidth requirements. Each texture sample may exceed four bytes, so each anisotropic pixel may require up to 512 bytes of data to be fetched from texture memory. This makes it common for video display devices to require a bandwidth of 300-600 MB/s, and texture filtering operations in some scenes to require hundreds of GB/s. Fortunately, something helps reduce this performance penalty: sample points can share cached samples, either between adjacent points or within the same pixel. Even with 16 samples, it's possible that not all 16 will be needed because only the more distant, highly tilted pixels will be particularly critical.
Combining these techniques, anisotropic filtering is becoming increasingly common in modern graphics hardware and video drivers today. Users can adjust the filtering ratio through driver settings, and developers can also implement their own texture filtering needs through APIs, allowing richer picture details to be presented. However, have you ever thought about how these technologies can further evolve in future image presentation?
