Anti-Aliasing

Geometric aliasing is often easily visible on straight edges of meshes - generally resulting in jaggies along the edges. This is simply because the edges of meshes often won’t precisely conform to the pixel grid, creating a stepping effect on the geometry.

Cracks in polygons are also a common cause. A crack occurs where the edges of two neighbouring polygons do not perfectly match up, e.g. small differences in unwelded vertex positions that can be solved by welding them or one edge butting up against two. This must be fixed in the artwork: clean meshes are essential for a good render.

Internal geometry aliasing can often be reduced by rounding and softening the edges, with bevels or normal smoothing, but for the wider silhouette, one of the many Anti-Aliasing Methods will be necessary. MSAA and EdgeAA are particularly good techniques for reducing this kind of aliasing.

Texture aliasing occurs on textured 3D objects when textures are in a higher resolution than the pixels on the screen it takes up, also known as its Texel Density. This doesn’t just apply to the visible colour channel - specular, roughness, and this type of aliasing will heavily impact normal maps.

The best solution to solve this kind of aliasing is to fix the artwork.

• Smooth it out; get the resolutions right vs the density of the texture on the screen. The UV coordinates on the mesh can be a big contributor: uneven UVs or hard joins can also exacerbate aliasing.
• Adjusting Mipmap levels and texture filter modes can also help reduce aliasing in these areas, with oversampling being especially effective but at a performance cost.
• Temporal and DLSS can also be used to smooth out this kind of aliasing in a pinch.

Normal map and roughness map aliasing are particularly important because they directly cause another type of aliasing: Shading aliasing.

Shading aliasing occurs when processing lighting and shading. Sharp changes in normal direction may result in a huge change in brightness from one pixel to another, resulting in aliasing. Another case could be reflections. If a reflected object has a lot of details, it can also be difficult to resolve aliasing here.

This is the most challenging type to remove as it isn’t as predictable as other causes of aliasing and can require significant samples to be reduced completely.

The best way to solve this type of aliasing is through careful consideration and content preparation. Increasing bevel radii or roughness to allow for greater distance of change will help a lot, but it can be time-consuming to add to complex models. DLSS does a great job at dealing with this type of aliasing, but it does come with its own quirks. You can use the normals, texture coordinates, and other views to help diagnose this case and see which solution is most appropriate for your setup.

Shadow aliasing forms part of shading aliasing but should be considered separately. It manifests itself as jagged edges along the lines of hard shadows and is caused when shadow maps are too low-resolution for the area they are asked to cover.

Solutions to this vary depending on setup and the scene - it may be fine at long distance or at a lower resoltuion, but close up the problem may become quite evident. The options are fairly straightforward: reduce the area covered by the light, increase shadow map resolution, or soften shadows to hide the problem.

Lastly, aliasing isn’t a problem unique to 3D scenes. Video Aliasing occurs when mixing videos of different resolutions or when scaling high-resolution content to a lower-resolution output. Similar to Texture aliasing but applied to a 2D context.

The solution to this is straightforward: either lower the resolution of the video before import to better match the context it’s being used in, or change the texture filter modes on the compositing node to better sample input the video.

Avoid creating too much detail per pixel

Very high polygon density doesn’t just impact performance, they can also cause aliasing issues as the details differ from slightly different view angles. Optimising a mesh for real-time can have a great benefit for aliasing too.

Likewise, using high-resolution textures on a tiny object will put a lot of detail on a tiny surface, which can also cause aliasing artefacts. Simply lowering the resolution of a texture to better match with its resolution in viewspace can improve aliasing significantly.

Avoid creating super bright thin lines

Pixel and sub-pixel wide lines can be especially hard to resolve; even with antialiasing methods in use, the line can appear uneven and transparent when examined closely. This can then further impact other effects, such as glows, which can be highly dependent on the brightness of pixels, and even perfect antialiasing can’t maintain a consistent brightness.

Increasing the thickness of lines can give enough width to resolve the unevenness and fading effects and allow more information for the antialiasing methods to resolve more effectively.

Be wary of bright specular highlights

Lighting can often generate very bright spots in a scene, which can generate aliasing along sharp bevels or within reflections. These can be particularly tricky to antialias because they can only be detected after the scene has been lit, and averaging the sharp change in brightness generates a lot of aliasing.

Solutions here generally involve increasing the roughness of a surface to smooth out where the specular area hits or adding softness to the emit light by projecting gradient textures (particularly for Area Lights).

Pay attention to Mipmaps

These properties are mainly applicable to textures applied to materials in a scene, which can be difficult to apply traditional AA methods to.

Mipmaps are automatically generated and applied to textures in Notch, helping to reduce aliasing in a scene. The solution essentially involves storing multiple copies of an image at lower resolutions and swapping them out depending on the distance to the camera. A lower-resolution texture generally has reduced high-contrast details and, therefore, reduces aliasing.

This process can introduce some blurriness to textures at low angles, so the Texture Mip Bias on any material node can be used to bias the mipmap swaps closer or farther from the camera. Raising the value will soften details in a texture and reduce aliasing while lowering the value will do the reverse.

Pay attention to Texture Filter Modes

Any image needs to be filtered when its relative resolution changes. Whether that’s a simple scaling in 2D, or its location on a mesh in 3D, the chosen Texture Filter Mode will dictate how to blend from one pixel to another.

In the case of reducing aliasing, setting the UV Texture Filter Mode to Oversampling applies 64 samples per pixel to the texture, dramatically improving this form of aliasing. However, this does come with a greater performance impact, so other methods (such as adjusting the mipmaps) should be investigated first.