Progressive
Shading Rate
When using the REYES render engine, the shading rate is a fundamental quality control parameter and formally speaking, it defines the rate (or frequency) at which a surface is shaded. From The RenderMan Companion, page 214: " ... [The Shading Rate] controls the frequency of shading a surface. size is specified as an area in pixels: if size is 1, a surface is shaded about once per pixel. Large values of size cause cruder but faster shading. "
In 3Delight, the shading rate actually controls how finely surfaces are tessellated. Since the shading rate is specified in "area of pixels", micro-polygon renderers simply tessellate surfaces so that each micro-polygon is of the specified area. And since every micro-polygon is an atomic unit of shading , we automatically obtain the desired shading rate. There is an important implication to this:
Higher shading rates (such as 20) not only make objects look blurrier (less frequent shading), but also make surface silhouettes look less smooth. This is because the shading rate and the tessellation are interconnected in a micro-polygon based renderer.
Note however that shading rate has absolutely no effect on edge anti-aliasing, which is controlled through the filtering parameters described next.
In practice, the following shading rate values are common:
| Shading Rate | Description |
|---|---|
| 0.1 to 1.0 | For high quality renders. Even lower shading rates can be used for extremely detailed shaders or textures. Some shaders are not written with anti-aliasing in mind and can exhibit artifacts (especially in animation), those also require low shading rates. |
| 1.0 to 2.0 | For medium quality renders. |
| > 2.0 | Draft renders and shadow map renders. |
Oversampling
The oversampling (or supersampling) defines the number of sub-samples (or sub-pixels) there is in each pixel and in each direction. This means that an Oversampling of 2 actually means 4 (2x2) samples for each pixel. Oversampling has a direct impact on the following features:
- Edge anti-aliasing: the higher the oversampling, the lower the probability of aliasing on geometric edges and sharp shading variations.
- Motion blur and depth of field quality: the higher the oversampling, the smoother the motion blur and depth of field effect.
Pixel Samples can have a substiancial impact on performance in the case of the path tracer. In REYES, this less the case. |
Filter Width
The width of the super sampling filter tells the renderer how many pixels to consider in the final result (also known as filter support). It is well known that film-grade quality anti-aliasing can only be achieved using sharper filters (such as ‘sinc’, ‘mitchell’ and ‘catmull’) and wide filter supports. Values of 2 to 4 are common for draft renders and values from 6 to 8 are common in high-end final renders.
Note that because ‘sinc’ and ‘catmull’ filters have negative lobes, it makes no sense to use a filter width smaller than 4 for these; to better understand the problem please refer to The RenderMan Companion, page 176.
Filter width doesn't affect render times (or very little). |
Filter Type
Specify what filter to use when combining the pixel samples together. The most useful filters are: ‘sinc’, ‘mitchell’ and ‘catmull’. ‘box’ filter is commonly used for shadow map rendering or when oversampling is disabled (Oversampling set to 1) ‘gaussian’ filter is good when softer results are desired but tends to be too blurry when the filter width is higher than 2 or 3.
Filter type does not affect rendering time. Filter settings that affect render time are the oversampling and filter width. |