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:
Performance Note
Pixel Samples can have a substiancial impact on performance in the case of the path tracer. In REYES, this less the case.
Most importantely, pixel samples do not multiply the samples set for global illumination. Those are two independent settings. This means that increasing pixel samples to have, for example, smoother motion-blur does't affect the global illumination quality and render time.
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.
Performance Note
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.
Performance Note
Filter type has no impact on performance.
Smooth Subdivision Threshold
Specifies the level of geometric approximation from which the object will be rendered as a subdivision surface instead of a plain polygon mesh. For example, if the Render Level subdivision property (in Softimage's Geometric Approximation) is set to 1 and this property is set to 2, then 3Delight for Softimage will simply render a polygonal mesh that has been subdivided once. But if you set this property to 1, then 3Delight for Softimage will render the polygon mesh as a perfectly smooth subdivision surface. It is better to render subdivision surfaces instead of subdividing polygonal meshes too much. The default value is 1 (3Delight for Softimage will render meshes as smooth subdivision surfaces as soon as Render Level property is equal or larger than 1). A per-object control is also available as explained in Quality Properties.
Premultiply Colors With Alpha
By default, the renderer with pre-multiply all colors by the alpha. Switching off this flag will force the colors to be not multiplied by the alpha.