This page contains information about the Raytrace and Antialiasing settings.
In V-Ray, an image sampler is an algorithm for sampling and filtering the image function. It produces the final array of pixels that constitute the rendered image. V-Ray for Rhino implements two algorithms for sampling an image: Progressive and Bucket.
The Raytrace rollout provides controls related to sampling methods and anti-aliasing filters.
The following example shows the basic difference between an image with anti-aliasing, and one without:
The left images are jagged around the edges of the sphere, while the right are smooth. Here are close-ups of the two images:
This example briefly demonstrates the effect of different anti-aliasing filters on the final result.
Note that rendering with a particular filter is not the same as rendering without a filter and then blurring the image in a post-processing program like Adobe Photoshop. Filters are applied on a sub-pixel level, over the individual sub-pixel samples. Therefore, applying the filter at render time produces a much more accurate and subtle result than applying it as a post effect.
This example demonstrates the effect anti-aliasing filters have on moire effects in images. Sharpening filters (e.g. Catmull-Rom) may enhance moire effects, even if your image sampling rate is very high. Blurring filters (e.g. Area) reduce moire effects.
Note that moire effects are not necessarily a result of poor image sampling. In general, moire effects appear simply because the image is discretized into square pixels. As such, they are inherent to digital images. The effect can be reduced through the usage of different anti-aliasing filters, but is not completely avoidable.
The scene is very simple: a sphere with a very fine checker map applied, texture filtering is off. The images were rendered with a very high sampling rate (15 subdivs, or 225 rays/pixel). This is enough to produce quite an accurate approximation to the pixel values. Note that the image looks quite different depending on the filter:
No one image sampler is best for all scenes or workflows. Choosing the best image sampler is usually a matter of experimentation, but there are a few guidelines you can follow.
Image samplers require a substantial amount of RAM to store render information. This is especially true for the Progressive sampler, which stores the entire image in memory before beginning the rendering process. The Bucket sampler, on the other hand, stores only the summed result of all sub-samples for a pixel and so usually requires less RAM. Using large bucket sizes might require more memory.