This page provides information on the Image Sampler rollout in the Render Settings.

 

Overview

In V-Ray, an image sampler refers to an algorithm for calculating a pixel's color based on the colors within and around it.

Each pixel in a rendering can have only one color. To get the color of a pixel, V-Ray calculates it based on the object's material, direct light striking the object, and indirect lighting in the scene. But within a single pixel there might be multiple colors, which may come from multiple objects whose edges intersect at the same pixel, or even difference in brightness on the same object due to changes in object shape or falloff and/or shadowing of light sources.

To determine the right color for such a pixel, V-Ray looks at (or samples) colors from different parts of the pixel itself as well as the pixels around it. This process is called image sampling. V-Ray includes two main image samplers, each with its own approach to sampling and its own parameters: Progressive and Bucket. 

 

 

 

 

 

 

 

 

 

 

What is Anti-Aliasing?

One of the functions of image sampling is anti-aliasing, which is the reduction of jagged edges in a rendering. The following example shows the basic difference between an image with anti-aliasing, and one without. 

If only one sample is taken for the each of the pixels around the edge of the sphere, the choice of pixel color is limited to the dark gray at the edge of the object, or the (white) background. Using one of these colors (i.e. taking only one sample) makes the image look jagged. This is the equivalent of no anti-aliasing at all.

If two or more samples are taken in each pixel, the colors are averaged, and pixels at the edge of the object end up being a color in between the dark gray of the sphere and the background. These in-between colors make the object appear smoother in the final rendering.

 

 

 

Image Sampler

Sampler Type – Specifies the image sampler type. Specific parameters for the selected type appear at the bottom of this rollout.  

Progressive – Progressively samples the entire image. See the Progressive Sampler for additional parameters. 
Bucket – Takes a variable number of samples per pixel depending on the difference in the intensity of the pixels. See the Bucket Sampler section for additional parameters. 

Min Shading Rate – Controls the number of primary rays shot for AA (anti-aliasing) versus secondary rays for other effects like glossy reflections, GI, area shadows, etc. Higher values mean that less time will be spent on AA, and more effort will be put in the sampling of shading effects. This approach is especially useful with the Progressive image sampler.

Render Mask Mode – Enables the render mask feature. The render mask allows you to define which pixels of the image are calculated. The rest of the pixels are left intact. This feature works best with the Bucket image sampler. The following types are available:

Disabled – The render mask is not used.
Texture – A texture map is used for the render mask. Black values in the map define pixels which are not rendered. Pixels with any other values are rendered. 

Anti-Aliasing Filter – Enables AA filtering in the image. When disabled, V-Ray applies an internal 1x1 pixel box filter.

Filter Type – Specifies the filter type to be used for anti-aliasing. V-Ray supplies eight types of Anti-aliasing filters: Box, Area, Triangle, Lanczos, Sinc, CatmullRom, Gaussian and Cook Variable. Each has advantages and disadvantages, which make them useful for different tasks.

Size –  Determines the size of the filter in pixels. Higher values yield blurrier results. To produce physically accurate results, the minimum value of this parameter is 1 and the maximum value is 20.

 

 

 

Progressive Sampler

 The Progressive sampler renders the entire image progressively in passes, unlike the bucket method.

 

The advantage of this sampler is that you can see an image very quickly, and then let it refine for as long as necessary as additional passes are being computed. This is contrast to the bucket-based image samplers, where the image is not complete until the final bucket is done.

A disadvantage is that more data needs to be kept in memory, especially when working with render elements. Also, when using distributed rendering, because of the continuous refinement, frequent communication between the client machine and the render servers is required, which may reduce the CPU utilization on the render slaves. This effect can be controlled to some extent using the Ray bundle size parameter.

Avoid using the Progressive  sampler with sharpening image filters (Catmull-Rom, Mitchell-Netravali) as this may slow down the rendering - additional image samples will be required to resolve sharpening filters properly. V-Ray will print a warning in this case in the V-Ray messages window.

Min. subdivs – Controls the minimum number of samples that each pixel in the image receives. The actual number of the samples is the square of the subdivs.

Max. subdivs – Controls the maximum number of samples that each pixel in the image receives. The actual number of the samples is the square of the subdivs. If zero, the number of samples is not limited.

Noise threshold – The desired noise level in the image. If this is 0.0, the entire image is sampled uniformly until either the Max. subdivs value is reached or the Max. Render time in Min limit is reached.

Max. Render Time in Min – The maximum render time in minutes. When this number of minutes is reached, the renderer stops. This is the render time for the whole frame; it includes any GI prepasses like light cache, irradiance map, etc. If this is 0.0, the render is not limited in time.

Ray Bundle Size – Useful for distributed rendering to control the size of the chunk of work that is handed to each machine. When using distributed rendering, higher values may help to utilize CPUs on the render servers better.

Image Effects Update Freq. –

Autoswitch to Effects Result –

Animated Noise Pattern –

 

 

Bucket Sampler

 

This sampler makes a variable number of samples per pixel based on the difference in intensity between the pixel and its neighbors.

This is the preferred sampler for images with lots of small details (like VRayFur for example) and/or blurry effects (DOF, motion blur, glossy reflections etc).

The diagram above shows visually the way V-Ray is placing samples when using the Bucket sampler. The black squares represent the pixels of the image while the dots represent the individual samples. In the first pass V-Ray always places the minimum number of samples determined by the Min. subdivs parameter. Then the color of the samples is compared and more are added where needed in the following passes.

 

 

 

 

Lock Subdivs – Sets a fixed number of samples taken for each pixel.

Min subdivs – Determines the initial (minimum) number of samples taken for each pixel. You rarely need to set this to more than 1, except if you have very thin lines that are not captured correctly, or fast moving objects if you use motion blur. The actual number of samples is the square of this number (e.g. 4 subdivs produce 16 samples per pixel).

Max subdivs – Determines the maximum number of samples for a pixel. The actual maximum number of samples is the square of this number (e.g. 4 subdivs produces a maximum of 16 samples). Note that V-Ray may take less than the maximum number of samples, if the difference in intensity of the neighboring pixels is small enough.

Threshold – The threshold that is used to determine if a pixel needs more samples.

Animated Noise Pattern –

 

 

Render Region Division

Width – Determines the maximum region width in pixels.

Height – Determines the maximum region height in pixels.

Measurement –

Sequence Type –

Reverse –