Versions Compared

Old Version 1

changes.mady.by.user Kristin Ivanova

Saved on

compared with

New Version 2

changes.mady.by.user Kristina Gaytandzhieva

Saved on

Key

  • This line was added.
  • This line was removed.
  • Formatting was changed.

This page provides information on the Sampler tab of Image Sampler rollout under the Sampler tab in V-Ray's Render s Render Settings.

 

Overview

The Sampler tab in V-Ray's Render Settings hosts multiple options related to V-Ray's specific image sampling algorithms.

UI Paths


Overview

...

Section
Column
width50%

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 edge 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. Different image sampling methods are discussed below.


UI Path: ||Properties Editor|| > Render > Sampler tab


UI Expand
title

...

||Properties Editor||

...

> Render > Sampler

...

 

Image Removed

Rollouts

The Sampler tab includes the following rollouts:

...

typecircle

...

tab

Image Added

Column
width5%


Column
width45%

Image Added
Image courtesy of Tuna Unalan

Multiple colors within a single pixel. What color should the pixel be? 


...


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.

Section
Column
width20%


Column
width60%
Before after
afterLabel24
darktrue
beforeLabel1
Panel

Image Added

Panel

Image Added

Column
width20%



Progressive Sampler

...


Section
Column
width50%

Sampler Type – Specifies the image sampler type:

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 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.

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 Render time 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 in order 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.

UI Text Box
typeinfo

Unlike the bucket image sampler, the Progressive sampler doesn't have a mechanism to recover if a DR server goes offline during rendering before sending back the results from its calculations. The render process may hang indefinitely, waiting for the missing data to arrive. This will be corrected in a future release.


Anti-Aliasing Filter

Filter Type – Specifies the filter type to be used for anti-aliasing. V-Ray supplies eight types of Anti-aliasing filters: None, Area, Box, Catmull-Rom, Cook Variable, Gaussian, Lanczos, Mitchel-Netravali, Sinc, and Triangle. Each has advantages and disadvantages, which make them useful for different tasks. V-Ray GPU supports only Box, Area, Lanczos, and Gaussian filter types.

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 1.000, and the maximum value is 20.000.  For more information, see the Anti-aliasing Filters example and the Anti-aliasing Filters and Moire Effects example below. 

Animated Noise Pattern – 


Render Mask

Type – 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 V-Ray frame buffer and 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 that are not rendered. Pixels with any other values are rendered. 
Object – A custom set of objects to render can be defined. 
Object IDs – Only objects with specified Object IDs will be rendered; you can list more than one by using commas to separate them.

For more information, see the Render Mask example .

Column
width5%


Column
width30%

Image Added



...

Anchor
AAF
AAF

Example: Anti-Aliasing Filters


Here is an example briefly demonstrating 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. The zoomed in images below have been zoomed in and cropped 300%.


Section
Column
width5%


Column
width30%

Image Added

Filtering is off.


Image Added

Lanczos filter, size 2.5


Image Added

Triangle filter

Column
width30%

Image Added

Sinc Filter, size 2.5


Image Added

Box Filter, size 2.5


Image Added

Area filter, size 2.5

Column
width30%

Image Added

Catmull-Rom


Image Added

Cook Variable, size 2.5


Image Added

Gaussian, size 2.5

Column
width5%



...

Anchor
AAME
AAME

Example: Anti-aliasing Filters and Moire Effects


This example demonstrates the effect anti-aliasing filters have on moire effects in your images. Sharpening filters may enhance moire effects, even if your image sampling rate is very high. Blurring filters 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. 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:

Section
Column
width25%


Column
width50%
Image slider
Panel
borderStylenone

Image Added

No Filter

Panel
borderStylenone

Image Added

Box Filter

Panel
borderStylenone

Image Added

Area Filter, size 1.5

Panel
borderStylenone

Image Added

Area Filter, size 4.0

Panel
borderStylenone

Image Added

Triangle Filter, size 1.5

Panel
borderStylenone

Image Added

Lanczos Filter

Panel
borderStylenone

Image Added

Catmull Rom

Panel
borderStylenone

Image Added

Gaussian Filter, size 1.5

Panel
borderStylenone

Image Added

Gaussian filter, size 6.0

Drag the slider to change the filter type.

Column
width25%



...


Example: Stages of Rendering with the Progressive Sampler

Section
Column
width25%


Column
width50%
Image slider
minLabel1 pass
maxLabel256 passes
Panel
borderStylenone

Image Added

Image after 1 pass

Panel
borderStylenone

Image Added

Image after 16 passes

Panel
borderStylenone

Image Added

Image after 64 passes

Panel
borderStylenone

Image Added

Image after 256 passes

Column
width25%




Bucket Sampler

...


Section
Column
width50%

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 will 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. V-Ray GPU's default Max subdivs value is 48.

Noise Limit – The threshold that will be used to determine, if a pixel needs more samples.


Bucket Size

Bucket Size – Determines the maximum region width/height in pixels.

Sequence –

Reverse Sequence – 

Column
width5%


Column
width30%

Image Added


...

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


Image Added


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.


...

Anchor
RM
RM

Example: Render Mask


Section
Column
width8%


Column
width40%

Image Added

The original image.


Image Added

The same image, only objects with chrome material were re-rendered.

Column
width4%


Column
width40%

Image Added

The actual render mask image - RGB channels.


Image Added

The actual render mask image - Alpha channel.

Column
width8%