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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


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title||Properties Editor|| > Render > Sampler tab

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Image courtesy of Tuna Unalan

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


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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. 

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Progressive Sampler


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Sampler Type

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– 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

Limit – 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.

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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. 

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 – When enabled, the sampling pattern will change with time. Disabling will make the sampling pattern be the same from frame to frame in an animation, which might be undesirable in some cases. Note that re-rendering the same frame will produce the same result in both cases.

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

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 .

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The Rays Per Pixel and Samples Limit options are unique to V-Ray GPU. 

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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 Limit – 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 (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.

Rays Per Pixel – The number of rays that are traced for each pixel during one image pass. The greater the value, the smoother the picture from the very beginning of the rendering with GI, but interactivity may be significantly diminished. Increasing this value also reduces the amount of data transferred from the render servers back to client machine.

Samples Limit – Determines the maximum number of samples that each pixel in the image receives. V-Ray performs adaptive sampling on the image, trying to put more samples into areas that have more noise. If the Samples Limit is set to 0, V-Ray renders with the default value of 2500.

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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. 

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. 

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.

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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

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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%.

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Filtering is off.

 

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Lanczos filter, size 2.5


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Triangle filter

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Sinc Filter, size 2.5


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Box Filter, size 2.5


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Area filter, size 2.5

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Catmull-Rom


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Cook Variable, size 2.5


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Gaussian, size 2.5

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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 produce 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 samplesif a pixel needs more samples.

Adaptivity Clamp – Specifies an intensity limit for the samplers to avoid excessive sampling of overexposed areas. Lower values mean a lower limit and potentially noisy overexposed areas. Higher values produce more samples in overexposed areas.

Firefly Removal – This option is available in the Bucket Sampler type only. Removes fireflies from the render and optimizes the render times. Further, it removes the flickering effect in animations. Lower values are less aggressive at removing fireflies while higher values are more effective but can start removing actual parts of the image such as small bright highlights. This option is not available with V-Ray GPU.

Anti-Aliasing Filter

Filter Type – Specifies the filter type to be used for anti-aliasing. V-Ray GPU supports Box, Area, Lanczos, and Gaussian filter types. 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 1.000, 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. 

Ray GPU.


Anti-Aliasing Filter

Filter Type – Specifies the filter type to be used for anti-aliasing. V-Ray GPU supports Box, Area, Lanczos, and Gaussian filter types. 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 1.000, 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 – When enabled, the sampling pattern will change with time. Disabling will make the sampling pattern be the same from frame to frame in an animation, which might be undesirable in some cases. Note that re-rendering the same frame will produce the same result in both cases.


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 .

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Bucket Options

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Bucket Size – Determines the size of the bucket (width and height are equal) in pixels.

Sequence – Determines the order in which the buckets are calculated.

Top-Bottom – Buckets are calculated from top to bottom.
Left-Right – Buckets are calculated from left to right.
Checker – Every other bucket is calculated, creating a checker-like pattern of calculated buckets.
Spiral – Buckets are calculated in a spiral pattern.
Triangulation – 
Hilber curve – 
Random – Buckets are calculated in a random order.

Reverse Sequence – Reverses the bucket calculation order.

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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).

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