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Image Sampler (Antialiasing)

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General


Parameters


Fixed rate sampler


Adaptive DMC sampler


Adaptive subdivision sampler


Notes

General

In V-Ray, an image sampler
refers to an algorithm for sampling and filtering the image function,
and producing the final array of pixels that constitute the rendered
image.

 

V-Ray implements several algorithms for sampling an image.
All image samplers support MAX's standard antialiasing filters,
although at the cost of increased rendering time. You can choose
between Fixed rate
sampler, Adaptive DMC
sampler and Adaptive subdivision
sampler.

Parameters

Image sampler

 

Type - specifies the image sampler type:

 

Fixed
- this sampler always takes the same number of samples per pixel;

 

Adaptive DMC
-
this
sampler takes a variable number of samples per pixel depending on the
difference in the intensity of the pixels;

 

Adaptive subdivision
-
this sampler divides the image into an adaptive grid-like structure and
refines depending on the difference in pixel intensity.

 

Antialiasing filter

 

This section allows you to choose an antialiasing filter.
All standard
3ds Max filters are supported with the exception of the Plate Match filter. See the Examples section
for more information on antialiasing filters.

Fixed
rate
sampler

This is the simplest image
sampler, and it takes a fixed
number of samples for each pixel.

 

Subdivs -
determines number of samples per pixel. When this is set to 1, one
sample
at the center of each pixel is taken. If this is greater than 1, the
samples are distributed within the pixel. The actual number of pixels
is the square of this parameter (e.g. 4
subdivs produce 16
samples per pixel).

Adaptive
DMC
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). It also takes up less RAM than the Adaptive subdivision sampler.

 

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 pixels 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 sampler 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 neighbouring pixels is small enough.

 

Use DMC sampler
threshold - when this is on (the default), V-Ray will use
the threshold specified in the DMC
sampler to determine if more samples are needed for a pixel.
When this is off, the Color
threshold parameter will be used instead.

 

Color threshold
- the threshold that will be used to determine if a pixel needs more
samples. This is ignored if the Use
DMC sampler threshold option is on.

 

Show samples
- if this is on, V-Ray will show an image where the pixel brightness is
directly proportional to the number of samples taken at this pixel.
This is useful for fine-tuning the antialiasing of the image.

Adaptive
subdivision
sampler

This is an advanced image sampler capable of
undersampling
(taking less than one sample per pixel). In the absence of blurry
effects (direct GI, DOF, glossy reflection/reftaction etc) this is the
best preferred image sampler in V-Ray. On average it takes fewer
samples (and thus less time) to achieve the same image quality as the
other image samplers. However, with detailed textures and/or blurry
effects, it can be slower and produce worse results than the other two
methods.

 

Also note that this sampler takes up more RAM than the other
two samplers - see the Notes
below.

 

Min. rate
- controls minimum number of samples per pixel. A value of zero means
one sample per pixel; -1
means one sample every two pixels; -2
means
one sample every 4
pixels etc.

 

Max. rate
- controls maximum number of samples per pixel; zero means one sample
per pixel, 1 means four samples, 2 means eight samples etc.

 

Color threshold
- determines the sensitivity of the sampler to changes in pixel
intensity. Lower values will produce better results, while higher
values will be faster, but may leave some areas of similar intensity
undersampled.

 

Randomize samples
-
displaces the samples slightly to produce better antialiasing of nearly
horizontal or vertical lines.

 

Object outline
- this will cause the image sampler to always supersample object edges
(regardless of whether they actually need to be supersampled). This
option has no effect if DOF or motion blur is enabled.

 

Normals -
this will supersample areas with sharply varying normals. This option
has no effect if DOF or motion blur is enabled.

 

Show samples
- if this is on, V-Ray will show an image where the pixel brightness is
directly proportional to the number of samples taken at this pixel.
This is useful for fine-tuning the antialiasing of the image.

Notes

• Which sampler to use for a given scene? The answer is best
  found with experiments, but here are some tips:
  
  
  
  
  
  
  • For smooth scenes with only a few blurry effects and
    smooth textures, the Adaptive
    subdivision sampler with its ability to undersample the
    image is unbeatable.
    
    
    
    
    
    
  • For images with detailed textures or lots of geometry
    detail and only a few blurry effects, the Adaptive
    DMC sampler performs best. Also in the case of animations
    involving detailed textures, the Adaptive
    subdivision sampler might produce jittering which the Adaptive DMC sampler avoids.
    
    
    
    
    
    
  • For complex scenes with lots of blurry effects and/or
    detailed textures, the Fixed rate
    sampler performs best and is very predictable with regards to the
    quality and render time.
    
    
    
    
    
    
  
  
  
• A note on RAM usage:
  image samplers require substantial amount of RAM to store information
  about each bucket. Using large bucket sizes may take a lot of RAM. This
  is especially true for the Adaptive
  subdivision sampler, which stores all individual
  sub-samples taken within a bucket. The Adaptive
  DMC sampler and the Fixed
  rate sampler on the other hand only store the summed
  result of all sub-samples for a pixel and so usually require less RAM.