Image Sampler (Antialiasing)
Fixed rate sampler
Adaptive DMC sampler
Adaptive subdivision sampler
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. You can choose between Fixed rate sampler, Adaptive DMC sampler and Adaptive subdivision sampler.
Image sampler - specifies the image sampler type:
Fixed Rate - 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.
On - enables or disables the antialiasing filter and allows you to select the filter type to be used for antialiasing. V-ray supplies seven types of Antialiasing filters: Box, Area, Triangle, Lanczos, Sinc, CatmullRom and Gaussian. Each of those has advantages and disadvantages which make them useful for different tasks.
Size - this parameter determines the size of the filter in pixels. Higher values yield blurrier results.
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).
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 and/or blurry effects (DOF, motion blur, glossy reflections etc).
The following diagram shows visually the way V-Ray is placing samples when using the Adaptive DMC 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 samples is compared and more are added where needed in the following passes.
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 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.
Use DMC sampler threshold - when this is on , 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 Threshold parameter will be used instead.
Threshold - the threshold that will be used to determine if a pixel needs more samples.
Show Samples - if this is on, V-Ray will show an image where the pixel color is determined by the number of samples taken at this pixel where blue means that the Min subdivs was used and red means that the Max subdivs is used. This is useful for fine-tuning the antialiasing of the image.
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/refraction 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.
The following diagram shows visually the way V-Ray works when using the Adaptive Subdivision image sampler. With this mode V-Ray creates a secondary grid on top of the pixel grid and uses this grid to position the samples. This allows it to use less than a sample per pixel. After the first pass the samples are compared and if the difference between two samples is bigger than the values in the thresholds the grid is subdivided and more samples are added. During the whole time V-Ray has to keep the whole grid in the memory which makes this method less memory efficient compared to the other two methods - 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.
Jitter - displaces the samples slightly to produce better antialiasing of nearly horizontal or vertical lines.
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.
Edges - 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.
Normals threshold - determines the sensitivity of the sampler to the variation of normals.