This sampler makes a variable number of samples per pixel based on the difference in intensity between the pixel and its neighbors.
The following diagram shows visually the way V-Ray is placing samples when using the Adaptive 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.
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 neighboring 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.