The Fill node fills all areas surrounded by white pixels, and generates a specific input for the Fill to random grey, the Fill to random color and the Fill to UV nodes.
The Fill node accepts:
a mask greyscale input whose light parts surround areas that must be filled
The Fill node generates a single RGBA texture that contains the bounding box of each filled area.
The Fill node accepts the following parameters:
resolution is the resolution of the effect and only influences how details of the mask (and not the source if any) is captured. It is advised to be careful with using high values here, as the computation time may become very long. Setting it higher than the input’s resolution will not yield any benefit - only increase the computation time.
iterations is the number of iterations of the fill algorithm. The optimal value for this parameter depends on the input image. Starting with 5 or 10, then increasing the value depending on the result is a good way of finding it.