Dilation together with such transformations as erode, opening and closing is one of the basic operations of the mathematical morphology.
The filter enlarges the image area broadening its pixels.
The image after the filter becomes lighter and smoother. That means, dark details are made weaker or just disappear, which depends only on relation of their sizes and brightnesses to the determined parameters of filters.
This is the operation of defining local maximum on a circle which is defined by a structure forming element.
Size (size) parameter defines the area of filter influence around each point.
Iteration (iteration) parameter defines the amount of iterations.