are all variants of so-called smoothing filters. They produce a response that is the local average of the samples of a signal. Such an operation tends to reduce the local variability of sample values and thus decreases signal noise and smooths the signal. However, averaging also smears image edges resulting in a blurred picture. BoxFilter
returns a matrix with constant coefficients equal to the inverse of the filter's dimensions. This FIR filter is commonly known as a moving-average filter.