Box blur

A box blur is a spatial domain linear filter in which each pixel in the resulting image has a value equal to the average value of its neighboring pixels in the input image. It is a form of low-pass ("blurring") filter and also called box linear filter which can written in this way like 3*3 Matrix of 1/9 * determinant matrix

    [ 1 1 1
      1 1 1
      1 1 1 ]