Box blur

A box blur (also known as a box linear filter) 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.

A 3 by 3 box blur ("radius 1") can be written as matrix Due to its property of using equal weights, it can be implemented using a much simpler accumulation algorithm, which is significantly faster than using a sliding-window algorithm.

[3] In the frequency domain, a box blur has zeros and negative components.

The example does not handle the edges of the image, which would not fit inside the kernel, so that these areas remain unblurred.

In practice, the issue is better handled by: [3] A number of optimizations can be applied when implementing the box blur of a radius r and N pixels:[6]