Laplace pyramid uses gaussian filter or binomial filter?

This might be a stupid question. But when I read about Lplacian image pyramids, my understanding was the images are initially blurred and low passed using a gaussian filter. Then i tried to implement it in matlab using "buldLpyr.m" which was avilable in the "matlabPyrTool" from Simoncelli. I have seen a lot of researches referring to this while constructing image pyramids. In this function I have observed they have used a filter named binom5, which is a binomial filter of size 5 for the initial blurring and low-passing the images. Can someone explained to me why?

Answer 1

[Constantino Carlos Reyes-Aldasoro]

The original Burt and Adelson paper specifically uses a Gaussian filter

https://ieeexplore.ieee.org/document/1095851

The Gaussian is used to blur when going up, and the a subtraction when going down is what creates the Laplacian from the Gaussian.

Not sure why a binomial is used instead of a Gaussian, but if so, it would be a modification and not the original.