## No, that’s not a Gaussian filter

Friday, February 6th, 2015

I recently got a question from a reader regarding Gaussian filtering, in which he says:

I have seen some codes use 3×3 Gaussian kernel like

`h1 = [1, 2, 1]/4`

to do the separate filtering.

The paper by Burt and Adelson (The Laplacian Pyramid as a Compact Image Code, IEEE Transactions on Communication, 31:532-540, 1983) seems to use 5×5 Gaussian kernel like

`h1 = [1/4 - a/2, 1/4, a, 1/4, 1/4-a/2]`

,and

`a`

is between 0.3-0.6. A typical value of`a`

may be 0.375, thus the Gaussian kernel is:

`h1 = [0.0625, 0.25, 0.375, 0.25, 0.0625]`

or

`h1 = [1, 4, 6, 4, 1]/16`

.

I have written previously about Gaussian filtering, but neither of those posts make it clear what a Gaussian filter kernel looks like.