## Gaussian filtering with the Image Processing Toolbox

Tuesday, October 6th, 2009

**Edit May 2018:** Since publishing this post, the MATLAB Image Processing Toolbox has added the function `imgaussfilt`

that correctly applies a Gaussian smoothing filter. For Gaussian derivatives, the recommendations here still apply.

If you don’t use DIPimage, you probably use MATLAB’s Image Processing Toolbox. This toolbox makes it really easy to do convolutions with a Gaussian in the wrong way. On three accounts. The function `fspecial`

is used to create a convolution kernel for a Gaussian filter. This kernel is 2D. That’s the first problem. The other two problems are given by the default values of its parameters. The default value for the kernel size is `[3 3]`

. The default value for the σ (sigma) is 0.5. (more…)