IDL program

Interactive Data Language

Convolving with User defined Kernels

As described previously, the SMOOTH function gives equal weight to the neighbouring pixels.  IDL also allows us to define the form of our filter (kernel, smoother, mask etc) and convolve it with an image. We can therefore create a Gaussian-weighted 5´5 kernel of the form

and convolve it with an image using the following commands

kernel = [[1,2,3,2,1],[2,7,11,7,2],[3,11,17,11,3], $

         [2,7,11,7,2],[1,2,3,2,1]]

tv, CONVOL(noisy_image,kernel,TOTAL(kernel))

The command: TOTAL(kernel) in the previous line automatically scales the kernel so that the dynamic range of the processed pixel is more or less preserved (it is the same as putting the fraction outside the kernel, as in section a).