MATLAB: Possible to apply filter2 to only values above a limit

contourfilter2gaussianplot

I have an array which I'm attempting to filter with a Gaussian blur to smooth the surface and contour plots. Without any filtering, this is the resulting contour plot:
This code:
load 'A'
G=fspecial('gaussian',[5 5],2);
Af=filter2(G,A,'same');
contour(X,Y,A);
Gives the following contour plot:
As you can see, the contours are nicely smoothed, but the filter has blurred the transitions too much and shifted them wider and outwards.
My Question:
Is it possible to refer to just array elements above a certain value for the filtering?
I'm sure it must be and I'm just being stupid not figuring it out.
Cheers

Best Answer

Compute the filtered version for all pixels, and simply replace the pixels above a certain value with their filtered value:
G = fspecial('gaussian',[5 5],2);
Af = filter2(G,A,'same');
M = A > thresh;
A(M) = Af(M);
contour(X,Y,A);
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