Filter image that contains NaNs in Matlab?

Question

I have a 2d array (doubles) representing some data, and it has a bunch of NaNs in it. The contour plot of the data looks like this:

Answer 1

One approach would be to replace the NaN values with nearest-neighbor interpolates using scatteredInterpolant (or TriScatteredInterp in older MATLAB versions) before performing the filtering, then replacing those points again with NaN values afterward. This would be akin to filtering a full 2-D array using the 'replicate' argument as opposed to the 'symmetric' argument as a boundary option for imfilter (i.e. you're replicating as opposed to reflecting values at the jagged NaN boundary).

Here's what the code would look like:

% Make your filter:
filtWidth = 7;
imageFilter = fspecial('gaussian', filtWidth, filtWidth);

% Interpolate new values for Nans:
nanMask = isnan(rfVals);
[r, c] = find(~nanMask);
[rNan, cNan] = find(nanMask);
F = scatteredInterpolant(c, r, rfVals(~nanMask), 'nearest');
interpVals = F(cNan, rNan);
data = rfVals;
data(nanMask) = interpVals;

% Filter the data, replacing Nans afterward:
dataFiltered = imfilter(data, imageFilter, 'replicate', 'conv');
dataFiltered(nanMask) = nan;