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I have a $80\times200$ matrix, and I want to plot its contents with the contourf command in MATLAB, as follows:

\begin{align} &\text{[C,h] = contourf(mat,100);}\\ &\text{set(h,'LineColor','none');} \end{align}

The resulting image, as you can see, has some step-like discontinuities where the white part meets the coloured part. Is there any way to smooth this region with curve-fitting tool or other methods?

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  • $\begingroup$ I like getting very high count of levels before truncating the data. What if you used 300 or more? $\endgroup$ – EngrStudent Oct 5 '15 at 21:20
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Is the white part NaNs?

If so, then you will need to use some sort of extrapolation to smooth that region. The function inpaint_nans may be appropriate (it smoothly fills in NaN regions, essentially by solving a Laplace equation). If more smoothing is needed, you could then follow Juan's approach (i.e. gaussian blur).

Another thing you might consider: I do not know what the purpose of your display is, but you might consider just using imagesc() instead of contourf(). For example

contourf(I,100); 

should be similar to

imagesc(I); colormap(jet(100));

which just quantizes the colormap used to render the image data. (Quantizing the colormap will typically be much faster though, compared to computing 100 contours.)

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You can regard your original matrix as an image (i.e., a real-valued function $I = I(x, y)$), then you can apply a Gaussian filter (convolve $I$ with a Gaussian kernel), and finally you can get the contours of the filtered image/matrix. MATLAB's Image Processing toolbox already has the functionality available.

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