Question

I would like to ask a question regarding single channel image interpolation. Single channel is chosen just for simplicity otherwise I’m working on multiple channel images.
Assume there is a single channel image with pure black background ( pixel intensity 0) on which there are some pixels with non-zero intensity values. I want to apply an interpolation algorithm to fill the entire black area of the image with interpolated values coming from the neighboring non-zero intensity pixels.

What interpolation algorithm would you recommend for a smooth interpolation applicable to this problem?

As inputs, we of course know the location of those non-black pixels and their intensity. But the location is somewhat random ( in one row may be 10 pixels, in another row only 8).

Answer 1

The regular interp2 will not work here, since your points are not located at regular intervals (Not sitting on a grid).
You can either try TriScatteredInterp or download inpaint_nans from the file exchange.

Here is the solution in your case with TriScatteredInterp:

function solveStackOverflowProblem()
    im = imread('https://i.stack.imgur.com/lMaYR.png');
    im = im(:,:,2);
    [i,j] = find(im);
    y = j; x = i;
    indexes = sub2ind(size(im),i,j);
    interpolator = TriScatteredInterp(x,y,double(im(indexes)));

    [Y,X] = meshgrid( 1:size(im,2),1:size(im,1));
    reconstructedImage = interpolator(X,Y);

    figure;imshow(reconstructedImage/255)
end