Curve fitting for each pixel in an image series

I have a 3d array for size (1236,1626,20)-Its a series of 20 images. Now, I want to fit a curve to each pixel in the image.

1) The code below does the job but takes huge amount of time. I want to increase the speed of execution. Let me know how this can be done.

pCell=cell(1236,1626);
for x=1:1:1236
    for y=1:1:1626
        fx=phaseMat(x,y,1:20);
        fy=reshape(fx,[],20);
        pCell{x,y}=fit(fy',set(:),'poly4');
    end
end

2) Also, How can I save this polynomial matrix in a file for future use.