Convert image to an abstract picture

imgfft.m

%% run in Octave: 
%% source 'imgfft.m'

filename = 'image.jpg';
img = imread(filename);

img2=double(img);

img3= (img2(:,:,1)+img2(:,:,2)+img2(:,:,3))/3;

img3f = fftshift(fft2(img3));
img4f=log(abs(img3f));

minimal = min(min(img4f));
maximal = max(max(img4f));
img5f = (img4f - minimal) * (255/maximal);

img5u=uint8(img5f);

img5i=gray2ind(img5u); 

imwrite(ind2rgb(img5i,prism()),strcat(filename,'.png'));

%% prism() opens a Figure window
delete(1);