function jwrite_retina(fid, data, nx, ny)

numPixel = length(data);

fprintf(fid, '%d\n', numPixel);
im0 = reshape(data, nx, ny)';
[im_on, im_off] = retina(im0, 7, 0.3);
im1 = im_on - im_off;

for m=1:nx,
    for n=1:ny,
        fprintf(fid, '%f\n', im1(m, n));
    end
end