function jwrite_retina(fid, data, nx, ny)

numPixel = length(data);

fprintf(fid, '%d\n', numPixel);
im0 = reshape(data(m,:), nx, ny)';
    imwrite(im0, ['mnist_' num2str(label) '_' num2str(m) '.tif']);
    [im_on, im_off] = retina(im0, 7, 0.3);
    imwrite(0.5*(im_on - im_off) + 0.5,  ['mnist_retina_' num2str(label) '_' num2str(m) '.tif']);

for n=1:numPixel,
	fprintf(fid, '%f\n', data(n));
end