Changing quantization level of an image in Matlab

clear 

close all 

im=imread('SpaceElevator.jpg'); 

quanta = 256; 

imq1 = double(im) / 255; 

imq1 = uint8(im * quanta); 

imq1 = double(im) / quanta; 

figure(53);imshow(imq1); 

quanta = 64; 

imq2 = double(im) / 255; 

imq2 = uint8(im * quanta); 

imq2 = double(im) / quanta; 

figure(54);imshow(imq2); 

quanta = 32; 

imq3 = double(im) / 255; 

imq3 = uint8(im * quanta); 

imq3 = double(im) / quanta; 

figure(55);imshow(imq3); 

quanta = 16; 

imq4 = double(im) / 255; 

imq4 = uint8(im * quanta); 

imq4 = double(im) / quanta; 

figure(56);imshow(imq4); 

figure(57); 

subplot(4,1,1);imshow(imq1); 

subplot(4,1,2);imshow(imq2); 

subplot(4,1,3);imshow(imq3); 

subplot(4,1,4);imshow(imq4); 

here an example result (famous pic of lena)