how to represents image as a color blocks ?

Hi,

i've quantisized my image using this code :

a=size(img);
w=a(2);
h=a(1);
im=img/255;
imq=zeros(100);
for i=1:h
 for j=1:w
  th=1/n;
 for k=1:n
    if(im(i,j)>th)
        imq(i,j)=th+1/n;
    th=th+1/n;
 end
 end
 end
end

But then i want to try to represent my image as example below. Thus, can differentiate between the BG and objects of the image. Could anyone please help me how to do it please ?

thank you so much :)