function zad3(M, levels)
    M=rgb2gray(M);
    H = imhist(M, levels);
    [x y] = size(H);
    tmp = zeros(256,1);
    interval = floor(256/levels)
    leftIndex = 1;
    for i=1:x
        rightIndex = floor(i*interval);
        tmp(leftIndex:rightIndex) = H(i);
        leftIndex = floor(i*interval)+1;
    end
    z=[0:1:255]';
    plot(z, tmp);
endfunction


M=imread("lena.jpg");
zad3(M,255)