What is wrong with this code?

I am using mkpp() command to construct the polynomial of 'cameraman.tif' but getting the error-

"Error using mkpp (line 62)

The requested number of polynomial pieces, 3, is incompatible with the proposed size, [1],

of a coefficient and the number, 1, of scalar coefficients provided."

MATLAB code

clc
close all
clear all

% Read an image
X=imread('cameraman.tif');
figure,imshow(X);
[r c noc]=size(X);

% Gray Scale Conveersion
if noc > 1
    Xn=rgb2gray(X);
else
    Xn=X;
end

% Extracting Histogram from image
figure,imhist(X);

% Extracting pixel intensity values
i=1;
while i ~= 256
    for j=1:c
        z=X(i,j);
        disp(z);
    end
i=i+1
end

 breaks=[70 80 90 100]
  
%for b=1:z
 %    X(b)=X(b)+1;
  %   disp(X(b));

%end
pp=mkpp(breaks,X(i,j));

Please help me to rectify the error.