What should I do?-Array indices must be positive integers or logical values.

My code

clc
clear 
close all
a=imread('Screenshot_20210628.jpg');
g =rgb2gray(a);
arr=zeros(1,256);
[x,y,z]=size(g);
for i=1:x
    for j=1:y
        m=g(i,j);
        arr(m)=arr(m)+1;
    end
end
stem(arr);

Array indices must be positive integers or logical values.

Error in line 11

arr(m)=arr(m)+1;

[Stephen23]

It looks like you are writing your own histogram code. Is there a reason why you cannot just use one of these?:

https://www.mathworks.com/help/images/ref/imhist.html

https://www.mathworks.com/help/matlab/ref/matlab.graphics.chart.primitive.histogram.html

To fix that error remember that MATLAB indexing starts at one, not zero.

Answer 1

[Wan Ji]

Hi,

g(i,j) may be zero, then m becomes zero. change it like this

clc
clear 
close all
a=imread('Screenshot_20210628.jpg');
g =rgb2gray(a);
arr=zeros(1,256);
[x,y,z]=size(g);
for i=1:x
    for j=1:y
        m=g(i,j)+1;
        arr(m)=arr(m)+1;
    end
end
stem(arr);

[Worrakarn Panyaboon]

Thanks for your help it gives me the correct result now