Array Indices Error In Histogram Equalisation

%Practical 6 Histogram Equalisation
close all;
clear all;
clc;
a=imread('HG.jpg');
a1=double(a);
a2=rgb2gray(uint8(a1));
[row, col]=size(a2);
c=row*col;
h=zeros(1,300);
z=zeros(1,300);
for m = 1:1:row
    for n = 1:1:col
        t=a2(m,n);
        h(t+1)=h(t+1)+1;
    end
end
pdf=h/c;
cdf(1)=pdf(1);
for x=2:1:256
    cdf(x)=pdf(x)+cdf(x-1);
end
new=round(cdf*256);
new=new+1;
for p=1:1:row
    for q=1:1:col
        temp=a2(p,q);
        b(p,q)=new(temp);
        t=b(p,q);
        z(t+1)=z(t+1)+1;
    end
end
b=b-1;
subplot(2,2,1)
imshow(uint8(a2))
title('Original Image');

subplot(2,2,2)
bar(h)
title('Histogram of Original Image');

subplot(2,2,3)
imshow(uint8(b))
title('Histogrammed Image');

subplot(2,2,4)
bar(z)
title('Eq. Histogram');






Error:
Array indices must be positive integers or logical values.

Error in Equal (line 28)
        b(p,q)=new(temp);

Answer 1

[Walter Roberson]

a=imread('HG.jpg');
a1=double(a);
a2=rgb2gray(uint8(a1));

the result of the above should be uint8 because the input is uint8 -- but the output values can include 0.

for p=1:1:row
    for q=1:1:col
        temp=a2(p,q);
        b(p,q)=new(temp);

the a2 values can include 0, so temp can be 0, so new(temp) could be an attempt to index new at index 0.

Caution: you cannot just use new(temp+1) as that risks adding 1 to uint8(255) which does not give 256 and instead gives 255.