Why Matlab shows "Index exceeds matrix dimensions."? [closed] - matlab

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Here is my matlab code:
gg=imread('fsu_Westcott.jpg');
data1=gg(:,1);
histArray1=zeros(1,256);
x=0:1:255;
for n=1:length(data1)
histArray1(1,data1(n)+1)=histArray1(1,data1(n)+1)+1;
end
for n=1:length(data1)
number1=sum(histArray1(1:n));
end
plot(x,number1,'r')
Why it shows "Index exceeds matrix dimensions."? before I finally plot? I am new and thanks in advance! :)

Answer 1

On the line:
number1=sum(histArray1(1:n));
you are asking for cells 1 to n of array histArray1 but n goes from 1 to length(data1) which is larger than the length of histArray1 (256). So it is out of bounds.
This loop:
for n=1:length(data1)
number1=sum(histArray1(1:n));
end
seems unnecessary if you want to plot the histogram anyway.
One more tip, there is a function called hist which you could use to both compute the histogram and plot the result in a barchart in one line:
hist(data1(:), 0:255)

Answer 2

To me it looks like you have a couple things you'll want to fix. To fix the error on the line Simon pointed out, I think you'll want to have your 2nd For loop going from 1 to length(histArray) (or 256) instead of length(data1). The second problem I see is that in the 2nd For loop you aren't building an array--you're just redefining the variable number1 over and over. You should probably put number1(n)=sum(histArray1(1:n)); inside that for loop instead. This doesn't have to do with the error you're seeing but it might help you get what you want out of the script.