plot histogram without using matlab hist() function

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ws il 22 Dic 2011
Commentato: Saad Alzubaidi il 24 Set 2022
Hi all
There is a function called hist(), but if I want to plot a graph without using hist() command, how to plot a graph? I means using command to do the job same as hist().
Thank you.
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Aditi Shetty il 19 Ago 2018
a=rgb2gray(A);
subplot(3,1,1);
imshow(a);
title('original image');
[r,c]=size(a);
z=zeros(1,256);
for i=1:r
for j=1:c
b=a(i,j);
z(b+1)=z(b+1)+1;
end
end
N=sum(z);
p=zeros(1,256);
s=zeros(1,256);
c=zeros(1,256);
r=zeros(1,256);
for k=1:256
p(k)=z(k)/N;
if k==1
c(k)=p(k);
s(k)=c(k)*255;
r(k)=floor(s(k));
else
c(k)=c(k-1)+p(k);
s(k)=c(k)*255;
r(k)=floor(s(k));
end
end
subplot(3,1,3)
stem(r,z)
title('histogram')
Ritvik Ramesh Palvankar il 10 Set 2019
Can you explain me the code after "for k=1:256". I did not understand the part where you took s(k)=c(k)*255
Also, why is zero matrix used and why is c(k-1) added to p(k)

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Risposta accettata

Naz il 22 Dic 2011
It depends on how you want to bin your data and what kind of data you have.
The idea of hist function is similar to stacks of coins: Let's say you have a bag of coins and after you separate them by values and stack on one another, you will get different heights. The hist function does the same.
data=[1 3 5 7 4 8 0 1 3];
If you want to distribute your data into 10 bins, you would create a new array of size 10:
histArray=zeros(1,10); % prealocate
x=0:1:9;
then, you would run a forloop to count how many times you encounter in a particular value:
for n=1:length(data)
histArray(1,data(n)+1)=histArray(1,data(n)+1)+1; % every time you meet the particular value, you add 1 into to corresponding bin
end
bar(histArray)
There could be another case. Let's say you want to distribute your data into 5 bins only (0 and 1 go in the 1st bin, 2 and 3 go in the 2nd...). In this case, you would run the same loop but with more complicated conditioning:
histArray=zeros(1,5);  %prealocate
x=0:2:8 % create bin numbers for plot
for n=1:length(data)
histArray(1,floor(data(n)/2)+1)=histArray(1,floor(data(n)/2)+1)+1;
% every time you meet the particular value
%you add 1 into to corresponding bin
end
bar(x,histArray)
You can design your own hist function to fit you needs
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Anna Kasdan il 7 Ott 2018
Hi! I am trying to do this with data that includes negative numbers, and I get the error 'Subscript indices must either be real positive integers or logicals.' Any thoughts? The data I am working with is:
n = 200; a = 0; b = 2; data = b.* randn(1, n) + a;
Sahitya Bonumaddi il 1 Set 2021
i'm stuck here too

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Più risposte (2)

Adrian Lukasik il 13 Mag 2015
Modificato: Adrian Lukasik il 13 Mag 2015
hello I have another problem. The same thing, but in 3D: There is a function called hist3(), but if I want to plot a graph without using hist3() command, how to plot a graph? I means using command to do the job same as hist3(). I have matrix b, 2x1000, and the task about making histogram plot without hist3() function.
Thank you.
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Walter Roberson il 13 Mag 2015
You should open a new Question for that.
Once you have the counts for each grid-point, use bar3()

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Saad Alzubaidi il 24 Set 2022
clear all,clc;
imtool(x)
for r=1:3
v=x(:,:,r);
h(1:255,3)=0;
for i=1:size(x,1)
for j=1:size(x,2)
h(v(i,j)+1,r)=h(v(i,j)+1,r)+1;
end
end
end
figure,plot(h);
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Saad Alzubaidi il 24 Set 2022
This is the code you requested, for the color image.

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