plot histogram without using matlab hist() function

Question

ws 2011-12-22

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/24536-plot-histogram-without-using-matlab-hist-function

评论： Saad Alzubaidi 2022-9-24

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 2018-8-19

在 MATLAB Online 中打开

    A=imread('<your image path>');
    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 2019-9-10

Hey Adil,

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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Answer 1

Naz 2011-12-22

3
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https://ww2.mathworks.cn/matlabcentral/answers/24536-plot-histogram-without-using-matlab-hist-function#answer_32236

在 MATLAB Online 中打开

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 2018-10-7

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 2021-9-1

i'm stuck here too

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Answer 2

Adrian Lukasik 2015-5-13

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https://ww2.mathworks.cn/matlabcentral/answers/24536-plot-histogram-without-using-matlab-hist-function#answer_178996

编辑：Adrian Lukasik 2015-5-13

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 2015-5-13

You should open a new Question for that.

Once you have the counts for each grid-point, use bar3()

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Answer 3

Saad Alzubaidi 2022-9-24

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/24536-plot-histogram-without-using-matlab-hist-function#answer_1060020

在 MATLAB Online 中打开

clear all,clc;
x=imread(imgetfile);
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);