Error in code: while trying to plot average histogram

I have a folder in that folder I have some images and I want to plot a average histogram of that images. My code is given below:

myFolder = 'folder path'; 
filePattern = fullfile(myFolder, '*.jpg') ;
theFiles = dir(filePattern);
 S=0;
for k = 1 : length(theFiles)
	% Get the input filename.
	baseFileName = theFiles(k).name;
	fullFileName = fullfile(myFolder, baseFileName);
	% Read in the image
    I = imread(fullFileName);
    raw = im2double(I(:,:,1));
    maxv=max(max(raw));
    minv=min(min(raw));
    theImage= (raw-minv)./(maxv-minv);
    [N,edges]=histcounts(theImage,nbins); %nbins= 512
    for i=1:length(N)
     S(i,:)=S(i,:)+N;     % the accumlator
     S(i,:)=S(i,:)/length(theFiles);
     S1=S(i,:);
    end
end
in=linspace(0,1,512);
plot(in,S1,'linewidth',2); 

But I am getting a error :

"Unable to perform assignment because the size of the left side is 1-by-1 and the size of the right side is 1-by-512.

S(i,:)=S(i,:)+N; % the accumlator "

How to solve this error can anyone help? what modification do I need to make in the code to get rid of this error?

Answer 1

[Image Analyst]

Try this:

% Computes average histogram of all images in a folder.
% Demo by Image Analyst, March, 2021.
clc;    % Clear the command window.
close all;  % Close all figures (except those of imtool.)
clearvars;
workspace;  % Make sure the workspace panel is showing.
format long g;
format compact;
fontSize = 16;
fprintf('Beginning to run %s.m ...\n', mfilename);

myFolder = pwd;
filePattern = fullfile(myFolder, '*.jpg') ;
theFiles = dir(filePattern);
numberOfBins = 256;
numberOfFiles = length(theFiles);
allPixelCounts = zeros(1, numberOfBins);
for k = 1 : numberOfFiles
	% Get the input filename.
	baseFileName = theFiles(k).name;
	fullFileName = fullfile(myFolder, baseFileName);
	% Read in the image
	theImage = imread(fullFileName);
	% Look at red channel, or entire image (if it's already grayscale).
	theImage = im2double(theImage(:,:,1));
	
	% Display image
	subplot(2, 1, 1);
	imshow(theImage, []);
	drawnow;
	caption = sprintf('#%d of %d : %s', k, numberOfFiles, baseFileName);
	title(caption, 'Interpreter', 'none');
	
	% Get the histogram.
	[thesePixelCounts, edges] = histcounts(theImage,numberOfBins); %nbins= 512
	allPixelCounts = allPixelCounts + thesePixelCounts;
	subplot(2, 1, 2);
	bar(allPixelCounts, 1);
	grid on;
	drawnow;
end
subplot(2, 1, 2);
% Get average
allPixelCounts = allPixelCounts / numberOfFiles;
bar(allPixelCounts, 1);
grid on;
title('Average Histogram');
xlabel('Gray Level');
ylabel('Pixel Count');
grayLevel = 0 : (numberOfBins - 1);
% Optional.  Plot lines from tip of bar to tip of bar.
% hold on;
% plot(grayLevel, allPixelCounts, 'r.-', 'LineWidth', 1);
% hold off;

fprintf('Done running %s.m\n', mfilename);

[Vaswati Biswas]

Awesome.Thank you so much. But now I am having a graph like this (shown below).This is the output of " Plot lines from tip of bar to tip of bar" of your demo code. Can you please suggest me how can I get a smooth curve following the trend of the graph means the envelope of the histogram?

[Image Analyst]

You can easily create a smoothed signal with movmean() or sgolayfilt()

allPixelCounts = sgolayfilt(allPixelCounts, 2, 9);

[Vaswati Biswas]

It works! thanks