how to store and plot values in a loop?

The code below currently reads in all the jpg images in a file and outputs the average intensity of the imagearray (sum of image matrix), what I am struggling to do, is convert this code so that it measures the intensity of each singular image, stores the value and then plots the change in intensity across all the images.

ImageFolder = 'H:\My Documents\Dissertation';

if ~isfolder(ImageFolder)

ErrorMessage = print('Error: The following folder does not exist: Please specify a new folder.', ImageFolder);

uiwait(warndlg(ErrorMessage));

ImageFolder = uigetdir();

if ImageFolder == 0

return;

end

end

FileType = fullfile(ImageFolder, '*.jpg');

TheImages = dir(FileType);

for k = 1:length(TheImages)

baseFileName = TheImages(k).name;

fullFileName = fullfile(TheImages(k).folder, baseFileName);

if exist(fullFileName,'file')

imageArray = imread(fullFileName);

end

meanIntensity = mean(imageArray(:));

matrix(k) = mean(imageArray(:));

end

plot(k,meanIntensity,'-.x');

hold on

Answer 1

[Image Analyst]

Try it like this:

ImageFolder = 'H:\My Documents\Dissertation';
if ~isfolder(ImageFolder)
	ErrorMessage = print('Error: The following folder does not exist: Please specify a new folder.', ImageFolder);
	uiwait(warndlg(ErrorMessage));
	ImageFolder = uigetdir();
	if ImageFolder == 0
		return;
	end
end
filePattern = fullfile(ImageFolder, '*.jpg');
TheImages = dir(filePattern);
for k = 1 : 10% length(TheImages)
	baseFileName = TheImages(k).name;
	fullFileName = fullfile(TheImages(k).folder, baseFileName);
% 	if ~isfile(fullFileName,'file') % Will never happen because you used dir()
% 		continue;
% 	end
	imageArray = imread(fullFileName);
	meanIntensity(k) = mean(imageArray(:));
end
plot(meanIntensity,'-.x', 'LineWidth', 2, 'MarkerSize', 16);
hold on
grid on;
title('Image Means', 'FontSize', 18);
xlabel('Index', 'FontSize', 18);
ylabel('Mean Gray Level', 'FontSize', 18);

[Jamal Riaz]

Hi mate, that works brilliant but I dont understand why, any chance you could explain the changes you made?

[Image Analyst]

When you did this:

    meanIntensity = mean(imageArray(:));
    matrix(k) = mean(imageArray(:));
end
plot(k,meanIntensity,'-.x');

you assigned the mean intensity to a scalar called "meanIntensity". You also assigned it to an element of "matrix". However you didn't plot the vector called "matrix". You plotted the scalar "meanIntensity", which is just one number that holds the mean intensity of the very last image that was read in. So that plot will only plot a single dot, not the entire list. To plot ALL the mean intensities, you'd have to plot the (poorly-named) "matrix".

Secondly, you read in the image only if it exists, but compute the mean intensity regardless if it exists or not because that was outside the "if". So if the image didn't exist, you'd be measuring the last imageArray that DID exist. However, it's not even needed because if we used dir(), then we'd never get files that don't exist since dir() returns files that only DO exist. Hence the "if" block was not needed. It didn't hurt, but it was not needed either.

[Jamal Riaz]

Thanks, You are really are an asset to the MATLAB community :)