Getting the Wrong Output While Using Image Batch Processor (Edited Version)

Greetings, everyone.

I am a beginner in MATLAB and I just started to learn it for my bachelor thesis. So, I created a function that counts porosity from an image and feed that function into batch processor to process hundreds of image. I used the simpe formula (black pixel/total pixel) * 100 to generate porosity value and for 1 image, I expected to only get 1 porosity value. Therefore, I wanted the output table to be (the number of images)x1. But after running a trial with 12 images processed by a porosity calculator function in image batch processor, I got 12x2 table where each desired output is a vector(12,1).

Here's my code:

function porosity = porosity_function(image)
% Calculates the porosity of an image.
% Args:
%   image: A MATLAB array representing the image.
% Returns:
%   The porosity of the image
black_pixels = sum(image == 0);
total_pixels = size(image, 1) * size(image, 2);
porosity = (black_pixels * 100) / total_pixels;
end

And here's a few sample images (all are binary image, originally a SEM -scanning electron microscope- image of a limestone with 2000-8000x magnification). In my field of study (chemistry), pore is one of the key characteristics that represents a material/substance and there are many methods to measure it. For my thesis, I compare porosity calculated digitally (from an image and using MATLAB) and experimentally (using gas sorption analyzer instrument with nitrogen adsorption method). I have 100+ SEM images to process, so I need to put it in batch processor to save time.

Perhaps anyone could tell me what's wrong with my function? Any help would be appreciated.

Answer 1

[Walter Roberson]

The problem is not the porosity function: the problem is the way you are storing the results into the output table.

You are probably doing something like

for i = 1 : number_of_files
    T(i).output = Porosity_results;
    T(i).fileName = filenames{i};
end

when you should instead be doing

for i = 1 : number_of_files
    T(i).output = Porosity_results(i);
    T(i).fileName = filenames{i};
end

or better yet make the table in one call, such as

T = table(Porosity_results, filenames(:), 'VariableNames', {'output', 'fileName'});

[Shafa Salsabila]

Hi, sorry for the late reply, your answer is very helpful. Now my code works, eventhough I run it without MATLAB's batch processor :)

function batch_process_images(image_folder)
% Batch process images in a folder and its subfolders, calculating porosity for each image.
% Args:
%   image_folder: Path to the main folder containing images and subfolders.

% List all image files in the main folder and its subfolders
image_files = dir(fullfile(image_folder, '**', '*.png'));  % Change the extension as needed

num_files = numel(image_files);
porosity_results = zeros(num_files, 1);
filenames = cell(num_files, 1);

for i = 1:num_files
    image_path = fullfile(image_files(i).folder, image_files(i).name);
    image = imread(image_path);
    
    % Calculate porosity for the current image
    black_pixels = sum(image(:) == 0);  % Flatten the image to a vector
    total_pixels = numel(image);
    porosity_results(i) = (black_pixels * 100) / total_pixels;
    
    filenames{i} = image_files(i).name;
end

% Create a table with porosity results and filenames
T = table(porosity_results, filenames, 'VariableNames', {'output', 'fileName'});

% Display the table
disp(T);

% If you want, you can also save the table as a CSV file
writetable(T, 'porosity_results.csv');

end

image_folder = 'C:\image\path'; % Change this to the actual path of your main folder
batch_process_images(image_folder);

[Walter Roberson]

We recommend that you do not use image as the name of a variable, as doing so interfers with calling the MATLAB function named image