How to Save image Features in .mat file??

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saeeda saher
saeeda saher on 27 Apr 2018
Commented: Ameer Hamza on 30 Apr 2018
I am trying to extract facial features from image using HOG and trying to save them in .mat file, but when i run my code it saves the features of all images in one column. I want to save the features of each image in separate row.
Here is my CODE:
myFolder = 'folder'; % or whatever.
if ~isdir(myFolder)
errorMessage = sprintf('Error: The following folder does not exist:\n%s', myFolder);
filePattern = fullfile(myFolder, '*.jpg');
matFiles = dir(filePattern);
for k = 1:length(matFiles)
baseFileName = matFiles(k).name;
img = fullfile(myFolder, baseFileName);
fprintf(1, 'Now reading %s\n', img);
storedStructure = imread(img);
% Now do whatever you need to do with the structure you recalled.
%figure % New figure, do not specify the index
FaceDetect = vision.CascadeObjectDetector;
FaceDetect.MergeThreshold = 7 ;
BB = step(FaceDetect,storedStructure); %figure(2),imshow(img);
for i = 1:size(BB,1)
rectangle('Position',BB(i,:),'LineWidth',3,'LineStyle','- ','EdgeColor','r');
% figure
for i = 1:size(BB,1)
J= imcrop(storedStructure,BB(i,:));
% Create a folder with the base file name
[~, baseFileNameNoExt, ~] = fileparts(baseFileName);
outputFolder = fullfile(myFolder, baseFileNameNoExt);
if ~exist(outputFolder, 'dir')
fprintf('Created folder : %s\n', outputFolder);
% Prepare output filename
outputFileName = fullfile(outputFolder, baseFileName);
% Write file to that folder
imwrite(J, outputFileName);
fprintf(' Copied %s to the folder called %s.\n', baseFileName, outputFolder);

Accepted Answer

Ameer Hamza
Ameer Hamza on 27 Apr 2018
In your code, the matrix you want to save is X, not J. Also, you are also calculating HOG feature for the last image. To calculate for all images and save them write your code as follows.
  • Before the start of first for loop add the following line
X = [];
  • At the end of inner for loop add the following line, like this
fprintf(' Copied %s to the folder called %s.\n', baseFileName, outputFolder); % line from your code
X{k, i} = HOG(J);
Each row in X represents HOG feature for one complete image. Each element in the row represents HOG features for one bounding box.
Then save the features like this
save('features.mat', 'X');

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More Answers (1)

Walter Roberson
Walter Roberson on 27 Apr 2018
You are doing a loop with imcrop, but you are only storing the output for the current iteration in J. Afterwards, J is going to have the value it had on the last iteration of the loop. You are then applying HOG only to that one cropped version.
You should be calculating the HOG inside the loop and saving all of the results.

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