How to save a single .mat file of features for many images (loop for)? - matlab

Question

I trained two-class-classification (svmtrain) with 15 features for 18 images and I have many objects in a single image. I want to save single .mat file of features of these images. My problem is when I run this code, I have just the variables of last image.
This is my code:
NbIm = size(names1,1);
n1 = 1;
n2 = NbIm;
for n = n1:n2
%1- Read the original image
%2- Processing : Segmentation
%3- characterization :
[B3,L3,N3] = bwboundaries(ICellules); (see picture)
CC = bwconncomp(L3);
BW = bwlabel(L3);
stats1 = regionprops(CC,'Area','Centroid','Eccentricity','Perimeter','ConvexArea','ConvexHull','ConvexImage','MajorAxisLength','MinorAxisLength','Orientation','Solidity','BoundingBox');
for k = 1:length(B3),
V = []; glcm = [];
V = Im_originale(BW==k);
glcm = graycomatrix(V,'Offset',[2 0],'Symmetric', true);
stats= graycoprops(glcm);
Contrast_Cellule = stats.Contrast;
Correlation_Cellule = stats.Correlation;
Energy_Cellule = stats.Energy;
Homogeneity_Cellule = stats.Homogeneity;
Area_cellule = stats1(k).Area;
Perimeter_cellule = stats1(k).Perimeter;
Circularity_cellule = (4*pi*Area_cellule)/Perimeter_cellule^2;
Centroid_cellule = stats1(k).Centroid;
Compactness_cellule = Perimeter_cellule^2/(4*pi*Area_cellule);
MajorAxis_cellule = stats1(k). MajorAxisLength;
MinorAxis_cellule = stats1(k). MinorAxisLength;
Orientation_cellule = stats1(k).Orientation;
Eccentricity_cellule = stats1(k).Eccentricity;
Solidity_cellule = stats1(k).Solidity;
boundary3 = B3{k};
[cc] = chaincode(boundary3);
ai = cc.code;
ai = ai.';
output = calc_harmonic_coefficients(ai,30);
Ampl = 0.5*sqrt((output(1)^2)+(output(2)^2)+(output(3)^2)+(output(4)^2));
Feat(k,:) = [Area_cellule,Perimeter_cellule,Circularity_cellule,Compactness_cellule, Solidity_cellule,Eccentricity_cellule,MajorAxis_cellule,MinorAxis_cellule, Centroid_cellule,Ampl,Contrast_Cellule,Correlation_Cellule,Energy_Cellule,Homogeneity_Cellule];
end
end
save('FeatTrain.mat', 'Feat');

Answer 1

Every time you run the inner loop (k=...) you overwrite Feat, without ever saving it.
If you want to have a single variable for Feat, instead of saving multiple .mat files there are 2 ways to it:
If every time you run the inner loop the size of Feat is the same, you can make it a 3D matrix, by changing you line to Feat(n-n1+1,k,:)=[.... This will make a 3D matrix where each Feat(n,:,:) will be the features of each image.
If instead every time you run the inner loop Feat can change size, then use a cell array, as in Feat{n-n1+1}(k,:)=[....