MATLAB: Keep SURF features from many images

feature extraction

Hello everybody,
Currently I wanted to extract SURF feature, let say from bunch of images stored in one folder. I run the following code, I managed to get the feature from the last image only. How can we keep the features for all images we extracted?
Thanks.
 srcFiles = dir('D:\Phd Study\Matlab Food\fooddemo\try\*.jpg');  % the folder in which ur images exists
for i = 1 : length(srcFiles)
    filename = strcat('D:\Phd Study\Matlab Food\fooddemo\try\',srcFiles(i).name);
    I = imread(filename);
    a=rgb2gray(I);
        points = detectSURFFeatures(a);
        [features, valid_points] = extractFeatures(a, points);
     end 
    figure; imshow(I); hold on;
    plot(valid_points.selectStrongest(10),'showOrientation',true);

Best Answer

The most general form is
[features{i}, valid_points{i}] = extractFeatures(a, points);
if features is just a single number, you can use
[features(i), ...
if features is always a column vector of the same length, you can use
[features(:,i), ...
if features is always a row vector of the same length, you can use
 [features(i,:), ...
if features is always a matrix of same size, you can use
[features(:,:,i)
and so on, same for valid_points, of course.
In this case it is efficient to pre-allocate the feature, like
feature = zeros(1, length(srcFiles))
or using
features(1, length(srcFiles)) = 0;
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