Extract features, sift detector

I m little confused about Andrea Vedaldi implementation of th开发者_开发技巧e algorithm. I m trying to extract features with the algorithm sift of the toolbox.

I m using this command [frames,descriptors] = sift(image, 'Verbosity', 1); so I ve got the frames which is 4xk matrix and the descriptors which is 128xK. I want to use a vector as a feature. Which of the two matrices should i use as a feature? Has anyone idea?

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The descriptors are what you compare in order to determine matches.

I1 = double(rgb2gray(imread('image1.png'))/256) ;
I2 = double(rgb2gray(imread('image2.png'))/256) ;

[frames1,descriptors1] = sift(I1, 'Verbosity', 1) ;
[frames2,descriptors2] = sift(I2, 'Verbosity', 1) ;

matches = siftmatch(descriptors1, descriptors2) ;

You now have a matrix of matched features between the two images.

To visualize the results add the following line to the above

plotsiftmatches(I1,I2,frames1,frames2,matches);

Vedaldi's report can be found here.