HOG Descriptor Vector layout and how to save them to text file

Question

I am new to open CV so currently struggling with it. I have extracted HOG features using following definition:

HOGDescriptor hog(Size(16,16), Size(16,16), Size(16,16), Size(8,8), 9);

It returns 36 dimensional feature vector / pixel. Now I want to separate all these 36 values in a row and save it in text file. I don't know how to do it. Please do guide me.

Thanks in advance.

herohuyongtao · Accepted Answer · 2014-02-27T11:26:01.987

0

After you compute the features, i.e. descriptors by cv::HOGDescriptor::compute, it's a vector<float>, so just access it like normal vector<float>s.

And if you want to split them into 36-by-36 style, you can do like this:

for (int i=0; i<descriptors.size()/36; i++)
{
    // ... handle 36 values here
    for (int j=0; j<36; j++)
    {
        if (36*i+j < descriptors.size()) // make sure not out-of-bound
        {
            float temp = descriptors[36*i+j];
            ...
        }
    }   
}

edited Feb 27 '14 at 11:26

answered Feb 27 '14 at 10:50

herohuyongtao

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Thanks a lot for your answer. I need to get first 36 values then next 36 and so on ...is their anything in open CV like descriptors(1:36) (as its in Matlab)? – user3319734 Feb 27 '14 at 10:56
@user3319734 I found one way to do this, check out [here](http://stackoverflow.com/a/421615/2589776). Or simply use a `for`-loop. – herohuyongtao Feb 27 '14 at 10:59
could you please write a for loop for that? – user3319734 Feb 27 '14 at 11:07
so "temp" will have 36 values? – user3319734 Feb 27 '14 at 11:20
@user3319734 `temp` is a `float`... You need to learn basic stuff of `C++`. Start from this [book list](http://stackoverflow.com/questions/388242/the-definitive-c-book-guide-and-list). – herohuyongtao Feb 27 '14 at 11:26
Thanks ... can I change temp to array of 36 dimensions, and then in the inner most loop temp array fills values ? – user3319734 Feb 27 '14 at 12:13

HOG Descriptor Vector layout and how to save them to text file

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