feature extraction - what is the meaning of intensity order in image processing? -

i'm reading article. article explains new feature descriptor such sift , surf , it's name mrogh.

in part of article, there sentence:

in our work, sample points segmented based on intensity orders , gradients pooled each segment. 

my question is:

• what meaning of intensity order , local intensity of point in image?

thanks,

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edit:

@yves daoust linked me here , answer.

the explanation seems rest in quote paper: "specifically, first sort sample points in support region according intensities. divide them 𝑘 segments equally according orders. finally, gradient information of sample points in each segment pooled, , gradient orientation histograms in these 𝑘 segments concatenated form representation of support region."