Method for processing digital data comprising a quantisation step which consists in calculating in a dimension space d at least one leader index I l for at least one part of the vectors l, the said vectors l constituting descriptors of input data, the method being characterised in that the said leader index I 1 corresponds to the number of vectors that precede the said leader l in reverse lexicographical order without the step of determining all the leaders, and that the step of calculating the leader index I 1 comprises one step of calculating selected from the group consisting of: - step of calculating the norm r δ, d p of the said leader l(x 1, x 2,...x d), where x 1 to x d are sorted in increasing order, where the norm r δ, d p is defined as r δ, d p = ∑ | x i / δ |, i=1..d, and recursive counting steps on the coordinates x i with the value of i ranging from d to 1, the s aid counting steps consisting in counting the vectors in which the coordinate x i is comprised between x i+1 and MIN x i + 1, F r δ, i p, the index I l being equal to the sum of the results of the counting steps adding the difference between min(F(T(x 1)) x 2) and x l, the function T(x i) returning the result of dividing the coordinate x i raised to the power p by a precision factor delta, the result of the said division being rounded to the nearest integer, and F being a function that returns an integer value w in which the value T (w) is lower than or equal to the argument A of the said function F; - step of calculating the norm r δ, d p of the said leader l(x 1, x 2,...x d), where x 1 to x d are sorted in decreasing order, and recursive counting steps on the coordinates x i with the value of i ranging from 1 to d, the said counting steps consisting in counting the vectors in which the coordinate x i is comprised between x i+1 and MIN x i − 1, F r δ, i p, the index I l being equal to the sum of the results of the counting steps adding the difference between min(F(T(x d)) x d-1) and x d, the function T(x i) returning the result of dividing the coordinate x i raised to the power p by a precision factor delta, the result of the said division being rounded to the nearest integer, and F being a function that returns an integer value w in which the value T (w) is lower than or equal to the argument A of the said function F. - step of calculating the norm r δ, d p of the said leader l(x 1, x 2,...x d), where x 1 to x d are sorted in increasing order, where the norm r δ, d p is defined as r δ, d p = ∑ | x i / δ |, i=1..d, and recursive counting steps on the coordinates x i with the value of i ranging from d to 1, the s aid counting steps consisting in counting the vectors in which the coordinate x i is comprised between x i+1 and MIN x i + 1, F r δ, i p, the index I l being equal to the sum of the results of the counting steps adding the difference between min(F(T(x 1)) x 2) and x l, the function T(x i) returning the result of dividing the coordinate x i raised to the power p by a precision factor delta, the result of the said division being rounded to the nearest integer, and F being a function that returns an integer value w in which the value T (w) is lower than or equal to the argument A of the said function F; - step of calculating the norm r δ, d p of the said leader l(x 1, x 2,...x d), where x 1 to x d are sorted in decreasing order, and recursive counting steps on the coordinates x i with the value of i ranging from 1 to d, the said counting steps consisting in counting the vectors in which the coordinate x i is comprised between x i+1 and MIN x i − 1, F r δ, i p, the index I l being equal to the sum of the results of the counting steps adding the difference between min(F(T(x d)) x d-1) and x d, the function T(x i) returning the result of dividing the coordinate x i raised to the power p by a precision factor delta, the result of the said division being rounded to the nearest integer, and F being a function that returns an integer value w in which the value T (w) is lower than or equal to the argument A of the said function F.