7. The method of claim 6 , wherein iteratively selecting the sub-collection of buckets from the first collection of buckets and from the second collection of buckets further includes iteratively selecting buckets that are most discriminative of the labels based on the labeled image representations, and wherein the method further comprises training respective classifiers for the labels based on the selected buckets that are most discriminative of the labels.
8. The method of claim 7 , wherein the sub-collection of buckets is selected with AdaBoost learning.