I realized the embedding result on ICCV submission is a little weird. For CAR data set, Npair loss R@1 acc on testing set is 53% and EPSHN is 72%. I feel this might be related to the initial learning rate. Since in all the tests in the paper, I set the learning rate with 0.0005.
I try to run tests on two approaches EP(easy positive) and EPSHN(easy positive with semi-hard negative) with the incremental initial rate from 0.0001, 0.0002, 0.0004, 0.0008 to 0.0016.
And I get this result.
It looks like EPSHN can afford a large learning rate for a better result, but the EP cannot afford the large learning rate.