Method of unsupervised domain adaptation in ordinal regression

An ordinal regression unsupervised domain adaption network for jointly training of a transferable feature extractor network, an ordinal regressor network, and an order classifier network, comprising:

• a source of labeled source images and unlabeled target images;
• a transferable feature extractor network, operatively connected to said source of labeled source images and unlabeled target images, to output image representations, said image representations being realized by a minimax optimization procedure;
• a domain discriminator network operatively connected to said transferable feature extractor network;
• an ordinal regressor network operatively connected to said transferable feature extractor network;
• and
• an order classifier network operatively connected to said transferable feature extractor network and said domain discriminator network;
• said domain discriminator network being trained, using said image representations from said transferable feature extractor network, to distinguish between source images and target images;
• said ordinal regressor network being trained, using a full set of source images from said transferable feature extractor network;
• said order classifier network being trained, using a pair of source images from said transferable feature extractor network.