NICT-NAIST System for WMT17 Multimodal Translation Task

This paper describes the NICT-NAIST system for the WMT 2017 shared multimodal machine translation task for both language pairs, English-to-German and English-to-French. We built a hierarchical phrase-based (Hiero) translation system and trained an attentional encoder-decoder neural machine translation (NMT) model to rerank the n-best output of the Hiero system, which obtained significant gains over both the Hiero system and NMT decoding alone. We also present a multimodal NMT model that integrates the target language descriptions of images that are similar to the image described by the source sentence as additional inputs of the neural networks to help the translation of the source sentence. We give detailed analysis for the results of the multimodal NMT model. Our system obtained the first place for the English-to-French task according to human evaluation.