CIDEr metric downweights the n-grams common in all image captions, which are similar to tf-idf.
we use three standard image captioning evaluation metrics, BLEU (Papineni et al., 2002) and METEOR (Denkowski and Lavie, 2014), RE-OUGE (Lin, 2004) and CIDEr (Vedantam et al., 2015), to evaluate the quality of both the generated templates and generated captions.