Image-Captioning Model Compression

Image captioning is a very important task, which is on the edge between natural language processing (NLP) and computer vision (CV). The current quality of the captioning models allows them to be used for practical tasks, but they require both large computational power and considerable storage space. Despite the practical importance of the image-captioning problem, only a few papers have investigated model size compression in order to prepare them for use on mobile devices. Furthermore, these works usually only investigate decoder compression in a typical encoder-decoder architecture, while the encoder traditionally occupies most of the space. We applied the most efficient model-compression techniques such as architectural changes, pruning and quantization to several state-of-the-art image-captioning architectures. As a result, all of these models were compressed by no less than 91% in terms of memory (including encoder), but lost no more than 2% and 4.5% in metrics such as CIDEr and SPICE, respectively. At the same time, the best model showed results of 127.4 CIDEr and 21.4 SPICE, with a size equal to only 34.8 MB, which sets a strong baseline for compression problems for image-captioning models, and could be used for practical applications.