MobiVQA: Efficient On-Device Visual Question Answering

Visual Question Answering (VQA) is a relatively new task where a user can ask a natural question about an image and obtain an answer. VQA is useful for many applications and is widely popular for users with visual impairments. Our goal is to design a VQA application that works efficiently on mobile devices without requiring cloud support. Such a system will allow users to ask visual questions privately, without having to send their questions to the cloud, while also reduce cloud communication costs. However, existing VQA applications use deep learning models that significantly improve accuracy, but is computationally heavy. Unfortunately, existing techniques that optimize deep learning for mobile devices cannot be applied for VQA because the VQA task is multi-modal—it requires both processing vision and text data. Existing mobile optimizations that work for vision-only or text-only neural networks cannot be applied here because of the dependencies between the two modes. Instead, we design MobiVQA, a set of optimizations that leverage the multi-modal nature of VQA. We show using extensive evaluation on two VQA testbeds and two mobile platforms, that MobiVQA significantly improves latency and energy with minimal accuracy loss compared to state-of-the-art VQA models. For instance, MobiVQA can answer a visual question in 163 milliseconds on the phone, compared to over 20-second latency incurred by the most accurate state-of-the-art model, while incurring less than 1 point reduction in accuracy.