Interframe Coding of Global Image Signatures for Mobile Augmented Reality

For mobile augmented reality, an image captured by a mobile device´s camera is often compared against a database hosted on a remote server to recognize objects in the image. It is critically important that the amount of data transmitted over the network is as small as possible to reduce the system latency. A low bitrate global signature for still images has been previously shown to achieve high-accuracy image retrieval. In this paper, we develop new methods for interframe coding of a continuous stream of global signatures that can reduce the bitrate by nearly two orders of magnitude compared to independent coding of these global signatures, while achieving the same or better image retrieval accuracy. The global signatures are constructed in an embedded data structure that offers rate scalability. The usage of these new coding methods and the embedded data structure allows the streaming of high-quality global signatures at a bitrate that is less than 2 kbps. Furthermore, a statistical analysis of the retrieval and coding performance is performed to understand the trade off between bitrate and image retrieval accuracy and explain why interframe coding of global signatures substantially outperforms independent coding.