Abstract—The efficient transmission of large resolution im-ages and, in particular, the interactive transmission of images in a client-server scenario, is an important aspect for many applications. Among the current image compression standards, JPEG2000 excels for its interactive transmission capabilities. In general, three mechanisms are employed to optimize the trans-mission of images when using the JPEG2000 Interactive Protocol (JPIP): 1) packet re-sequencing at the server; 2) prefetching at the client; and 3) proxy servers along the network infrastructure. To avoid the congestion of the network, prefetching mechanisms are not commonly employed when many clients within a local area network (LAN) browse images from a remote server. Aimed to maximize the responsiveness of all the clients within a LAN, this work proposes the use of prefetching strategies at the proxy server –rather than at the clients. The main insight behind the proposed prefetching strategies is a user-navigation model and a semantic map that predict the future requests of the clients. Experimental results indicate that the introduction of these strategies into a JPIP proxy server enhances the browsing experience of the end-users notably. Index Terms—Interactive image transmission, JPEG2000, JPIP, prefetching strategies, user-navigation model, semantic map. I.

The efficient transmission of large resolution images is a key aspect in many applications to minimize the transmission costs and to enhance the browsing experience. Among the currently available standards for the coding and transmission of imagery, JPEG2000 excels for its superior coding performance and advanced capabilities. The JPEG2000 Interactive Protocol (JPIP) minimizes the amount of information transmitted in a client-server scenario. Nonetheless, JPIP does not provide mechanisms to re-use data already delivered to clients browsing the same image within a local network. Common HTTP proxy servers are not able to understand the syntax of JPIP, thus specialized JPIP proxy servers are put in practice. This work improves the capabilities of traditional JPIP proxy servers by means of a user-navigation model that, together with prefetching strategies, allows the server to anticipate (potential) future requests of clients. Experimental evidence indicates that the introduction of the navigational model into a JPIP proxy server enhances the browsing experience notably.

Remote browsing of images is receiving much attention lately, mostly in niche applications like geographical information systems or in the telemedicine scenery. Interactive transmission of compressed images has been identified as the most competitive approach, being JPIP, JPEG2000 Interactive Protocol, a key-enabler for these situations. Also, it has been reported that JPIP Proxy Servers help to increase the transmission performance, and that prefetching strategies help to lower responsiveness time. In this paper we contribute a smart JPIP Proxy Server that, thanks to a prefetching strategy undertaken during idle transmission times, largely improves the viewing experience of the final user because of its anticipation of future navigation requests. Experimental results are reported for a remote sensing and a medical environment, respectively performing panning and zoom in, showing enhanced performance in both cases.

Region Of Interest (ROI) coding is a mechanism deployed in several image coding systems to enable different degrees of coding priority to specific regions of the image. JPEG2000 standard provides two ROI coding methods. However, both of them are based in mechanisms that scale the quantized coefficients. This compels to encode the additional bit-planes needed for the scaling, causing a penalization in the overall coding performance, and the ROIs can not be modified without a complete re-encoding of the image. This paper introduces two ROI coding methods that use Rate-distortion optimization techniques toprioritize arbitrary ROIs over the rest of the image without penalizing the overall coding performance. Experimental results suggest that the proposed methods achieve a close tooptimal accuracy, improving the Implicit ROI coding method in terms of ROI rate distortion performance.

Quality scalability is a fundamental feature of JPEG2000, achieved through the use of quality layers. Two points, related with the use of quality layers, may need to be addressed when dealing with JPEG-2000 code-streams: 1) the lack of quality scalability of single quality layer code-streams, and 2) the non rate-distortion optimality of windows of interest transmission. This paper introduces a new rate control method that can be applied to already encoded code-streams, addressing these two points. Its main key-feature is a novel characterization that can fairly estimate the rate-distortion slope of the coding passes of code-blocks without using any measure based on the original image or related with the encoding process. Experimental results suggest that the proposed method is able to supply quality scalability to already encoded code-streams achieving a near-optimal coding performance. The low computational costs of the method makes it suitable for use in interactive transmissions.

The JPEG2000 standard does not specify how to perform the rate control strategy, needed either to achieve a target bitrate, or to construct quality layers. In this paper, an efficient rate control algorithm is described. It is based on the interleaving of coding passes and it has a low computational complexity. The proposed algorithm encodes only the coding passes included in the final codestream, and it fully avoids the need of any post compression rate distortion stage. Extensive experimental results show that the encoding performance of our method is competitive and similar to the optimal strategy. In addition, this proposal allows the extraction of a target bitrate from a codestream without the need of either knowing the original image, or of decoding any part of the codestream. The performance of this kind of extraction is equivalent to that obtained when decompressing a codestream organized in quality layers.