Hindawi Publishing Corporation EURASIP Journal on Advances in Signal Processing Volume 2010, Article ID 803542, 11 pages doi:10.1155/2010/803542 Research Article Enhanced JPEG2000 Quality Scalability through Block-Wise Layer Truncation Francesc Auli-Llinas, Joan Serra-Sagrist ` a, and Joan Bartrina-Rapesta Department of Information and Communications Engineering, Universitat Aut` onoma de Barcelona, 08290 Cerdanyola del Vall` es, Spain Correspondence should be addressed to Francesc Auli-Llinas, fauli@deic.uab.es Received 1 December 2009; Revised 3 March 2010; Accepted 26 April 2010 Academic Editor: Liang-Gee Chen Copyright © 2010 Francesc Auli-Llinas et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Quality scalability is an important feature of image and video coding systems. In JPEG2000, quality scalability is achieved through the use of quality layers that are formed in the encoder through rate-distortion optimization techniques. Quality layers provide optimal rate-distortion representations of the image when the codestream is transmitted and/or decoded at layer boundaries. Nonetheless, applications such as interactive image transmission, video streaming, or transcoding demand layer fragmentation. The common approach to truncate layers is to keep the initial prefix of the to-be-truncated layer, which may greatly penalize the quality of decoded images, especially when the layer allocation is inadequate. So far, only one method has been proposed in the literature providing enhanced quality scalability for compressed JPEG2000 imagery. However, that method provides quality scalability at the expense of high computational costs, which prevents its application to the aforementioned applications. This paper introduces a Block-Wise Layer Truncation (BWLT) that, requiring negligible computational costs, enhances the quality scalability of compressed JPEG2000 images. The main insight behind BWLT is to dismantle and reassemble the to-be-fragmented layer by selecting the most relevant codestream segments of codeblocks within that layer. The selection process is conceived from a rate-distortion model that finely estimates rate-distortion contributions of codeblocks. Experimental results suggest that BWLT achieves near-optimal performance even when the codestream contains a single quality layer. 1. Introduction Quality scalability is an important feature provided by modern image and video coding systems to allow the transmission and/or decoding of compressed codestreams at several bitrates without sacrificing coding performance. Quality scalability is key in applications like interactive image transmission, video streaming, or transcoding, among others. Commonly, it is achieved by means of the formation of successive layers of quality that, progressively decoded, provide optimal rate-distortion representations of the image. JPEG2000 [1] is a prominent image coding standard that provides advanced features such as lossy and lossy-to- lossless compression, random codestream access, and five different progression orders: scalability by quality, by spatial location, by resolution, and by component. To suit quality scalability requirements of applications, JPEG2000 permits the user to specify the layer allocation of the codestream. The density and bitrate distribution of layers are selected at encoding time, determining the rate-distortion optimality of the codestream [2]. It is important to construct codestreams containing a layer allocation that works well for most applications. Nonetheless, the practical use of quality layers must consider that, once the codestream is constructed, the layer allocation cannot be modified without the full reencoding of the image, or the use of computationally intensive techniques like for example [3] or [4]. If the codestream had an inadequate layer allocation, the quality of decoded images could be penalized by more than 10 dB, especially when insufficient quality layers are available (see Section 4). The high degree of flexibility provided by JPEG2000 is adjusted through several coding parameters that are all set at encoding time. For simplicity, applications and