After the success of the series of JPEG standards, the committee decided it was appropriate to revisit the lossless coding mode within JPEG. This mode had been a late addition to the standard, and in the baseline form of JPEG (not using arithmetic coding) the algorithm used was not really close to 'state of the art' techniques. In addition, it really was not closely related to the block based DCT techniques which characterised the lossy compression that had become the norm. Looking at user requirements, particularly those of the medical imaging business which was concerned about potential large errors being introduced through lossy compression, the scope of the new standard was defined as effective lossless and near lossless compression of continuous-tone, grey scale and colour still images. By near lossless, it was agreed that a scheme was needed that guaranteed a maximum error between the original image data and the reconstructed image data.
A number of contenders for a suitable algorithm were proposed, and the committee carried out an extensive set of measurements to determine the best contender. The winner of these objective tests was agreed to be the LOCO
algorithm from HP Labs, whose web site offers extensive documentation and sample code. As well as being the leading contender, HP and Mitsubishi both agreed to offer their patents on a royalty and license fee free basis, ensuring that implementors would hopefully not need to make any payments to implement the new standard. As well as offering effective compression, the algorithm was also relatively easy to implement efficiently in PC software, and produces fast code.
A major side effect of undertaking this standards activity was that some of the other contenders such as CALIC, FELICS, and Ricoh's CREW algorithm in particular had some very attractive features - for example, in the ability to provide a single codestream which could provide lossy and lossless images without additional processing. Although outside the direct scope of JPEG-LS, these features and the discussions they provoked directly led to the development of the architectural approach of the new JPEG 2000 standard.
The standard is currently avalable for download from the ITU-T as their Recommendation T.87
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