TobepublishedinProceedingsofspieVol.4115.Seehttp://itSwww.epfl.ch/-dsanta/forthefinalreference these numbers are very dependent on the optimization, targeted ap s and other factors of the different implementatio As a rough indication of complexity we provide the run times of the different algorithms on a Linux based PC. This only gives an appreciation of the involved complexit 3.3. Functionalities Comparing how well different functionalities are fulfilled in the different standards is also a difficult issue. In the next section we provide a functionality matrix that indicates the set of supported features in each standard and an appreciation of how well they are fulfilled. Although in most cases this appreciation is based on the other results presented here, in some others it is based on the capabilities provided by the different algorithms 4. RESULTS The algorithms have been evaluated with seven images from the JPEG 2000 test set, covering various types of imagery. The mages"bike"(2048x2560) and"cafe"(2048x2560)are natural,"cmpnd1"(512x768)and"chart"(1688x2347)are compound documents consisting of text, photographs and computer graphics, aerial2"(2048x2048)is an aerial photography, "target"(512x512)is a computer generated image and"us"(512x448)an ultra scan. All these images have a depth of 8 bits per pixel The results have been generated on a PC with a 550 MHz Pentium Ill processor, 512 kB of cache and 512 MB of raM under Linux 2. 12. The software implementations used for coding the images are: the JPEG 2000 Verification Model (VM) 6.1(ISO/EC JTC1/SC29/WGIN1580), the MPEG-4 MoMuSys VM of Aug 1999(ISO/EC JTC1/SC29/WGllN2805) heiNdependentJpeGGroupJpeGimplementation(http://www.ijg.org/),version6b,theSpmgJpeG-lsimplementation oftheUniversityofBritishColumbia(http://spmg.ece.ubcca/),version2.2,theLosslessjPegcodecofCornellUniversity ( ftp: //ftp. cs. cornell. edu/pub/multimed), version 1.0, and the libpng implementation of PNG (ftp: //ftp uu. net/graphics/png) version 1. 0.3 4.1. Lossless compression Table I summarizes the lossless compression efficiency of lossless JPEG (L-JPEG), JPEG-LS, PNG and JPEG 2000 for all e test images For JPeg 2000 the reversible dwt filter, referred to as JPEG 2000R, has been used. In the case of L-JPEG optimized Huffman tables and the predictor yielding the best compression performance have been used for each image. For PNG the maximum compre setting has been used, while for JPEG-LS the default options were chosen. MPEG-4 VTC is not considered, as it does not provide a lossless functionality Table 1. Lossless compression ratios I JPEG 2000R JPEG-LS L-JPEG PNG l.84 cafe 149 1.57 1.36144 cmpd chart 282200241 aerial 147 143148 2.598.701 3.04 241294 average 2.09352 It can be seen that in almost all cases the best performance is obtained by JPEG-LS. JPEG 2000 provides, in most cases, competitive compression ratios with the added benefit of scalability. PNG performance is similar to the one of JPEG 2000 As for lossless JPEG, it does not perform as well as the other, more recent, standards. One notable exception to the general trend is the"target"image, which contains mostly patches of constant gray level as well as gradients. For this type of images, PNG provides the best results, probably because of the use of LZ77. Another exception is the"cmpndI"image, in which JPEG-LS and PNG achieve much larger compression ratios. This image contains for the most part black text on aTo be published in Proceedings of SPIE Vol. 4115. See http://ltswww.epfl.ch/~dsanta/ for the final reference. 4 these numbers are very dependent on the optimization, targeted applications and other factors of the different implementations. As a rough indication of complexity we provide the run times of the different algorithms on a Linux based PC. This only gives an appreciation of the involved complexity. 3.3. Functionalities Comparing how well different functionalities are fulfilled in the different standards is also a difficult issue. In the next section we provide a functionality matrix that indicates the set of supported features in each standard and an appreciation of how well they are fulfilled. Although in most cases this appreciation is based on the other results presented here, in some others it is based on the capabilities provided by the different algorithms. 4. RESULTS The algorithms have been evaluated with seven images from the JPEG 2000 test set, covering various types of imagery. The images “bike” (2048x2560) and “cafe” (2048x2560) are natural, “cmpnd1” (512x768) and “chart” (1688x2347) are compound documents consisting of text, photographs and computer graphics, “aerial2” (2048x2048) is an aerial photography, “target” (512x512) is a computer generated image and “us” (512x448) an ultra scan. All these images have a depth of 8 bits per pixel. The results have been generated on a PC with a 550 MHz PentiumTM III processor, 512 kB of cache and 512 MB of RAM under Linux 2.2.12. The software implementations used for coding the images are: the JPEG 2000 Verification Model (VM) 6.1 (ISO/IEC JTC1/SC29/WG1 N 1580), the MPEG-4 MoMuSys VM of Aug. 1999 (ISO/IEC JTC1/SC29/WG11 N 2805), the Independent JPEG Group JPEG implementation (http://www.ijg.org/), version 6b, the SPMG JPEG-LS implementation of the University of British Columbia (http://spmg.ece.ubc.ca/), version 2.2, the Lossless JPEG codec of Cornell University (ftp://ftp.cs.cornell.edu/pub/multimed), version 1.0, and the libpng implementation of PNG (ftp://ftp.uu.net/graphics/png), version 1.0.3. 4.1. Lossless compression Table 1 summarizes the lossless compression efficiency of lossless JPEG (L-JPEG), JPEG-LS, PNG and JPEG 2000 for all the test images. For JPEG 2000 the reversible DWT filter, referred to as JPEG 2000R, has been used. In the case of L-JPEG optimized Huffman tables and the predictor yielding the best compression performance have been used for each image. For PNG the maximum compression setting has been used, while for JPEG-LS the default options were chosen. MPEG-4 VTC is not considered, as it does not provide a lossless functionality. Table 1. Lossless compression ratios JPEG 2000R JPEG-LS L-JPEG PNG bike 1.77 1.84 1.61 1.66 cafe 1.49 1.57 1.36 1.44 cmpnd1 3.77 6.44 3.23 6.02 chart 2.60 2.82 2.00 2.41 aerial2 1.47 1.51 1.43 1.48 target 3.76 3.66 2.59 8.70 us 2.63 3.04 2.41 2.94 average 2.50 2.98 2.09 3.52 It can be seen that in almost all cases the best performance is obtained by JPEG-LS. JPEG 2000 provides, in most cases, competitive compression ratios with the added benefit of scalability. PNG performance is similar to the one of JPEG 2000. As for lossless JPEG, it does not perform as well as the other, more recent, standards. One notable exception to the general trend is the “target” image, which contains mostly patches of constant gray level as well as gradients. For this type of images, PNG provides the best results, probably because of the use of LZ77. Another exception is the “cmpnd1” image, in which JPEG-LS and PNG achieve much larger compression ratios. This image contains for the most part black text on a