>On 2/12/05, Paul Wasserman, discombobulated, unleashed: > >>consider that upsizing any JPEG >>would mean starting from a file that already has less information than >>was originally captured. > >Hi Paul, > >Could you elaborate on this please? Have you any specific references you >could point me towards? > . . . >Cheers, > Cotty
Well, this is basically in the nature of JPEG. Like pretty much all compression algorithms, Jpeg relys on identical or repeating values in a file to save the data in less space. Before jpeg compresses the data, it evaluates the color and, to a lesser degree, the luminance values of each pixel in the file. If the values of nearby pixels are similar, it makes those values the same so that it can better compress the data. The lower the jpeg quality selected, the more compression you get, because more of the information has been converted to identical values. As far as references go, http://www.prepressure.com/techno/compressionjpeg.htm has a pretty good technical description of the process, but just google "jpeg compression algorithim" for more. Paul Wasserman * **** ******* *********************************************************** * For list instructions, including unsubscribe, see: * http://www.a1.nl/phomepag/markerink/eos_list.htm ***********************************************************
