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September 2005
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2005.09.08 22:11 "Re: creating JPEG file", by Joris Van Damme
Philip Watkinson wrote: > What is the format of a JPEG file? Is a > JPEG file a TIFF file with JPEG encoding? No, absolutely not. JPEG is an independent file format that has nothing to do with TIFF. There is, however, a more or less opposite relation. A seperate tile/strip inside a TIFF file with JPEG compression, is more or less a JPEG file, instead of the other way around. I say 'more or less' for two seperate reasons: 1) such a JPEG tile/strip/file is not strictly required to contain one specific element of JPEG, namely the 'tables', on the condition that tables that apply to all tiles/strips are given in the JpegTables tag. This tag, then, too, is more or less a JPEG file, except that it contains tables only, thus complementing the JPEG in each tile/strip. 2) an independent JPEG file normally contains additional markers identifying color space and stuff. A JPEG compressed tile or strip inside a TIFF should normally not contain these markers. This is why LibTiff depends on LibJpeg, passing each individual tile/strip to the LibJpeg library, doing only some additional funny stuff in case the JpegTables tag is present. And not the other way around, LibJpeg does not depend on LibTiff. Joris Van Damme info@awaresystems.be http://www.awaresystems.be/ Download your free TIFF tag viewer for windows here: http://www.awaresystems.be/imaging/tiff/astifftagviewer.html