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January 2007
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2007.01.31 18:06 "Re: Interpreting SubIFDs tag", by Phil Harvey
I would like to hear an authoritative answer on this, but as far as I know, the IFD0->IFD1->IFDN chain is the only one which actually uses the next-IFD pointer to chain IFD's. It is common practice to put a zero next-IFD pointer at the end of other IFD's, but I've never seen this pointer used. - Phil On 31-Jan-07, at 12:05 PM, tiff-request@lists.maptools.org wrote: > Message: 1 > Date: Wed, 31 Jan 2007 11:53:37 +0100 > From: mikk <mikk@go2.pl> > Subject: [Tiff] Interpreting SubIFDs tag > To: tiff@lists.maptools.org > Message-ID: <45C07531.8080604@go2.pl> > Content-Type: text/plain; charset=ISO-8859-2; format=flowed > > Hello all, > I'm a bit confused with interpreting SubIFDs tag value. > > Each value of N values in SubIFDs tag is an offset (from the beginning > of the TIFF file, as always) to a child IFD. But is each value of N > values an offset to a single child IFD, or to the first IFD from a > linked list of IFDs? When I read each of these N child IFDs, am I > supposed to interpret NextIFDOffset field and read next directory from > this position for each of child IFDs? > > Could anyone put some light on this, please? > > Thanks in advance, kind regards, > > mikk > > > > ------------------------------ > > Message: 2 > Date: Wed, 31 Jan 2007 17:39:04 +0100 > From: "Reinhard Mayr aka Czerwinski" <czerwinski1977@gmx.net> > Subject: [Tiff] 16bit grayscale with colormap > To: tiff@lists.maptools.org > Message-ID: <20070131163904.36820@gmx.net> > Content-Type: text/plain; charset="iso-8859-1" > > Hello, > > I deal with 16bit grayscale TIFFs. The files originate from a 12bit > CCD, so the linear conversion 16bit->8bit turns my image almost black. > > To cope with that, I would like to add a ColorMap into the TIFF. > For testing, I altered an existing 16bit file: > o photometrics = 3 (ColorMap) > o added a colormap (tag 0140), length: 3*2^16= 196608 bytes > > Porgrams either refuse this file (ImageMagick viewer) or ignore the > colormap and treat as if without (ImageJ). > > Is this a proper interpretation of the TIFF specs (TIFF6 specs p.23 > allow only 4/8 bits per sample -- why?)? How can I work with the > data in terms of leaving original values untouched and just change > a LUT/ColorMap/whatever? > > Thanks for all advices, hints & pointers! > > Cz. > -- > Der GMX SmartSurfer hilft bis zu 70% Ihrer Onlinekosten zu sparen! > Ideal für Modem und ISDN: http://www.gmx.net/de/go/smartsurfer > > > ------------------------------ > > Message: 3 > Date: Wed, 31 Jan 2007 14:56:52 -0200 > From: Toby Thain <toby@smartgames.ca> > Subject: Re: [Tiff] 16bit grayscale with colormap > To: "Reinhard Mayr aka Czerwinski" <czerwinski1977@gmx.net> > Cc: tiff@lists.maptools.org > Message-ID: <8D6BFBC5-5621-404D-9492-2D89DA20BB1F@smartgames.ca> > Content-Type: text/plain; charset=ISO-8859-1; delsp=yes; format=flowed > > > On 31-Jan-07, at 2:39 PM, Reinhard Mayr aka Czerwinski wrote: > >> Hello, >> >> I deal with 16bit grayscale TIFFs. The files originate from a 12bit >> CCD, so the linear conversion 16bit->8bit turns my image almost >> black. > > Maybe I'm missing something, but why don't you just multiply by 16 > before storing in TIFF? > > --Toby > >> >> To cope with that, I would like to add a ColorMap into the TIFF. >> For testing, I altered an existing 16bit file: >> o photometrics = 3 (ColorMap) >> o added a colormap (tag 0140), length: 3*2^16= 196608 bytes >> >> Porgrams either refuse this file (ImageMagick viewer) or ignore the >> colormap and treat as if without (ImageJ). >> >> Is this a proper interpretation of the TIFF specs (TIFF6 specs p.23 >> allow only 4/8 bits per sample -- why?)? How can I work with the >> data in terms of leaving original values untouched and just change >> a LUT/ColorMap/whatever? >> >> Thanks for all advices, hints & pointers! >> >> Cz. >> -- >> Der GMX SmartSurfer hilft bis zu 70% Ihrer Onlinekosten zu sparen! >> Ideal für Modem und ISDN: http://www.gmx.net/de/go/smartsurfer >> _______________________________________________ >> Tiff mailing list: Tiff@lists.maptools.org >> http://lists.maptools.org/mailman/listinfo/tiff >> http://www.remotesensing.org/libtiff/ > > > > > ------------------------------ > > _______________________________________________ > Tiff mailing list > Tiff@lists.maptools.org > http://lists.maptools.org/mailman/listinfo/tiff > > End of Tiff Digest, Vol 32, Issue 19 > ************************************