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August 1994
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1994.08.23 14:10 "Re: TIFF photometric question", by Adrian Phillips
On Aug 10, 10:37am, Sam Leffler wrote: > Subject: Re: TIFF photometric question > To: tiff@sgi.sgi.com > Subject: TIFF photometric question > Date: Wed, 10 Aug 1994 11:40:57 CDT > From: "Adrian Phillips (Tandem User)" <adrian.phillips@dnmi.no> > > We are converting a raw group 3 fax message embedded in another to postscript > holding the messages on disk in compressed (g3 or g4) format . We use pbm's > g3topbm to convert to pbm, pnmtotiff to convert to tiff, and then tiff2ps to > convert to postscript for printing. > > Why not just use fax2tiff? > > After the pnmtotiff, the tiff images have photometric min-is-black - the images > we're originally scanned in with white background and black foreground. When > the last version of tiff2ps is used the images come out thus, but if the new > version 3.3 is used, the images come out reversed. I interpret min-is-black to > mean that this reversing should take place (TIFF spec says > WhiteIsZero/BlackIsZero) - is this correct ? > > Sounds like pnmtotiff is setting the Photometric tag incorrectly. It > should be MinIsWhite instead of MinIsBlack. The change between v3.2 and > v3.3 was to eliminate the use of the Photometric tag in the G3+G4 decoders. > This is according to the spec (though contrary to my intuition, but that's > neither here nor there). Basically G3/G4-encoded data is defined to be > MinIsWhite (i.e. you the run codes are inherently encoded to mean white or > black independent of any Photometric tag value). In v3.2 the library > interpreted the run codes according to the value of the Photometric tag > while in v3.3 it always assigns a 0/1 value according to the CCITT spec. > > Your can switch to fax2tiff or change pnmtotiff to emit a different > Photometric tag value. > > Sam > > > >-- End of excerpt from Sam Leffler This is a coninuation of this problem. Please excuse my lack of TIFF knowledge. I changed pnmtotiff to set min-is-white but now (using alpha15) the maps come out black ! I checked with tiff2ps and tiffgt and its definitely looking white on black. Now, is this white on black info. in the TIFF "lines" and saying min-is-white just makes it use whats there (and min-is-black reversing this) or is this a problem somewhere else ? I would like to use fax2tiff but the fax info is packed within a message, g3topbm skips over leading info. until a fax message is found which makes life easier. Thanks, Adrian -- ------------------------------------------------------------------------- = Adrian Phillips at | BUT any thoughts in this are purely = = The Norwegian Meteorological | my own and have nothing to do with = = Institute | this establishment, thankfully. = = Net: adrian.phillips@dnmi.no | Phone: 47 22 96 32 09 Fax: 47 22 96 30 50