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From: "Adrian Phillips (Tandem User)" <adrian.phillips@dnmi.no>
Message-Id: <9408230910.ZM14097@freeze.oslo.dnmi.no>
Date: Tue, 23 Aug 1994 09:10:12 -0500
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To: tiff@sgi.sgi.com
Subject: Re: TIFF photometric question
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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



