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RedHat 9 (Linux i386) - man page for tifftopnm (redhat section 1)

tifftopnm(1)									     tifftopnm(1)

NAME
       tifftopnm - convert a TIFF file into a portable anymap

SYNOPSIS
       tifftopnm [-alphaout={alpha-filename,-}] [-headerdump] [-respectfillorder] [tiff-filename]

       You  may  abbreviate  any  option  to its shortest unique prefix.  You may use two hyphens
       instead of one in options.  You may separate an option and its value either by  an  equals
       sign or white space.

DESCRIPTION
       Reads a TIFF file as input.  Produces a portable anymap as output.  The type of the output
       file depends on the input file - if it's black & white, generates  a  pbm  file;  if  it's
       grayscale,  generates a pgm file; otherwise, a ppm file.  The program tells you which type
       it is writing.

       This program cannot read every possible TIFF file -- there are myriad  variations  of  the
       TIFF   format.	However,  it  does  understand	monochrome  and  gray  scale,  RGB,  RGBA
       (red/green/blue with alpha channel), CMYK  (Cyan-Magenta-Yellow-Black  ink  color  separa-
       tion),  and  color  palette  TIFF files.  An RGB file can have either single plane (inter-
       leaved) color or multiple plane format.	The  program  reads  1-8  and  16  bit-per-sample
       input, the latter in either bigendian or littlendian encoding.  Tiff directory information
       may also be either bigendian or littendian.

       One reason this program isn't as general as TIFF programs often are is that  it	does  not
       use  the  TIFFRGBAImageGet()  function of the TIFF library to read TIFF files.  Rather, it
       uses the more primitive TIFFReadScanLine() function and decodes it itself.

       There is no fundamental reason that this program could not read other kinds of TIFF files;
       the existing limitations are mainly because no one has asked for more.

       The  PNM  output  has  the same maxval as the Tiff input, except that if the Tiff input is
       colormapped (which implies a maxval of 65535) the PNM output has a maxval of 255.   Though
       this  may  result  in  lost  information, such input images hardly ever actually have more
       color resolution than a maxval of 255 provides and people often cannot deal with PNM files
       that  have  maxval  >  255.  By contrast, a non-colormapped Tiff image that doesn't need a
       maxval > 255 doesn't have a maxval > 255, so when we see a non-colormapped maxval  >  255,
       we take it seriously and produce a matching output maxval.

       The  tiff-filename  argument  names the regular file that contains the Tiff image.  If you
       specify "-" or don't specify this argument, tfftopnm uses Standard Input. In either  case,
       the file must be seekable.  That means no pipe, but any regular file is fine.

OPTIONS
       -alphaout=alpha-filename
	      tifftopnm creates a PGM (portable graymap) file containing the alpha channel values
	      in the input image.  If the input image  doesn't	contain  an  alpha  channel,  the
	      alpha-filename  file  contains  all  zero (transparent) alpha values.  If you don't
	      specify -alphaout, tifftopnm does not generate an alpha  file,  and  if  the  input
	      image has an alpha channel, tifftopnm simply discards it.

	      If  you  specify	-  as the filename, tifftopnm writes the alpha output to Standard
	      Output and discards the image.

	      See pnmcomp(1) for one way to use the alpha output file.

       -respectfillorder
	      By default, tifftopnm ignores the "fillorder" tag in the TIFF input, which means it
	      may  incorrectly interpret the image.  To make it follow the spec, use this option.
	      For a lengthy but engaging discussion of why tifftopnm works this way  and  how  to
	      use the -respectfillorder option, see the note on fillorder below.

       -headerdump
	      Dump  TIFF file information to stderr.  This information may be useful in debugging
	      TIFF file conversion problems.

       All options can be abbreviated to their shortest unique prefix.

NOTES
   Fillorder
       There is a piece of information in the header of a TIFF	image  called  "fillorder."   The
       TIFF  specification quite clearly states that this value tells the order in which bits are
       arranged in a byte in the description of the  image's  pixels.	There  are  two  options,
       assuming  that  the  image  has a format where more than one pixel can be represented by a
       single byte: 1) the byte is filled from most signficant bit to least signficant bit  going
       left to right in the image; and 2) the opposite.

       However,  there	is confusion in the world as to the meaning of fillorder.  Evidence shows
       that some people believe it has to do with byte order when a single value  is  represented
       by two bytes.

       These  people cause TIFF images to be created that, while they use a MSB-to-LSB fillorder,
       have a fillorder tag that says they used LSB-to-MSB.  A program that properly interprets a
       TIFF image will not end up with the image that the author intended in this case.

       For  a  long time, tifftopnm did not understand fillorder itself and assumed the fillorder
       was MSB-to-LSB regardless of the fillorder tag in the TIFF header.  And as far as I  know,
       there  is  no  legitimate  reason  to  use a fillorder other than MSB-to-LSB.  So users of
       tifftopnm were happily using those TIFF images that had incorrect fillorder tags.

       So that those users can continue to be happy, tifftopnm today continues to ignore the fil-
       lorder  tag unless you tell it not to.  (It does, however, warn you when the fillorder tag
       does not say MSB-to-LSB that the tag is being ignored).

       If for some reason you have a TIFF image that actually has LSB-to-MSB fillorder,  and  its
       fillorder  tag  correctly  indicates  that,  you  must use the -respectfillorder option on
       tifftopnm to get proper results.

       Examples of incorrect TIFF images are at ftp://weather.noaa.gov.  They are apparently cre-
       ated by a program called faxtotiff.

       This note was written on January 1, 2002.

SEE ALSO
       pnmtotiff(1), pnmtotiffcmyk(1), pnmcomp(1), pnm(5)

AUTHOR
       Derived	by Jef Poskanzer from tif2ras.c, which is Copyright (c) 1990 by Sun Microsystems,
       Inc.  Author: Patrick J. Naughton (naughton@wind.sun.com).

					  02 April 2000 			     tifftopnm(1)


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