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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  separation),  and  color  palette
       TIFF  files.   An  RGB  file can have either single plane (interleaved)
       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 fillorder 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 created 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)