tifftopnm

tifftopnm(1)                General Commands Manual               tifftopnm(1)

NAME
       tifftopnm - convert a TIFF file into a portable anymap

SYNOPSIS
       tifftopnm  [-alphaout={alpha-filename,-}]  [-headerdump]  [-respectfil-
       lorder] [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 li-
       brary to read TIFF files.  Rather, it uses the more primitive TIFFRead-
       ScanLine() 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 informa-
       tion, 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  im-
       age  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 seek-
       able.  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  con-
              tains 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 en-
              gaging 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 de-
       scription 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 fil-
       lorder.  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  as-
       sumed  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, how-
       ever, 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)