tifftopnm



Tifftopnm User Manual(0)                              Tifftopnm User Manual(0)




NAME

       tifftopnm - convert a TIFF file into a PNM image



SYNOPSIS

       tifftopnm

       [-alphaout={alpha-filename,-}]     [-headerdump]    [-respectfillorder]
       [-byrow] [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

       This program is part of Netpbm(1).

       tifftopnm reads a TIFF file as input and produces a PNM image  as  out-
       put.   The  type of the output file depends on the input file - if it’s
       black & white, generates a PBM image; if it’s  grayscale,  generates  a
       PGM image; otherwise, a PPM image.  The program tells you which type it
       is writing.

       If the TIFF file contains multiple  images  (multiple  ’directories,’),
       tifftopnm  generates  a  multi-image  PNM output stream.  Before Netpbm
       10.27 (March 2005), however, it would just ignore  all  but  the  first
       input image.

       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.

       There  are  many TIFF formats that tifftopnm can read only if the image
       is small enough to fit in memory.  tifftopnm uses  the  TIFF  library’s
       TIFFRGBAImageGet()  function  to  process  the TIFF image if it can get
       enough memory for TIFFRGBAImageGet() to store the whole image in memory
       at  once (that’s what TIFFRGBAImageGet() does).  If not, tifftopnm uses
       a more primitive row-by-row conversion  strategy  using  the  raw  data
       returned  by  TIFFReadScanLine()  and native intelligence.  That native
       intelligence does not know as many formats as TIFFRGBAImageGet()  does.
       And certain compressed formats simply cannot be read with TIFFReadScan-
       Line().

       Before Netpbm 10.11 (October 2002), tifftopnm  never  used  TIFFRGBAIm-
       ageGet(),  so  it could not interpret many of the formats it can inter-
       pret today.

       There is no fundamental reason that this program could not  read  other
       kinds  of  TIFF  files  even when they don’t fit in memory all at once.
       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
       image  that doesn’t need a maxval > 255 doesn’t have a maxval > 255, so
       when tifftopnm sees a non-colormapped maxval > 255, it takes  it  seri-
       ously and produces a matching output maxval.

       Another exception is where the TIFF maxval is greater than 65535, which
       is the maximum allowed by the Netpbm formats.  In that case,  tifftopnm
       uses  a  maxval  of 65535, and you lose some information in the conver-
       sion.

       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 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 pamcomp(1)foronewaytouse 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.


       -byrow This option can make tifftopnm run faster.

              tifftopnm  has two different ways to do the conversion from Tiff
              to PNM, using two different facilities of the TIFF library:




       Whole Image
              Decode the entire image into memory at once,  using  TIFFRGBAIm-
              ageGet(), then convert to PNM and output row by row.


       Row By Row
              Read,  convert, and output one row at a time using TIFFReadScan-
              line().



              Whole Image is preferable because the Tiff library does more  of
              the  work,  which  means  it understands more of the Tiff format
              possibilities now and in the future.  Also, some compressed TIFF
              formats don’t allow you to extract an individual row.

              Row  By Row uses far less memory, which means with large images,
              it can run in environments where Whole Image cannot and may also
              run faster.  And because Netpbm code does more of the work, it’s
              possible that it can be more flexible or at  least  give  better
              diagnostic information if there’s something wrong with the TIFF.

              In Netpbm, we stress function over performance, so by default we
              try Whole Image first, and if we can’t get enough memory for the
              decoded image or TIFFRGBAImageGet() fails, we fall back  to  Row
              By  Row.   But  if you specify the -byrow option, tifftopnm will
              not attempt Whole Image.  If Row By Row does not work, it simply
              fails.

              See  Color Separation (CMYK) TIFFs  for a description of one way
              Row By Row makes a significant difference in your results.

              Whole Image costs you precision when your TIFF image  uses  more
              than 8 bits per sample.  TIFFRGBAImageGet() converts the samples
              to 8 bits.  tifftopnm then scales them back to maxval 65535, but
              the lower 8 bits of information is gone.

              Before  Netpbm 10.11 (October 2002), tifftopnm always did Row By
              Row.  Netpbm 10.12 always tried Whole Image first.  -byrow  came
              in with Netpbm 10.13 (January 2003).


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





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  repre-
       sented  by  a  single byte: 1) the byte is filled from most significant
       bit to least significant 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 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.



   Color Separation (CMYK) TIFFs
       Some  TIFF  images  contain color information in CMYK form, whereas PNM
       images use RGB.  There are  various  formulas  for  converting  between
       these two forms, and tifftopnm can use either of two.

       The  TIFF  library  (Version 3.5.4 from libtiff.org) uses Y=(1-K)*(1-B)
       (similar  for  R  and  G)  in  its  TIFFRGBAImageGet()  service.   When
       tifftopnm  works  in  Whole Image mode, it uses that service, so that’s
       the conversion you get.

       But when tifftopnm runs in Row By Row mode, it does not use TIFFRGBAIm-
       ageGet(),  and you get what appears to be more useful: Y=1-(B+K).  This
       is the inverse of what pnmtotiffcmyk does.

       See the -byrow option for more information on Whole Image versus Row By
       Row mode.

       Before Netpbm 10.21 (March 2004), tifftopnm used the Y=(1-K)*(1-B) for-
       mula always.




SEE ALSO

       pnmtotiff(1), pnmtotiffcmyk(1), pamcomp(1), pnm(1)



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).



netpbm documentation             27 March 2005        Tifftopnm User Manual(0)

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