Ubuntu Manpage: tifftopnm - convert a TIFF file into a PNM image

NAME

       tifftopnm - convert a TIFF file into a PNM image

SYNOPSIS

       tifftopnm

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

DESCRIPTION

This program is part of Netpbm(1).

tifftopnm reads a TIFF file as input and produces a PNM image as output. The type of the output file
depends on the input file - if it's black and white, tifftopnm generates a PBM image; if it's grayscale,
it generates a PGM image; otherwise, the output is PPM. 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.

The tiff-filename argument names the file that contains the Tiff image. If you specify "-" or don't
specify this argument, tifftopnm uses Standard Input.

In either case, before Netpbm 10.70 (March 2015), the file must be seekable. That means no pipe, but any
regular file is fine. In current Netpbm, the file need not be seekable, but if it isn't, tifftopnm
creates a temporary regular file containing the entire image, so you must have resources for that (and it
may defeat your reason for using a pipe).

TIFF Capability
pamtotiff uses the Libtiff.org TIFF library (or whatever equivalent you provide) to interpret the TIFF
input. So the set of files it is able to interpret is determined mostly by that library.

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 transparency
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 littlendian.

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 TIFFReadScanLine().

Before Netpbm 10.11 (October 2002), tifftopnm never used TIFFRGBAImageGet(), so it could not interpret
many of the formats it can interpret 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.

Output Image
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 tifftopnm
sees a non-colormapped maxval > 255, it takes it seriously 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
conversion.

OPTIONS

In addition to the options common to all programs based on libnetpbm (most notably -quiet, see
Common Options ⟨index.html#commonoptions⟩ ), tifftopnm recognizes the following command line options:

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.

-alphaout=alpha-filename
tifftopnm creates a PGM file containing the alpha channel values in the input image. If the input
image doesn't contain a transparency channel, the alpha-filename file contains all zero
(transparent) transparency values. If you don't specify -alphaout,

tifftopnm does not generate a transparency file, and if the input image has an transparency
channel, tifftopnm simply discards it.

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

See pamcomp(1) for one way to use the transparency 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 ways to do the conversion from Tiff to PNM, using respectively two facilities of
the TIFF library:

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

Row By Row
Read, convert, and output one row at a time using TIFFReadScanline()

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.

The Netpbm native code may do something correctly that the TIFF library does incorrectly, or vice
versa.

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 ⟨#cmyk⟩ 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.

In many versions of the TIFF library, TIFFRGBAImageGet() does not correctly interpret TIFF files
in which the raster orientation is column-major (i.e. a row of the raster is a column of the
image). With such a TIFF library and file, you must use -byrow to get correct output.

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).

-orientraw
A TIFF stream contains raster data which can be arranged in the stream various ways. Most
commonly, it is arranged by rows, with the top row first, and the pixels left to right within each
row, but many other orientations are possible.

The common orientation is the same one the Netpbm formats use, so tifftopnm can do its jobs quite
efficiently when the TIFF raster is oriented that way.

But if the TIFF raster is oriented any other way, it can take a considerable amount of processing
for tifftopnm to convert it to Netpbm format.

-orientraw says to produce an output image that represents the raw raster in the TIFF stream
rather than the image the TIFF stream is supposed to represent. In the output, the top left
corner corresponds to the start of the TIFF raster, the next pixel to the right is the next pixel
in the TIFF raster, etc. tifftopnm can do this easily, but you don't get the right image out.
You can use pamflip to turn the output into the image the TIFF stream represents (but if you do
that, you pretty much lose the benefit of -orientraw).

With this option, tifftopnm always uses the Row By Row method (see -byrow).

This option was new in Netpbm 10.42 (March 2008). Before that, tifftopnm generally produces
arbitrary results with TIFF images that have an orientation other than the common one.

-verbose
Print extra messages to Standard Error about the conversion.

-headerdump
Also 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 represented 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 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. ⟨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 TIFFRGBAImageGet(), 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) formula always.

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).

DOCUMENT SOURCE

       This manual page was generated by the Netpbm tool 'makeman' from HTML source.  The  master  documentation
       is at

              http://netpbm.sourceforge.net/doc/tifftopnm.html