tifftopnm Man page

tifftopnm General Commands Manual tifftopnm

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
library to read TIFF files. Rather, it uses the more primitive TIFF‐
ReadScanLine() 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
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 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 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 repre‐
sented 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
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, 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, pnmtotiffcmyk, pnmcomp, 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