NAME
pnmtotiff - convert a portable anymap into a TIFF file
SYNOPSIS
pnmtotiff [-none|-packbits|-lzw|-g3|-g4] [-2d] [-fill] [-predictor n]
[-msb2lsb|-lsb2msb] [-rowsperstrip n] [-minisblack|-miniswhite]
[-truecolor] [-color] [-indexbits 1|2|4|8] [pnmfile]
Minimum unambiguous abbreviations of options are acceptable.
DESCRIPTION
Reads a PNM image as input. Produces a TIFF file as output.
The output goes to Standard Output, which must be a seekable file.
That means no pipes, but any regular file should work.
OPTIONS
By default, pnmtotiff creates a TIFF file with no compression. This is
your best bet most of the time. If you want to try another compression
scheme or tweak some of the other even more obscure output options,
there are a number of flags to play with.
Actually, the best default would be to use LZW compression, which is
what pnmtotiff used to do by default. However, the Tiff library no
longer does LZW compression due to concerns with violating Unisys’s
patent on LZW compression.
The -none, -packbits, -lzw, -g3, -g4, -flate, and -adobeflat options
are used to override the default and set the compression scheme used in
creating the output file. The CCITT Group 3 and Group 4 compression
algorithms can only be used with bilevel data. -lzw doesn’t really
work because the Tiff library doesn’t do LZW compression. It used to,
but its developers removed the function out of concern about violating
Unisys’s patent. This option remains in case you use a Tiff library
that cooperates, now or in the future. The -2d and -fill options are
meaningful only with Group 3 compression: -2d requests 2-dimensional
encoding, while -fill requests that each encoded scanline be zero-
filled to a byte boundry. The -predictor option is only meaningful
with LZW compression: a predictor value of 2 causes each scanline of
the output image to undergo horizontal differencing before it is
encoded; a value of 1 forces each scanline to be encoded without
differencing.
By default, pnmtotiff creates a TIFF file with msb-to-lsb fill order.
The -msb2lsb and -lsb2msb options are used to override the default and
set the fill order used in creating the file.
The fill order is the order in which pixels are packed into a byte in
the Tiff raster, in the case that there are multiple pixels per byte.
msb-to-lsb means that the leftmost columns go into the most significant
bits of the byte in the Tiff image. However, there is considerable
confusion about the meaning of fill order. Some believe it means
whether 16 bit sample values in the Tiff image are little-endian or
big-endian. This is totally erroneous (The endianness of integers in a
Tiff image is designated by the image’s magic number). However,
ImageMagick and older Netpbm both have been known to implement that
interpretation. 2001.09.06.
If the image does not have sub-byte pixels, these options have no
effect other than to set the value of the FILLORDER tag in the Tiff
image (which may be useful for those programs that misinterpret the tag
with reference to 16 bit samples).
The -rowsperstrip option can be used to set the number of rows
(scanlines) in each strip of data in the output file. By default, the
output file has the number of rows per strip set to a value that will
ensure each strip is no more than 8 kilobytes long.
The -minisblack and -miniswhite option force the output image to have a
"minimum is black" or "minimum is white" photometric, respectively. If
you don’t specify either, pnmtotiff uses minimum is black except when
using Group 3 or Group 4 compression, in which case pnmtotiff follows
CCITT fax standards and uses "minimum is white." This usually results
in better compression and is generally preferred for bilevel coding.
Before February 2001, pnmtotiff always produced "minimum is black," due
to a bug. In either case, pnmtotiff sets the photometric
interpretation tag in the TIFF output according to which photometric is
actually used.
-truecolor tells pnmtotiff to produce the 24-bit RGB form of TIFF
output if it is producing a color TIFF image. Without this option,
pnmtotiff produces a colormapped (paletted) 8-bit TIFF image unless
there are more than 256 colors (and in the latter case, issues a
warning).
The -truecolor option can prevent pnmtotiff from making two passes
through the input file, thus improving speed and memory usage. See the
section MULTIPLE PASSES.
If pnmtotiff produces a grayscale TIFF image, this option has no
effect.
-color tells pnmtotiff to produce a color, as opposed to grayscale,
TIFF image if the input is PPM, even if it contains only shades of
gray. Without this option, pnmtotiff produces a grayscale TIFF image
if the input is PPM and contains only shades of gray, and at most 256
shades. Otherwise, it produces a color TIFF output. For PBM and PGM
input, pnmtotiff always produces grayscale TIFF output and this option
has no effect.
The -color option can prevent pnmtotiff from making two passes through
the input file, thus improving speed and memory usage. See the section
MULTIPLE PASSES.
The -indexbits option is meaningful only for a colormapped (paletted)
image. In this kind of image, the raster contains values which are
indexes into a table of colors, with the indexes normally taking less
space that the color description in the table. pnmtotiff can generate
indexes of 1, 2, 4, or 8 bits. By default, it will use 8, because many
programs that interpret TIFF images can’t handle any other width.
NOTES
There are myriad variations of the TIFF format, and this program
generates only a few of them. pnmtotiff creates a grayscale TIFF file
if its input is a PBM (monochrome) or PGM (grayscale) file. pnmtotiff
also creates a grayscale file if it input is PPM (color), but there is
only one color in the image. If the input is a PPM (color) file and
there are 256 colors or fewer, but more than 1, pnmtotiff generates a
color palette TIFF file. If there are more colors than that, pnmtotiff
generates an RGB (not RGBA) single plane TIFF file. Use pnmtotiffcmyk
to generate the cyan-magenta-yellow-black ink color separation TIFF
format.
The number of bits per sample in the TIFF output is determined by the
maxval of the PNM input. If the maxval is less than 256, the bits per
sample in the output is the smallest number that can encode the maxval.
If the maxval is greater than or equal to 256, there are 16 bits per
sample in the output.
Multiple Passes
pnmtotiff reads the input image once if it can, and otherwise twice.
It needs that second pass to analyze the colors in the image and
generate a color map (pallette) and determine if the image is
grayscale. So the second pass only happens when the input is PPM. And
you can avoid it then by specifying both the -truecolor and -color
options.
If the input image is small enough to fit in your system’s file cache,
the second pass is very fast. If not, it requires reading from disk
twice, which can be slow.
When the input is from a file that cannot be rewound and reread,
pnmtotiff reads the entire input image into a temporary file which can,
and works from that. Even if it only needs one pass.
SEE ALSO
tifftopnm(1), pnmtotiffcmyk(1), pnmdepth(1), pnm(5)
AUTHOR
Derived by Jef Poskanzer from ras2tiff.c, which is Copyright (c) 1990
by Sun Microsystems, Inc. Author: Patrick J. Naughton
(naughton@wind.sun.com).
24 January 2001 pnmtotiff(1)