After I updated netpbm I noticed that the according man pages no longer
contained the proper man page but only a pointer man page.
Reproducible: Always
Steps to Reproduce:
1. emerge current stable netpbm
2. man pgm
Actual Results:
pgm(5) Netpbm pointer man pages pgm(5)
pgm is part of the Netpbm package. Netpbm documentation is kept in HTML
format.
Please refer to <http://netpbm.sourceforge.net/doc//pgm.html>.
If that doesn't work, also try <http://netpbm.sourceforge.net> and
emailing Bryan Henderson, bryanh@giraffe-
data.com.
Note that making the documentation available this way was a choice of the
person who installed Netpbm on this
system. It is also possible to install Netpbm such that you would simply
see the documentation instead of the
message you are reading now.
Oct 15:46:37 Netpbm pgm(5)
Expected Results:
pgm
Updated: 03 October 2003
Table Of Contents
NAME
pgm - Netpbm grayscale image format
DESCRIPTION
This program is part of Netpbm.
The PGM format is a lowest common denominator grayscale file format. It is
designed to be extremely easy to learn and write programs for. (It's so simple
that most people will simply reverse engineer it because it's easier than
reading this specification).
A PGM image represents a grayscale graphic image. There are many psueudo-PGM
formats in use where everything is as specified herein except for the meaning
of individual pixel values. For most purposes, a PGM image can just be thought
of an array of arbitrary integers, and all the programs in the world that
think they're processing a grayscale image can easily be tricked into
processing something else.
The name "PGM" is an acronym derived from "Portable Gray Map."
One official variant of PGM is the transparency mask. A transparency mask in
Netpbm is represented by a PGM image, except that in place of pixel
intensities, there are opaqueness values. See below.
The format definition is as follows. You can use the libnetpbm C subroutine
library to conveniently and accurately read and interpret the format.
A PGM file consists of a sequence of one or more PGM images. There are no
data, delimiters, or padding before, after, or between images.
Each PGM image consists of the following:
A "magic number" for identifying the file type. A pgm image's magic number is
the two characters "P5".
Whitespace (blanks, TABs, CRs, LFs).
A width, formatted as ASCII characters in decimal.
Whitespace.
A height, again in ASCII decimal.
Whitespace.
The maximum gray value (Maxval), again in ASCII decimal. Must be less than
65536, and more than zero.
Newline or other single whitespace character.
A raster of Height rows, in order from top to bottom. Each row consists of
Width gray values, in order from left to right. Each gray value is a number
from 0 through Maxval, with 0 being black and Maxval being white. Each gray
value is represented in pure binary by either 1 or 2 bytes. If the Maxval is
less than 256, it is 1 byte. Otherwise, it is 2 bytes. The most significant
byte is first.
A row of an image is horizontal. A column is vertical. The pixels in the image
are square and contiguous.
Each gray value is a number proportional to the intensity of the pixel,
adjusted by the CIE Rec. 709 gamma transfer function. (That transfer function
specifies a gamma number of 2.2 and has a linear section for small
intensities). A value of zero is therefore black. A value of Maxval represents
CIE D65 white and the most intense value in the image and any other image to
which the image might be compared.
Note that a common variation on the PGM format is to have the gray value be
"linear," i.e. as specified above except without the gamma adjustment.
pnmgamma takes such a PGM variant as input and produces a true PGM as output.
In the transparency mask variation on PGM, the value represents opaqueness. It
is proportional to the fraction of intensity of a pixel that would show in
place of an underlying pixel. So what normally means white represents total
opaqueness and what normally means black represents total transparency. In
between, you would compute the intensity of a composite pixel of an "under"
and "over" pixel as under * (1-(alpha/alpha_maxval)) + over *
(alpha/alpha_maxval). Note that there is no gamma transfer function in the
transparency mask.
Characters from a "#" to the next end-of-line, before the maxval line, are
comments and are ignored.
Note that you can use pnmdepth to convert between a the format with 1 byte per
gray value and the one with 2 bytes per gray value.
There is actually another version of the PGM format that is fairly rare:
"plain" PGM format. The format above, which generally considered the normal
one, is known as the "raw" PGM format. See pbm for some commentary on how
plain and raw formats relate to one another.
The difference in the plain format is:
-
There is exactly one image in a file.
-
The magic number is P2 instead of P5.
-
Each pixel in the raster is represented as an ASCII decimal number (of
arbitrary size).
-
Each pixel in the raster has white space before and after it. There must be
at least one character of white space between any two pixels, but there is no
maximum.
-
No line should be longer than 70 characters.
Here is an example of a small image in the plain PGM format:
P2
# feep.pgm
24 7
15
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 3 3 3 3 0 0 7 7 7 7 0 0 11 11 11 11 0 0 15 15 15 15 0
0 3 0 0 0 0 0 7 0 0 0 0 0 11 0 0 0 0 0 15 0 0 15 0
0 3 3 3 0 0 0 7 7 7 0 0 0 11 11 11 0 0 0 15 15 15 15 0
0 3 0 0 0 0 0 7 0 0 0 0 0 11 0 0 0 0 0 15 0 0 0 0
0 3 0 0 0 0 0 7 7 7 7 0 0 11 11 11 11 0 0 15 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Programs that read this format should be as lenient as possible, accepting
anything that looks remotely like a PGM.
COMPATIBILITY
Before April 2000, a raw format PGM file could not have a maxval greater than
255. Hence, it could not have more than one byte per sample. Old programs may
depend on this.
Before July 2000, there could be at most one image in a PGM file. As a result,
most tools to process PGM files ignore (and don't read) any data after the
first image.
SEE ALSO
pnm, pbm, ppm, pam, libnetpbm, programs that process PGM,
AUTHOR
Copyright (C) 1989, 1991 by Jef Poskanzer.
bash-2.05b$ etcat uses netpbm
[ Colour Code : set unset ]
[ Legend : (U) Col 1 - Current USE flags ]
[ : (I) Col 2 - Installed With USE flags ]
U I [ Found these USE variables in : media-libs/netpbm-10.20 ]
+ + svga : Adds support for SVGAlib (graphics library)
+ + jpeg : Adds JPEG image support
+ + tiff : Adds support for the tiff image format
+ + png : Adds support for libpng (PNG images)
+ + zlib : Adds support for zlib (de)compression
- - debug : Tells configure and the makefiles to build for debugging. Effects
vary across packages, but generally it will at least add -g to CFLAGS.
Remember to set FEATURES=nostrip too
If you look in /usr/share/doc/netpbm-10.20/USERDOC.gz, you will see that
the failure to include meaningful man pages appears to be the fault of the
upstream netpbm developer (obviously misguided, as far as I'm concerned).
USERDOC does suggest a recipe for fixing this:
VIEWING NETPBM DOC WITH TRADITIONAL MAN PROGRAM
-----------------------------------------------
Some people want to be able to access the Netpbm documentation with an
existing man program that doesn't know HTML. You can install the
documentation that way, with some loss of quality. Download the HTML
files, format them into plain displayable text with 'lynx -dump', and
then put those files into a man "cat" directory such as /usr/man/cat1.
The program 'makecat' in the 'buildtools' directory of the Netpbm source
tree does the lynx -dump on a set of files, so do something like this
example:
mkdir netpbmdoc
cd netpbmdoc
wget --recursive --relative http://netpbm.sourceforge.net/doc/
/usr/src/netpbm/buildtools/makecat *.html
cp *.1 /usr/man/cat1/
cd ..
rm -r netpbmdoc
man pnmtogif
Note that many of the Netpbm documentation files are not manuals for
particular programs, so the usual flat namespace limitation of man
pages will be exacerbated.
I would suggest at least to add the html documentation, that can be found at
http://netpbm.sourceforge.net/doc/, into /usr/share/doc/netpbm-10.20 (and
perhaps mention it in the pointer man pages), since the documentation produced
by /var/tmp/portage/netpbm-10.20/work/netpbm-10.20/buildtools/makecat is not
always convincing (e.g. man pgm -> end of lines are not translated correctly,
and so the example image is scattered over lines):
Here is an example of a small image in the plain PGM format: P2 # feep.pgm
24 7 15 0 0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 3 3 3 3
0 0 7 7
7 7 0 0 11 11 11 11 0 0 15 15 15 15 0 0 3 0 0 0 0 0 7 0 0 0 0
0 11 0 0
0 0 0 15 0 0 15 0 0 3 3 3 0 0 0 7 7 7 0 0 0 11 11 11 0 0 0
15 15 15 15
0 0 3 0 0 0 0 0 7 0 0 0 0 0 11 0 0 0 0 0 15 0 0 0 0 0 3
0 0 0 0
0 7 7 7 7 0 0 11 11 11 11 0 0 15 0 0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0
0 0 0 0 0 0 0 0 0 0 0
There are other packages that do not have man pages. But they at least have
some sensible documentation in /usr/share/doc which is not the case for netpbm.
