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User manual for Netpbm(0) User manual for Netpbm(0)
NAME
netpbm - netpbm library overview
Overview Of Netpbm
Netpbm is a package of graphics programs and a programming library.
There are over 220 separate programs in the package, most of which have 'pbm',
'pgm', 'ppm', 'pam', or 'pnm' in their names. For example, pamscale(1)and
giftopnm(1).
For example, you might use pamscale to shrink an image by 10%. Or use pamcomp to
overlay one image on top of another. Or use pbmtext to create an image of text.
Or reduce the number of colors in an image with pnmquant.
Netpbm is an open source software package, distributed via the Sourceforge netpbm
project .
Table Of Contents
? Overview Of Netpbm
? The Netpbm Formats
? Implied Format Conversion
? Netpbm and Transparency
? The Netpbm Programs
? Common Options
? Directory
? How To Use The Programs
? The Netpbm Library
? netpbm-config
? Memory Usage
? CPU Usage
? Companion Software
? PHP-NetPBM
? Other Graphics Software
? Image Viewers
? Visual Graphics Software
? Programming Tools
? Tools For Specific Graphics Formats
? Document/Graphics Software
? Other
? Other Graphics Formats
? History
? Author
The Netpbm Programs
The Netpbm programs are generally useful run by a person from a command shell, but
are also designed to be used by programs. A common characteristic of Netpbm pro-
grams is that they are simple, fundamental building blocks. They are most powerful
when stacked in pipelines. Netpbm programs do not use graphical user interfaces
and do not seek input from a user. The only programs that display graphics at all
are the very primitive display programs pamx and ppmsvgalib, and they don't do any-
thing but that.
Each of these programs has its own manual, as linked in the directory below.
The Netpbm programs can read and write files greater than 2 GiB wherever the under-
lying system can. There may be exceptions where the programs use external
libraries (The JPEG library, etc.) to access files and the external library does
not have large file capability. Before Netpbm 10.15 (April 2003), no Netpbm pro-
gram could read a file that large.
Common Options
There are a few options that are present on all programs that are based on the
Netpbm library, including virtually all Netpbm programs. These are not mentioned
in the individual manuals for the programs.
You can use two hyphens instead of one on these options if you like.
-quiet Suppress all informational messages that would otherwise be issued to Stan-
dard Error. (To be precise, this only works to the extent that the program
in question implements the Netpbm convention of issuing all informational
messages via the pm_message() service of the Netpbm library).
-version
Instead of doing anything else, report the version of the libnetpbm library
linked with the program (it may have been linked statically into the pro-
gram, or dynamically linked at run time). Normally, the Netpbm programs and
the library are installed at the same time, so this tells you the version of
the program and all the other Netpbm files it uses as well.
-plain If the program generates an image in Netpbm format, generate it in the
"plain" (aka "ascii") version of the format, as opposed to the "raw" (aka
"binary") version.
This option was introduced in Netpbm 10.10 (October 2002).
Directory
Here is a complete list of all the Netpbm programs (with links to their manuals):
Netpbmprogramdirectory(1)
How To Use The Programs
As a collection of primitive tools, the power of Netpbm is multiplied by the power
of all the other unix tools you can use with them. These notes remind you of some
of the more useful ways to do this. Often, when people want to add high level
functions to the Netpbm tools, they have overlooked some existing tool that, in
combination with Netpbm, already does it.
Often, you need to apply some conversion or edit to a whole bunch of files.
As a rule, Netpbm programs take one input file and produce one output file, usually
on Standard Output. This is for flexibility, since you so often have to pipeline
many tools together.
Here is an example of a shell command to convert all your of PNG files (named
*.png) to JPEG files named *.jpg:
for i in *.png; do pngtopnm $i | ppmtojpeg >'basename $i .png'.jpg; done
Or you might just generate a stream of individual shell commands, one per file,
with awk or perl. Here's how to brighten 30 YUV images that make up one second of
a movie, keeping the images in the same files:
ls *.yuv
| perl -ne 'chomp;
print yuvtoppm $_ | ppmbrighten -v 100 | ppmtoyuv >tmp$$.yuv;
mv tmp$$.yuv $_
'
| sh
The tools find (with the -exec option) and xargs are also useful for simple manipu-
lation of groups of files.
Some shells' 'process substitution' facility can help where a non-Netpbm program
expects you to identify a disk file for input and you want it to use the result of
a Netpbm manipulation. Say the hypothetical program printcmyk takes the filename
of a Tiff CMYK file as input and what you have is a PNG file abc.png.
Try:
printcmyk <({ pngtopnm abc.png | pnmtotiffcmyk ; })
It works in the other direction too, if you have a program that makes you name its
output file and you want the output to go through a Netpbm tool.
The Netpbm Formats
All of the programs work with a set of graphics formats called the 'netpbm' for-
mats. Specifically, these formats are pbm(1), pgm(1), ppm(1), and pam(1).
The first three of these are sometimes known generically as 'pnm'.
Many of the Netpbm programs convert from a Netpbm format to another format or vice
versa. This is so you can use the Netpbm programs to work on graphics of any for-
mat. It is also common to use a combination of Netpbm programs to convert from one
non-Netpbm format to another non-Netpbm format. Netpbm has converters for about
100 graphics formats, and as a package Netpbm lets you do more graphics format con-
versions than any other computer graphics facility.
The Netpbm formats are all raster formats, i.e. they describe an image as a matrix
of rows and columns of pixels. In the PBM format, the pixels are black and white.
In the PGM format, pixels are shades of gray. In the PPM format, the pixels are in
full color. The PAM format is more sophisticated. A replacement for all three of
the other formats, it can represent matrices of general data including but not lim-
ited to black and white, grayscale, and color images.
Programs designed to work with PBM images have 'pbm' in their names. Programs
designed to work with PGM, PPM, and PAM images similarly have 'pgm', 'ppm', and
'pam' in their names.
All Netpbm programs designed to read PGM images see PBM images as if they were PGM
too. All Netpbm programs designed to read PPM images see PGM and PBM images as if
they were PPM. See
Implied Format Conversion .
Programs that have 'pnm' in their names read PBM, PGM, and PPM but unlike 'ppm'
programs, they distinguish between them and their function depends on the format.
For example, pnmtopng(1)createsablackandwhitePNG output image if its input is PBM
or PGM, but a color PNG output image if its input is PPM. And pnmrotate produces
an output image of the same format as the input. A hypothetical ppmrotate program
would also read all three PNM input formats, but would see them all as PPM and
would always generate PPM output.
Programs that have "pam" in their names read all the Netpbm formats: PBM, PGM, PPM,
and PAM. They sometimes treat them all as if they are PAM, using an implied con-
version, but often they recognize the individual formats and behave accordingly,
like a "pnm" program does. See Implied Format Conversion .
If it seems wasteful to you to have three separate PNM formats, be aware that
there is a historical reason for it. In the beginning, there were only PBMs. PGMs
came later, and then PPMs. Much later came PAM, which realizes the possibility of
having just one aggregate format.
The formats are described in the specifications of pbm(1), pgm(1), ppm(1), and
pam(1).
Implied Format Conversion
A program that uses the PGM library subroutines to read an image can read a PBM
image as well as a PGM image. The program sees the PBM image as if it were the
equivalent PGM image, with a maxval of 255. note: This sometimes confuses people
who are looking at the formats at a lower layer than they ought to be because a
zero value in a PBM raster means white, while a zero value in a PGM raster means
black.
A program that uses the PPM library subroutines to read an image can read a PGM
image as well as a PPM image and a PBM image as well as a PGM image. The program
sees the PBM or PGM image as if it were the equivalent PPM image, with a maxval of
255 in the PBM case and the same maxval as the PGM in the PGM case.
A program that uses the PAM library subroutines to read an image can read a PBM,
PGM, or PPM image as well as a PAM image. The program sees a PBM image as if it
were the equivalent PAM image with tuple type BLACKANDWHITE. It sees a PGM image
as if it were the equivalent PAM image with tuple type GRAYSCALE. It sees a PPM
image as if it were the equivalent PAM image with tuple type RGB. But the program
actually can see deeper if it wants to. It can tell exactly which format the input
was and may respond accordingly. For example, a PAM program typically produces
output in the same format as its input.
Netpbm and Transparency
In many graphics formats, there's a means of indicating that certain parts of the
image are wholly or partially transparent, meaning that if it were displayed 'over'
another image, the other image would show through there. Netpbm formats deliber-
ately omit that capability, since their purpose is to be extremely simple.
In Netpbm, you handle transparency via a transparency mask in a separate (slightly
redefined) PGM image. In this pseudo-PGM, what would normally be a pixel's inten-
sity is instead an opaqueness value. See pgm(1). pamcomp(1)isanexampleofapro-
gramthatuses a PGM transparency mask.
Another means of representing transparency information has recently developed in
Netpbm, using PAM images. In spite of the argument given above that Netpbm formats
should be too simple to have transparency information built in, it turns out to be
extremely inconvenient to have to carry the transparency information around sepa-
rately. This is primarily because Unix shells don't provide easy ways to have
networks of pipelines. You get one input and one output from each program in a
pipeline. So you'd like to have both the color information and the transparency
information for an image in the same pipe at the same time.
For that reason, some new (and recently renovated) Netpbm programs recognize and
generate a PAM image with tuple type RGB_ALPHA or GRAYSCALE_ALPHA, which contains a
plane for the transparency information. See thePAMspecification(1).
The Netpbm Library
The Netpbm programming library, libnetpbm(1),makesiteasytowriteprograms that manip-
ulate graphic images. Its main function is to read and write files in the Netpbm
formats, and because the Netpbm package contains converters for all the popular
graphics formats, if your program reads and writes the Netpbm formats, you can use
it with any formats.
But the library also contain some utility functions, such as character drawing and
RGB/YCrCb conversion.
The library has the conventional C linkage. Virtually all programs in the Netpbm
package are based on the Netpbm library.
netpbm-config
In a standard installation of Netpbm, there is a program named netpbm-config in the
regular program search path. We don't consider this a Netpbm program -- it's just
an ancillary part of a Netpbm installation. This program tells you information
about the Netpbm installation, and is intended to be run by other programs that
interface with Netpbm. In fact, netpbm-config is really a configuration file, like
those you typically see in the /etc/ directory of a Unix system.
Example:
$netpbm-config --datadir
/usr/local/netpbm/data
If you write a program that needs to access a Netpbm data file, it can use such a
shell command to find out where the Netpbm data files are.
netpbm-config is the only file that must be installed in a standard directory (it
must be in a directory that is in the default program search path). You can use
netpbm-config as a bootstrap to find all the other Netpbm files.
There is no detailed documentation of netpbm-config. If you're in a position to
use it, you should have no trouble reading the file itself to figure out how to use
it.
Memory Usage
An important characteristic that varies among graphics software is how much memory
it uses, and how. Does it read an entire image into memory, work on it there, then
write it out all at once? Does it read one and write one pixel at a time? In
Netpbm, it differs from one program to the next, but there are some generalizations
we can make.
Most Netpbm programs keep one row of pixels at a time in memory. Such a program
reads a row from an input file, processes it, then writes a row to an output file.
Some programs execute algorithms that can't work like that, so they keep a small
window of rows in memory. Others must keep the entire image in memory. If you
think of what job the program does, you can probably guess which one it does.
When Netpbm keeps a pixel in memory, it normally uses a lot more space for it than
it occupies in the Netpbm image file format.
The older programs (most of Netpbm) use 12 bytes per pixel. This is true even for
a PBM image, for which it only really takes one bit to totally describe the pixel.
Netpbm does this expansion to make implementing the programs easier -- it uses the
same format regardless of the type of image.
Newer programs use the 'pam' family of library functions internally, which use mem-
ory a little differently. These functions are designed to handle generic tuples
with a variable numbers of planes, so no fixed size per-tuple storage is possible.
A program of this type uses 4 bytes per sample (a tuple is composed of samples),
plus another 4 bytes per tuple. In a graphic image, a tuple is a pixel. So an
ordinary color image takes 16 bytes per pixel.
When considering memory usage, it is important to remember that memory and disk
storage are equivalent in two ways:
? Memory is often virtual, backed by swap space on disk storage. So accessing
memory may mean doing disk I/O.
? Files are usually cached and buffered, so that accessing a disk file may
just mean accessing memory.
This means that the consequences of whether a program works from the image file or
from a memory copy are not straightforward.
Note that an image takes a lot less space in a Netpbm format file, and therefore in
an operating system's file cache, than in Netpbm's in-memory format. In non-Netpbm
image formats, the data is even smaller. So reading through an input file multiple
times instead of keeping a copy in regular memory can be the best use of memory,
and many Netpbm programs do that. But some files can't be read multiple times. In
particular, you can't rewind and re-read a pipe, and a pipe is often the input for
a Netpbm program. Netpbm programs that re-read files detect such input files and
read them into a temporary file, then read that temporary file multiple times.
A few Netpbm programs use an in-memory format that is just one bit per pixel.
These are programs that convert between PBM and a format that has a raster format
very much like PBM's. In this case, it would actually make the program more com-
plicated (in addition to much slower) to use Netpbm's generic 12 byte or 8 byte
pixel representation.
By the way, the old axiom that memory is way faster than disk is not necessarily
true. On small systems, it typically is true, but on a system with a large network
of disks, especially with striping, it is quite easy for the disk storage to be
capable of supplying data faster than the CPU can use it.
CPU Usage
People sometimes wonder what CPU facilities Netpbm programs and the Netpbm program-
ming library use. The programs never depend on particular features existing
(assuming they're compiled properly), but the speed and cost of running a program
varies depending upon the CPU features.
One area of particular importance is floating point arithmetic. The Netpbm image
formats are based on integers, and Netpbm arithmetic is done with integers where
possible. But there is one significant area that is floating point: programs that
must deal with light intensity. The Netpbm formats use integers that are propor-
tional to brightness, and brightness is exponentially related to light intensity.
The programs have to keep the intermediate intensity values in floating point in
order not to lose precision. And the conversion (gamma function) between the two
is heavy-duty floating point arithmetic.
Programs that mix pixels together have to combine light intensity, so they do heavy
floating point. Three of the most popular Netpbm programs do that: pamscale(1)
(shrink/expand an image), pamcomp(1)(overlay an image over another one), and
pamditherbw(1)(Makeablackandwhiteimage that approximates a grayscale image).
The Netpbm image formats use 16 bit integers. The Netpbm code uses 'unsigned int'
size integers to work with them.
Companion Software
<h3 id="php-netpbm">PHP-NetPBM</h3>
If you're using Netpbm to do graphics for a website, you can invoke the Netpbm pro-
grams from a PHP script. To make this even easier, check out PHP-NetPBM , a PHP
class that interacts with Netpbm. Its main goal is to decrease the pain of using
Netpbm when working with images in various formats. It includes macro commands to
perform manipulations on many files.
I can't actually recommend PHP-NetPBM. I spent some time staring at it and was
unable to make sense of it. Some documentation is in fractured English and other
is in an unusual character set. But a PHP expert might be able to figure it out
and get some use out of it.
Other Graphics Software
Netpbm contains primitive building blocks. It certainly is not a complete graphics
software library.
Graphics Viewers
The first thing you will want to make use of any of these tools is a viewer. (On
GNU/Linux, you can use ppmsvgalib in a pinch, but it is pretty limiting). zgv is a
good full service viewer to use on a GNU/Linux system with the SVGALIB graphics
display driver library. You can find zgv at ftp://ftp.ibib-
lio.org/pub/Linux/apps/graphics/viewers/svga .
zgv even has a feature in it wherein you can visually crop an image and write an
output file of the cropped image using pamcut(1).
See the -s option to zgv.
For the X inclined, there is also xzgv.
xloadimage and its extension xli are also common ways to display a graphic image in
X.
gqview is a more modern X-based image viewer.
qiv is a small, very fast viewer for X.
To play mpeg movies, such as produced by ppmtompeg, try mplayer(1)or
xine .
See ftp://metalab.unc.edu/pub/Linux/apps/graphics/viewers/X .
Visual Graphics Software
Visual graphics software is modern point-and-click software that displays an image
and lets you work on it and see the results as you go. This is fundamentally dif-
ferent from what Netpbm programs do.
ImageMagick is like a visual version of Netpbm. Using the X/Window system on Unix,
you can do basic editing of images and lots of format conversions. The package
does include at least some non-visual tools. convert, mogrify, montage, and ani-
mate are popular programs from the ImageMagick package. ImageMagick runs on Unix,
Windows, Windows NT, Macintosh, and VMS.
xv is a very old and very popular simple image editor in the Unix world. It does
not have much in the way of current support, or maintenance, though.
The Gimp is a visual image editor for Unix and X, in the same category as the more
famous, less capable, and much more expensive Adobe Photoshop, etc. for Windows.
See http://www.gimp.org .
Electric Eyes, kuickshow, and gthumb are also visual editors for the X/Window sys-
tem, and KView and gwenview are specifically for KDE.
Programming Tools
If you're writing a program in C to draw and manipulate images, check out gd .
Netpbm contains a C library for drawing images, but it is probably not as capable
or documented as gd. You can easily run any Netpbm program from a C program with
the pm_system function from the Netpbm programming library, but that is less effi-
cient than gd functions that do the same thing.
Ilib is a C subroutine library with functions for adding text to an image (as you
might do at a higher level with pbmtext, pamcomp, etc.). It works with Netpbm
input and output. Find it at k5n.us . Netpbm also includes character drawing
functions in the libnetpbm(1)library,buttheydonothaveas fancy font capabilities
(see ppmlabel(1) for an example of use of the Netpbm character drawing functions).
GD is a library of graphics routines that is part of PHP. It has a subset of
Netpbm's functions and has been found to resize images more slowly and with less
quality.
Tools For Specific Graphics Formats
mencode, which is part of the mplayer(1)package, creates movie files. It's like a
much more advanced version of ppmtompeg(1),withouttheNetpbm building block simplic-
ity.
To create an animated GIF, or extract a frame from one, use gifsicle. gifsicle
converts between animated GIF and still GIF, and you can use ppmtogif and giftopnm
to connect up to all the Netpbm utilities. See http://www.lcdf.org/gifsicle .
To convert an image of text to text (optical character recongition - OCR), use gocr
(think of it as an inverse of pbmtext). See http://altmark.nat.uni-magde-
burg.de/~jschulen/ocr/ .
http://schaik.com/pngsuite contains a PNG test suite -- a whole bunch of PNG
images exploiting the various features of the PNG format.
Another version of Netpbm's pnmtopng/pngtopnm is at http://www.schaik.com/png/pnm-
topng.html(1).
The version in Netpbm was actually based on that package a long time ago, and you
can expect to find better exploitation of the PNG format, especially recent
enhancements, in that package. It may be a little less consistent with the Netpbm
project and less exploitive of recent Netpbm format enhancements, though.
pngwriter is a C++ library for creating PNG images. With it, you plot an image
pixel by pixel. You can also render text with the FreeType2 library.
jpegtran Does some of the same transformations as Netpbm is famous for, but does
them specifically on JPEG files and does them without loss of information. By con-
trast, if you were to use Netpbm, you would first decompress the JPEG image to
Netpbm format, then transform the image, then compress it back to JPEG format. In
that recompression, you lose a little image information because JPEG is a lossy
compression. Of course, only a few kinds of lossless transformation are possible.
jpegtran comes with the Independent Jpeg Group's ( http://www.ijg.org) JPEG
library.
Some tools to deal with EXIF files (see also Netpbm's jpegtopnm(1)and pnmto-
jpeg(1)):
To dump (interpret) an EXIF header: Exifdump (( http://topo.math.u-
psud.fr/~bousch/exifdump.py) ) or Jhead .
A Python EXIF library and dumper: http://pyexif.sourceforge.net.
Here's some software to work with IOCA (Image Object Content Architecture):
ImageToolbox ($2500, demo available). This can convert from TIFF -> IOCA and back
again. Ameri-Imager(1) ($40 Windows only).
pnm2ppa converts to HP's 'Winprinter' format (for HP 710, 720, 820, 1000, etc). It
is a superset of Netpbm's pbmtoppa and handles, notably, color. However, it is
more of a printer driver than a Netpbm-style primitive graphics building block.
See The Pnm2ppa /Sourceforge Project
Document/Graphics Software
There is a large class of software that does document processing, and that is some-
what related to graphics because documents contain graphics and a page of a docu-
ment is for many purposes a graphic image. Because of this slight intersection
with graphics, I cover document processing software here briefly, but it is for the
most part beyond the scope of this document.
First, we look at where Netpbm meets document processing. pstopnm converts from
Postscript and PDF to PNM. It effectively renders the document into images of
printed pages. pstopnm is nothing but a convenient wrapper for Ghostscript , and
in particular Netpbm-format device drivers that are part of it. pnmtops and pbm-
toepsi convert a PNM image to a Postscript program for printing the image. But to
really use PDF and Postscript files, you generally need more complex document pro-
cessing software.
Adobe invented Postscript and PDF and products from Adobe are for many purposes the
quintessential Postscript and PDF tools.
Adobe's free Acrobat Reader displays PDF and converts to Postscript. The Acrobat
Reader for unix has a program name of 'acroread' and the -toPostScript option (also
see the -level2 option) is useful.
Other software from Adobe, available for purchase, interprets and creates
Postscript and PDF files. 'Distill' is a program that converts Postscript to PDF.
xpdf also reads PDF files.
GSview, ghostview, gv, ggv, and kghostview are some other viewers for Postscript
and PDF files.
The program ps2pdf, part of Ghostscript, converts from Postscript to PDF.
Two packages that produce more kinds of Encapsulated Postscript than the Netpbm
programs, including compressed kinds, are bmeps and imgtops .
dvips converts from DVI format to Postscript. DVI is the format that Tex produces.
Netpbm can convert from Postscript to PNM. Thus, you can use these in combination
to work with Tex/Latex documents graphically.
wvware converts a Microsoft Word document (.doc file) to various other formats.
While the web page doesn't seem to mention it, it reportedly can extract an embed-
ded image in a Word document as a PNG.
Document Printer converts various print document formats (Microsoft Word, PDF,
HTML, etc.) to various graphic image formats. ($38, Windows only).
Latex2html converts Latex document source to HTML document source. Part of that
involves graphics, and Latex2html uses Netpbm tools for some of that. But
Latex2html through its history has had some rather esoteric codependencies with
Netpbm. Older Latex2html doesn't work with current Netpbm. Latex2html-99.2beta8
works, though.
Other
The file program looks at a file and tells you what kind of file it is. It recog-
nizes most of the graphics formats with which Netpbm deals, so it is pretty handy
for graphics work. Netpbm's anytopnm(1)programdependsonfile. See
ftp://ftp.astron.com/pub/file .
The Utah Raster Toolkit serves a lot of the same purpose as Netpbm, but without the
emphasis on format conversions. This package is based on the RLE format, which you
can convert to and from the Netpbm formats. The website of the Geometric Design
And Computation group in the Department of Computer Science at University of Utah
used to (ca. 2002) have information on the Utah Raster Toolkit, but now it doesn't.
Ivtools is a suite of free X Windows drawing editors for Postscript, Tex, and web
graphics production, as well as an embeddable and extendable vector graphic shell.
It uses the Netpbm facilities. See http://www.ivtools.org .
The program morph morphs one image into another. It uses Targa format images, but
you can use tgatoppm and ppmtotga to deal with that format. You have to use the
graphical (X/Tk) Xmorph to create the mesh files that you must feed to morph.
morph is part of the Xmorph package. See http://www.colorado-
research.com/~gourlay/software/Graphics/Xmorph .
Other Graphics Formats
People never seem to tire of inventing new graphics formats, often completely
redundant with pre-existing ones. Netpbm cannot keep up with them. Here is a list
of a few that we know Netpbm does not handle (yet).
Various commercial Windows software handles dozens of formats that Netpbm does not,
especially formats typically used with Windows programs. ImageMagick is probably
the most used free image format converter and it also handles lots of formats
Netpbm does not.
? VRML (Virtual Reality Modelling Language)
? CAL (originated by US Department Of Defense, favored by architects).
http://www.landfield.com/faqs/graphics/fileformats-faq/part3/sec-
tion-24.html(1)
? array formats dx, general, netcdf, CDF, hdf, cm
? CGM+
? Windows Meta File (.WMF). Libwmf converts from WMF to things like Latex,
PDF, PNG. Some of these can be input to Netpbm.
? Microsoft Word .doc format. Microsoft keeps a proprietary hold on this for-
mat. Any software you see that can handle it is likely to cost money.
? RTF
? DXF (AutoCAD)
? IOCA (Image Object Content Architecture) The specification of this format
is documented by IBM:
Data Stream and Object Architectures: Image Object Content Architecture
Reference . See above for software that processes this format.
? OpenEXR is an HDR format (like PFM(1)). See
http://www.openexr.com .
? Xv Visual Schnauzer thumbnail image. This is a rather antiquated format
used by the Xv program. In Netpbm circles, it is best known for the fact
that it is very similar to Netpbm formats and uses the same signature ('P7')
as PAM because it was developed as sort of a fork of the Netpbm format spec-
ifications.
? YUV 4:2:0, aka YUV 420, and the simlar YUV 4:4:4, YUV 4:2:2, YUV 4:1:1, YUV
4:1:1s, and YUV 4:1:0. Video systems often use this.
History
Netpbm has a long history, starting with Jef Poskanzer's Pbmplus package in 1988.
The file HISTORY in the Netpbm source code contains a historical overview as well
as a detailed history release by release.
Author
Netpbm is based on the Pbmplus package by Jef Poskanzer, first distributed in 1988
and maintained by him until 1991. But the package contains work by countless other
authors, added since Jef's original work. In fact, the name is derived from the
fact that the work was contributed by people all over the world via the Internet,
when such collaboration was still novel enough to merit naming the package after
it.
Bryan Henderson has been maintaining Netpbm since 1999. In addition to packaging
work by others, Bryan has also written a significant amount of new material for the
package.
netpbm documentation 24 August 2006 User manual for Netpbm(0)
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