Pnmtops User Manual

# pnmtops

Updated: 21 February 2024
Table Of Contents

## NAME

pnmtops - convert PNM image to Postscript

## SYNOPSIS

pnmtops [-scale=s] [-dpi=N[xN]] [-imagewidth=n] [-imageheight=n] [-width=N] [-height=N] [-equalpixels] [-bitspersample=N] [-turn|-noturn] [-rle|-runlength] [-flate] [-ascii85] [-nocenter|-center] [-nosetpage|-setpage] [-level=N] [-dict] [-vmreclaim] [-psfilter] [-noshowpage] [-verbose] [pnmfile]

All options can be abbreviated to their shortest unique prefix. You may use two hyphens instead of one. You may separate an option name and its value with white space instead of an equals sign.

## DESCRIPTION

This program is part of Netpbm.

pnmtops reads a Netpbm image stream as input and produces Encapsulated Postscript (EPSF) as output.

(Note: people usually render the name as "PostScript," but we use standard typography in the Netpbm manual, so capitalize only the first letter).

If the input file is in color (PPM), pnmtops generates a color Postscript file. Some Postscript interpreters can't handle color Postscript. If you have one of these you will need to run your image through ppmtopgm first.

If you specify no output dimensioning options, the output image is dimensioned as if you had specified -scale=1.0, which means approximately 72 pixels of the input image generate one inch of output (if that fits the page).

Use -imagewidth, -imageheight, -equalpixels, -width, -height, and -scale to adjust that.

Each image in the input stream becomes one complete one-page Postscript program in the output. (This may not be the best way to create a multi-page Postscript stream; someone who knows Postscript should work on this).

The line at the top of the file produced by pnmtops is either "%!PS-Adobe-3.0 EPSF-3.0" or just "%!PS-Adobe-3.0". The numbers do not reflect the Postscript language level, but the version of the DSC comment specification and EPS specification implemented. The Postscript language level is in the "%%LanguageLevel:" comment. pnmtops omits "EPSF-3.0" if you specify -setpage, because it is incorrect to claim EPS compliance if the file uses setpagedevice.

### What is Encapsulated Postscript?

Encapsulated Postscript (EPSF) is a subset of Postscript (i.e. the set of streams that conform to EPSF is a subset of those that conform to Postscript). It is designed so that an EPSF stream can be embedded in another Postscript stream. A typical reason to do that is to have an EPSF stream that describes a picture you can put in a larger document.

But EPSF is not an image format -- converting from Netpbm format to EPSF really means generating a program to print that Netpbm image on paper. Note that there are myriad ways to print an image on paper; pnmtops command line options let you control some of them.

An Encapsulated Postscript document conforms to the DSC (Document Structuring Convention). The DSC defines some Postscript comments (they're comments from a Postscript point of view, but have semantic value from a DSC point of view).

More information about Encapsulated Postscript is at http://www.tailrecursive.org/postscript/eps.html.

Many of the ideas in pnmtops come from Dirk Krause's bmeps. See SEE ALSO.

## OPTIONS

In addition to the options common to all programs based on libnetpbm (most notably -quiet, see Common Options), pnmtops recognizes the following command line options:

-imagewidth, -imageheight
  Tells how wide and high you want the image on the page, in inches. The aspect ratio of the image is preserved, so if you specify both of these, the image on the page will be the largest image that will fit within the box of those dimensions.

  If these dimensions are greater than the page size, you get Postscript output that runs off the page.

  You cannot use imagewidth or imageheight with -scale or -equalpixels.

-equalpixels
  This option causes the output image to have the same number of pixels as the input image. So if the output device is 600 dpi and your image is 3000 pixels wide, the output image would be 5 inches wide.

  You cannot use -equalpixels with -imagewidth, -imageheight, or -scale.

-bitspersample=N
  This option selects the number of bits for each component of each pixel in the Postscript output. By default, pnmtops chooses the value that corresponds to the maxval of the PNM input, subject to constraints of the Postscript language. In particular, if you don't select Postscript level 2 (-level) with built-in Postscript (-psfilter), the most bits per pixel you can have is 8.

  The value must be 1, 2, 4, 8, or 12, with 12 being restricted to the case described above.

  This option was new in Netpbm 10.51 (June 2010).

-scale
  tells how big you want the image on the page. The value is the number of inches of output image that you want 72 pixels of the input to generate.

  But pnmtops rounds the number to something that is an integral number of output device pixels. E.g. if the output device is 300 dpi and you specify -scale=1.0, then 75 (not 72) pixels of input becomes one inch of output (4 output pixels for each input pixel). Note that the -dpi option tells pnmtops how many pixels per inch the output device generates.

  If the size so specified does not fit on the page (as measured either by the -width and -height options or the default page size of 8.5 inches by 11 inches), pnmtops ignores the -scale option, issues a warning, and scales the image to fit on the page.

-dpi=N[xN]

  This option specifies the dots per inch resolution of your output device. The default is 300 dpi. In theory PostScript is device-independent and you don't have to worry about this, but in practice its raster rendering can have unsightly bands if the device pixels and the image pixels aren't in sync.

  Also this option is crucial to the working of the equalpixels option.

  If you specify NxN, the first number is the horizontal resolution and the second number is the vertical resolution. If you specify just a single number N, that is the resolution in both directions.

-width, -height
  These options specify the dimensions, in inches, of the page on which the output is to be printed. This can affect the size of the output image.

  The page size has no effect, however, when you specify the -imagewidth, -imageheight, or -equalpixels options.

  These options may also affect positioning of the image on the page and even the paper selected (or cut) by the printer/plotter when the output is printed. See the -nosetpage option.

  The default is 8.5 inches by 11 inches.

-turn
-noturn
  These options control whether the image gets turned 90 degrees. Normally, if an image fits the page better when turned (e.g. the image is wider than it is tall, but the page is taller than it is wide), it gets turned automatically to better fit the page. If you specify the -turn option, pnmtops turns the image no matter what its shape; If you specify -noturn, pnmtops does not turn it no matter what its shape.
-rle
-runlength
  These identical options tell pnmtops to use run length compression in encoding the image in the Postscript program. This may save time if the host-to-printer link is slow; but normally the printer's processing time dominates, so -rle has no effect (and in the absence of buffering, may make things slower).

  This may, however, make the Postscript program considerable smaller.

  This usually doesn't help at all with a color image and -psfilter, because in that case, the Postscript program pnmtops creates has the red, green, and blue values for each pixel together, which means you would see long runs of identical bytes only in the unlikely event that the red, green, and blue values for a bunch of adjacent pixels are all the same. But without -psfilter, the Postscript program has all the red values, then all the green values, then all the blue values, so long runs appear wherever there are long stretches of the same color.

  Here is an explanation by Jef Poskanzer of why he invented the -rle option:

  > I just spent a few hours modifying my pbmtops filter to produce run length encoded PostScript output. The results are not spectacular for me - yes, the files are smaller, but the printing times are about the same. But I'm printing over the network. If you were stuck with the serial line, this would be a big win. I've appended a sample program generated by my filter. If anyone sees ways to improve the code, please let me know, I'm not much of a PostScript hacker. This version of pbmtops will be distributed to comp.sources.misc and expo.lcs.mit.edu sometime in October. - Jef

  This is from a forum about Postscript (http://www.lngpstscrpt.tk/re-postscript-run-length-encoding-again), extracted in October 2010. Jef added -rle in August 1988. In those days, RS-232 lines (referred to as "serial" in the quotation) were typically 9600bps. 2400 bps lines were still around. What the quotation calls "the network" is probably a 10 Mbps Ethernet connection.

-flate
  This option tells pnmtops to use "flate" compression (i.e. compression via the "Z" library -- the same as PNG).

  See the -rle option for information about compression in general.

  You must specify -psfilter if you specify -flate.

  There exist modern versions of pnmtops that cannot do flate compression; these versions were built without the Z library and built not to require the Z library. If you have such a version, it fails with an explanatory error message when you specify -flate.

  This option was new in Netbpm 10.27 (March 2005).

  Before Netpbm 10.32 (February 2006), you could not specify -rle and -flate together.

-ascii85
  By default, pnmtops uses "asciihex" encoding of the image raster. The image raster is a stream of bits, while a Postscript program is text, so there has to be an encoding from bits to text. Asciihex encoding is just the common hexadecimal representation of bits. E.g. 8 1 bits would be encoded as the two characters "FF".

  With the -ascii85 option, pnmtops uses "ascii85" encoding instead. This is an encoding in which 32 bits are encoded into five characters of text. Thus, it produces less text for the same raster than asciihex. But ascii85 is not available in Postscript Level 1, whereas asciihex is.

  This option was new in Netbpm 10.27 (March 2005).

-psfilter
  pnmtops can generate two different kinds of Encapsulated Postscript programs to represent an image. By default, it generates a program that redefines readstring in a custom manner and doesn't rely on any built-in Postscript filters. But with the -psfilter option, pnmtops leaves readstring alone and uses the built-in Postscript filters /ASCII85Decode, /ASCIIHexDecode, /RunLengthDecode, and /FlateDecode.

  This option was new in Netbpm 10.27 (March 2005). Before that, pnmtops always used the custom readstring.

  The custom code can't do flate or ascii85 encoding, so you must use -psfilter if you want those (see -flate, -ascii85).

-level
  This option determines the level (version number) of Postscript that pnmtops uses. By default, pnmtops uses Level 2. Some features of pnmtops are available only in higher Postscript levels, so if you specify too low a level for your image and your options, pnmtops fails. For example, pnmtops cannot do a color image in Level 1.

  This option was new in Netpbm 10.27 (March 2005). Before that, pnmtops always used Level 2.

-dict
  This causes the Postscript program create a separated dictionary for its local variables and remove it from the stack as it exits.

  This option was new in Netbpm 10.27 (March 2005).

-vmreclaim
  This option causes the Postscript program to force a memory garbage collection as it exits.

  This option was new in Netbpm 10.27 (March 2005).

-nocenter
  By default, pnmtops centers the image on the output page. You can cause pnmtops to instead put the image against the lower left corner of the page with the -nocenter option. This is useful for programs which can include PostScript files, but can't cope with pictures which are not positioned in the lower left corner.

  If you want to position an image on the page arbitrarily, use pamcomp to create an image of the full page with the image in question at the proper place and the rest of the page white, and use pnmtops to convert the composed result to Encapsulated Postscript.

  For backward compatibility, pnmtops accepts the option -center, but it has no effect.

-setpage
  This causes pnmtops to include a "setpagedevice" directive in the output. This causes the output to violate specifications of EPSF encapsulated Postscript, but if you're not using it in an encapsulated way, may be what you need. The directive tells the printer/plotter what size paper to use (or cut). The dimensions it specifies on this directive are those selected by the -width and -height options or defaulted.

  From January through May 2002, the default was to include "setpagedevice" and this option did not exist. Before January 2002, there was no way to include "setpagedevice" and neither the -setpage nor -nosetpage option existed.

-nosetpage
  This tells pnmtops not to include a "setpagedevice" directive in the output. This is the default, so the option has no effect.

  See the -setpage option for the history of this option.

-noshowpage
  This tells pnmtops not to include a "showpage" directive in the output. By default, pnmtops includes a "showpage" at the end of the EPSF program. According to EPSF specs, this is OK, and the program that includes the EPSF is supposed to redefine showpage so this doesn't cause undesirable behavior. But it's often easier just not to have the showpage.

  This options was new in Netpbm 10.27 (March 2005). Earlier versions of pnmtops always include the showpage.

-showpage
  This tells pnmtops to include a "showpage" directive at the end of the EPSF output. This is the default, so the option has no effect.

  This option was new in Netpbm 10.27 (March 2005).

-verbose
  This causes informational messages about the conversion process and result.

## LIMITATIONS

If the PNM image has a maxval greater than 255, pnmtops will produce output with 8 bits per sample resolution unless you specify -psfilter, even though Postscript Level 2 has a 12 bits per sample format. pnmtops's custom raster-generating code just doesn't know the 12 bit format.

## APPLICATIONS

You can use the Postscript output a number of ways. Many printers take Postscript input (but you still need some kind of printer driver to transport the Postscript to the printer).

There is also the Ghostscript program (not part of Netpbm), which takes Postscript as input and generates an output stream to control any of myriad models of printer (but you still need some kind of printer driver to transport that stream to the printer).

Ghostscript also can convert the Postscript file to PDF, which is a very popular document and image format. Use Ghostscript's pdfwrite output device type. The program ps2pdf (distributed with Ghostscript) is a convenient way to run Ghostscript with pdfwrite. For more information about converting to and from PDF, see Document/Graphics Software.

## SEE ALSO

bmpp converts from Netpbm and other formats to Encapsulated Postscript. bmpp has a few functions pnmtops does not, such as the ability to use LZW compression.

pnm, gs, psidtopgm, pstopnm, pbmtolps, pbmtoepsi, pbmtopsg3, ppmtopgm,

## HISTORY

Copyright (C) 1989, 1991 by Jef Poskanzer.

Modified November 1993 by Wolfgang Stuerzlinger, wrzl@gup.uni-linz.ac.at

The program was originally pbmtops. It became pgmtops in October 1988 and was merged with ppmtops to form pnmtops in January 1991. ppmtops came into being some time before September 1989.

## Table Of Contents

- SYNOPSIS
- DESCRIPTION
- OPTIONS
- LIMITATIONS
- APPLICATIONS
- SEE ALSO
- HISTORY