Content-type: text/html Manpage of JPEG2PS

JPEG2PS

Section:  (1)
Updated: 1999-07-14
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NAME

jpeg2ps - convert JPEG compressed images to PostScript Level 2

 

SYNOPSIS

jpeg2ps [options] file.jpg > file.eps

 

DESCRIPTION

jpeg2ps converts JPEG files to PostScript level 2 EPS. In fact, jpeg2ps is not really a converter but a "wrapper": it reads the image parameters (width, height, number of color components) in a JPEG file, writes the according EPS header and then copies the compressed JPEG data to the output file. Decompression is done by the PostScript interpreter (only PostScript Level 2 and 3 interpreters support JPEG compression and decompression). If you have a slow communication channel and a fast printer, sending compressed image data is a big win.

 

OPTIONS

-a
auto rotate feature
-b
binary mode
-h
hex mode (ASCIIHex encoding)
-o name
output file name
-r dpi
resolution value (0 = read from file if possible)

 

DESCRIPTION (LONG)

jpeg2ps reads a JPEG file (*not* stdin) and writes a DSC-compliant EPS file containing the compressed JPEG data in PostScript format to stdout. The produced EPS files contain the necessary DSC comments including BoundingBox, so they may be imported in page layout applications. However, they do not contain preview images, so you will only see a gray box on screen.

If the auto rotate feature is activated with the -a option, images with width > height are automatically rotated to landscape mode. Don't use this option if you simply want to generate EPS files for inclusion in your documents. Note: prior to version 1.6, jpeg2ps always "autorotated" images with width > height which was especially bad for TeX users. I hope this change helps the TeX community in better using jpeg2ps!

jpeg2ps performs some sanity checks with the JPEG data. It detects several kinds of corrupt input data, but it is not absolutely foolproof. One special feature is that you can feed Macintosh JPEG files (PICT-JPEG) to jpeg2ps. These normally have several hundred bytes of additional stuff before the JPEG data. This PICT rubbish is simply ignored by jpeg2ps.

 

Output modes

By default, jpeg2ps sends the image data in ASCII85 encoded form which is suitable for any communication channel (serial, parallel or whatever). If you are *sure* that your channel is truly 8-bit clean, you can force 8-bit data with the -b option. Note that this normally does not apply to 8-bit serial or even parallel channels since some control characters are reserved for the communications protocol. You can use binary data e.g.:

-
with some networked printers
-
with direct-access PostScript interpreters, e.g. Ghostscript
-
serial or parallel channels using Binary Control Protocol (BCP).

Using the -h option, jpeg2ps generates 7-bit clean data by using ASCIIHex encoding instead of the more space-efficient ASCII85 encoding.

 

Scaling and resolution

Concerning the size of the printed image, you have three options:

Default behaviour:
By default, jpeg2ps tries to fit the image on the page, rotating it if necessary (image width exceeds image height) when the -a option was supplied on the command line. The image is scaled in a way to use at least one full edge of the paper. A 20 pt margin is subtracted on each side. "Page" means A4 size if compiled with "-DA4", letter size otherwise.
Using resolution value from the file:
The option "-r 0" instructs jpeg2ps to look for a JFIF density/resolution marker and use that value. Automatic scaling and rotation are disabled. However, if no resolution information is found in the file, jpeg2ps applies the default algorithm described above.
Explicitly setting the resolution:
Using "-r <dpi>" you can force jpeg2ps to use a certain dpi value. Since automatic actions are also disabled in this case, you are responsible for choosing a reasonable resolution value. For example, you can print a 300 dpi image half-sized by supplying -r 600.

 

Messages

jpeg2ps issues three kinds of messages:

Notes:
have informational character
Warnings:
a potential problem with the file was recognized, processing continues.
Errors:
Either a severe problem within the JPEG file was found or the file explores JPEG features not compatible with PostScript Level 2.

Note that there are some JPEG producers which do not exactly conform to the specification and that the JPEG spec itself does not cover every aspect of the file format. You are on the safe side if you demand JFIF files which are happily accepted by jpeg2ps. (For further information see the JPEG FAQ by Tom Lane.)

 

Adobe Photoshop CMYK files

This is what the Independent JPEG Group has to say about Photoshop CMYK files (quoted from libjpeg.doc, part of the IJG JPEG library):

CAUTION: it appears that Adobe Photoshop writes inverted data in CMYK JPEG files: 0 represents 100% ink coverage, rather than 0% ink as you'd expect. This is arguably a bug in Photoshop, but if you need to work with Photoshop CMYK files, you will have to deal with it in your application. We cannot "fix" this in the library by inverting the data during the CMYK<=>YCCK transform, because that would break other applications, notably Ghostscript. Photoshop versions prior to 3.0 write EPS files containing JPEG-encoded CMYK data in the same inverted-YCCK representation used in bare JPEG files, but the surrounding PostScript code performs an inversion using the PS image operator. I am told that Photoshop 3.0 will write uninverted YCCK in EPS/JPEG files, and will omit the PS-level inversion. (But the data polarity used in bare JPEG files will not change in 3.0.) In either case, the JPEG library must not invert the data itself, or else Ghostscript would read these EPS files incorrectly.

Accordingly, jpeg2ps tries to detect such files (by looking for Adobes APP marker) and inverts the colors in the case of 4-component images. This inversion takes place in the PostScript setup instructions, not by changing the image data.

 

Further Information

If you like to know more about the inner workings of jpeg2ps, the JPEG standard and its integration in PostScript Level 2, the JFIF file format, JPEG/TIFF *and* if you can read German, you may want to check out my article in a German computer magazine:

"Gut verpackt - Drucken von JPEG-Bildern mit PostScript Level 2" c't, Magazin fuer Computertechnik, Heise Verlag Hannover, 6/94, p.236 ff.

This article is also available in PDF format from my WWW page: http://www.pdflib.com/jpeg2ps/

Note that there is a related PostScript programm called "viewjpeg.ps" which is part of the Ghostscript distribution. viewjpeg.ps operates similarly to jpeg2ps, but the PostScript interpreter does the "wrapping" of JPEG data itself. With viewjpeg.ps you can e.g. view JPEG files directly within GhostScript or another interpreter with access to the file system.

 

AUTHOR

Copyright (C) 1994-99 Thomas Merz (tm@muc.de)

jpeg2ps is available from http://www.pdflib.com/jpeg2ps/ and many other sites, notably CTAN mirrors.

Manual page by Andreas Hirczy <ahi@itp.tu-graz.ac.at>, based on the file "jpeg2ps.txt" from the original sources, version 1.5

 

Disclaimer

This software is free. You are granted the right to use and copy it. This software may not be sold or bundled with any commercial package without express written permission of the author.

The author accepts no responsibility for damages resulting from the use of this software and makes no warranty, either express or implied, including but not limited to, any implied warranty of merchantability or fitness for a particular purpose. This software is provided as is, and you assume all risks when using it.


 

Index

NAME
SYNOPSIS
DESCRIPTION
OPTIONS
DESCRIPTION (LONG)
Output modes
Scaling and resolution
Messages
Adobe Photoshop CMYK files
Further Information
AUTHOR
Disclaimer

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Time: 20:04:05 GMT, May 04, 2000