ps2pdf: PostScript-to-PDF converter

`ps2pdf`: PostScript-to-PDF converter

## Table of contents

> - Overview
> - Usage
> - Options
> - Limitations
> - Known problems
> - Benefits of using `ps2pdf`
> - Acknowledgments

For other information, see the Ghostscript overview.

# Overview

`ps2pdf` is a work-alike for nearly all the functionality (but not the user interface) of Adobe's AcrobatTM DistillerTM product: it converts PostScript files to Portable Document Format (PDF) files.

`ps2pdf` is implemented as a very small command script (batch file) that invokes Ghostscript, selecting a special "output device" called `pdfwrite`. In order to use `ps2pdf`, the `pdfwrite` device must be included in the makefile when Ghostscript was compiled; see the documentation on building Ghostscript for details: this is currently the case on all platforms, in Ghostscript as we distribute it.

# Usage

The usage for `ps2pdf` is

> `ps2pdf` [options] input.ps output.pdf

or, on Unix systems and some versions of Windows NT and OS/2

> `ps2pdf` input.ps

which is equivalent to

> `ps2pdf` input.ps input.pdf

There are actually three different `ps2pdf`* scripts: the name `ps2pdf` above refers to any of them.

- `ps2pdf12` will always produce PDF 1.2 output (Acrobat 3-and-later compatible).
- `ps2pdf13` will always produce PDF 1.3 output (Acrobat 4-and-later compatible).
- `ps2pdf` per se currently produces PDF 1.2 output (Acrobat 3-and-later compatible). However, this may change in the future. If you care about the compatibility level of the output, use `ps2pdf12` or `ps2pdf13`, or use the `-dCompatibility=`1.x switch in the command line.

All of these scripts actually call a script named `ps2pdfwr`. Normally, you will not need to do anything with this script. The Unix `ps2pdfwr` script assumes that the Ghostscript executable is named `gs`; the DOS and MS Windows `ps2pdfwr.bat` script assumes the executable is named `gswin32c`. On DOS or MS Windows, if the executable has a different name, you must edit the `ps2pdfwr.bat` script file: look for the line that says

> `set PS2PDFGS=gswin32c`

and change it to

> `set PS2PDFGS=`executable_name

# Options

The options in the command line may include any switches that may be used with Ghostscript's PostScript and PDF interpreter (see here for a complete list), although almost none of them are useful with `ps2pdf`. More importantly, options may include `-d`parameter=value or `-s`parameter=string switches for setting "distiller parameters", Adobe's documented parameters for controlling the conversion process. The PostScript `setdistillerparams` and `currentdistillerparams` operators are also recognized when running `ps2pdf`, and provide an equivalent way to set these parameters from within the PostScript input file.

`ps2pdf` recognizes all of the Acrobat Distiller 3 parameters documented in Adobe Technical Note #5151 except for the `ImageDict` parameters, but only a subset have an effect:

> Parameter name |  | Initial value |  | Notes
> `ASCII85EncodePages` |  | false
> `AlwaysEmbed` |  | []
> `AutoFilterColorImages` |  | true |  | 1
> `AutoFilterGrayImages` |  | true |  | 1
> `ColorImageDepth` |  | -1
> `ColorImageDownsampleType` |  | /Subsample |  | 3
> `ColorImageResolution` |  | 72
> `CompatibilityLevel` |  | 1.3
> `CompressPages` |  | true
> `ConvertCMYKImagesToRGB` |  | true
> `CoreDistVersion` |  | 3000
> `DownsampleColorImages` |  | false
> `DownsampleGrayImages` |  | false
> `DownsampleMonoImages` |  | false
> `EmbedAllFonts` |  | true
> `EncodeColorImages` |  | true
> `EncodeGrayImages` |  | true
> `EncodeMonoImages` |  | true
> `GrayImageDepth` |  | -1
> `GrayImageDownsampleType` |  | /Subsample |  | 3
> `GrayImageResolution` |  | 72
> `LZWEncodePages` |  | false |  | 2
> `MaxSubsetPct` |  | 35
> `MonoImageDepth` |  | -1
> `MonoImageDict` |  | << >>
> `MonoImageDownsampleType` |  | /Subsample
> `MonoImageFilter` |  | /CCITTFaxEncode
> `MonoImageResolution` |  | 300
> `NeverEmbed` |  | []
> `SubsetFonts` |  | true
> `UseFlateCompression` |  | true

(note 1) `AutoFilterxxxImages` doesn't examine the image to decide between JPEG and `LZW/Flate` compression: it always uses `LZW/Flate` compression.

(note 2) Because of Unisys's threats regarding the Welch patent, `ps2pdf` cannot actually use LZW compression: instead, it treats all requests for LZW compression as calling for `Flate` compression if `UseFlateCompression` is true and `CompatibilityLevel` >= 1.2, and ignores them otherwise.

(note 3) The `xxxDownsampleType` parameters can also have the value /Bicubic (a Distiller 4 feature), which is currently treated as equivalent to /Average.

The remaining Distiller 3 parameters are defined and can be set and queried, but do not have any effect:

> Parameter name |  | Initial value
> `AntiAliasColorImages` |  | false
> `AntiAliasGrayImages` |  | false
> `AntiAliasMonoImages` |  | false
> `AutoRotatePages` |  | /None
> `ColorACSImageDict` |  | << >>
> `ColorConversionStrategy` |  | /LeaveColorUnchanged
> `ColorImageDict` |  | << >>
> `ConvertImagesToIndexed` |  | false
> `GrayACSImageDict` |  | << >>
> `GrayImageDict` |  | << >>
> `ImageMemory` |  | 250000
> `PreserveHalftoneInfo` |  | false
> `PreserveOPIComments` |  | false
> `PreserveOverprintSettings` |  | false
> `TransferFunctionInfo` |  | /Apply
> `UCRandBGInfo` |  | /Remove

`ps2pdf` does not implement the Acrobat Distiller 4 parameters. Settings for these parameters will be ignored, except that setting the `EndPage` parameter will cause an error.

# Limitations

In some situations, `ps2pdf` will convert text to high-resolution bitmapped fonts rather than to embedded outline fonts. Currently, this will always occur when the PostScript file uses CID-keyed or double-byte fonts, or in some cases if it uses fonts with non-standard encodings; it may occur in other cases as well.

The PDF output always represents the colors of text and graphics in DeviceGray or DeviceRGB color space; all other color spaces are converted to these. However, for images, it will retain the original color space for DeviceGray, DeviceRGB, DeviceCMYK, certain CIEBased spaces, and Indexed spaces based on these.

`ps2pdf` will sometimes convert PostScript constructs to lower-level ones, even if a higher-level construct is available. For example, if the PostScript file uses `charpath` to set a clipping path consisting of text, `ps2pdf` will write the clipping path as a path in the PDF file, rather than as text, even though PDF is able to express clipping with text. This is only a performance issue, and will be improved incrementally over time.

`ps2pdf` ignores the PDF 1.3 (Acrobat 4.x) pdfmarks related to document content structure: `StRoleMap`, `StClassMap`, `StPNE`, `StBookmarkRoot`, `StPush`, `StPop`, `StPopAll`, `StBMC`, `StBDC`, `EMC`, `StOBJ`, `StAttr`, `StStore`, `StRetrieve`, `NamespacePush`, `NamespacePop`, and `NI`. While this causes some structural information to be omitted from the output file, the displayed and printed output are normally not affected.

# Known problems

Distiller parameters should only be saved by `save` and restored by `restore`, but they are also saved `gsave` and restored by `grestore`.

Changing the value of the `CompressPages` parameter after any marks have been made on the page may cause a crash.

Setting a value for the `ColorACSImageDict`, `ColorImageDict`, `GrayACSImageDict`, or `GrayImageDict` parameter will probably cause a crash.

# Benefits of using `ps2pdf`

According to users, the greatest benefit of `ps2pdf` is that it is more robust than Acrobat Distiller: it will process complex and difficult PostScript files that Acrobat Distiller is not able to handle.

For certain documents, `ps2pdf` is much faster than Adobe Distiller, and may be suitable for run-time conversions. George White, a heavy user of `ps2pdf`, remarks:

> I haven't seen a head to head comparison, but Distiller seems slower when running on what should be a faster system (for instance, Distiller on a PPC Mac vs a 25 MHz 68040 NeXT running `ps2pdf`), so I think this is fair -- also, one of Mark Doyle's postings indicated that Distiller was not fast enough for use as a run-time server. In contrast, I find that I can use `ps2pdf` as a post-processor during routine document creation.

On the other hand, there are some documents for which `ps2pdf` may be much slower than Acrobat Distiller. Caveat user.

Many users report that the combination of `ps2pdf` with Acrobat is superior to using a generic PostScript viewer (`psview` or `ghostview`), particularly for documents with many pages where the navigational support in PDF files reduces the overhead involved in navigating conventional PostScript documents.

# Acknowledgments

Thanks to George N. White III <aa056@chebucto.ns.ca> of the Ocean Sciences Division of the Bedford Institute of Oceanography in Dartmouth, Nova Scotia for extensive testing of early versions of `ps2pdf`, and for contributing most of this writeup.

Thanks to Martin Hosken of SIL International <http://www.sil.org> for help with testing `ps2pdf` with a wide variety of international fonts.

Copyright © 1996, 2000 Aladdin Enterprises. All rights reserved.

This file is part of Aladdin Ghostscript. See the Aladdin Free Public License (the "License") for full details of the terms of using, copying, modifying, and redistributing Aladdin Ghostscript.

Ghostscript version 6.0, 3 February 2000