Why do people still use Postscript?

Question

I submitted a journal paper this morning, and they asked me to include a PDF file, which I expected, and a Postscript (PS) file.

Generating the PS file proved more difficult, because some of my LaTeX commands, which I always compiled with pdflatex, wouldn't compile with latex (in particular including graphics).

I ended up converting the PDF into a PS file, but obtained a file 4 times the size (approx 20 MB instead of 5 MB).

It also seems that opening a Postscript file with any modern reader takes longer, as it has to 'convert' (compile maybe? or interpret?) the file.

I was wondering -- what's the use of Postscript today? Are there advantages over the more modern and widely used PDF?

Answer 1

Postscript is still used as an intermediate document format, since it is a fully fledged programming language allowing you to compute graphics, which PDF doesn't. PDF shows just the result (after some conversions, sometimes called "Distillation") of the computation Postscript is able to do.

The Postscript based PSTricks package is an example that heavily makes use of graphical computation. It can even solve differential equations. And if you have a Postscript printer, it can do these computations for you.

EDIT, to answer Daniels comment:

One feature that makes Postscript the preferred format, in particular for a publisher, is its editability. If, for instance, line art in a document is too faint, the publisher may want to enhance it a bit globally before giving the document to press. This very issue was raised, e. g., in this question.

With Postscript, doubling the line width in the whole document is easily accomplished by putting

userdict /setlinewidth {2 mul systemdict /setlinewidth get exec} put

into the document header.

With PDF such a tweak is much more complicated.

Answer 2

From a publishers perspective, I think, the only fundamental reason is legacy software. Postscript has been a long-lasting and broadly accepted standard. Updating the existing tool chains to PDF would require a massive investment.

So I think, it is all about history. There is a great Q&A that discusses the fundamental differences between Postscript (PS) and PDF from a technical perspective: Fundamental differences : PSTricks, TikZ/PGF and others, but misses a bit on the (historical) significance of these technical differences:

Basically, the technical differences are:

• PS is a (Turing-)complete language that permits to defer arbitrary computations to rendering time, that is, when the PS file is used (i.e., printed).
• In PDF, all calculations have be completed when the PDF file is produced.

At its time, the PS model had some clear advantages:

• In the 80s a decent workstation (VAX-11) was able to compute 1.5 million instructions per second (MIPS) and was equipped with maybe 1 MiB of RAM.

• Rendering a complete A4 page at 150x150 dpi resolution on such a system was already challenging. Going higher (300x300 or 600x600 dpi) was basically impossible.

• However, even at that time, a laser printer was able to print a page with 200x200 dpi or more.

• Industrial printing machines used by publishers were already able to cope with much higher resolutions.

By delegating the computational intensive part to use-time, that is, the printing device, PS provided portability between all these devices and made it possible to prepare high-quality documents even on affordable computers. Instead of equipping every workstation with enough RAM and CPU power to render pages at 200x200 dpi (not to speak about the disk sizes and network throughput one needs to store and transfer the resulting documents), it was enough to have one $10,000 laser printer to do the job for the complete department. If the book got professionally published, the $10,000,000 industrial printer could process the same PS document to render it at 1200x1200 dpi.

20 year later, the CPU power and available amount of RAM is 4,000 times higher. Printers featuring a PS raster image processor (RIP), however, are still relatively expensive:

• Already in the 90s, "software-RIPs" (e.g., ghostscript) became popular. Ghostscript does all rendering on your computer and thereby makes it possible to print PS documents even on an affordable printer that does not feature a hardware RIP.

• By the year 2000, the ordinary PC and network throughput has become so powerful that "software-RIPing" before printing is typically a lot faster than using the printer's built-in RIP – especially when printing complex PS documents.

• In the same decade, PDF became popular, so also the importance of PS as the broadly supported standard for printer documents declines.

Answer 3

As you've already experienced, there's a tendency for modest-sized ps files to blow up to enormous pdf files. This is because postscript, being a general programming language, has enormous potential for algorithmic compression.

For a simple example, consider a sheet of 5mm graph paper. A pdf would contain the end-points for every line. In postscript, however, this could be accomplished with 2 loops.

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Converting backwards, from pdf back to ps, is not capable in general of making use of algorithmic compression. The pdf would have to be analyzed by some really smart AI/expert. The normal conversion is just to represent the same pdf structures with postscript, which tends to be more verbose. Eg. a 32-bit binary integer will take 4 bytes in a pdf, but it will take 1..14 bytes in a (ascii) text representation.

Answer 4

There is also a Latex-specific historical reason why some publishers still request PS versions of documents. This is relevant primarily in cases in which the publisher just takes an author-prepared document and prints it (or puts it online); for example, many conference proceedings in computer science are produced this way.

Previously, the typical toolchain for Latex users involved EPS figures for vector graphics, latex, dvips, and ps2pdf. With this kind of toolchain it was easy to produce broken PDF files that did not properly embed all fonts that they used. Fixing this was a bit painful if you just have the broken PDF file, but it is usually fairly easy with standard tools if you have the original PS file. Hence publishers asked for the PS version so that they can re-do the PS-to-PDF conversion for the authors.

Nowadays everyone uses PDF figures for vector graphs and pdflatex to compile their Latex files. This way anyone can easily produce valid PDF files with all fonts correctly embedded.

Publishers are a bit slow to learn that the world has changed, and they are a bit slow to update their tools. For example, I am aware of a publisher that has a web system that requires that you submit a PS file along with the PDF file, but they do not really need those PS files anymore, so they nowadays recommend that the authors just submit some dummy PS file and name it so that the publisher knows that it should be ignored...

Answer 5

One reason I recently learned about is that you can generate a printer-specific PS file (e.g. by using your PDF reader's print to file feature), which already contains all the printer settings you chose, which is very helpful for complex print jobs (e.g. containing different but same-size paper media) that need to be printed again every now and then.

Answer 6

In my world they are two sides of the same coin. PDF is a display format. Postscript is a printer control language. Both were created by Adobe but for slightly different jobs. PDF is difficult to program against for sorting or adding objects (yes I know you can do it in Acrobat, etc. - try sorting or adding dynamic text to 250,000 pages and let me know how long it takes!) PDF does not have tray logic - all pages must be printed on the same paper stock, not so with Postscript. If there is any chance that the original data might end up in a book/collection where the printer might have to pull glossy paper stock for images, or card stock for covers - can't use PDF. Also depending on the printer - for almost any printer - all it can really print is either Postscript or PCL. Anything else requires your computer it "translate/convert" which adds another layer of what can possibly go wrong? So I think the question really is what the end user envisions they will have to do with the data - and that they don't want to be responsible for the conversion.

Answer 7

I simply use ps for creating my graphics and embed these in plain TeX, which is processed by pdfTeX. Advantage: portability and full generality of the graphics. PStricks uses ps under the hood, and is in LaTeX, and because of that is restricted by the inheritance of LaTeXs picture environment. The big advantage is that you don't have to be aware of ps. No experience with PStricks on the issue. Disadvantage: In PStricks for example not all orientations of straight lines are possible. Advantage: a wealth of PStricks examples are available. I have created a library of ps pictures, which is called PSlib and made avaible on NTGs WWW. An article on the matter has appeared in GUST bulletin and has been submitted to MAPS. My work is similar to the work of Don Lancaster. The files I submit are the ps pictures and the plain TeX source code. I process it by pdfTeX. MAPs editors convert my plain TeX material into CONTeXt and that has proven to work fine. I suppose that GUST works along similar lines. I have no experience in how to submit to a general publisher. Kees van der Laan

Answer 8

So, PDF and PostScript are targeted to different needs. If you want to VIEW a document you use PDF. IF you want to print a document, especially in a large batch print facility, you use PostScript.

Answer 9

I avoid using pdf, if pdf is all I can find then I first convert it with ghostscript. PDF has plenty of security and privacy issues. Most PDF viewers have zero focus on privacy, postscript files don't have nearly as many "features"(i.e. underhanded attack vectors), and postscript viewers, the ones I have used at least, restrict access to the filesystem. However, I wouldn't trust printers to not be vulnerable to filesystem access from postscript files. In circumstances requiring privacy the use of PDF as opposed to PostScript should be considered a hostile act.

Answer 10

Postscript is still important for people who need to create documents programmatically. Imagine you need to create a nice printable document based on an input from a user. Since you do not know what the input would be like, your document cannot be created beforehand. It has to be created on the fly.

LaTeX is well designed for this kind of task but, unless your application is web based, you need to have LaTeX installed on the user's machine, which is not always feasible. On the other hand, PostScript viewers are ubiquitous and free, e.g. Adobe Acrobat, so having your application create PostScript files,rather than LaTeX is an advantage.

Answer 11

The practical reason why they ask for postscript is because they want the highest possible quality source file. When you convert to PDF it does things like scale/compress images, substantiate formula based drawing to fixed coords and so on. It is possible to use better quality settings than the defaults when generating a PDF, but people tend not to.

No matter what interprets the code the values become baked in at the point it is run. ie. as it is converted to PDF.

So outputting a PDF and then converting back to a PS is really missing the point. The quality is already lost. Just as if a photographer wanted a RAW to keep extra photo info, you can't take a JPEG and convert it back to one.

(Printer toolchains have been able to easily convert between PS and PDF for over a decade, it isn't a legacy issue)

• The advantage of using PS is that the printed result will be closer to what was originally intended.
• The advantage of using PDF is that the printed result is repeatably what is baked into the PDF.

Since I worked on the code that does the conversion I thought I would be helpful. But it is clear that new people are not welcome here and that plausible but incorrect guesswork is favoured over fact. Daniel's answer has a lot of correct technical details but then jumps to the wrong conclusion. Postscript is not some out of date thing that is being left behind, it is THE format that printers use and that whatever you send will be converted to at some point.

Answer 12

with pdf and post script if we install the resources on the printer, then we can reduce the file size and get good quality of printing. for archiving purpose in pdf we need to embed the resources in the file and provide security to that with rc4 128 bit encryption using sha hash algorithms

Answer 13

PDF format is for rasterizing and viewing of a document. PostScript is for printing the document. PDF is not a programming language. It is a display language. Postscript is a complete programming language. For example, with PostScript you can add code that will generate a diagram or chart or graphic on the fly or even an entire form. With PDF you would need a Human to create the charts or graphics using a software program and then insert it into a PDF. But if you were generating statements for a million customers you don't have the time to generate a million different charts. In PostScript you can just add code that generates the graphic on the fly on the printer based on data from another system or based on data in the PS file. Incredibly powerful!