[vox-tech] ps versus pdf - fonts and quality

[Henry House]

På söndag, 22 augusti 2004, skrev Peter Jay Salzman:
[...]
> I've noticed that, consistently, pdf looks better than ps on the screen.
> 
> Actually, pdf tends to look ORDERS OF MAGNITUDE better than ps for really old 
> scientific papers that I download off the journal's archive.  The two formats
> print at the same quality, but the screen quality of pdf for these old
> documents (1960ish - 1995ish) is truly orders of magnitude better than ps.
> 
> For recent documents, say documents that I download off http://xxx.lanl.gov,
> the screen quality is about equal (although I still think that pdf is
> somewhat better than ps, but I can't be sure).  Print quality is about equal.
> 
> What's going on here?  Why do these older ps documents look awful on screen
> but print at the same quality as pdf?

This probably is related to the type of fonts used (type 1, type 3,
truetype, or something else), how well-hinted they are, and how smart the
PDF-creation software was. But this is just speculation.

Very old documents may be scanned bitmaps, not text at all.

> And why does the quality of ps vary so much?

Postscript is a turing-complete programming environment, supporting a
multitude of different ways to construct shapes and text.  Is was intended
as the foundation of a operating system for a printer. Many programs
generate postscript code that is broken or weird in some way. PDF is a
more-compact format optimized for displaying graphics. I hope that
explanation helps a little.

Would you care to provide any specific examples of documents that motivated
your question?

-- 
Henry House
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