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

[Micah J. Cowan]

On Sun, Aug 22, 2004 at 10:01:23AM -0400, Peter Jay Salzman wrote:
> I download a lot of scientific papers off the web.  They almost always come
> in two formats: postscript (ps) and portable document format (pdf).
> 
> 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?
> 
> And why does the quality of ps vary so much?

Quality of the viewer may play a part. In general, I've noticed that
Acrobat Reader nearly always produces better renderings than ghostscript or
xpdf.

I've frequently seen the reverse of what you mention though: that the
pdf looks orders of magnitude uglier. This is usually because acroread
doesn't handle bitmaps or Type 3 fonts very gracefully. However,
in the case of documents produced from TeX, I think sometimes a
converter to post-script may use the Type 3 fonts, where a converter
to PDF may convert them to Type 1. This might produce the effects
you're noticing...?

1960ish on.... for the most part, these were probably roff/troff/nroff
docs? Usually the PS looks fine to me from these... the PDF
conversion often looks better (simply due to a better renderer), but I
wouldn't say "orders of magnitude."

You have some links?

-- 
Micah J. Cowan
micah at cowan.name