[tex-live] Bug#773668: okular shows "jumping" letters in pdf documents generated using pdflatex with russian babel

Werner LEMBERG wl at gnu.org
Fri Dec 26 05:52:42 CET 2014

>     Unfortunately, FreeType's weakest point is the hinting of Type1
>     fonts.  While CFF fonts are handled extremely well due to the
>     new engine contributed by Adobe,
> Well, given your statements, I feel the need to report having the
> exact opposite experience, when it comes to Computer Modern and
> similar.  Not that I expect you to magically solve it, but FYI ...

Well, there is no need for `magic': FreeType always have had an API
function to adjust the darkening threshold values (or even switching
off stem darkening completely), and since the last FreeType version it
is even possible to adjust those values at compile time.

> The xpdf viewer uses the freetype rasterization engine, and when
> Derek (Noonburg, the author/maintainer of xpdf, as I expect you
> know) started using the new Adobe engine in version 3.04, the result
> is that CM fonts are rasterized much darker, to the point of nearly
> appearing to be bold fonts.  (I looked around in my sources to see
> if that was in fact happening before I realized where the problem
> was.)

Stem darkening issues were discussed on the FreeType mailing list (and
Derk reads that list AFAIK).  So he should be aware how to fix or
ameliorate the problem.  I guess that the next xpdf version provides
better results.

> In other mail, Derek showed me examples of CJK output where the new
> rasterizer unquestionably does a much better job.  But not CM.  (He
> also mentioned that he might be able to do gamma corrections at the
> xpdf level to improve stuff, but probably not get back to the
> original rendering.)

Yep.  Essentially, it is *not* FreeType's fault that the results are
suddenly much darker.  It's a general problem of the rendering stack,
especially with X11, where blitting is done in the wrong color space,
thus extremely exaggerating the effects of stem darkening.

If you try Acroread (which basically uses the same CFF engine as
FreeType does – and certainly *with* stem darkening), both your test
files render just fine.


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