[Rd] RFC: Kerning, postscript() and pdf()

Thu Oct 16 17:56:25 CEST 2008

Prof. Ripley,

I am sure I speak for many others when I say Thank You for this and all the other great work that you do.  R is already capable of producing high quality graphics, this will just make them better.  Kerning is one of those things that generally don't get noticed unless done wrong/poorly, so I expect in the future people will look at their graphs and know that they look great, but not understand why, or the work that you put into giving them that extra quality.  So I just wanted to take this chance to say thank you (I/we probably don't say it enough).

Also Thank You to the rest of R core for all the great work.

R: Come for the price, Stay for the Quality

--
Gregory (Greg) L. Snow Ph.D.
Statistical Data Center
Intermountain Healthcare
greg.snow at imail.org
801.408.8111

> -----Original Message-----
> From: r-devel-bounces at r-project.org [mailto:r-devel-bounces at r-
> project.org] On Behalf Of Prof Brian Ripley
> Sent: Thursday, October 16, 2008 3:03 AM
> To: R-devel at r-project.org
> Subject: Re: [Rd] RFC: Kerning, postscript() and pdf()
>
> I've now implemented B and C in R-devel, with C as the default.
>
> On Sun, 12 Oct 2008, Prof Brian Ripley wrote:
>
> > Ei-ji Nakama has pointed out (from another Japanese user, I believe)
> that
> > postscript() and pdf() have not been handling kerning correctly, and
> this is
> > a request for opinions about how we should correct it.
> >
> > Kerning is the adjustment of the spacing between letters from their
> natural
> > width, so that for example 'Yo' is usually typeset with the o closer
> to the Y
> > than 'Yl' would be.  Kerning is not very well standardized, so that
> for
> > example R's default Helvetica and its URW clone (Nimbus Sans) have
> quite
> > different ideas of the amount of kerning corrections for 'Yo'. This
> matters,
> > because not many people actually see Helvetica when viewing R's
> PostScript or
> > PDF output, but rather a similar face like Nimbus Sans or Arial, or
> in the
> > case of Acrobat Reader, a not very similar face.  Kerning is only a
> feature
> > of some proportionally spaced fonts and so not of Courier nor CJK
> fonts.
> >
> > The current position (R <= 2.8.0) is that string widths have been
> computing
> > using kerning from the Adobe Font Metric files for the nominal font,
> but the
> > strings have been displayed without using kerning (at least in the
> viewers we
> > are aware of, and the PostScript and PDF reference manuals mandate
> that
> > behaviour, if rather obscurely).  This means that in strings such as
> 'You',
> > the width used in the string placement differs from that actually
> displayed.
> >
> > For postscript(), this doesn't have much impact, as centring or right
> > justification ('hadj' in text()) is done by PostScript code and
> computes the
> > width from the actual font used (and so copes well with font
> substitution).
> > It might affect the fine layout in plotmath, but using strings which
> would be
> > kerned in annotations is not common.
> >
> > For pdf() the effect is more commonly seen, as all text is set
> > left-justified, and the computed width is used to centre/right-
> justify.
> >
> > There are several things we could do:
> >
> > A.  Do nothing, for back compatibility.  After all, this has been
> going on
> > for years and no one has complained until last month.
> >
> > B.  Ignore kerning, and hence change the string width computations to
> match
> > the current display.  This is more attractive than it appears at
> first sight
> > -- as far as I know all other devices ignore kerning, and we are
> increasingly
> > used to seeing 'typeset' output without kerning.  It would be
> desirable when
> > copying graphs by e.g. dev.copy2eps from devices that do not kern.
> >
> > C.  Insert kerning corrections by splitting up strings, so e.g. 'You'
> is set
> > as (Y)-140 kc(ou): this is what TeX engines do.
> >
> > D.  Compute the position of each letter in the string and place them
> > individually.
> >
> > C and D would give visually identical output when the font used is
> exactly as
> > specified, and hopefully also when a substitute font is using with
> the same
> > glyph widths (as substituting Nimbus Sans for Helvetica, at least for
> some
> > versions of each), but where the substitute is a poor match, C ought
> to look
> > more elegant but line up less well.  D would produce much larger
> files than
> > C.
> >
> > We do have the option of not changing the output when there is no
> kerning.
> > That would be by far the most common case except that some fonts
> (including
> > Helvetica but not Nimbus Sans) kern between punctuation and a space,
> e.g. ',
> > '.  I'm inclined to believe that most uses of ',' in R graphical
> output are
> > not punctuation (certainly true of R's own examples), and also that
> we
> > nowadays do not expect to see kerning involving spaces.
> >
> > Ei-ji Nakama provided an implementation of C for pdf() and D for
> postscript()
> > (thanks Ei-ji, and apologies that we did not have a chance to discuss
> the
> > principles first).  I'm inclined to suggest that we should go
> forwards with
> > at most two of these alternatives, and those two should be the same
> for
> > postscript() and pdf() -- my own inclination is to B and C.
> >
> > So questions:
> >
> > 1) Do people feel strongly that we should preserve graphical output
> from past
> > versions of R, even when there are known bugs?  I can see the need to
> > reproduce published figures, but normally this would also need using
> the same
> > version of R.
> >
> > 2) Is kerning worth pursuing?
> >
> > 3) If so, is elegant looking output more important than exact layout?
> >
> > 4) If we allow kerning, should it be the default (or only) option?
> >
> > To see that sometimes there can be a large effect, try in
> postscript() or
> > pdf()
> >
> > xx <- 'You You You You You You You You'
> > plot(0,0,xlim=c(0,1),ylim=c(0,1),type='n')
> > abline(v=0)
> > text(0, 0.5, xx, adj=0)
> > abline(v=strwidth(xx))
> > x2 <- strsplit(xx, "")
> > w <- sapply(x2, strwidth)
> > abline(v=sum(w))
> >
> > The leftmost of the right pair of lines is the computed width, the
> rightmost
> > the (normal) displayed width.
> >
> > Unless there are cogent reasons to bring this forward to 2.8.1, any
> changes
> > would be as from 2.9.0.
> >
> > Brian Ripley
> >
> > --
> > Brian D. Ripley,                  ripley at stats.ox.ac.uk
> > Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
> > University of Oxford,             Tel:  +44 1865 272861 (self)
> > 1 South Parks Road,                     +44 1865 272866 (PA)
> > Oxford OX1 3TG, UK                Fax:  +44 1865 272595
> >
>
> --
> Brian D. Ripley,                  ripley at stats.ox.ac.uk
> Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
> University of Oxford,             Tel:  +44 1865 272861 (self)
> 1 South Parks Road,                     +44 1865 272866 (PA)
> Oxford OX1 3TG, UK                Fax:  +44 1865 272595
>
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