Re: Sample inkjet printouts

[Berthold Horn <bkph@ai.mit.edu>]

At 00:53 1999-04-01 +0100, Rebecca and Rowland wrote:

>It's easier to read to my eye, and looks more like the definitive versions
>printed in Knuth's book.  You're quite right about the evenness of the
>grey, but what's that got to do with anything?  I'm comparing the printouts
>not with a subjective aesthetic standard, but with a definitive printed
>standard in Knuth's books.

Well, since Knuth use the MetaFont version it is a priori clear which one 
will pass your test :-).

>> It would be nice then to use e.g.
>> cmr10 at 10pt rather than cmr12 at 12pt, since the latter introduces
>> a confounding difference in round-off that has little to do with
>> "quality" (see below).  The obvious difference in x-height rounding
>> in CMR12 at 300dpi obscures any other differences there might be.
>
>But this is *exactly* the sort of quality point I've been talking about!

But who is to say which is a better representation of the underlying 
continuous glyph shape?  The one rounds down, the other rounds up.  
The one looks compact and squashed compared to the same font at other
pix-per-em, while the other looks open and expanded  compared to the 
same font at  other pix-per-em.

>Of *course* you'd expect ATM and Metafont to produce similar results in
>limited cases.  When you're working at medium to low resolution, such
>rounding problems are inevitable, and are a very serious quality issue.  If
>ATM is such a good rendering engine, it ought to be able to handle all the
>borderline cases at lower resolutions excellently.  Since it can't, it's
>not as good as some people claim.

How do you conclude it can't?  It is  more readable, and has more even
grey.  One can now argue about which discrete approximation is better.

>> Note that 12pt at 300dpi is 59.775.. pixels.  So a x-height of
>> 0.430555.. em corresponds to 21.448 pixels. Apparently the alignment
>> zone at the x-height is causing the rasterizer to round this level
>> upward in the Type 1 font while Metafont rounds it downward. CM at
>> 12pt is where this difference shows up most noticably.  You don't see
>> this with CM at 10pt.  This has been noted before, and I suspect is
>>why you chose that particular size and resolution.
>
>I chose that particular size (not resolution - that's fixed) because it
>shows up more problems than other sizes on my printer.  Of *course* I
>showed you the worst case.

:-)  It is interesting that even in this worst case, I don't see your point other
than that ATM happens to round up the x-height and Metafont rounds it down
(one pixel difference on your 300 dpi device).

>>I find the Type 1 version more "open" and more  readable.  It is only
>>"wrong" if you assume that it should round off  to the underlying grid
>>in exactly  the same way as the Metafont version does, which is not
>>possible given the very different way the grid-fitting happens.
>
>Your aesthetic judgement isn't relevant: what matters is how well the two
>printed versions match the definitive printed versions of the Computer
>Modern founts in Knuth's books.  Do that comparions.  What do you think?

Somehow you are stacking the deck.  If you are saying is the Metafont
version on your ink jet closer to the the Metafont version in Knuth's book
than the Type 1 version on your ink jet is, then we know what answer to
expect.

>> So the gap is 17/1000 of an em or 0.204pt at a font size of 12pt.
>> You don't have to make the font size very small before that is a pixel
>> or less.  It is not a good idea to design a font with such close
>> approaches, since it dramatically limits what adjustements are allowed
>> in grid-fitting.
>
>Erm...  Surely that means it's only a bad idea if you don't pay enough
>attention to detail when writing the code to produce the fount?

Well, I tend to disagree.  It is better to write the font code so that there
remains enough freedom at small sizes to shift things by one pixel.
The extremely close approach of the F to the r can only be safe if
their are strong constraints on the alignment zones which reduce the
ability of the rasterizer to make adjustments needed for good rendering
at low resolution. 

>> Same in "OzTeX", and also the acronym "ATM".
>> But with the ragged printing of the ink jet its hard to say much more.
>
>You've spotted yet more problems with a PS Type 1 fount rendered by ATM,
>haven't you?  That was Monotype Joanna.

I didn't know what font it was.  In that case your code for generating
these special acronyms is too font specific (and not tuned for Joanna).

>>Anyway, I don't think we can settle this via words alone.  Maybe you can
>>find someone with a scanner and put up the comparison for others to see.
>>Of course, as I said, it would make more sense to show CMR10 at 10pt
>>than CMR12 at 12pt.
>
>Well, no, it makes more sense to show cmr12 at 12pt, because that
>demonstrates the problems better.

You would say that :-)  I think it makes more sense to use any of a
number of other combinations because 12pt on a 300 dpi printer
is a special borderline case for the CM fonts.

>>By the way, I couldn't find information on the Deskwriter 520 on the

>>HP web site, even under "discontinued products"  - so I don't know
>>much about its properties.
>
>300dpi monochrome inkjet, able to print 600dpi along one axis; but OzTeX
>doesn't allow you to use a non-square resolution.

Why does OzTeX care?  With ATM you can print to any resolution isotropic,
or not.  Which seems like another advantage, since quite a few printers
these days have twice the resolution along the horizontal axes than the vertical...

Regards, Berthold.



Berthold K.P. Horn	mailto:bkph@ai.mit.edu  http://www.ai.mit.edu/people/bkph/bkph.html

Would you say I have a plethora of piņatas?