Sample inkjet printouts

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

Hi:

At 20:28 1999-03-23 +0000, Rebecca and Rowland wrote:

>[snip]

>btw Berthold - have you received my test prints yet?

 Thanks for sending the sample printouts.  I must say that at first I 
 thought you might have mislabelled them, since to my eyes they do not
 prove your point. In fact, to me the PK version of CMR12 looks "choppier," 
 with not as  even grey as the Type 1 version of CMR12.  Part of the 
 difference may be that  the Type 1 version is suppressing overshoots at 
 this size, while the  PK version seems to render rounded glyphs larger 
 than the flat-topped glyphs.  

 Since we obviously have some biases here, the only sensible thing I
 can see to do is to scan the pages in and put them up on a web page
 somewhere for people to look at.  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.

> Here's some samples of LaTeX output, printed on my HP Deskwriter 520
> by OzTeX 3.0 using the HP DW 6.0.3 LocalTalk driver running on a Mac
> Performat 475 using System 7.6.1 

> The two sets of prints are rendered by ATM Deluxe 4.0.3 in the case
> of the CM/PS founts, and Metafont 2.718 using the Laserwriter mode in
> the case of the `straight' CM founts.  All prints were made at the
> normal 300 dpi printing resolution of the DW 520.

> The paper's a bit iffy, so you'll notice a bit of fuzziness here and
> there which has nothing to do with either ATM or Metafont.

> Things to note: the large sizes are identical no matter what does the
> rendering, which implies there's nothing wrong with the founts.

 or more accurately: "which implies there's nothing wrong with the OUTLINES"

> The page of CM/PS at 12pt obviously has an excessive ex height.  

 Let's instead say that the apparent x-height of the rasterized Type 1
 fonts is larger than that of the bitmaps derived from the Metafont
 code. This doesn't mean that one of them is "wrong".  It's a difference
 in how they are rounding off to the discrete grid.

 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 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.

> The problem is clear when you look at the test page containing the word
> `French' repeated at various sizes:  The `Fr' combination runs
> together at several sizes of thge CM/PS founts, while there's a clear
> gap between the two letters in the Metafont versions.

 Well first of all, notice the extreme kerning (KPX F r -81.595) which
 brings the serif on the left of the r right underneath the descending
 serif on the tip of the F.  Then, the bottom of the serif on the F
 comes down to 458/1000 em, while the top of the r rises to 441/1000 em.
 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.  Apparently Knuth arranged for the grid fitting in
 the Metafont code to take into account the Fr kern pair.  The Type 1
code for F does not have any adjustments related to the Type 1 code
for r.

 As a matter of interest, I do find some collisions in the cover letter itself.
 In particular the A in LaTeX overprints the stem of the A, and the X 
 touches the E.  Same in "OzTeX", and also the acronym "ATM".  
 But with the ragged printing of the ink jet its hard to say much more.

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.

Regards, Berthold.

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.

>>For an  interesting comparison see: http://www.yandy.com/compare.htm

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?