BoundingBox in PostScript output for A4 is too large and the computation with its comment are bogus

Reinhard Kotucha reinhard.kotucha at
Mon Mar 11 06:45:59 CET 2024

On 2024-03-10 at 04:45:51 +0000, Al Ma wrote:

 >> I think that it's quite useful to provide a HiResBoundingBox
 >> comment as well. The latter allows real numbers instead of
 >> integers.

 > Almost no reals can be spelt out. Do you probably mean the
 > rationals or the rationals representable in decimal notation?
 > Notice that the width of A4 is 21 cm / (2,54 cm/in) × 72 pt/in =
 > 75600/127 pt, which cannot be represented exactly using the decimal
 > notation.

It's not necessary to provide exact values.  Assume that that 1 bp is
about 0.35 mm.  With three decimal digits the resolution is 350 nm,
the wavelength of visible light.  The resolution of a phototypesetter
(2540 dpi) is 10 𝜇m.

There is absolutely no need to express 75600/127 with more than 3 or 4
decimal digits.  Even then additional rounding errors will be
introduced by successive processing steps.  But three or four decimal
digits are better than none.


Reinhard Kotucha                            Phone: +49-511-3373112
Marschnerstr. 25
D-30167 Hannover                    mailto:reinhard.kotucha at

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