Digital BW, The Print

--- In DigitalBlackandWhiteThePrint@yahoogroups.com, "ferdinand_paris" 
<ferdinand_paris@y...> wrote:
> --- In DigitalBlackandWhiteThePrint@yahoogroups.com, "Stephen Billard"
> <stephen@s...> wrote:
> > Actually, it looks like QuadToneRIP will get close to the 3mm
> > border. Anyway, rounding gives 3.18mm which is as close as my ruler
> > will measure.
> 
> Yes, but it depends on how you are sizing the image.  I use Qimage to
> resize the image, and work in metric.  The Epson driver mandated a 3mm
> margin, so on an A4 page the image size needed to be 204x291mm.  
> 
> However if you send this sized image to QTR, it splits it over 4
> pages.  So I had to reduce it to 202x289.  You could use a 3.18 margin
> I guess, if you print program works in fractions of a mm.  I can see
> how to do this in Qimage, but there would be some trial and error to
> work out precisely what sized image you can send to QTR before it
> insists on splitting it over several pages.  Just one .01mm too much
> would be fatal.

Unit conversion is much more complicated than a simple US vs metric
issue.  Conversions almost always involve round-offs or truncations.

Here's a few tidbits:

How big is A4 paper?  If you start with A0 being 1 square meter and 
start halving you end up with A4 = 210.2 x 297.3mm (or so).  I believe by
definition all the A sizes are truncated to even mm's -- hence A4 = 210x297mm
So while the halving algoritm is nice in concept, you actually loose .5mm
every once in a while.

The Epson printer being a piece of hardware is actually defined by how
many dots does it accept across a sheet of paper.  Even though it is
manufactured in a "metric" country, for all the low level specs the unit
used is 1 dot = 1/360 inch.  Margins are defined as 42 dots which is 
converted to 2.96mm rounded up to 3 mm.

Then you have printer descriptor files that where defined by Postscript
and Adobe.   The base units are points.  Postscript points are defined
as 1/72 inch.  (aside:  there are at least 5 different definitions of what
a point is).   Some code handles fractional points, some only integer.
So to be safe when you convert the 42 dot margin, you've got to round 
up to 9 points or 45 dots -- losing 3 dots on each side.  But of course
when you go to metric again some other piece of software again takes
the "safe" route and rounds 9pts = 3.175mm up to 4 mm.

So you can see things get whittled down at every turn.  Mac OS X takes
the approach of just chopping off images that are slightly too big.  That
may be the better choice than splitting into multiple pages which
never seems very desirable.

Roy

> 
> Stephen - I'm having a problem with QTRgui and Qimage working
> together.  If I start QTRgui after QImage has printed all its print
> jobs to file, no problem.  But if I start it first, then after the
> first print job is done, QTRgui gives me an error message "Unable to
> move xxxxx.tif to to the 'Processed' folder.  Folder monitoring
> disabled".
> 
> If I then restart folder monitoring, all works as it should.  It's
> hard to replicate this problem, as it seems to happen once, and then
> goes away.  Subsequent attempts to print with QTRgui monitoring the
> output folder are successful.  
> 
> It's only a minor annoyance, but a puzzling one.
> 
> F_P