[Openicc] [Gimp-print-devel] Drop size calibration

[Robert Krawitz]

   Date: Mon, 28 Jan 2008 01:16:26 +0000
   From: "Alastair M. Robinson" <blackfive at fakenhamweb.co.uk>

   Robert Krawitz wrote:

   > The exact technique I use is to interleave fixed 10% stripes of a
   > larger drop size with variable stripes (0-100%) of a smaller drop
   > size.  I then look for where there's no visible banding; that spot
   > should indicate where equal amounts of ink are being printed with both
   > drop sizes.

   Clever :)

   > I've tried with 5% instead of
   > 10%, and get essentially the same results.

   Have you tried heavier ink coverage, rather than lighter?

Yes, with basically the same results (that's an interesting
question).  I've tried 5%, 10%, and 30%, and it's basically the same
each time (30% is difficult because the intersection point is very
dark, but as best as I could tell the results were basically the
same).

   > I'm also seeing slightly different results for cyan
   > vs. black (by maybe 5%), but that's likely to be within margin of
   > error for the printer.

   I guess yellow is going to be the hardest to calibrate visually in
   this manner - I presume the various inks are supposed to have
   identical dropsizes, yes?

On Epson printers, yes.  I think Canon printers, and possibly some HP
printers, can differ (my recollection is that some inks have one drop
size while others have multi-level inks).

   > Right now I don't know why this is happening, or what it means.  In
   > any case, this is the testpattern config file that I'm using for this
   > (you'll need the most recent CVS update for all of this to work
   > correctly).  Perhaps I'll try these drop sizes and see what happens.

   I'd be very interested to hear how they perform.  Sadly it'll be a
   while before I have time to play with any of this myself, but I
   shall certainly have a go in due course :)

This *should* make it much easier to tune printers in the future, if I
can solve this little conundrum.  It should be possible to get the
drop sizes correct within an hour or so, rather than having to spend
hours with it and then have to go back and retune later.

-- 
Robert Krawitz                                     <rlk at alum.mit.edu>

Tall Clubs International  --  http://www.tall.org/ or 1-888-IM-TALL-2
Member of the League for Programming Freedom -- mail lpf at uunet.uu.net
Project lead for Gutenprint   --    http://gimp-print.sourceforge.net

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