[Openicc] Drop size calibration

[Roy Harrington]

Hi Robert,
As far as I can tell your method is matching the density of a 10% large dot
with
say a 20% small dot.  But in a real print the transition from small dot to
large
dot happens at a much higher percentage -- say 100% small to 50% large.
So while it would seem that mathematically its the same thing, the
non-linearity
of dot gain makes a difference.  Small dots have more relative dot gain than
larger dots because the circumference to area ratio is larger.  I suspect
this is
a least one factor causing your "larger" small dots.

I think you can use the same idea but make the constant strip 100% small dot
and
the gradient strip the large dot.  This is basically what I measure.  I like
your idea about making the different ranges for each dot size, I may have
to try something similar.  (I've been using an environment variable to force
single dots but this requires 3 print jobs not 1).

Roy

On Jan 27, 2008 4:31 PM, Robert Krawitz <rlk at alum.mit.edu> wrote:

> I'm experimenting with another approach to drop size calibration.
> This uses the new segmented dither algorithm to print stripes using
> different drop sizes.
>
> 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.  For example, if there is no banding at 20%, that means
> 2 small drops are equivalent to 1 large drop.
>
> The only problem I'm having is that this method is yielding very
> different results on the RX580 from what I've already tuned, and my
> tunings agree with Roy Harrington's.  I've tried with 5% instead of
> 10%, and get essentially the same results.
>
> Using this method, I've derived ratios of approximately 0.33:0.43:1.00
> for the smallest set of drops on the RX580, but the ratios currently
> in use are 0.23:0.37:1.00.  For the large drops, I'm getting ratios of
> 0.17:0.47:1.0 (vs. 0.071:0.30:1.0 that we're currently using).  The
> ratio between the small and medium drops in the large set should be
> very close to the ratio between the small and large drops in the large
> set, but the eyeball approach isn't quite giving that result (it's off
> by about 10%).  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.
>
> 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.
>
> printer "escp2-rx580";
> hsize 1.0;
> vsize 0.2;
> left 0.0;
> top 0.0;
> mode gray 16;
> steps 100;
> blackline 0;
> parameter "DitherAlgorithm" "Segmented";
> parameter "ColorCorrection" "Raw";
> parameter "Resolution" "1440x1440ov";
> parameter "PrintingMode" "BW";
> ...
>
> --
> 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
>
> "Linux doesn't dictate how I work, I dictate how Linux works."
> --Eric Crampton
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.freedesktop.org/archives/openicc/attachments/20080127/b356962b/attachment-0001.htm