[Openicc] New options on the mainline

[Robert Krawitz]

I added some new options on the mainline, to assist people who want to
linearize the driver.  These have only been added to the Epson driver,
at least at this time.  By default, all of these options are disabled,
so the driver uses whatever values have been set internally.

1) Drop size selection.  There are three new settings, Drop Size
   Small, Drop Size Medium, and Drop Size Large, that can be used to
   specify the relative sizes of the three drops.  The screening code
   assumes that the ratios specified relate to the number of drops of
   each size that will produce a constant darkness; sizes of 0.25,
   0.5, and 1.0 mean that 4 small drops are treated as equivalent to 2
   medium drops or 1 large drop.

   * The largest drop size you want active should be set to 1.
     Normally that means the large drop size.  However, if you don't
     want to use the large drop size (at very high resolution), you
     may set one of the smaller drops to 1.

   * A drop size of 0 is not used.  So if you set the large drop size
     to 1, the small drop size to 0.25, and the medium drop size to 0,
     only the small and large drops will be used.

   * Drop sizes should be specified in ascending order, other than
     drops of 0 size.  For example, you should not set the small drop
     size to 0.5 and the medium drop size to 0.25.  If you do, the
     results are undefined.

2) Light ink value options.  These options, which are available for
   whichever light inks are available on the particular printer, can
   be used to set the intensity relative to the dark ink.  "Intensity"
   means the inverse of the amount of ink required to achieve a
   particular darkness.  For example, a Light Cyan Value of 0.25 means
   that the driver will trade off 4 drops of light ink for 1 drop of
   dark ink.

3) Light ink transition options.  These options, which are available
   for each channel with light inks, specify at what point the driver
   will start using dark ink.  This is expressed as a fraction of the
   intensity of the light ink.  For example, if Light Cyan Transition
   is set to 0.40, the driver will start using dark ink when the
   amount of light ink reaches 40%.  So and the Light Cyan Value is
   0.25, the driver will start using dark ink at 0.1 (6554 on a raw
   scale of 0-65535).

4) Light ink scaling options.  These options replace the previous
   light ink transition options, which basically just adjusted the
   density of the light ink relative to the dark ink.  I expect that
   these will be the least useful of the new options, but I may be
   wrong.

The defaults for these values are not constants; they vary based on
the printer settings chosen (paper type, ink type, resolution,
possibly other factors).  To determine the defaults for these values,
I recommend using the GIMP plugin included with Gutenprint.  The steps
to follow are:

1) Select the combination of printer options you wish to use (the
   printer options are all on the main window), to the right of the
   preview).  In particular, it's important to select the media type,
   ink type, ink set, and resolution.  Print Quality should be set to
   Manual Control.  I recommend that Adjust dot size as necessary not
   be used.

2) Click the Output tab on the top right of the plugin window, select
   the desired output type, and click the Adjust Output... button.
   This will open a Print Color Adjust window.

3) Click the Set Defaults button at the bottom of the Print Color
   Adjust window.  This will set these new parameters to their default
   values for the combination of settings chosen.

   Note that you may use another Gutenprint-based application, such as
   PhotoPrint, as long as it has a Set Defaults button for the output
   settings with the same functionality as the GIMP plugin's (it sets
   the color settings to their defaults, but does not change the
   printer settings).

(I should probably change the way the GCR adjustments behave so that
they act the same way.)

As far as actually performing linearization, set the following options
(all in the Print Color Adjust window):

* Image Type should be set to Manual Control.

* Dither Algorithm should be set to your choice.

* Color Correction should be set to one of the following:

  + Raw if you want to adjust all the settings manually.  In Raw color
    correction mode, there will be no automatic correction of any
    kind, including density adjustment.  If you're not careful, you
    may find yourself using an excessive amount of ink with this
    setting.  You will need to adjust the Density control or the
    controls for the densities of the individual colors.  You may want
    to use this to establish custom densities and ink limits to
    achieve maximum gamut.

  + Density if you want to use Gutenprint's choice of density, but
    otherwise have no automatic color correction applied.  This choice
    of setting should be safe (at least in RGB mode; in CMYK mode it's
    possible for too much ink to be applied).  This is useful if
    you're satisfied with Gutenprint's default ink limits, but want to
    adjust the linearization yourself.

  + Uncorrected if you want to use Gutenprint's choice of
    linearization, but otherwise have no cross-channel correction
    applied.  If you're satisfied with Gutenprint's linearization and
    want to profile the driver, this may be a good selection.

  I do not recommend using the default, which is usually High
  Accuracy.  This setting performs inter-channel adjustments in HSL
  space, which probably won't yield the optimum results.

Comments please.

-- 
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