[Openicc] New options on the mainline

[Gerhard Fuernkranz]

Robert Krawitz wrote:
> 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,

Instead of three parameters, shouldn't this better be a (variable sized)
array in order to specify a varying number of drop sizes?

Btw, it's possibly also noteworthy, that usually at different DPI
resolutions different number of ink levels are available.

> 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.

I'm wondering, whether user-supplied channel-splitting/calibration
curves, i.e. Cyan input => Dark Cyan and Cyan input => Light Cyan,
wouldn't provide more flexibility for the user to establish an arbitrary
blending between the dark and light inks? I guess that such curves would
also make 2) 3) and 4) obsolete?

> 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.

Do "raw" and "density" mode honor user-supplied linearization curves? Or
in other words, which mode do I need to select, if I want _Gutenprint_
to apply _my own_ linearization (and possibly channel-splitting) curves,
which I supply as parameters? (my understanding is that this is
basically the most desired mode of operation, at least for CMYK
printers, and for CcMmYKk printers which are not operated in a
multicolor mode, but which emulate CMYK by channel splitting).

>   + 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.

And how to deal with multicolor printers? Do I understand correctly,
that there is currently no print mode available, which accepts "DeviceN"
input (i.e. one input channel for each ink)?

Regards,
Gerhard