[Openicc] Drop size calibration

[Hal V. Engel]

On Monday 28 January 2008 16:31:46 Robert Krawitz wrote:
>    From: "Hal V. Engel" <hvengel at astound.net>
>    Date: Mon, 28 Jan 2008 15:12:41 -0800
>
>    On Monday 28 January 2008 14:31:45 Gerhard Fuernkranz wrote:
>    > Hal V. Engel wrote:
>    > > I suspect that drop size calibration has a lot in common with
>    > > calibrating the light/dark ink transitions in CcMmYKk type printers.
>    >
>    > Btw: This statement, which brings drop sizes and light/dark
>    > transitions into relation, reminds me on another approach I have
>    > seen somewhere in the literature. This approach does the
>    > dark/light splitting in the dithering engine: It treats the
>    > e.g. 16 dot-on-dot overprint combinations of the three dot sizes
>    > of "C" and the three dot sizes of "c" as if they were 15 drop
>    > sizes of a single virtual cyan channel. Then these 15 virtual
>    > drop sizes are sorted by density, and dithering is done between
>    > the resulting 16 virtual levels. A requirement for this approach
>    > is of course that the hues of the dark and light inks must match
>    > sufficiently well, i.e. the dark inks should be basically the
>    > same colorant as the light ones, but at a higher concentration. I
>    > have no idea though, how well this approach works in practice...
>    >
>    > > It is posted here:
>    > > http://lprof.sourceforge.net/images/Channel-Error.jpg
>
>    I could recreate these without too much trouble.  I improved the
>    spreadsheet since I created that graphic and it now graphs the K
>    channel.  I could simply print out a new target with the GutenPrint
>    default settings and re-measure it and drop those measurements into
>    the spread sheet.  I could post the spreadsheet where people could
>    have a closer look since this would have the graphs and the
>    measurement data.  In addition others could use the spread sheet to
>    plot other things, for example, how the hue of a channel changes
>    with density.  I could have this available tommow (to allow for
>    drying before measurement) if anyone is interested.  It only takes
>    about 5 minutes to measure a target and about one minute to get the
>    measurements into the spreadsheet once the target is ready to
>    measure.
>
> I'd be very interested in this.
>
> If you want to isolate issues of drop size vs. light ink, you can do
> this:
>
> 1) Print normally at very high resolution (5760x1440 or higher), where
>    only the smallest drop size is used.  2880x2880 or 5760x2880 may be
>    even better due to the form factor, but on most printers those
>    resolutions have problems near the bottom of the page.

The targets I used were printed at 2880x2880 so it looks like this is probably 
light/dark ink transition rather than drop size related.   So are these 
higher resolutions only using the smallest dot size?  If that is the case 
does the dithering setting matter at these resolutions?

>
> 2) Print at lower resolution using "4 color standard" (i. e. CMYK)
>    ink.
>
> You can also print using CMYK at high resolution if you want a
> baseline.
>
> I'm very interested in how Ordered New dither performs against
> Ordered.  Ordered dither is just 2 levels, so it fills up one drop
> size before starting to use the next.  Ordered New uses 3 levels, and
> it starts a new drop size when the previous one is 50% in use.

Gerhard asked me to do a target with more patches.  So I have just printed out 
a target with a 128 patch ramp for each channel but no CMY ramp since this 
was about all I could get on one page.  Once the target is dry I will measure 
it and post the results somewhere.

Hal