[Gimp-print-devel] Re: Light inks (was: HP deskjet 690c)

[Dave H. <da...@mi...>]

Andy Thaller wrote:
> 
> Well, actually it's some time since I've done any work on the canon
> driver and I still can't test 6 color printing lacking the appropriate
> ink :-/
> So what exaclty did you do to make it work or would you mind adding it
> to the canon driver also?
> 
> Andy.
> 

It seems that in the olden days (before the last round of major
dither changes), the values of "light" inks were pre-set in
init_dither (variables lc_level etc). In print-dither 1.19, for
example, the values are (24576/65536) = 0.37.

However, now, it seems that in order to get "light" ink output,
you have to explicitly tell the dither code to do it.

What I did was this:-

If you are *not* using 4-level dithers (i.e. in the canon case
you are not "using_dmt"):-

dither_set_light_inks(dither, light_cyan_density, light_magenta_density,
light_yellow_density, v->density);

where the values are the density of the light ink compared to the
ordinary one. What happens if you specify a "light ink density" and
then don't supply a buffer to dither_cmyk(), I don't know!

If you are using DMT, then it seems to become more complicated.
Instead of calling dither_set_c_ranges_simple(), for each colour
that has a light ink, you have to call dither_set_c_ranges() instead.
This takes an array that seems to map the "equivalent dot size"? to
the dither output ('01', '10' or '11') and which ink to use (0=light,
1=dark).

I fathomed all this out by looking in the source of print-escp2.c.
Whether I could put it into print-canon without breaking it is
another matter!

Robert, does this make sense or am I writing drivel? How do you work
out the values of the dither knobs? Do you print colour gradients and
look at the transitions?

Dave

-- 
Dave Hill, Kempston, Bedford UK		da...@mi...
				davehill at users.sourceforge.net
Sicth munce ago, I cutn't evun spel enjuneer, and now I are one!