[argyllcms] Re: ArgyllCMS V1.1.0 RC1 is now available

  • From: Gerhard Fuernkranz <nospam456@xxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Mon, 09 Nov 2009 00:35:10 +0100

Alastair M. Robinson wrote:
> Hi,
> Gerhard Fuernkranz wrote:
>> And I tend to agree - when the "gamma" value is getting too large
>> then a wedge with a linearly spaced steps in device space is possibly
>> no longer optimal for characterizing the response wrt. a perceptual
>> metric.
> Yup - but to my mind the bigger problem is that such a gamma
> adjustment means ink coverage is no longer directional proportional to
> input value,

This applies indeed to the other, gamma-adjusted space presented by the
driver to the user. It certainly suffers from the problem that summing
the colorant values won't sum up the actual ink amounts (but there is a
non-linear relationship). I understand that this is the obvious reason
why you wanted to calibrate the _raw_ space of the halftoning engine

There was likely a misunderstanding regarding my statement you cited
above. I actually meant that I agree that for characterizing the _RAW_
space of the halftoning engine (i.e. the space with the extremely high
dot gain (or extremely high "gamma")), a wedge with linear steps in
device space is likely no longer optimal (but a non-linearly spaced
wedge may be more suitable).

But back to the TAC calculation: While for a printer with CMYK inks only
the raw space of the halftoning engine may indeed have the desired
properties (i.e. laid down ink amount proportional to the colorant value
sent to the driver), I'm wondering whether this still applies when light
inks come into the play and the driver needs to separate e.g. the cyan
channel into dark cyan and light cyan. Is the sum of the dark and light
cyan ink amounts still proportional to the cyan colorant value sent to
the driver then? If not, we have lost again...


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