Re: Decent results with Gutenprint - the poor man's RIP.
Re: Decent results with Gutenprint - the poor man's RIP.
- Subject: Re: Decent results with Gutenprint - the poor man's RIP.
- From: Graeme Gill <email@hidden>
- Date: Wed, 21 Jun 2006 11:41:23 +1000
Robert L Krawitz wrote:
That's due to excess ink. That's actually a reason why I think 16
bits might be necessary even if a driver is well linearized -- the
correct amount of ink when a single channel is printed might not be
right when multiple channels are printed.
Sorry, I can't see the connection. Multichannel ink limiting is
normally done in the profile, because it has the mechanism
to implement something that depends on the level of all channels,
something that per channel linearization doesn't.
In the ColorBus RIP we had a couple of per channel settings,
both aimed at limiting the maximum ink in that channel. This
was due to the inkjets having a larger dot size than pixel
spacing, so high DPI often had inherently 200% or 400% dot overlap
per channel. So the first step was to limit the individual (raw)
channel values to some lower %. Having tamed each channel to only
put out up to 100% ink (and also linearised it into something
resembling an L* curve), the profile would then implement the
total area coverage ink limiting to (typically) 250 - 350%.
There was simply no advantage in using more than 8 bits into
all this - the inherent noise in images, plus the noise
in the screening obliterate any 8 bit quantisation artefacts.
There was considerable advantage in using more than 8 bits
out of all this, ie. for the raw device channel value to the
screening.
Graeme Gill.
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