Re: Epson Phoro printers - 16 bit?
Re: Epson Phoro printers - 16 bit?
- Subject: Re: Epson Phoro printers - 16 bit?
- From: Robert L Krawitz <email@hidden>
- Date: Wed, 16 Jul 2003 20:16:24 -0400
From: Ray Maxwell <email@hidden>
Date: Wed, 16 Jul 2003 10:35:33 -0700
I cannot address the issue of eight or sixteen bits when using the Epson
drivers, however, I can give some information about these printers when
driven by third party RIPs or Controllers.
The raw data sent from a RIP or Controller to the Epson printer is two bits
per ink channel. This means that you can select no drop, small drop, medium
drop, or large drop for each of the seven ink channels. You also can choose
the interleaving mode of the printer.
So the question is not how many bits per color the printer will take, but
how many screen tiles the RIP can select from for a given toneal value,
resolution and interleaving mode.
Inkjet drivers generally don't work by means of screen tiles; they
generally either use stochastic screening (comparing each position to
the value in a carefully constructed tiled matrix, and either printing
or not printing) or some kind of error diffusion (feeding the
difference between the value at the position to the value printed into
the nearby positions, to increase or decrease the chance of their
printing). There are variations, such as variable drop size on most
newer printers, but the basic principles remain the same. The
interleaving (weave) mode doesn't matter; the resolution only matters
insofar as the aspect ratio and desired amount of ink to be printed
changes (well, you could come up with a screening algorithm that tried
to generate screens at certain spatial frequencies, but Gimp-Print
doesn't do that).
I do know that some third party RIPs have 12 bit input addresses to
their linearization tables. This would imply that they have 4096
levels of screening.
Gimp-Print uses 16 bit values internally. 12 linear bits is probably
just about good enough for current inkjet printers, though (I think I
read on the old email@hidden list that that's what
Piezography uses).
The real question is does a RIP or Controller maintain more than 8
bits per channel when selecting a screening tile in the RIP.
Actually, it's the other way around: even an 8-bit RIP needs more than
8 linear bits of precision for deciding whether to print a dot. If
you only had 8 bits, you could not print with less than 1/256 ink
coverage, which is surprisingly dark, particularly at high resolutions
on most printers.
--
Robert Krawitz <email@hidden>
Tall Clubs International --
http://www.tall.org/ or 1-888-IM-TALL-2
Member of the League for Programming Freedom -- mail email@hidden
Project lead for Gimp Print --
http://gimp-print.sourceforge.net
"Linux doesn't dictate how I work, I dictate how Linux works."
--Eric Crampton
_______________________________________________
colorsync-users mailing list | email@hidden
Help/Unsubscribe/Archives:
http://www.lists.apple.com/mailman/listinfo/colorsync-users
Do not post admin requests to the list. They will be ignored.