Re: Resolution and banding

[Kennedy McEwen <rkm@kennedym.demon.co.uk>]

In article <5.1.0.14.1.20020601215341.00b141c0@smtp.liveinbalance.com>, 
Tom Sawyer <tom@liveinbalance.com> writes
>This is a great thread you folks have started as its starting to take 
>some of the mystery out of the Epson printing process. Am I correct 
>that the printer puts one of the six inks in one spot on the page? I.E. 
>all non-CcYMmK colors are actually dithered (Saurat lives)?
>
Yes, they are all dithered unless the tone exactly matches the colour of 
one of the inks.  However, the dither algorithm used (and if you run a 
patent search you will find details of over two dozen patents that Epson 
has on the process) is similar in concept to that of a delta-sigma 
analogue to digital convertor where the quantisation noise is 
distributed equally across the page rather than maintained within a 
single "dither cell", as is often the case.  Consequently the full 
resolution of the image (up to the resampling limit) can be retained 
enabling the finest detail to be reproduced while the tonal error is 
distributed over a larger area, making it almost imperceptible.

>Rumors of earlier discussions passed on to me could be summarized as 
>"any image resolution of density higher than 240ppi has no affect on 
>the printed image".

That's certainly a rumour - and it's certainly wrong for any recent 
Epson printer.  Try a detailed print at 480ppi and then downsample the 
data to 240ppi and print again.  If the printer couldn't cope with more 
than 240ppi then the 480ppi print would not have any more detail - but 
it does, although you may need a magnifier to see it.  Average human eye 
resolution is around 250ppi at a 10" viewing distance, so your eyesight 
could be nominally perfect according to the optician but you might not 
see the difference that another person will.
-- 
Kennedy
Yes, Socrates himself is particularly missed;
A lovely little thinker, but a bugger when he's pissed.
Python Philosophers
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