Digital BW, The Print

----- Original Message ----- 
From: "Roy Harrington" <roy@...>
To: <DigitalBlackandWhiteThePrint@yahoogroups.com>
Sent: Saturday, November 29, 2003 7:47 PM
Subject: Re: [Digital BW] 16 bit printing


> It was interesting to read that Paul has seen real print
evidence
> of 8 bit versus 16 bit in the curves.  Gimp-print and I'd bet
all
> the Epson drivers use 16 bit internally.  In the realm where
the
> numbers represent "human" perceived values, 8 bit or 256 values
> is plenty for all practical purposes.  But once you get into
the
> driver the values eventually have to represent quantities of
ink
> on the paper.  So while the ratio between 10%K and 100%K
> in our PS files is a factor of 10x, when you get to ink on the
page
> this could easily be a factor of 1000x in ink volume, which is
> why 16 bits are needed.  All the QuadToneRIP and Gimp-print
> code starts with 8 bit from the image data files, converts to
> 16 bit first and then all curves, dithering, etc. stays with 16
bit.
> (BTW, this is analogous to the need for 16 bit in scanning
where
> the raw values represent light energy values).
>
> What Paul does with RGB separation curves is very much like
> part of the driver conversion to ink volumes.  So it not too
> surprising that he can get some improvement using 16bit.  I
> don't know if the Windows print spooler chops down to 8bit
> and if it does whether it does it "intellegently" like PS does.
> (Maybe PS chops before sending?).   I haven't found a way so
> far to get 16 bits throught the OS X printing system either.
>
> Roy

Roy,

Paul could see a better rounding off in the curves computations.
And that quality could survive the Windows drop to 8 bit at the
driver input + the 16 bit juggling in the driver + its 8 bit
output to the printer. There's still one improvement possible: 16
bit input to the driver in Windows. I could be wrong about 8 bit
printer input (driver output) but I think it is unlikely that the
printengine is 16 bit per channel.

Ernst