Digital BW, The Print

Hi Roy,

Can you help me reconcile your point below on mapping between the number of
bits in an image and the number of bits used to control the inks in a
printer, with my real world experience.

My real world tests show me that I can print at least 10 bits of
discontinuous (1024 step wedge) gray tonal resolution from essentially 3
black/gray inks on glossy paper printed on a 4800 with Imageprint and
measured with a spectro. That's way more than 1 bit or 2 bits per ink.
Surely the RIP / Driver must do some magic to translate image tones into
printer tones, I guess by manipulating those 33 printer dots per image dot?

Also even with my fairly poor eyesight I can perceive a discontinuous gray
level of around 0.25 L* (i.e. probably 4 - 500 levels between black and
white) and so I believe that we really do need more than 8 bits in our
images, and its great that the printers can already support 10+bits. Now if
only all the drivers and RIPs did.

Mike

"Inkjet printing, especially, requires dithering over an area for perception
of grays.
The printers take no where near 16 bits of data. The most any of the Epson
printers take currently is 2 bits for any ink. In fact all the of K7 and K6
setups
use only 1 bit -- none of the setups use variable dot size. The point being:
what
difference does it make to go 16 bit to 1 or 2 bit directly or use the 8 bit
value
as an intermediate? As can be seen from Tyler's print scans, number of gray
inks has one of the biggest effects. For a K7 ink system you can probably
estimate about 4 bits or 16 possible grays at each position -- based on a
combo
of about 2 inks at any point. But this is still way short of the 8 bits you
feed the
driver"


On 14/11/06, Roy Harrington <roy@... > wrote:
>
>
> This 8-bit vs 16-bit discussion keeps coming up but the assumptions made
> are
> always over-simplified. If you just "do the math" and say 8 bit means
> there are
> only 256 grays and 16 bit gives 1000s of grays it's real easy to fall in
> the trap of
> claiming that 16 bits are necessary.
>
> Couple things to consider:
>
> Any perception of gray -- whether it's our eyes or a high tech measuring
> device --
> is over a multiple pixel area. Take a smooth gradient and counting number
> of
> grays is almost entirely a factor of the specs on the measuring device.
> Use your eyes and you'll count something like 100 grays, use a
> densitometer
> that reads 0.00 to 1.64 and you'll get 164 grays, use and eye-one and
> it'll be
> a 1000 grays. This is regardless if you use an 16 bit directly or convert
> it to
> 8 bit before sending to the driver.
>
> Inkjet printing, especially, requires dithering over an area for
> perception of grays.
> The printers take no where near 16 bits of data. The most any of the Epson
>
> printers take currently is 2 bits for any ink. In fact all the of K7 and
> K6 setups
> use only 1 bit -- none of the setups use variable dot size. The point
> being: what
> difference does it make to go 16 bit to 1 or 2 bit directly or use the 8
> bit value
> as an intermediate? As can be seen from Tyler's print scans, number of
> gray
> inks has one of the biggest effects. For a K7 ink system you can probably
> estimate about 4 bits or 16 possible grays at each position -- based on a
> combo
> of about 2 inks at any point. But this is still way short of the 8 bits
> you feed the
> driver.
>
> I think once you get to the point where adjacent drops of ink are bleeding
> into each other on the paper the result is no longer really digital or
> quantized.
> It's much closer to a continuous, analog image like a silver print made of
> chunks
> of silver.
>
> I'd venture a guess that most all "real" pictures have less than 8 bits of
> "real data".
> I.e . by the time you finish editing the image the low bits of high bit
> data are
> mostly noise. This isn't to say that you can start with only 8 bits in a
> scan for
> instance because which are the good bits is in different in the shadows
> and
> highlights. I do mostly 4x5 film scans and the smoothest gradients I ever
> see
> still appear fairly noisy in 8-bit histograms. Digital cameras are less
> noisy but
> the bottom bit of 8 bit data is typically pretty noisy.
>
> Unfortunately its a bit difficult to demonstate all this in any foolproof
> way. So I
> guess the 16 bit discussion will persist and IMHO the main benefit of
> getting a full
> 16 bit throughout will be to take the issue off the table.
>
> Roy
>
> --- In DigitalBlackandWhiteThePrint@yahoogroups.com
> <DigitalBlackandWhiteThePrint%40yahoogroups.com>, "Steven Karafyllakis"
> <stevekphoto@...> wrote:
> >
> > David;
> >
> > > Well linearized output of well optimized images, both at 8 bit,
> > have about as
> > > many levels as the eye can distinguish.
> >
> > This is excatly the assumption I'm questioning; OK, so if you laid
> > the steps out in a row, perhaps most people couldn't distinguish
> > from one to the next. If you laid out all the tonal steps in an
> > average 4x5 or 8x10 neg you certainly couldn't distinguish them,
> > they would appear continuous even though theoretically since the
> > image is made of dots (silver grain) it isn't really continuous. And
> > yet in terms of nuanced subtle gray transitions and tonal richness,
> > the difference between an inkjet printed in 256 steps and an
> > SG "continuous tone" print from 4x5 neg or bigger, is usually quite
> > obvious. It comes back to sheer information density, and a 256 shade
> > gray-scale can never quite reach it.
> >
> >
> > High bit is wonderful to allow for
> > > adjustments, be it to capture, process, or output, but once things
> > are optimal,
> > > it is, for the most part, overkill. So I see high bit more as a
> > way to improve
> > > problem images or processing or printing than to further improve
> > top notch
> > > stuff.
> >
> > I agree with your evaluation in this regard; but one thing I haven't
> > gotten clear on yet: does hi-bit equal more shades of gray, or
> > simply more control over the existing shades? And if the printer
> > driver converts back to 8-bit before printing, how does it help,
> > beyond, as you stated, allowing for corrections and more accurate
> > mapping of the existing shades?
> >
> > What I'm suggesting, (wishfull thinking really) is killing the
> > sacred cow and setting up a system based on a more continuous gray-
> > scale of 512 shades. A scanner function that would scan directly to
> > B&W in 512 shades. A monochrome digicam sensor that outputs 512
> > shades in raw format. Software that supports editing of the files
> > without downgrading to 256. And a printer driver that could make use
> > of that and deliver at least SOME of the extra info to the paper.
> > Remember, I'm looking for headroom, not neccessarily a quantum leap.
> >
> >
> > BTW, David, when IS PFP 2.0 going to be released?
> >
> > Steven Karafyllakis
> >
> >
> > > C. David Tobie
> > > Product Technology Manager
> > > ColorVision Business Unit
> > > Datacolor Inc.
> > > CDTobie@
> > > www.colorvision.com
> > >
> > >
> > >
> > > [Non-text portions of this message have been removed]
> > >
> >
>
>   
>


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