Digital BW, The Print

Small question for QTR curve design experts...

I'm starting to get some very good results now out of QTR (on a 1280
with UT2 inks), but am a bit stuck on one issue: the density difference
between 100% black and 99% black is much too large, so that, if an image
contains a large area of 100% and an adjacent area of 99%, the edge
between them is clearly visible and the 99% region looks dark gray
rather than nearly black.

The problem occurs both with the provided 1280 UT2 curve (the carbon
curve for HPR paper, FWIW) and with a modified version of the same curve
that I linearized myself using the eye-one procedure described in the
documentation.  In a different experiment, I was able to get the black
values closer together by cranking up the GRAY_SHADOW parameter, but
just doing this, of course, makes the whole print very dark.  

What's the right approach to this issue?

Many thanks,

    - Benjamin Pierce
      http://www.cis.upenn.edu/~bcpierce/photos

I have seen the same thing on a 7000.

Bill

on 10/28/04 9:14 PM, Benjamin C. Pierce wrote:

> Small question for QTR curve design experts...
> 
> I'm starting to get some very good results now out of QTR (on a 1280
> with UT2 inks), but am a bit stuck on one issue: the density difference
> between 100% black and 99% black is much too large, so that, if an image
> contains a large area of 100% and an adjacent area of 99%, the edge
> between them is clearly visible and the 99% region looks dark gray
> rather than nearly black.
> 
> The problem occurs both with the provided 1280 UT2 curve (the carbon
> curve for HPR paper, FWIW) and with a modified version of the same curve
> that I linearized myself using the eye-one procedure described in the
> documentation.  In a different experiment, I was able to get the black
> values closer together by cranking up the GRAY_SHADOW parameter, but
> just doing this, of course, makes the whole print very dark.
> 
> What's the right approach to this issue?
> 
> Many thanks,
> 
>     - Benjamin Pierce
>       http://www.cis.upenn.edu/~bcpierce/photos
> 
> 
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[Non-text portions of this message have been removed]

[Apologies for the double posting: I sent this query to the list a few days
ago but have not had any reponses except one other person observing the same
behavior on a 7000.  Since I haven't solved it myself either and have had no
luck finding relevant information in the archives, I'm reposting in case Roy
or someone else who might have an answer missed it the first time
around... -Benjamin]

Small question for QTR curve design experts...

I'm starting to get some very good results now out of QTR (on a 1280
with UT2 inks), but am a bit stuck on one issue: the density difference
between 100% black and 99% black is much too large, so that, if an image
contains a large area of 100% and an adjacent area of 99%, the edge
between them is clearly visible and the 99% region looks dark gray
rather than nearly black.

The problem occurs both with the provided 1280 UT2 curve (the carbon
curve for HPR paper, FWIW) and with a modified version of the same curve
that I linearized myself using the eye-one procedure described in the
documentation.  In a different experiment, I was able to get the black
values closer together by cranking up the GRAY_SHADOW parameter, but
just doing this, of course, makes the whole print very dark.  

What's the right approach to this issue?

Many thanks,

    - Benjamin Pierce
      http://www.cis.upenn.edu/~bcpierce/photos

>Small question for QTR curve design experts...
>
>I'm starting to get some very good results now out of QTR (on a 1280
>with UT2 inks), but am a bit stuck on one issue: the density difference
>between 100% black and 99% black is much too large, so that, if an image
>contains a large area of 100% and an adjacent area of 99%, the edge
>between them is clearly visible and the 99% region looks dark gray
>rather than nearly black.

I'm not an expert yet, but ...

The step you're seeing is probably the difference between LIMIT_K and 
BOOST_K. LIMIT_K controls the linear-ish region of black ink usage, 
and BOOST_K controls only maximum black.

Reduce BOOST_K and the step will be more subtle, but you will pay in 
reduced Dmax.

Increase LIMIT_K and (assuming it was right in the first place) you 
may lose some of the differentiation between 99%, 98%, 97% etc. In 
this case you'll also need to re-linearize, and you may also need to 
adjust the GRAY_VAL numbers (ink partitioning).

Which is preferable may depend on your style. If you make images with 
large areas of maximum black, you won't want to compromise Dmax. If 
you don't, you probably care more about shadow differentiation.

In an ideal world, you wouldn't need BOOST_K at all, and everything 
would be smooth.

The above is based more on my understanding of the theory than on a 
lot of practical experience, so I'm open to being corrected by 
somebody who knows better.

   -Paul
kb5mu@...