Digital BW, The Print

I'm really impressed (and getting more impressed by the day) with 
IJC/OPM - thanks to Joe and Richard for their help and also for the 
new tutorial.

One question though; When I print the target for linearisation my 
densitometer reads step 26 darker than step 25 but to the eye there 
is no difference whatsoever. If I linearise using the readings am I 
in effect wasting shadow detail by having step 25 and 26 identical to 
the eye even though step 26 is "densitometer darker"? Would I be 
better tweaking the inks or the sliders to get a visible difference 
between 25 and 26 before completing the profile?

Thanks in advance.

John,

I had the same question, and here is how I resolved it along with my 
reasoning. 

I use L* readings from my Eye One instead of using density units.  L* 
readings, which are plotted on a linear scale, should show roughly 
the  same difference between steps on a linear profile.  If a glossy 
paper has a paper white of L* 95, and deepest black of L* 6, then 
there is a total difference of 89 L* units.  Divide this by 26 (the 
number of steps in the IJC linearization routine) and each step 
should be differ by about 3.4 L* units.  That helps me better put it 
into quantitative terms.  

When step 25 and 26 both look the same by eye, I take readings with 
my EyeOne.  If step 26 reads 6.0 and step 25 reads 6.3 or 6.4, they 
are so close as to be nearly indistinguisable both by eye and by L* 
readings.  They are both essential black, and looking at a desired 
difference of 3.42 helps me put it into perspective.  In this case, I 
will select 25 as my ink limit.  My reasoning is that if I use 26, 
there is essentially no tonal separation between 25 and 26, which 
forces IJC to make more extreme adjustments to give me a linear tone 
scale.  Getting closer to being linear before asking IJC to do its 
math will give me smaller adjustments.  I seem to get a better 
profile that way and don't notice any loss of black.

If step 26 reads L* 6.0 and step 25 reads 7.0, tonal separation is 
more substantial (even if it may still be tough to see by eye) and I 
would probably choose 26 as my ink limit.  If the difference is 1 or 
greater, I always go with the darker test patch.

Maybe not totally scientific, but it seems to make sense and works 
for me.

Lou

--- In 
DigitalBlackandWhiteThePrint@yahoogroups.com, "johndavidgill2003" 
<jdgill@l...> wrote:
> 
> I'm really impressed (and getting more impressed by the day) with 
> IJC/OPM - thanks to Joe and Richard for their help and also for the 
> new tutorial.
> 
> One question though; When I print the target for linearisation my 
> densitometer reads step 26 darker than step 25 but to the eye there 
> is no difference whatsoever. If I linearise using the readings am I 
> in effect wasting shadow detail by having step 25 and 26 identical 
to 

> the eye even though step 26 is "densitometer darker"? Would I be 
> better tweaking the inks or the sliders to get a visible difference 
> between 25 and 26 before completing the profile?
> 
> Thanks in advance.

I would take step 26's reading, do the linearization, print the step wedge
again (linearised this time) and check the separation.  Only then would I
make any sacrifices...Just a thought.  The trickier issue is when,
unlinearised, step 25 measures darker than 26!

> From: ldina <lbdina@...>
> Reply-To: <DigitalBlackandWhiteThePrint@yahoogroups.com>
> Date: Mon, 24 Jan 2005 20:07:40 -0000
> To: <DigitalBlackandWhiteThePrint@yahoogroups.com>
> Subject: [Digital BW] Re: IJC/OPM - DMax "darker than the eye can see".
> 
> 
> 
> John,
> 
> I had the same question, and here is how I resolved it along with my
> reasoning. 
> 
> I use L* readings from my Eye One instead of using density units.  L*
> readings, which are plotted on a linear scale, should show roughly
> the  same difference between steps on a linear profile.  If a glossy
> paper has a paper white of L* 95, and deepest black of L* 6, then
> there is a total difference of 89 L* units.  Divide this by 26 (the
> number of steps in the IJC linearization routine) and each step
> should be differ by about 3.4 L* units.  That helps me better put it
> into quantitative terms.
> 
> When step 25 and 26 both look the same by eye, I take readings with
> my EyeOne.  If step 26 reads 6.0 and step 25 reads 6.3 or 6.4, they
> are so close as to be nearly indistinguisable both by eye and by L*
> readings.  They are both essential black, and looking at a desired
> difference of 3.42 helps me put it into perspective.  In this case, I
> will select 25 as my ink limit.  My reasoning is that if I use 26,
> there is essentially no tonal separation between 25 and 26, which
> forces IJC to make more extreme adjustments to give me a linear tone
> scale.  Getting closer to being linear before asking IJC to do its
> math will give me smaller adjustments.  I seem to get a better
> profile that way and don't notice any loss of black.
> 
> If step 26 reads L* 6.0 and step 25 reads 7.0, tonal separation is
> more substantial (even if it may still be tough to see by eye) and I
> would probably choose 26 as my ink limit.  If the difference is 1 or
> greater, I always go with the darker test patch.
> 
> Maybe not totally scientific, but it seems to make sense and works
> for me.
> 
> Lou

Steve,

Picking 25 or 26 seems to work fine when they are fairly close, and 
printing the target after linearization does show separation.  My 
guess is that the linearized target would show separation even if 
steps 25 and 26 were identical since that is what IJC is programmed 
to do (at least that's my understanding).  I guess I take a 
conservative approach and don't want to push the adjustments too 
far.  

If step 25 is darker than 26, I'd say we just exceeded the ink limit 
of the paper and would choose 25.  

Lou

--- In DigitalBlackandWhiteThePrint@yahoogroups.com, Steve Kale 
<stevekale@b...> wrote:
> I would take step 26's reading, do the linearization, print the 
step wedge
> again (linearised this time) and check the separation.  Only then 
would I
> make any sacrifices...Just a thought.  The trickier issue is when,
> unlinearised, step 25 measures darker than 26!

--- In DigitalBlackandWhiteThePrint@yahoogroups.com, "johndavidgill2003" <jdgill@l...> wrote:
> 
> I'm really impressed (and getting more impressed by the day) with 
> IJC/OPM - thanks to Joe and Richard for their help and also for the 
> new tutorial.
> 
> One question though; When I print the target for linearisation my 
> densitometer reads step 26 darker than step 25 but to the eye there 
> is no difference whatsoever. If I linearise using the readings am I 
> in effect wasting shadow detail by having step 25 and 26 identical to 
> the eye even though step 26 is "densitometer darker"? Would I be 
> better tweaking the inks or the sliders to get a visible difference 
> between 25 and 26 before completing the profile?

Not really up on IJC, but this is a general problem with densitometers and spectrophotometers. They all read with the same 45 degree illuminant, 0 degree observer or visa-versa. It's a highly flawed model. Humans viewing a picture don't use anything even close.

I'm tinkering with multishot cameras and colormetric filters right now, trying to work out a more useful model, but I'm in over my head. I can see something's broken, but can't get a handle on fixing it...

Just a couple of thoughts to add to what Lou  and Steve have
been discussing in this thread:

It's useful to think of what these numbers do to your images before
you make a profile "by the numbers" alone. It's true that steps should
separate equally and that 25 should have whatever separation the aims
dictate from step 26.

But think of what your image has down there. The IJC aims often
have too much shadow detail for some images. In the case of some
of my scans from Delta 3200, I wouldn't need to show all that grain
"detail" down in the 95-100% range. Rather, I would like some separation
for the sake of tonal continuity, but very little. This doesn't apply
to all images all the time, so some judgment is required.

I would advise that when you have an otherwise good profile, but
with a compressed shadow in the 24-25-26 area, you print a sample
image first and see what it looks like.

In the past, this issue has caused me to hand-linearize just so that I
can shape the shadows the way I see fit for a given group of pictures.
Fortunately, the IJC curves are easy to move in very fine increments so
that I can hit the lin curve without IJC doing the math. It only takes
a few more rounds of trial-and-error, but is worth it only for high-end
finished results, not for casual proofing and such.

Antonis



--- In DigitalBlackandWhiteThePrint@yahoogroups.com, "johndavidgill2003" <jdgill@l...> 
wrote:

..........

> One question though; When I print the target for linearisation my 
> densitometer reads step 26 darker than step 25 but to the eye there 
> is no difference whatsoever. If I linearise using the readings am I 
> in effect wasting shadow detail by having step 25 and 26 identical to 
> the eye even though step 26 is "densitometer darker"? Would I be 
> better tweaking the inks or the sliders to get a visible difference 
> between 25 and 26 before completing the profile?