Digital BW, The Print

What is the opinion of folks with regards to the Lab a and b values 
that should be strived for when producing a neutral curve?

I've been playing around for a good few days now trying to produce a 
neutral curve, and seem to be going around in circles at the moment, 
with values within plus or minus 0.5 for both Lab a and b; are these 
figures considered OK or should I continue with more iterations?

I'm using QTR with a 1290s and a UT3D inkset, and using an XRite Pulse 
for my readings,

Jamie.

Jamie,

 

I now tend to have the "neutral" curves go, more or less, smoothly from the
paper white to the black values for Lab a & b.  I have more of the change
take place at the white end, so that by 50% it's essentially neutral or
close to the K value.  What I don't do much any more is fight the paper
white at the light end where lots of it is showing through between the ink
dots, unless I'm intentionally trying to do a split tone. 

 

I also don't consider Lab a = 0 to be "neutral."  I like a slight positive
"selenium" look.

 

I'm not sure anyone can actually see a 0.5 variance in a print.  At the
point you're at 0.2, you're fighting the noise of the systems.  For
perspective, my X-Rite and PFP spectros can disagree with each other by up
to a full 1.0 a and b.  

 

If you have a silver print you like, consider using it as a standard and
visually evaluating the inkjet test strips next to it.  Lighting and
adjacent colors can affect how the test strip will look.

 

Don't let the small changed in tone drive you crazy. 

 

Good luck.

 

Paul

www.PaulRoark.com <http://www.paulroark.com/>  

 

 

  _____  

From: DigitalBlackandWhiteThePrint@yahoogroups.com
[mailto:DigitalBlackandWhiteThePrint@yahoogroups.com] On Behalf Of Jamie
Creed
Sent: Saturday, January 13, 2007 12:19 PM
To: DigitalBlackandWhiteThePrint@yahoogroups.com
Subject: [Digital BW] Lab a and b values for a neutral curve?

 

What is the opinion of folks with regards to the Lab a and b values 
that should be strived for when producing a neutral curve?

I've been playing around for a good few days now trying to produce a 
neutral curve, and seem to be going around in circles at the moment, 
with values within plus or minus 0.5 for both Lab a and b; are these 
figures considered OK or should I continue with more iterations?

I'm using QTR with a 1290s and a UT3D inkset, and using an XRite Pulse 
for my readings,

Jamie.

 



[Non-text portions of this message have been removed]

Hi Jamie... I've been making measuring stepwedges printed with
different ABW settings and also modifying IJC profiles (and measuring
the stepwedges) to try to make neutral K3 prints.  Keeping the A and B
values "vertical," i.e., with a relatively constant value from 0 to
100, makes a print that is definitely not neutral looking.  Also,
getting the values to go quickly from paper white to 0, and then
keeping the values at 0 until the last few steps, did not produce
neutral looking prints.  I think Paul has stated it pretty accurately
in his previous post.

Ed


--- In DigitalBlackandWhiteThePrint@yahoogroups.com, "Jamie Creed"
<jlcreed@...> wrote:

>
> What is the opinion of folks with regards to the Lab a and b values 
> that should be strived for when producing a neutral curve?
> 
> I've been playing around for a good few days now trying to produce a 
> neutral curve, and seem to be going around in circles at the moment, 
> with values within plus or minus 0.5 for both Lab a and b; are these 
> figures considered OK or should I continue with more iterations?
> 
> I'm using QTR with a 1290s and a UT3D inkset, and using an XRite Pulse 
> for my readings,
> 
> Jamie.
>

In a message dated 1/13/07 3:22:20 PM, jlcreed@... writes:


> What is the opinion of folks with regards to the Lab a and b values
> that should be strived for when producing a neutral curve?
> 
> I've been playing around for a good few days now trying to produce a
> neutral curve, and seem to be going around in circles at the moment,
> with values within plus or minus 0.5 for both Lab a and b; are these
> figures considered OK or should I continue with more iterations?
> 

Negative a* values give an unpleasant green look, even at fractional values, 
so you would probably want to err to the positive for a*; b* is a matter of 
preference, paper tone, and lighting. Its difficult to get things much tighter 
than fractional a/b values...

C. David Tobie
Product Technology Manager
ColorVision Business Division
DataColor Inc.
CDTobie@...
www.colorvision.com



[Non-text portions of this message have been removed]

Thanks Jamie for the question and Paul, Ed and David for their concise 
answers. I was spinning my head on this issue for quite some time...

Joost