Digital BW, The Print

Steve,

On Monday, December 22, 2003, at 01:00  PM, Steve Kale wrote:
> There could be printer differences, Eye-One (or other instrument)
> differences, or differences in drying time before measurement.  This
> why it is a good idea to do your own linearization.>
>
> Ok but you would agree that I am at least following the right procedure
> here?

Yes.

>> 3) Why is LK limited to 56 (cool)/ 60 (warm)?
> You answered this question in #4 below.
>
> Sorry my point was why around this level in the first place (in 4 I was
> simply referring to the cool curve having a slightly lower figure than 
> the
> warm).

As I recall the specific values were determined some time ago using an 
earlier beta version, prior to the implementation of the linearization 
feature.  The numbers were arrived at by trial and error, with some 
guidance from Roy.  The iterative process involved setting limit values 
for LK, LC, and LM, printing and measuring step wedges, plotting the 
density curves, and finally evaluating the curves for linearity.  We 
were also trying to equalize the densities of the cool and warm curves 
and adjust them, using the ink limit values.  A mid-tone (50%) density 
of about 0.6 was also a target value for adjustment.  Roy may wish to 
clarify, but I think that the linearization makes the absolute limit 
values used less critical in this regard.

>
>> 4) I assume the limits for LC and LM need to be the same to balance
>> against
>> metamerism and that LC and LM are used to cool the Epson K and LK (and
>> I guess it
>> follows that one might lower the LK limit a little in the cool file).
> The idea was to adjust LC and LM, relative to LK,  to produce a very
> cool curve that could be used for blending with the warm curve to
> produce the desired tone.
>>     Is a cool curve is
>> one that takes the warm and at 50:50 is neutral?
> It could be adjusted to do so, but perfect neutrality at 50% would be
> fortuitous.
>>
>> 5) If so, how does one measure neutral?
> You could use the LAB or XYZ values from the Eye-One to evaluate
> neutrality.
>>
>> 6) Was the cool file created by steadily increasing the limit on LC
>> and LM until this was
>> achieved?
> I wasn't shooting for neutral with the cool curve - just a very cool
> curve that could be subsequently blended with warm to get the desired
> tone.
>
>
> I guess I need a little more guidance on how you determine you have 
> obtained
> a cool curve (or neutral combination).  That is, when you are working 
> on
> _adjust[ing] LC and LM, relative to LK_ how do you know you have 
> reached the
> goal of a very cool curve (and so there is no need to go further)?

I just did it by eye to get a curve that printed the step wedge a cool, 
blue color.  It is then much easier to use the blender in the print 
driver to get close to "neutral" or whatever other hue you prefer for 
your prints by blending the cool and warm curves.

>
> <snip...

Carl