Digital BW, The Print

In a message dated 5/8/02 3:59:23 PM, jrandall@... writes:

>Aren't all the RGB partitioned curves (and the lumped RGB curves as 
>well) really just specific paper/inkset profiles with the color 
>(grayscale in this case) mapping values stored in three continuous 
>transfer curves (R,G,B) rather than as descrete values in a color 
>look-up table? 

Now heres someone who knows the true difference between 2d curves and 3d Look 
Up Tables! Always nice to find out someone is fluent in this stuff. The added 
advantage of the 3d LUTs are for correcting localized variations 
(non-linearities) that can't be reached by any one channel. In color terms 
(since its much easier to visualize than the gray inks) this means that if 
the medium saturation orange tones are too dark, or to saturated, or too red, 
that one specific area can be adjusted in an ICC profile, while a set of RGB 
curves could only make changes that would effect all reds or all yellows or a 
given lightness, no matter the exact hue or saturation. 

C. David Tobie
Design Cooperative
CDTobie@...

David:

Thanks for the color information, but I was asking a question re: 
this thread on B/W (no hue or saturation just 
luminosity/brightness).  If one was to build from scratch a pure B/W 
profile, am I still off base?  

Jeff Randall


 in Given the 
--- In DigitalBlackandWhiteThePrint@y..., CDTobie@a... wrote:
> 
> In a message dated 5/8/02 3:59:23 PM, jrandall@c... writes:
> 
> >Aren't all the RGB partitioned curves (and the lumped RGB curves 
as 
> >well) really just specific paper/inkset profiles with the color 
> >(grayscale in this case) mapping values stored in three continuous 
> >transfer curves (R,G,B) rather than as descrete values in a color 
> >look-up table? 
> 
> Now heres someone who knows the true difference between 2d curves 
and 3d Look 
> Up Tables! Always nice to find out someone is fluent in this stuff. 
The added 
> advantage of the 3d LUTs are for correcting localized variations 
> (non-linearities) that can't be reached by any one channel. In 
color terms 
> (since its much easier to visualize than the gray inks) this means 
that if 
> the medium saturation orange tones are too dark, or to saturated, 
or too red, 
> that one specific area can be adjusted in an ICC profile, while a 
set of RGB 
> curves could only make changes that would effect all reds or all 
yellows or a 

> given lightness, no matter the exact hue or saturation. 
> 
> C. David Tobie
> Design Cooperative
> CDTobie@d...

In a message dated 5/9/02 11:28:33 AM, jrandall@... writes:

>Thanks for the color information, but I was asking a question re: 
>this thread on B/W (no hue or saturation just 
>luminosity/brightness).  If one was to build from scratch a pure B/W 
>profile, am I still off base?  

But they are not black and white profiles... they are always color profiles, 
with varying hues and saturations in the target patches, and expectations of 
hue and saturation values coming back... and the resulting profiles are a 
series of Color Lookup Tables... so fooling them with a small gamut works 
better with some software than others, and replacing the expected colors with 
unrelated grays of varying brightness values will cause the software to 
process things like "lets see, I asked for bright red, which of these eight 
hunderd gray patches is the reddest?" which can actually be of value for 
previewing if you are using a variable tone ink set, but is quite limited for 
a neutral gray set. It would just print most of the possible combinations of 
of inks, map which of them best define which grays from the chart, and line 
them up in that order. This could have some unexcepted changes in there as it 
decides that the best medium gray is from one pair of inks, and the next step 
darker is better printed from an entirely different cart or carts.

C. David Tobie
Design Cooperative
CDTobie@...

CDTobie@... wrote:

>
> Now heres someone who knows the true difference between 2d curves and 
> 3d Look
> Up Tables! Always nice to find out someone is fluent in this stuff. 

Agreed!

> The added
> advantage of the 3d LUTs are for correcting localized variations
> (non-linearities) that can't be reached by any one channel. 

Which is EXACTLY why I was suggesting combining the curves with discrete 
profiles..  ;-)  I realize it breaks the rules, BUT we aren't talking 
about normal gamuts or color spaces either..  The gamut is so limited 
here that using a profile to force apart points along the profile (to 
add spread between values)  and to deal with media differences, while 
using the curves to provide a proper target hue may be a good interim 
approach..

Of course, the best approach would be custom profiles and  a monitor 
that showed perfect renditions of changes in hue perfectly while still 
properly limiting the on-screen gamut to match that of the ink profile..  

Even were that possible.

The problem is that looking for the subtle variations between Warm, 
Neutral, and Cold prints onscreen is likely to drive anyone crazy and 
certainly strain their eyes..

For that reason alone, pre-canned curves for each print temperature 
range are a good solution in my book.. My though with the profiles is 
just to bring those curves more cross-applicability.

Keith