Digital BW, The Print

Hi David,

I hope this will help you out. It is a bit technical, but it explains it we=
ll.


To make color separations, the three additive colors (red, green, and blue)=
 are 
translated into their subtractive counterparts (cyan, magenta, and yellow).=
 In theory, 
equal parts of cyan, magenta, and yellow combine to subtract all light refl=
ected from 
the paper and create black. Due to impurities present in all printing inks,=
 however, a 
mix of these colors instead yields a muddy brown. To compensate for this de=
ficiency 
in the color separation process, printers remove some cyan, magenta, and ye=
llow in 
areas where the three colors exist in equal amounts, and they add black ink=
. 

A given color can be translated from RGB mode to CMYK mode in an endless nu=
mber 
of ways. But prepress operators typically use one of the following ways to =
generate 
black in print:
*	In undercolor removal (UCR), black ink is used to replace cyan, magenta, =
and 
yellow ink in neutral areas only (that is, areas with equal amounts of cyan=
, magenta, 
and yellow). This results in less ink and greater depth in shadows. Because=
 it uses 
less ink, UCR is used for newsprint and uncoated stock, which generally hav=
e greater 
dot gain than coated stock.
*	In gray component replacement (GCR), black ink is used to replace portion=
s of 
cyan, magenta, and yellow ink in colored areas as well as in neutral areas.=
 GCR 
separations tend to reproduce dark, saturated colors somewhat better than U=
CR 
separations do and maintain gray balance better on press.

Choose the type of separation based on your paper stock and the requirement=
s of 
your print shop.

To adjust the separation type and black generation:

1.	In the Custom CMYK dialog box, select a separation type.

The Separation Options area displays a graph based on current settings show=
ing how 
neutral colors in the image will separate. In the graph, sometimes called a=
 gray ramp, 
neutral colors have equal parts of cyan, magenta, and yellow. The horizonta=
l axis 
represents the neutral color value, from 0% (white) to 100% (black). The ve=
rtical axis 
represents the amount of each ink that will be generated for the given valu=
e. In most 
cases, the cyan curve extends beyond the magenta and yellow curves, because=
 a 
small extra amount of cyan is required to produce a true neutral. 
2.	If you selected GCR as the separation type, choose an option for Black 
Generation:
*	None generates the color separation using no black plate.
*	The Light and Heavy settings decrease and increase the effect of the Medi=
um 
setting (the default). In most cases, Medium produces the best results. 
*	Maximum maps the gray value directly to the black plate. This option is u=
seful 
for images with a large amount of solid black against a light background, s=
uch as 
screen shots from a computer.
*	Custom lets you adjust the black generation curve manually. Before choosi=
ng 
Custom, first choose an option (Light, Medium, Heavy, or Maximum) that is c=
losest to 
the type of black generation you want. This gives you a black generation cu=
rve to use 
as a starting point. Then choose Custom, position the pointer on the curve,=
 and drag 
to adjust the black curve. The curves for cyan, magenta, and yellow are adj=
usted 
automatically relative to the new black curve and the total ink densities.

If needed, specify values for Black Ink Limit and Total Ink Limit (the maxi=
mum ink 
density your press can support). Check with your print shop to see if you s=
hould 
adjust these values. 

In the Gray Ramp graph, these limits determine the cutoff points for the CM=
YK curves.
4.	If you selected GCR as the separation type, specify an amount for underc=
olor 
addition (UCA) to increase the amount of CMY added to shadow areas. Check w=
ith 
your print shop for the preferred value. If you are unsure of this value, l=
eave it at 0%.

UCA compensates for the loss of ink density in neutral shadow areas. This a=
dditional 
ink produces rich, dark shadows in areas that might appear flat if printed =
with only 
black ink. UCA can also prevent posterization in subtle detail in the shado=
ws. 

Hope this helps
-Dean
www.deanmbeattiephoto.com
Fine Art Black and White Photography



--- In DigitalBlackandWhiteThePrint@yahoogroups.com, "David Wroblewski" 
<dawroblewski@y...> wrote:
> I've been looking at the specs for papers recently, and I've
> come across references to an "ink limit" for a paper--
> for example, the Photo Rag datasheet on the Hahnemühle web
> site characterizes the paper as having an "ink limit"
> of 240%.
> 
> I gather that this is terminology from the printing press
> world, and that it means how much ink (240% of what?)
> the paper will accept before it get soggy. Does it have any
> practical application in the digital b/w world of inkjet 
> printers? 
> 
> I've only ever worked with an Epson 2200 (Windows XP and lately
> QTR/Linux) so I assume that the media setting is the indirect
> control for this. Or is this indirectly controlled by the various 
> curves we use to print files in B&W? Maybe fancy rips allow one 
> to control this directly somehow? If so, is that useful in 
> practice?
> 
> Thanks,
> david