Digital BW, The Print

--- In DigitalBlackandWhiteThePrint@yahoogroups.com, David Burges
<davidburges@...> wrote:
>
> This one is especially interesting, there is concern about the way the  
> printing company manage the flow
> as the files are swinging from yellow to blue???

David,

I played around with a few conversion techniques (sRGB to CMYK) for
B&W images.  Thought you might be interested.  

Using Photoshop's Custom CMYK, I created separation parameters as
follows:  SWOP, 20% dot gain (you may need to use a different dot gain
depending on the press and paper), Maximum GCR, 100K, 240 Total Ink,
and 50 UCA.  The nice thing about this profile is that it will give
you a deep black, and could be used on nearly any output media, from
newsprint to fine coated stock (but you have to input the correct dot
gain for the paper/press combination).  

Then I created a 21 step grayscale in Photoshop, and converted to the
above profile using Perceptual intent (which I recommend for B&W
conversions, since you don't have to worry about losing color
saturation).  Pure black separates out to 44c/33m/32y/100K.  Middle
Gray separates to 2/1/1/59.  When you reach an RGB value of
153/153/153 (about 40% gray) all color inks have been removed from the
equation, and you get 0c/0m/0y/48K.  From this point all the way to
paper white, you have nothing but black ink being used.  The above
separation is pretty much guaranteed to give you a very neutral B&W on
press, unless you dealing with complete incompetents (and even then it
should be hard to screw up).  The very high percentage of K ink on
press will keep your file neutral, even if there is significant drift
or poor process control.  

The only thing I don't like about the Custom CMYK approach for B&W is
that the color inks drop off so quickly and you may see some
graininess in the 1/4 tones and highlights, since output nothing but
black ink.  To get those lighter tones, the ink dots will be smaller
and spread apart, so more paper white will show through.  But, for
B&W, Custom CMYK is a great solution if you don't have access to
profiling equipment.  

If you DO have access to good profiling software (ProfileMaker5,
Monaco Profiler, etc) a more elegant solution is to create your own
profile from available characterization data, using Max GCR.  Good
software will allow you to set the black and total ink limits, where
the black ink begins, saturation levels, etc.  With a profile like
this, you can still retain a high percentage of black ink throughout
the tonal range for stability and neutrality, but you can allow the
color inks to tail off a little more slowly as you approach paper
white.  For example, I built a profile using ProfileMaker5 and
characterization data from the Gracol G& data set, (which I used on a
recent job), using Max GCR, 100K, 320 Total Ink Limit, and Black start
at 0% black (ie, paper white).  Using this profile for conversion from
sRGB to CMYK gave me a value of 2c/2m/3y/3K in the 5% gray highlight
area.  A 25% gray will print as 7c/6m/8y/21K, which is pretty much
guaranteed to be black.  The results will be smoother in the
highlights, since you are adding a little bit more CMY ink to the
black ink.  Since black ink is about 3X as powerful as individual CMY
inks, neutrality is very likely, especially on a well run press.  Even
if the CMY inks drift a little, you should get a pretty neutral
result.  Not quite as bullet-proof as Custom CMYK, but it will be
smoother.  The Max GCR should keep your file safe from unwanted color
drift.  

In either case, you can tweak the K channel of the CMYK file after
conversion to adjust shadows, without affecting the color.  Either
approach works great for neutral B&W using 4/C process inks.  Your
route will depend on whether you have access to profiling software,
and the final result you want.  

Regards,

Lou