Page 119 - Graphic Design and Print Production Fundamentals

Graphic Design 107
Black Generation

We also have to provide instruction on how the black component of the CMYK mix will be created.
Remember that our subtractive primaries are CMY and that, theoretically, they provide all the colours in
the visible spectrum. Where does K (black) come in? To bridge the gap between theory and real world
performance, black ink does some very important things:

• It compensates for the spectral shortcomings of CMY inks: our inks are not perfect
representations of what cyan, magenta, and yellow colours should be.

• It eliminates registration problems in black type: if there were no discreet black ink, every
time we wanted to print black type we would have to stack cyan, magenta, and yellow on top
of one another and make sure they fit perfectly.
• It helps us achieve easier neutrals: we can use black to replace the grey component of colours
reducing the amount of CMY required to stay in balance on the press to provide consistent
neutral tones.
• It provides cost savings: black ink is cheaper than coloured ink.

• It increases contrast: black’s greater density extends the tonal range of CMYK printing and
improves the appearance of the final printed piece.

Since black is an add-on to our primary CMY colour set, we must provide instructions for its creation.
Typically, we specify the black start point, maximum black, and black strength.

• Black start point: The point at which black enters colour mixes (range of 0% to 50%). If the
black start point is 20%, then tones from white to 20% will carry CMY only.
• Maximum black: The upper allowable percentage of black ink used in the K separation
(range 70% to 100%).

• Black strength: The relative quantity of black versus cyan, magenta, and yellow in the neutral
grey component of colours (range 5 to 75%). As the number increases, colours can contain
more black.

Black strength settings are also referred to as grey component replacement (GCR) values in colour
separations. These may be set as percentages or simply as light, medium, and heavy, where more equals a
larger proportion of black taking the place of CMY in neutral tones. GCR is the successor to UCR (under
colour removal), which only moved exactly equivalent amounts of CMY to the black channel. UCR
separations exhibit a ‘skeletal’ black, where there is a small amount of content in the black separation.
With GCR, and as the black strength increases, more and more content moves into the black channel.

Final Processing

With the measurement file available, and total ink limit and black generation specified, processing can
start in the colour management software and an output profile created. It will take from two to five
minutes for all the calculations to complete. You may be prompted to specify whether to save the
profile in the system or user location, or both. The system location will make the profile available to