| Gray is
a color lacking a hue (also called achromatic color), or possessing
all the wavelengths of light in equal amounts so that none predominates.
(Romano, 1998). Grays are produced by the mixture of pigments.
The substractive colors, cyan, magenta, and yellow (CMY) combine
to produce a neutral gray.
Gray balance is the proper
percentage of combinations of cyan, magenta, and yellow inks
that produce neutral shades of gray. Hue (color) shifts will
occur when there is any imbalance of one of the components.
It is necessary that every printer determine their gray balance
for each combination of these components at specific line rulings.
This is obtained by using gray balance targets as shown left
and right. The targets represent only a few different dot percentages,
a chosen highlight (HL), quarter tone, midtone, three quarter
tone, and shadow dot (SH). Note: More gray balance blocks
can be used for a fingerprint. The actual number of blocks
used depends upon how much information is needed about different
neutral gray dot percentages.
Using a densitometer, a
neutral gray patch for each dot percentage can be recorded.
This information is then used by the prepress department to
set neutral gray control points for each halftone image. Knowing
the neutral gray control points will ensure more consistent
gray balance in printed reproductions.
The gray balance will vary
for each different ink set as well as the same ink set over
time. Therefore, it is recommended that the prepress department
develop an upper and lower control limit around the average
gray balance infor-mation. This will be the range the pressman
must fall within while printing. It is further recommended that
gray balance tests be repeated over time with the same ink set
if it has not been used for an extended period of time.
1. Romano, Richard
& Frank: The GATF Encylopedia of Graphic Communications,GATFPress,
1998: p. 368-9.
GENERAL HINTS FOR SUCCESS:
- Do not download the
sample target(s) above. They are .jpg/.gif images; the .eps
file that you will use are located below in the download section.
|
Download
