Graphics Programs Reference
In-Depth Information
Fig. 9-12-6
When the
Posterize
command
appears, type
21
in the
Levels
field and the
gradient will be divided
into a 21-step wedge.
select the
Rectangular Marquee
tool by holding down the
M
key.
Shift M
will toggle this from Elliptical to Rectangle
marquee, too. Select half the gradient running horizontally and
choose
Image-Adjust-Invert
or use the
Command/Control I
key command.
Some printers have difficulty producing good separation
between the blackest black (step 1) and the tone just next to it
(step 2). You may want to place some visual indicator in
between the two to make it easier to see. I added a pixel
border of white between the two squares as seen in Fig. 9-12-7.
In a perfect world, we hope to see a small amount of tonal
separation between these two squares in our print since the
first block is R0/G0/B0 and the second is a higher value like
R12/G12/B12/. We should be able to see the differences,
which is one reason a simple file like this is so useful. We
should also see a difference between the twenty-first square,
which is paper white at R255/G255/B255, and the square just
next to it. The image created here is perfectly neutral so examine
if you see color purity issues in some or all the squares after
printing. Do they all appear neutral gray under a light box or do
they have a color cast, and if so, is it even among all squares or
worse in some? This is a good image to test tonality, tonal
