Benefits of Dot-proofing
The only problem is that most use screening
technologies which are not really screens at all. At least
not as we know them in the offset world, i.e. lines per inch.
Instead they use techniques known as dithering, error diffusion
or frequency modulation. The benefit of these processes is
that they produce a smooth continuous-tone quality and work
well with color management to produce accurate color. The
problem is that they mask the many imperfections of the four-color
Even there¡¯s the same color saturation value
between continuous color proof and dot proof, human eyes will
feelcolors on dot proof are much more similar to the press
color, due to the existence of screen patterns.
One of the benefit from dot-proofing is known
as ¡®Detecting moire¡¯.
One of the most notorious of the ¡°process¡± imperfections is
moire and this happens when the four-color screen angles misalign.
The result is that unpleasant wavy pattern we all know so
well. This is called a screen or color moire. Then we have
what is known as subject moire. This happens when a busy pattern
in an image, such as a checkered fabric, interferes with or
complicates the screen angles.
For advertising proofs, you usually want the best color match.
But for overall quality control, you should be proofing with
the same file that will image the printing plate. Luckily,
inkjet technology has come a long way. At a resolution of
720 dots per inch and using screening software, an inkjet
proofer is capable of reproducing a halftone screen at 85
or 100 lpi.
As many of dot-proofing solution providers are
promoting, dot-proofing is said to be able provide 200 lpi
proof with 720 dpi proofers. This means a single cell which
can present 257 gradation levels at 3200 original DPI will
be limited to 3.6X3.6 (about 14) gradation levels. VisualDot
is overcoming this limitation with using 8 bit conversion
and HIFI inkjet technology like variable dots and diluted
inks, but the shape of dots with limited number of inkjet
droplet spots cannot be said to perfectly predict 100% of
moire in this case. Dot-proofing technology is not a kind
of magic and it is depending on the performance of proofer
machines. In this regards, you¡¯d better regard the purpose
of dot proof as ¡®to more press-look proof output¡¯ rather than
¡®to predict moire of press perfectly¡¯, when you¡¯re creating
dot-proof of 200 lpi at 720 DPI.
Another reason for the limitation in detecting moire with
dot proof is the existence of additional color spots in inkjet
proof. Inkjet inks have a much wider color gamut than offset
inks. So the system¡¯s color management software re-maps the
inkjet gamut to match the offset gamut, blending the colors
accordingly. As a result, it adds dots that are not normally
present in the CMYK rosette. This is especially true with
six-color proofers. While six colors provide an even wider
spectrum for matching special colors and different presses,
they add more dots to achieve the right blend.
In summary, theoretically it is impossible to
create the same look of press with lower resolution inkjet
But we can create as similar look of press as possible with
using dot proof technology. This means, customers will get
the proof output, at least better and more accurate than continuous
color proof output.
You¡¯ll find the difference in colors and details by simple
adoption of VisualDot module into the current proof workflow.