Oki 8c Plus - Manual (Page 14)

14 OKIPAGE 8c Plus
Printing colour
No matter how colours are specified, the printer is only able to
use a combination of three colours plus black to generate an
image on paper. To achieve this the printer uses processes known
as halftoning and dithering. Each addressable picture element
(pixel) on a monitor screen or printed output contributes to what
we see in the final image. The pixels are placed in close proximity
so the eye is unable to resolve individual dots. Colours of
adjacent pixels appear to merge and produce a new colour. Using
dot patterns of a given set of colours to generate new colours is
known as dithering. Shades of grey can be generated by using a
similar technique of black dot placement. This technique is
known as halftoning and gives rise to what we perceive as a
continuous tone image. Examples of dither and halftone are
shown below:
Colour registration
The CMYK printing process, as already stated, uses overlapping
inks of cyan, magenta and yellow. To produce the best possible
output, the colours must print in specific positions so that
overlaps and dithering are accurate. If the colours are not aligned,
the resulting print will have colour shifts (colours produced
where incorrect colours overlap to produce an undesired colour)
or appear blurred. Using black to print grey and also black in
text eliminates the problem in these instances but not when
colour is constructed from two or more of the process primaries.
The print below shows how registration problems can cause
undesired effects:
dither pattern halftone pattern
The entire printing area is split into sections known as cells
(much like a grid). The patterns within the cell are then altered
to obtain the required amount of greyscale. An area of an
image containing 50% grey will contain cells that have half
of the dots within the cell printed with black and the other
half left empty.
If your OKIPAGE 8c Plus shows problems as described above
then refer to your User’s Guide in the section entitled “Adjusting
Colour Registration”.