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24 February, 1999
IMAGE PROCESSING
(2) Dot screen separation
Dot screen areas are separated from non-dot screen areas (mainly text).
The machine determines that if white pixels are not detected around the non-white
pixels, it is a dot screen area.
The machine can do this by only referring to the green signal.
(3) Colored text separation
Black pixels and color pixels in text areas are identified by determining the
difference among the RGB maximum signal levels and the output levels of the
RGB video signals.
(4) Final evaluation circuit
The separation signal accompanies the data as it passes to the further stages of
image processing. The separation signal tells the image processing circuits
whether the data is black text, color text, or photo. The text areas are processed in
text mode and the photo areas are processed in photo mode in the subsequent
image processing steps.
Auto text/photo separation is mostly effective only for small characters or thin line
diagram elements. If there are large characters or solid line drawing elements in
the original, only the edges of these are processed using text mode; the inner
regions are processed using photo mode.
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