doug@xdos.UUCP (Doug Merritt) (01/09/90)
On the subject of smoothing digitized images of halftoned pictures,
e.g. from newspapers or magazines, the obvious approach is to translate
each square in the halftoned grid into a digital pixel with the corresponding
uniform grey value.
But I notice that actual newspaper pictures have an interesting peculiarity:
while light grey areas contain black ink circles on a white background,
the dark grey areas look like they contain white circles on a black
background. This appears to be due to the tendency of the ink dots to
run together when they reach a certain critical diameter, so that they
form a black square background with white centers in the places where
the lighter areas have vertices.
Should one just ignore this effect? Is this just an undesirable artifact
of newspaper halftone printing? Even if it is, is there some way to
correct the halftone-to-grey-scale transformation in such a way as
to get better results? For instance, is there subpixel information
that might be encoded in this smearing?
Also, how could one deal analytically with the fact that the centers
of the newspaper pixels shift in position towards the previous vertices
of the sampling grid as the tone increases in darkness? Or again, should
one just treat this as an optical illusion?
Doug
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Doug Merritt {pyramid,apple}!xdos!doug
Member, Crusaders for a Better Tomorrow Professional Wildeyed Visionary