Re: Gold resolution
Re: Gold resolution
- Subject: Re: Gold resolution
- From: Roberto Michelena <email@hidden>
- Date: Sat, 09 Mar 2002 11:28:58 -0500
>
> Various people have 'proved' mathematically that anything over 1.414x
>
> the linescreen is unnecessary. But as you've noticed, it sometimes
>
> doesn't look as good as 2x.
>
>
Whoever "proved" this does not understand PostScript halftone
>
screening algorithms. PostScript shapes dots within each halftone
>
cell based on the high resolution image data.
I believe there's an incomplete picture on each view here.
Those people who 'prove' the futility of data over 1.4x, as Thomas said,
don't understand Postscript screening.
Thomas, on the other hand, is limiting his comment to the screening
algorithm on a single color plate, and he is right on his assertion in that
context, but that doesn't propagate fully into color reproduction.
In a single color, the fact that PS cuts each halftone dot to the high-res
data, would amount to 3x holding more detail than 2x holding more than 1.4x.
And in fact, you might probably see eyelashes that are smaller than the
screening cell.
But when you add up the other colors, forming a rosette, the detail is lost
because of the spatial dispersion of the samples ("pointillist effect") that
is the basis of halftone color.
Similar than talking about megapixels on digital cameras. As each pixel is
tinted only a single primary color (RGB), the spatial resolution is less
than stated. Except for three-shot cameras that are almost inexistent now.
In printed halftone color, each halftone dot is a single ink, and it's the
combination of the four inks which makes the visual 'unit'.
But strong contrast details, however (ie black hairline), can to some extent
go past the resolution limitation and benefit from 2x or maybe even 3x.
And careful choice of angles and dot shapes can also improve the detail in
specific images.
And finally, stochastic screening blows past everything. At even 30 micron
stochastic, a 600dpi scan looks definitively better than a 300dpi one and of
course 300dpi way better than 150dpi.
-- Roberto Michelena
EOS S.A.
Lima, Peru
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