kluge@fujitsu.com.au said:
> That would make sense. Being a single-pass scanner, the R, G and B
> sensors can't possibly be in the same horizontal position, can they?
Some of what I know about scanners... (we make scanners, FYI.)
They can, sorta. Linear color CCD arrays are usually three lines of CCD
sensors with each line coated with a different color filter. Hence, they
are often called tri-linear arrays. The sensor samples the width of the
image all at once, then steps the sensor to the next position to get the
next line of the image.
The sensors are offset vertically (that is perpendicular to scan direction)
by some amount, but that is corrected by delaying the two earlier colors
to match the latest color, or with optics. We usually use delays.
Color digital cameras use area arrays. That is, they have an area of
pixels, like a TV screen in reverse, so that they can sample the whole
scene at once. No need for that when taking a picture of a document in
a transport or flat bed.
Colors can be offset by poor optics, because different colors can focus
at different distances. Astronomers know all about achromatic optics.
However, good, compact optics can be expensive, and that goes for scanner
optics as well . I've seen so-called 1200DPI scanners that can't focus on
a 150DPI feature. And colors can bleed by week electronics, too.
(Hell, the avision scanner right next to me claims to have 30bit color,
that's 10 bits per color, but it saturates so badly that it can't really
be getting better then 12bits, 4 bits per color, worth of significant
precision.)
Anyhow, the above is a bit of a simplification, but you get the idea.
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This archive was generated by hypermail 2b29 : Thu May 04 2000 - 21:59:17 PDT