Re: [photo-3d] digital

[Brian Reynolds <reynolds@xxxxxxxxx>]

Robert A. Schreiber wrote:
>     Foveon, Inc., just announced a new chip:  16.8 M pixel CMOS
> (complementary metal oxide semiconductor chip), with 2.5 times more
> transistors than a Pentium III...According to the announcement, top
> professional gear today captures about 6 M pixels....cameras chould be
> available by early 2001.  Kodak has also announced a 61 M CCD (charge
> coupled devie) chip.  This is the first time that a CMOS chip has
> surpassed a CCD chip, which has been the technology of the last 20
> years....
> 

There are professional cameras that capture more than 6 million
pixels.  Various Medium Format and Large Format backs can do this (at
an admittedly high price).  Six million (real) pixels is often given
as a usable size for a single frame of 35mm film.

People need to be careful about pixel counts.  There are many factors
that effect image quality.  Besides the number of pixels (really
sensor sites) there is the size of the sensor.  The current trend is
to pack more sensors into the same (or a smaller) overall size device.
As the individual sensor sites get smaller they are less sensitive to
light and you need better optics to deliver the necessary resolution
to sensor.  (See Richard Berry's "Choosing and Using A CCD Camera" for
a good discussion on matching optics to a CCD camera.)

What you really want is a device with more sensors that are the same
size or larger.  This makes the overall size of the device larger and
runs into a manufacturing problem.  Due to the way semiconductor
devices are manufactured, a certain percentage of the area of each
wafer (which has multiple chips on it) will be bad.  The larger
(physically) the chips are the fewer good chips you get per wafer.
This is one of the big reasons for making smaller chips (of all
types).  There are very large CCD chips available, but because of the
low yield of large devices the costs are astronomical.  (Just ask an
astronomer, they're the ones using these chips.  :)

-- 
Brian Reynolds                  | "Dee Dee!  Don't touch that button!"
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