Re: Cassini: where are colors and detail?
From: Chris L Peterson (clp_at_alumni.caltech.edu)
Date: 07/15/04
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Date: Thu, 15 Jul 2004 04:42:41 GMT
On Wed, 14 Jul 2004 21:34:21 -0600, "Roger N. Clark (change username to
rnclark)" <username@qwest.net> wrote:
>But now combine that image with lower resolution imaging spectroscopy,
>and you can resolve many of those discrepancies (see Figures 9A
>and 9B) in the above paper.
Agreed, although I would generally prefer the combination of an imaging
spectroscope and a high resolution sensor without a Bayer filter.
>You confuse cheap consumer digital camera problems with bayer sensor
>problems. In both high-end digital SLRs as well as any spacecraft
>application, the data are/would be treated in raw mode with
>full 12-bit digitization, just like with a monochrome CCD.
>The filter responses on top end cameras like the Canon 10D,
>which have been rated as the highest accuracy color response of
>any camera, digital or film, would be excellent in a spacecraft
>application. And in fact the response profiles of the 10D
>bayer filters are better than other filters that have flown on
>spacecraft and that returned scientificly valuable data,
>like Voyager and Viking.
Unfortunately, the 10D filters are not very Gaussian in profile. Indeed, they
have significant local minima, maxima, and flat zones that result in serious
ambiguities. The Sony sensors I've measured are worse. There are practical
problems with making dye filters that are monotonic on both sides of their
maxima. Of course, if you could solve this engineering problem, you would have a
sensor capable of generating better data.
>Given a 1-megapixel sensor with 3 filters in a wheel (3 megapixels
>sent down for color), versus a 3-megapixel bayer sensor, I would choose
>the bayer sensor, because 1) it has higher reliability (no moving parts),
>2) less mass and therefore cost, 3) color data are inherently registered,
>4) the inherent spatial resolution would be higher by about 1.6x
>over the monochrome sensor. Both systems can deliver equally
>accurate 12-bit data.
And I would choose a filter wheel system, because it eliminates the inherent
problem of unregistered images you get with a Bayer sensor, and because you get
approximately 1.6x higher intrinsic resolution.
Of course, in reality nobody would choose a 3-position filter for a science
mission, since there is no penalty for adding more positions and improving the
quality of the data- an option that isn't available for a sensor with an
integrated filter. And if you have an imaging spectroscope, you would be better
off using it with a B&W sensor so as to pair it with the higher resolution
imagery produced.
As you said, I think there is little else to be said. I'm sure you are correct
that color sensors will fly on future missions, but I doubt they will be the
primary imaging systems.
_________________________________________________
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com
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