Re: Cassini: where are colors and detail?

From: Chris L Peterson (clp_at_alumni.caltech.edu)
Date: 07/08/04 

Date: Thu, 08 Jul 2004 15:05:17 GMT

On Thu, 08 Jul 2004 07:07:52 -0600, "Roger N. Clark (change username to
rnclark)" <username@qwest.net> wrote:

>Forgive me if I misunderstand your position. I read in your post
>that even though bayer sensors may be used in future missions,
>you stated they are poor performers:

In terms of the spectral quality of the data from each of the three bands (or
four in the case of some sensors) they are poor performers _compared with_
cameras with external filters. In terms of spatial resolution they are poor
performers _compared with_ cameras with external filters. That does not make
them poor performers in general, nor does it mean they can't or won't be used in
certain instruments. A color sensor might be a good choice where the image isn't
being used for rigorous analysis, or where there is a requirement for fast
acquisition. It is never going to replace a camera with selectable filters for
the majority of imaging uses, however. Even if you could develop integral
filters of the same quality as external filters (which I doubt) the low number
of channels remains limiting.

>If you have any research published or on web sites that shows poor
>performance, please post them.

I have the response curves I collected with the 300D sensor and a couple of Sony
sensors. In all cases, the out-of-band leakage is severe across the entire range
(for instance, on the 300D, at 486nm, the red pixels responsivity is only 28dB
below the blue pixel responsivity. There is a band from 480nm to 500nm where the
blue/red ratio repeatedly goes through identical values.) You sure don't see
those kinds of effects with high quality filters! If you were using such
internal filters for order sorting, the spectral data would be very poor.

I'll send you the response curves I measured by private email.

_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

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