Re: Cassini: where are colors and detail?

From: Roger N. Clark (Change username to rnclark) (username_at_qwest.net)
Date: 07/06/04 

Date: Mon, 05 Jul 2004 19:22:16 -0600

Chris L Peterson wrote:
> On Mon, 05 Jul 2004 14:03:32 -0600, "Roger N. Clark (Change username to
> rnclark)" <username@qwest.net> wrote:
>
>
>>Color RGBG sesnors do provide good data, are linear and are great
>>scientifically as far as they go.
>
>
> I couldn't disagree more. They are acceptable for aesthetic images on continuum
> sources, and poor on anything with emission sources. So aesthetically, they
> would be okay for something like Saturn. Nevertheless, the dye filters are not
> good. They let other wavelengths through that contaminate the data, there are
> pixel-to-pixel non-uniformities that are difficult to quantify, and the Bayer
> pattern results in a loss of resolution and a decoupling of the spatial and
> color information. In short, they are not very useful for any real science.

Well, I guess I and many others are only doing fake science with digital
cameras by implication of your statements. People are using them for
spectroscopy, e.g. see:
http://www.astrosurf.com/buil/
http://www.astrosurf.com/buil/us/digit/spectra.htm

The spectral response on the 10D is well blocked over all wavelengths of the
sesnor, and there is no leakage. See the above link. I've independently
measured the response and agree with the above results.
Perhaps you've had bad experience with another sensor?

I'm using the 10D for surface brightness photometry, e.g. see
http://clarkvision.com/astro/surface-brightness-profiles/introduction.html

At work I am measuring reflectance on samples using macro lenses,
producing calibrated RGB 12-bit images at 8-microns per pixel.

Pixel to pixel non-uniformities are a non-issue. CCDs also have
these. Digital cameras are stable and produce absolutely superb
pictures, even when extremely stretched. Even if there were residual
variations, a flat field would remove them. Even CCD users do
flat fields.

Similar RGBG sensors have been proposed for NASA missions and I can
recall no criticism in technical reviews that they suffer from the
criticisms you claim.
>
>
>> Modern consumer
>>digital cameras provide excellent color. In fact Popular
>>Photography in its testing found that the canon 10D has the most
>>accurate color of any camera tested, film or digital (at the
>>time they tested).
>
>
> They do this in large part because of very smart internal image processing,
> which includes a good deal of knowledge about what the image is "supposed" to
> look like. I use a 300D myself, and I agree that it does very well, certainly
> better than film (which is itself an even worse medium for any kind of
> scientific work). But the Canon does not do well on things like nebulas where
> the light doesn't look anything like a typical terrestrial source.

This does not make sense. If the sensor is linear (it is), and the
filters well behaved (they are), the system provides good data
defined by the bandpass. Digital cameras could not "know" how
the vast variety pictures people take would look like and process
that accordingly. The way they take good pictures is
basic and fundamental linear response without serious artifacts,
just like any good scientific tool.

Roger
>
>
>>An RGBG sensor would be a great camera
>>on a mission, and they have been proposed in some instances...
>
>
> We'll see. As long as instrument payload is so valuable, I don't see it
> happening.
>
> _________________________________________________
>
> Chris L Peterson
> Cloudbait Observatory
> http://www.cloudbait.com

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