A method to improve color planetary imaging?

I really dislike the current method used on orbital and lander
spacecraft for color imaging. It consists of taking separate images
through three different visible light color filters representing Red,
Green, Blue light and combining them into a single color image.
The problem is calibrating the combination of these images taken
separately. So we have a spacecraft in orbit about Mars in Mars
Odyssey supposed to be able to take color images but there is so much
uncertainty in the combination of the colors that we've only had a few
visible light color images released.
And we have two lander spacecraft on Mars supposed to image in color
and each color image release creates controversy in the accuracy of
the color combinations used. It makes you long for the simple color
video cameras used on the Apollo moon missions.
The reason this method is used is that by using all the pixels in the
camera for a single color range you can gather more data in that
frequency range. However, there has been a method developed that
allows you to collect the same amount of data using fewer numbers of
pixels that might finally allow us to collect the full color range
simultaneously as with color video cameras:

Spider Eyes For Martian Robots
by Anil Ananthaswamy
San Francisco - March 28 2001
"The vibrating eyes of jumping spiders have inspired a new breed of
vision sensors that could give the next generation of Mars rovers
sharper eyesight, say researchers in California."
http://www.spacedaily.com/news/mars-general-01d.html

Visual sensor with resolution enhancement by mechanical vibrations
Koch Lab
Ania Mitros and Oliver Landolt
http://www.klab.caltech.edu/~ania/re...ib_retina.html



Bob Clark

Robert Clark wrote:

I really dislike the current method used on orbital and lander
spacecraft for color imaging. It consists of taking separate images
through three different visible light color filters representing Red,
Green, Blue light and combining them into a single color image.
The problem is calibrating the combination of these images taken
separately. So we have a spacecraft in orbit about Mars in Mars
Odyssey supposed to be able to take color images but there is so much
uncertainty in the combination of the colors that we've only had a few
visible light color images released.
And we have two lander spacecraft on Mars supposed to image in color
and each color image release creates controversy in the accuracy of
the color combinations used. It makes you long for the simple color
video cameras used on the Apollo moon missions.


The color filters are selected to spectually pass desired wavelengths of
interest to scientists,
and pretty color pictures are an afterthought. It doesn't take that
much to fool the human
eye. Use a spectrascope to compare a real scene vs the same scene
presented on a color
TV or monitor. The two will look way different, even though your eye
thinks that they
are identical. A color TV uses a combination of green light and red
light to create what
the eye sees as yellow. But there is no actual yellow light being
created by the TV set.
All that is happening is that the color TV is "tickling" your green and
your red (forgot if it's
cones or rods) in your retina in the same amount that true yellow light
would. In other words,
say yellow light causes 20% response in the red receptors, and 50%
response of the green
ones. Now, say that I take spectrully pure red light set to 20%, and
pure green set to 50%,
and shine that on your retina. You will think that it is yellow light.
Even though there is no
yellow light at all.

What scientists really want is a spectra for each pixel, so that they
can identify what
mineral those rocks are. After that they can process those spectras to
create pictures
as the eye would see it.

Also realize that the human eye's color difference resolution is about
half that of luminance
(B&W) resolution. Color TV broadcasts (anbalog or digital) take
advantage of this
and the bandwidth of the chroma (color difference) is half that of the
B&W (luma)
signal. NO point in transmitting what will never be missed by the viewer.

In article , Robert
Clark wrote:
I really dislike the current method used on orbital and lander
spacecraft for color imaging. It consists of taking separate images
through three different visible light color filters representing Red,
Green, Blue light and combining them into a single color image.

The production of "visible light" colour images is an incidental
byproduct of the science that the imagers are designed for. The purpose
of the imagers is (variously) to detect hazards (for which b/w would
suffice) and to identify minerals. To achieve the latter, a range of
filters are needed - considerably more than just "R G & B", there are at
least 2 in the near IR, and I wouldn't be surprised if there were UV
ones too. The selection of which filters to use, and how to combine them
to produce a "photo-realistic" image for the public, is as you say, a
vexed question. If you simply did not image the scene with any filter
vaguely like a "green", how are you going to produce a "photorealistic"
scene?
BTW, the whole issue of "photorealism" is much more complicated
when you ask "who's eyes am I doing this for?" Are you designing it for
a bi-chromatic person (one of the half-dozen types of colour blindness),
for a "normal vision" person (with 5-10% variations in the peak response
frequency of the R, G and B opsin dyes in their cone cells), or for the
rare tetrachromat women (who do have a noticeable enhanced colour
sensitivity)? Even within the "normal" population there is sufficient
variation that some people can differentiate some colour pairs that
others cannot differentiate.
How frequently do you update you colour calibration charts at
work? Every 6 months, or every 50 usages?

--
Aidan Karley,
Aberdeen, Scotland,
Location: 57°10'11" N, 02°08'43" W (sub-tropical Aberdeen), 0.021233

A key fact is that this would also improve infrared imaging. In most
studies you are given the infrared readings in the *separate* infrared
frequency ranges. Rarely are you given measurements that compare the
intensity of the readings across different infrared filters.
The reason is because of this same problem of calibrating the
comparison of the different filter images taken separately.
I'm saying if the readings were taken simultaneously, this would
result in a significant increase in the mineralogical inferences you
could make.


Bob Clark



Robert Casey wrote in message ...
Robert Clark wrote:

I really dislike the current method used on orbital and lander
spacecraft for color imaging. It consists of taking separate images
through three different visible light color filters representing Red,
Green, Blue light and combining them into a single color image.
The problem is calibrating the combination of these images taken
separately. So we have a spacecraft in orbit about Mars in Mars
Odyssey supposed to be able to take color images but there is so much
uncertainty in the combination of the colors that we've only had a few
visible light color images released.
And we have two lander spacecraft on Mars supposed to image in color
and each color image release creates controversy in the accuracy of
the color combinations used. It makes you long for the simple color
video cameras used on the Apollo moon missions.


The color filters are selected to spectually pass desired wavelengths of
interest to scientists,
and pretty color pictures are an afterthought. It doesn't take that
much to fool the human
eye. Use a spectrascope to compare a real scene vs the same scene
presented on a color
TV or monitor. The two will look way different, even though your eye
thinks that they
are identical. A color TV uses a combination of green light and red
light to create what
the eye sees as yellow. But there is no actual yellow light being
created by the TV set.
All that is happening is that the color TV is "tickling" your green and
your red (forgot if it's
cones or rods) in your retina in the same amount that true yellow light
would. In other words,
say yellow light causes 20% response in the red receptors, and 50%
response of the green
ones. Now, say that I take spectrully pure red light set to 20%, and
pure green set to 50%,
and shine that on your retina. You will think that it is yellow light.
Even though there is no
yellow light at all.

What scientists really want is a spectra for each pixel, so that they
can identify what
mineral those rocks are. After that they can process those spectras to
create pictures
as the eye would see it.

Also realize that the human eye's color difference resolution is about
half that of luminance
(B&W) resolution. Color TV broadcasts (anbalog or digital) take
advantage of this
and the bandwidth of the chroma (color difference) is half that of the
B&W (luma)
signal. NO point in transmitting what will never be missed by the viewer.

Robert Clark wrote:
A key fact is that this would also improve infrared imaging. In most
studies you are given the infrared readings in the *separate* infrared
frequency ranges. Rarely are you given measurements that compare the
intensity of the readings across different infrared filters.
The reason is because of this same problem of calibrating the
comparison of the different filter images taken separately.
I'm saying if the readings were taken simultaneously, this would
result in a significant increase in the mineralogical inferences you
could make.

But all this would do is increase the number of samples; it would not
solve the calibration problem. In fact, if you do the color calibration
"in the camera" you completely lose control over it. The result is just
the opposite of obtaining more reliable calibrations...

--
Greg Crinklaw
Astronomical Software Developer
Cloudcroft, New Mexico, USA (33N, 106W, 2700m)

SkyTools Software for the Observer:
http://www.skyhound.com/cs.html

Skyhound Observing Pages:
http://www.skyhound.com/sh/skyhound.html

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