Colors of mars

I just read an article with the title: "Nasa is sabotating true colors
of mars" Most articles starting with Nasa&sabotating are mostly not
very good pieces; but after reading this I'm curious if somebody can
explain the folowing:

In the piece the argument is made that the Mars admosphere is not red
and Nasa is color adjusting images to make it look red. They argue
that while the color-calibration pictures
(http://www.jpl.nasa.gov/mer2004/rove...s/image-2.html)
show green, orange, blue and a red square, the color balance has been
adjusted in the following picture (when you lake at the calibration
target) and the blue square has been changed to red (and the green to
yellow) this can be seen in the bottom part of this pictu
http://photojournal.jpl.nasa.gov/jpeg/PIA05015.jpg

Two reference sites with the story:

http://frontpage.fok.nl/news.fok?id=36985 in dutch but refering to the
following english site: http://www.enterprisemission.com/colors.htm

In article , Raoul wrote:
I just read an article with the title: "Nasa is sabotating true colors
of mars" Most articles starting with Nasa&sabotating are mostly not
very good pieces; but after reading this I'm curious if somebody can
explain the folowing:
That story is good old trolling. Pay no attention to it please.

One color correction that can be applied is to make the colors on the
sundial color target look the same as they did in the lab on Earth
under white light. This makes the colors of objects on Mars look the
way they would if they were illuminated by white light. But the
ambient light on Mars isn't white - the atmosphere makes it
reddish[*]. You might might argue that for the spacecraft and rocks
eliminating the colored light shows their "true" colors. But for the
sky this certainly isn't the case because it is a light source, not a
reflective object.

Another possible adjustment is to ignore the color target and use the
camera's original calibration so the RGB values approximate the
original spectrum of the light received. It seems reasonable to claim
that this is how the scene would look like to a person standing there
on Mars. I think that this adjustment is still not the "correct" one
because our brains perform some kind of automatic "white balance".
When you are looking at an image from Mars it occupies only a
relatively small angle while the rest of your field of view is filled
with familiar objects under white light. This makes the colors of the
picture seem much redder than they would if you were completely
surrounded by a scene with these lighting conditions and your brain
adjusted to the new value of "white". If you have ever taken a picture
in non-white light that was developed without color correction you
know the effect - the color looks much more exaggarated than you
remember it even if that are physically correct.
[*] Is it always reddish? Only when there is a dust storm? Is it
possible that the color correction applied to pictures was calculated
during a dust storm and is not necessarily applicable for pictures
taken on fair weather?

Oren Tirosh wrote:

One color correction that can be applied is to make the colors on the
sundial color target look the same as they did in the lab on Earth
under white light. This makes the colors of objects on Mars look the
way they would if they were illuminated by white light.

why not take a small lamp and calibrate at night?


[*] Is it always reddish? Only when there is a dust storm? Is it
possible that the color correction applied to pictures was calculated
during a dust storm and is not necessarily applicable for pictures
taken on fair weather?

toby wrote in message ...
Oren Tirosh wrote:

One color correction that can be applied is to make the colors on the
sundial color target look the same as they did in the lab on Earth
under white light. This makes the colors of objects on Mars look the
way they would if they were illuminated by white light.

why not take a small lamp and calibrate at night?

A reference color target is just as effective as a reference lamp.
There is no real technical challenge to be solved here - the issue is
what color correction *should* be applied. Unlike the issue of
coloring astronomy images the question of "true" colors is relevant
for Mars because one day people could walk on mars and say "hey, it
doesn't look like the pictures".

There are stories on the net on how the first Viking images showed
blue sky and brownish rocks and were then corrected to a much redder
tint. I am trying to come up with an explanation for this that doesn't
sound like a conspiracy theory (there are more than enough people
exploring that angle...)

Oren

In article , Exeter wrote:
(Raoul) wrote in
om:

I just read an article with the title: "Nasa is sabotating true
colors of mars"

Here's another article on it. What I find interesting are the pics shown
at the press conference that clearly show a bluish sky and no red tint
whatsoever. Also check out the picture that a "graphic expert" created
using the raw RGB data provided by JPL. Once again, nothing like the
reddish tinted pics in some of the NASA photos.

http://fire.prohosting.com/cleoger/marscolors/
You can more or less place your "graphic expert" in the same category
as the apollo hoax morons.

In article , Oren Tirosh wrote:
toby wrote in message ...
Oren Tirosh wrote:

One color correction that can be applied is to make the colors on the
sundial color target look the same as they did in the lab on Earth
under white light. This makes the colors of objects on Mars look the
way they would if they were illuminated by white light.

why not take a small lamp and calibrate at night?

A reference color target is just as effective as a reference lamp.
There is no real technical challenge to be solved here - the issue is
what color correction *should* be applied. Unlike the issue of
coloring astronomy images the question of "true" colors is relevant
for Mars because one day people could walk on mars and say "hey, it
doesn't look like the pictures".

There are stories on the net on how the first Viking images showed
blue sky and brownish rocks and were then corrected to a much redder
tint. I am trying to come up with an explanation for this that doesn't
sound like a conspiracy theory (there are more than enough people
exploring that angle...)

One place to begin is get hold of specs of the cameras used to take the
photos. The get info on what kind of distortion might occur at the chain
of taking the picture to one have the raw data here at earth. You'll
need some help from JPL people, or perhaps from people working on the
Athena project at Cornell.