And I'll echo my oft-repeated note, here, that "as seen by the eye on Mars" colors have to take into account that the diffused light from the sky is quite a bit redder on Mars than it is here on Earth. A surface that looks perfectly white sitting in a parking lot, or a desert, or pretty much anywhere in daylight on Earth will look distinctly red-tinged on Mars -- even assuming that the surface itself has not changed in any way.

-the other Doug

other Doug:

Except that, were you to be there, you'd see 'white' as, er, 'white'. Or not. There's a lot of work still to be done on how, exactly, human eyes would see Mars, and it's actually quite an important subject!

Bob Shaw

But would you see white as white?

there's a white sheet of paper on my desk, that lit by a little halogen bulb, looks fairly white.

If I lit it with a beige lamp, it'd look beige. If I lit it with a green lamp, it would look green. Outside now the street is lit with Sodium lamps - if I go out there, white cars will look kind of yellowey, they'd look a bit bluish if it were mercury lamps etc.


Doug

Well to side with Bob, a lot of it has to do with how your brain processes the relative colors (or in your case colours). Your example above features contrasts in ambient lighting-- from your lamp to the street and back again. Sit in an office all day without lighting contrasts and your mind will forget that the color bias of the fluorescent lights (blue-red depending on the actual bulb) until you step outside and notice how warm the lighting looks (deeper yellows). After a few minutes outside your mind will become accustomed to the new highlights until you step into a different lighting condition.

Anyone experienced in photography back in the days when we used a substance called "film" will be familiar with just how different various lighting conditions really are, and how the human brain compensates when the lighting bias is uniform.

At any rate, I do believe that after some time on Mars the initial shock of reds and oranges would fade and you would perceive whites as white. Kind of like the auto-color feature in Photoshop. If there is a study going on as Bob suggested above, I'd be fascinated to learn of the methodology.

(By the way are you really posting here at 3:00 am?)

The best indication, IMO, that pinkish/orange sky on Mars would not make white things appear pink/orange is the fact that the polar caps appear white as seen from Earth -- and that light has passed through the martian atmosphere twice, while light reflecting off of white paper seen on the surface would go through the "color filter" of the martian skies just once. Granted, the polar skies are probably less dusty than midlatitude.

Would the skies tint surface light some nonzero amount? Yes, but not greatly. In fact, a human retina on Mars would experience a lot of red/orange saturation, so a sheet of white paper might actually appear aqua/greenish to someone who had spent a few minutes taking the scenery in.

I dont want to know what it will look like when i've been there for 6 months, I want to know what it will look like when I open the hatch, fall backwards and land on my my $^#@ with awe!!!

Another JPL mosaic with a greenish overall hue is the Naturaliste view, or Burns Cliff

Also the latest Olympia panorama.

My best guess is that the greenish hue is caused by the 3-filter interpolation to a
full spectrum.
Naturaliste has been shot through L456 and yet it is greenish in hue too, yet not that pronounced as the others (L257's). Maybe they used information from L27 to complement the L456 view?


Naturaliste mosaic frame


Sol 422 -identical sol and chronologically ordered...

The works that I personally consider to look right are the Lion King and Rub-Al-Khali panoramas, they're masterpieces

I wonder to what extent temperature has significance on the perceived appearance.

Nico

Nix,

Temperature will have some effect on the non calibrated images but I suspect that it's too small to be significant for what's going on here. If you are using calibrated IMG's as the source there should be no temperature related effects.

There are two other environmental issues that haven't been mentioned that need to be factored in if we are serious about comparing reference calibration images from earth with attempts to emulate "real colour" in processed mission images.

Atmospheric opacity dramatically changes the effect of ambient lighting. Tau has ranged from 0.3 to ~ 3 throughout the mission. This affects the clarity of the images, the in fill lighting in shadows and, most importantly, the spectrum of the source light.

The optical characteristics of the local surface also has a noticable effect. The average albedo in Gusev is higher than at Meridiani (~0.23 vs ~0.17). Images are significatly affected by this. The calibration target is poorly placed to deal with this effect, a small target on the IDD would have been a useful addition IMO.

Helvick

Let's change that to "as photographed on Mars with a digital camera
white-balanced to whatever". This is equation confused by the unknown variable of human visual perception. You sit at your computer: the glow on your desk does not look bluish. Look around the room. It does not have the brownish tint of tungsten lighting. Go into the kitchen. You don't perceive the greenish fluorescent lamp hues. Go outside in late afternoon; you won't notice the warmish tones of the afternoon lighting. Get a digital camera, set the White Balance from 'auto' to 'daylight' or get a camera and put a roll of Ektachrome slide film in it. Photograph all those scenes. Develop/download and compare what the camera sees with what you saw.

What do you see?

--Bill

Actually, personally, I do notice. You being to 'ignore' it after a while - but on first look, one does notice these differences. When you put sunglasses on, things are tinted that colour. At no point when I wear them does that tint 'vanish'. The view remains the same. It doesnt fade to be neutral after a while. Perhaps it's different between people. Who knows.

Doug

Then again, over many generations, natural selection might favor the interpretation of a earth-based non-white as a Mars-based true-white due to the greater contrast provided...OUCH!
O.K. O.K.! I'll go away.

The importance of human perception of colour on Mars - perhaps crucial - will be seen when some future astronaut has to rapidly visually scan between a Martian scene and some form of computer display, and choose to click on the red button. Or not. Our physiological response to colour on Mars could be a matter of life and death. I've worked with two colour-blind electricians, and can I say that they added a certain degree of stress to the workplace! Imagine where we'd be on Mars...

Bob Shaw

While all this talk of the subjectivity of colour perception has some relevance, people often seem to forget that the spectrum emitted by a body is objective and measurable. Of course the rovers can only do a discrete sampling of the full spectrum, but barring any very sharp emission/absorption features, they can obtain reasonable calibrated spectra. Future missions could do much better.

Once the spectrum is known, it can, in principle, be reconstructed accurately on earth. This is an entirely objective procedure - perception hasn't entered yet. Of course if we want to reconstruct a large view, that would entail a huge amount of information - a spectrum for each pixel - but there's no fundamental constraint here.

My version of the statement "I want to know what the true colour of the surface of Mars is" is then "I want to have an image with such an accurately reconstructed spectrum enter my eyes". Of course the usual subjectivity enters if that image is presented on a small screen with some earthly ambient lighting. But in principle a room could be constructed with an accurate-spectrum panorama on the walls. Perhaps some VR headset would be easier.

Anyway, I'm not going to step onto the Martian surface, but I could find out what it would look like to set foot there.

Bill
As a person who did some *serious* amateur photography, I can tell you what you would see. The film would record the colour of the light source, so flouresenct lighting would give you that horrid geenish tinge while incandescent lighting can give you some surprisingly beautiful warm tones.

I have to concur with your point. What the camera (or film) sees is not necessary what the eye sees because there is more to vision then just light.

Robin

Robin, I would say that eyes see the same light, but film (or camera with disabled white autobalance) do not consider the environment and do not makes hue adaptation we automatically makes...
About Fredk considerations on the objectivity of Mars images, none of MER color filters matches exactly the response of human eye and in fact, to obtain a realistic image, RGB components would be a linear combination of these filtered images. This process mimic the real vision by making some approximations... and do not forget also similar limitations from any display devices, at the end of this chain... unless you purchased a "room with accurate-spectrum panorama on the walls"!