[ Updated : Scroll down for people who allready read the entire document ]

For a more scientific/mathematical view on "True colors on mars" please read :
http://www.atsnn.com/marscolors.html

I hope this post will help adress the countless "conspiracy style" webpages and postings I encounter each day, and that have cought the attention of the ill-informed and ignorant alike. The people who start these theories often did quite a bit of researching and experimenting before coming to the statements, so they are just from their point of view. Everyone has his area of expertise, and image capturing / postprocessing / color calibration is not one that is very easy, nor a very widespread one for that reason.

I write this little bit of clarification from the point of view of an experienced image postprocessor/photographer, and not that of a scientist, there have been enough fact-finders that use the power of math and science to explain it, but that does not seem to be enough.

My experiences on this area came from working for Canon, where I was tought a lot about the inner workings of CCD's and imaging devices such as scanners, and from a personal point of view, as being a photographer.

To simplify matters, I have made two sections - theory, explaining some of the knowledge needed to get to the conclusions I made in a very simplified yet still quite lengthy form, and some simple photos to show it after that. Skip the theory if you're not the type of person to read long stories.

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Start of theory/explaining
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All we are talking about here is "Color calibration" aka "whitebalancing".
These two words basically discribe the nightmare of all digital camera manifacturers, ever since the first was tested to capture a photo.

CCD's (CMOS etc, any electronic recording device) and film suffer from an issue that they cannot "change" the way they capture light.
The result of this is that with changing types of light (e.g. tungsten, lightbulbs, sunny daylight, cloudy daylight etc) the final image is rendered incorrectly (since the camera or film is programmed/designed to record at a certain color temperature by default)

Most analogue films are "daylight balanced", which means they render pretty accurate colors durning regular daylight, being anything lit by the sun. Try them in artificial light, and the results can vary from a light colorcast to green, purple, yellow etc.

The same thing goes for CCD's - the digital counterparts of film.
However the data they capture we can call "RAW", can be color profiled and processed in-camera, adapting it to whatever the camera is set to.

This color profiling is by no means a perfect art - There are countless variables that will mess up the presets for whitebalancing, and the only near-perfect way to calculate the type of light you are working in is to use a "graycard" - Fill the camera frame with a special type of standardized gray-card held in the same light you are shooting, set colorbalance to that, and voila..pretty good color rendition (If said recording device can actually adapt to shooting at such low or high color temperatures - measured in Kelvin)

The CCD's in the spirit and opportunity are, albeit more sophisticated, still cursed with the same basic problems that the cheapest webcam has to cope with, and this is the source for most "false color" theories I encounter on the net.

The images that get returned from the Rover's are actually 3 black and white captures - since the CCD cannot distinguish color! These 3 photos were taken through colorfilters - usually this would be one green, one red, one blue shot, and then merged together to form the final color image.

However the red filter is replaced by a filter that is more tolerant to near-infrared, and hence manually merging the RAW data from nasa WILL yield incorrect colors, unless you know how much to tweak the "Infra"RED image to balance for its extended infrared light capture. Yet people still try merging the 3 B&W images at home, and come up with skewed colors.

This process of color calibration is not an automated task - The sundial with it's 4 colored specs and gray-toned circles helps the people down here to understand what certain colors look like under given light up there, with the exception that the specs of color contain a pigment that looks quite different from regular paints when looked at through a near-infrared filter, again part of NASA's method to determine perfect whitebalancing. (or, according to the conspiracy theorists, the perfect way to mislead us so obviously!)

I do think that NASA did have this upon themselves, since the colors of the initial images released on the web differed quiet a bit, from pale to darkred - a nightmare for an image postprocessor like myself, and I cursed the unexperienced / timerushed person at NASA who allowed the images to be released in this state, at the time. In retrospect it possibly is due to pure timeconstraints and "public pressure" - SOMETHING had to get out, and it had to get out NOW, not in 1 hour, or two.

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End of theory/explaining
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Now, the photos.

Let's start with one of the other big sources of misunderstanding and misguidance :

Recent NASA press conference with color photo of Mars
As you see the photo is devoid of most red's


FACTS :
1) "Photo-of-a-photo" :
Whenever you capture a photo of something, your camera must be balanced to the lightsource at that location (99% of all modern day journalists use digital SLR cameras for their photographs). Judging the faces, the camera was properly whitebalanced to whatever light was used there. Updated : The photo itself isn't even properly toned - the faces are pale, and devoid of any human red/brown colors, this makes it even more appearent that the background shot was of a different whitebalance to begin with.

THIS MEANS IT CANNOT BE WHITEBALANCED AT THE SAME TIME FOR THE PROJECTION ON THE BACKGROUND, WHICH IS MADE OF LIGHT WITH A DIFFERENT COLOR TEMPERATURE! .

result : properly colored faces, anything not made of or shed upon by the same light will look WRONG/DISCOLORED.

2) Projectors have a tendency to wrongly calibrate/convert input to start with...if anyone here has ever used projectors for photos/images you will know it is by no means easy/possible to get things looking accurate.

MORE FACTS : What color does the MARS surface really have?
Just take a look at the photos made by the Hubble telescope, and you see the colors of mars as seen out of space - This is the color we have to compare to that photographed by the Spirit/Opportunity in proper daylight (sunset/sunrise will give skewed colors, either warmer or cooler).

Some people came up with photos from mars that had a blueish cast over them, and the source was...NASA. I did some research on this and came to the unsurprising result that the Hubble has as much problems color calibrating itself as any other CCD made by mankind. However, we can see a unique opportunity to compare older and more recent, technologically more advanced postprocessing / colorcalibration, due to several imaging-specific sattelite-based missions sent to mars after 96.

EXAMPLES : (As collected through simple google image searches "Hubble Mars 2001" for example)

1991 : Early hubble image I stumbled upon :


1995 : Calibrated with the knowledge of mars at that time, with sattelite data from dating back to the 70's (remember : nearly 2 decades were without sigificant sattelites sent to mars!)


1997 : The Global surveyor was sent to Mars, the first proper sattelite since many, many years. All images from NASA have a distinct change in color (more reddish) since that year (98-99 etc)


2001 : Mars Odyssey was sent out, specifically to capture the surface of mars (imaging mission). A host of new techniques and electronics to establish better color calibration of nearby mars for NASA.


2003 : A recent photo made by the Hubble...not unlike that of 2001, and very much like the colors we have witnessed on Spirit Photos - To my knowledge the spirit is located in the lighter colored areas, not on the poles (which have, generally, a much darker soil)


And for pure reference, A photo from the recent ESA (Mars Explorer) images, independandtly from NASA :


The sky in ONE of the NASA images (a panorama) _was_ doctored ...this was easy to check up, since the entire sky color was of exactly the same RGB value - and a rather silly way of trying to make it look better (problem with panorama's is that in parts shot into sun direction the sky tends to bleach out tremendously, giving you uneven skycolors which looks "crap")
The colors of the JPG's on the JPL website have been inconsistend to say the least - some were too dark, some were reddish, some yellowish. Please take a look at the properly calibrated TIFF's before judging. Also over time the images are corrected, where we can make the simple conclusion NASA is not trying to cover up, just fixing what they did wrong. Why not spend 1 day more per image to get them properly colored if this all would be a huge cover-up-and-desceive mission?

I dont feel I have put enough information in this posting, since there are a lot of more subtle things I could say to show people that there is no evil doctoring going on with the images and or color calibration, but the main conclusions are noted above.

[ UPDATED SECTION ]

1) Changed "photo of a photo" to update my thoughts about the photo itself - after looking at it for a little longer, it seems as the entire photo doesnt even have a proper whitebalance set (either in-camera or afterwards for processing it for the web). The red channel in that photo is quite badly represented, with the faces of the people being a bit pale and devoid of color - this magnifies the allready yellowish effect from the projection.

To clarify this for even the most stubborn people out there, I decided I'd just show a little "real life" situation - My monitor (9300 Kelvin) and a regular tungsten 150 watt bulb (about 2700 Kelvin). My camera had a tough job capturing the extremes, and especially the 9300K (very cool) monitor setup I have was giving him some trouble. Camera was a Fuji S2 12 mpixel digital SLR, for thos who care to know (not much unlike the cameras used by journalists, although these are mostly nikon/canon)



2) This image was created for "everyone" so apologise for my rather basic and non-technical usage of words and color/shapes ;-)

Most of my thoughts are embedded in the image, albeit shortened and without much detail. I noticed new discussions, where people were complaining about the atmosphere of mars being "blue" when viewed from outer space (Hubble) and "hence you can never have a red sky on the NASA/JPL ground images" .

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Thanks for your insightful analysis Majic! This is an issue that should be addressed considering its popularity. I can't quite figure what the "true color" conspiracy theorists are seeing in terms of a devious motive to alter the color. It doesn't seem to make sense to me. But it is annoying that there is so much variation just for the simple reason that one should like to have as real a picture as possible. But this raises a deeper issue...

"True color" is somewhat more of a philosophical issue than many people may realize. Colors are not actually properties of the objects that appear colored. Colors are a perceptual end-product involving several intermediary steps from the frequency of reflected light, atmosphere, perceptual lenses (which as you note may include photos of photos before reaching the observes' own bio-optics), and interpretation. You raise some of the complexities in this process of processing. As an example, I've noticed that if you look at pumpkin-seed butter under incandescent light inside, it's dark brown; but then step outside and look at the same butter in sunlight (direct or indirect) and it's bright light green without any trace of brownness! It's the most remarkable color transition I can recall having observed in one substance and quickly demonstrates how color is not a private property of a thing but is instead a property distributed over all interacting environmental elements.

Another thing to consider in this case is that Mars as a whole seen from a distance can appear to be of a different color based on what time of the year it's observed. If my recall is correct this is due to seasonal sand storms that Carl Sagan was involved in determining. Long ago it was proposed that the seasonal color change of Mars was a signature of seasonal plant growth .

This may be a useful report: Solving the color calibration problem of Martian lander images.

Ian, yes ...for me the whole problem you define is contained in the word "color balancing" or more commonly referred to as "whitebalance" ...and it is very, very complex. Well not really complex, it is very difficult to achieve properly. I read the report and it goes into quite some detail, but unfortunately it will not mean much to the "mars-color-conspirationists" . They have a tendency to skip everything that they percieve as threatening to their point of view, then look for quick other alternative ways as to why a few images are proof of NASA's giant cover-up (Oh and NASA pays ESA to do the same - and every amateur telescope-owning guy out there ...you can buy a descent telescope that can distinguish storms on mars for the price of the average quality hi-fi + television set - a few thousand dollars)

My point of view on this is that we can and HAVE established a given average color for regions on mars, and with this knowledge we can at least roughly compare to the photos made by the Spirit and Opportunity (Local variations in color, and time of the day not included) . To me the colors look pretty similar.

Yes I realised that seasonal changes will effect the color of mars, but this is easely distinguisheable from the postprocessing (which yields an overall color cast / colorisation, not just regional discolorations like storms etc)

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So what exactly is going on here, are conspiracy woo-woos looking at Mars photos with different color calibrations and claiming that NASA is covering up aliens or something? :-?

Ah, the innocence of youth. Do yourself a favour - don't click this link, and if anyone ever mentions the name "Hoagland", run. #-o

WHAT THE??? And the benefit of these claims are...

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Ah, the innocence of youth indeed....

Well, besides the entertainment value and the fact they are fun to pull to shreds, not much...

However, I've learned a lot about how digital cameras work and how NASA creates color images, so it's not a total loss...

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"Ignorance has caused more calamity than malignity" H.G. Wells

"Getting lost is part of exploring." Uniqua in "Backyardigans-Heart of the Jungle"

"Trying to wrap my head around creationist astronomy is like trying to ride a unicycle around a Moebius strip: it’s off-balance, physically impossible, full of one-sided arguments, and in the end you don’t go anywhere." Phil Plait

Okay, I didn't - what does the link say?

majic

Thanks for the great explanations. Your succinct and clear writing makes the issues easy to understand. I am interested in reading more on this topic , and in greater detail, if you care to make more posts. No doubt others are too.

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Here's an interesting question:

I take a picture indoors using daylight film and available light, which happens to be from the florencent tubes from the ceiling. The print ("Print A") comes back with a greensh tinge, because the color was not rebalanced in the printing process.

I scan the print into a computer, and then use Photoshop to adjust the color balance until the skin tones look natural to my eye (I'm no graphics pro, but I have tweaked photos to make them look better). I print "Print B" on an inkjet photo printer.

So which image shows the actual colors, and which "covers-up" the true colors, the image that shows the actual colors recorded on a medium design for sunlight, or the image altered with computer software to a subjective standard of my own color perception?

Another thought: is all black & white photography guilty of "hiding actual colors"?

That's why this whole "Mars color conspiracy" makes no sense to me. An image matching the appearance of Mars to a naked human eye on the surface of Mars may not necessarily hold the most scientific value, or even be the most aesthetic. People who work with images in news, advertizing and art alter the color of images all the time. My must the Mars images be different?

Dancar

It makes no sense to me either. The only conspiracy explanation i've heard that makes any sense (and not very much at that) is that NASA wants to show the world that mars is less "hospitable" then it really is.

Okay, we send a 800 million dollar probe to another planet, one that we know has a very thin atmosphere, colder then heck, no surface liquid water, and no oxygen, all facts we can gather from here on earth by any institution with a resonable size telescope, and NASA needs to fiddle with the color because they don't want folks to know that it really is more habitable then it really is...

Okaaaay

__________________
"Ignorance has caused more calamity than malignity" H.G. Wells

"Getting lost is part of exploring." Uniqua in "Backyardigans-Heart of the Jungle"

"Trying to wrap my head around creationist astronomy is like trying to ride a unicycle around a Moebius strip: it’s off-balance, physically impossible, full of one-sided arguments, and in the end you don’t go anywhere." Phil Plait

Yeah, wouldn't it be cheaper to just use a set that looked less hospitable?
Like this one.

What does the shade of the rocks and sky have to do with habitibility?

If NASA wanted to skew the pictures & data to fool the public, they would make Mars look more applealing, and maybe even make up evidence of life or signs of life. That would result in greater public support for goverment funding of more Mars probes and even manned missions.

My question for the woo-woos: Why would NASA cover up data about Mars as you allege when revealing everything would be benefical to NASA?

Dancar

Ah, the innocence of youth...

You forget that the Illuminati want to keep Mars's habitability a secret, so that they can hide there on their own when Planet X comes.

Excellent post Majic, thank you. Can this be used as the basis of a FAQ answer, given the popularity of topic?

Jon

Ah-ha! So That's the real reason behind President Bush's proposal. . . .

:P

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It has conspiracy woo-woos looking at Mars photos with different color calibrations and claiming that NASA is covering up aliens or something. :wink:

Why am I not surprised? Actually I suppose I am at least a little bit surprised that some people think different color calibrations is 'proof' of a cover-up by NASA. Usually they go on more 'substantive' evidence like vague pyramid shapes. :roll:

BTW, the Neuroquest in this Feb issue of Discover magazine is about this very thing. Click here to see it yourself. (DISCOVER Vol. 25 No. 02 | February 2004 | Mind & Brain)





In case the article goes away, a CG rubix-like cube is displayed twice, once under yellow light, once under blue. An arrow points to a blue-looking square in the first image, then to a yellow one. They turn out to be the same shade of grey actually.

I find this about the color calibration dial on the Rover.
http://www.keithlaney.com/spirit_col...alibration.htm


And this observation from another site.
http://www.goroadachi.com/etemenanki...ddencolors.htm


Comments?

Read a couple of the threads on this forum... The answer is here... And it's an easy one.

Short answer: The panoramic images use a near-infrared filter rather than a red filter to create the red part of the image. As it happens, the blue color spot is particularly bright in the near-IR range (actually, brighter than it is in the blue range), though it's not bright in the red range. So when you image it in the near-IR range and then convert that data into the red portion of the image, it ends up looking pink.

Long answer: Here

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Showing that Feynman was especially correct about some individuals.

The colour enthusiasts who have been critcising the MER images have conversely been waxing lyrical about the Mars Express images. the real reason for this is the blue and green tones in thr Mars express images, which fit their expectations, and the absence of them in the MER images.

Ironically the colour images from Mars Express's HRSC are made using the following bands:

Blue 430 +/- 45 nm
Green 530 +/- 45 nm
Red 750 +/- 20 nm

http://www.linmpi.mpg.de/~hoekzema/mars03.htm

These bands are very similar those used by the MER Pancam for most the colour images

Blue 480 +/- 10 nm (L6)
Green 530 +/- 10 nm (L5)
Red 750 +/- 10 nm (L2)

The main difference is that MER uses a slightly longer wavelength blue and the HRSC had broader bands. Therefore any colour differences between MER and Mars Express imagery must arise from processing, presentation, and perception differences, plus the fact that one is orbital and the other surface.

Any suggestions for the apparent green and bluish tints in the HRSC imagery which are almost certainly artefacts?

Jon

Actually, the biggest problem (that I've seen) is the fact that the blue patch on the MarsDial happens to be particularly bright in the near-infrared range. Since nothing that Mars Express is imaging has that strange property (that is, is much brighter in near-infrared than in red), no one notices Mars Express's color differences.

__________________
"Nobody understands quantum physics." -- Richard Feynman

"So, does quantum physics predict circular orbits for electrons?" -- Student in my Intro to Quantum class

Showing that Feynman was especially correct about some individuals.

Actually yes as posted in another thread by me :

"The blue color has allready been adressed in an ESA press conference, as being "a mineral" . Some research on this topic leads us to radiated Halite (aka salt!). This mineral forms after water condenses - and that is probably exactly what happens, or has happened in that valley (salt water from below the surface vaporising, or an ancient stream of water perhaps)."

The photo we are talking about :
http://www.esa.int/export/images/ob_22_reull_v,1.jpg

The mineral :
http://www.crystallineenergy.com/ima...s/blhalite.jpg

And the second, "green" photo :
http://members.chello.nl/j.lesnussa/mars4S.jpg

Please note that the mineral Peridotite (A magnesium silicate) has a green color and has been detected on mars previously.
http://ve.ou.edu/weaver/minerals_rocks/peridotite.jpg

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Strictly speaking, peridotite is a rock, no a mineral. Peridotite is composed mostly of the greenish minerals olivine and pyroxene. Bad Geology! [-X

Jon

Yeah, I'm not much of a geologist :/ [-( Anyways, doesnt change the fact that the ROCK (here, you have it) has an overal green appearance and has been previously detected on Mars in substantial quantities.

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Recent Nasa image released from spirit (30 jan. 2004), presumably with the L4 filter instead of the more commonly used L2 filter (Near Infrared) :

As you can see, the colordisk is looking fine, and the color of the land is still similar to what it looked like in previous photos with L2 filter for red.


[Updated : 31/01/2004 : 6:15 GMT]

NASA had some interesting text to go along with this image :

"In the upper left is a color image of the panoramic camera calibration target, also known as the martian sundial. The color panel of the calibration target looks almost exactly like it did on Earth, indicating that the color shown of Mars, though approximated, is close to true color.

The monochrome image in the upper right shows the sun, magnified five times. This image was acquired by the panoramic camera as part of a routine sequence of images designed to monitor the dust abundance in the martian atmosphere. The dust abundance appears to be decreasing slowly with time, consistent with the atmosphere continuing to clear after the large dust storm of last December."

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Nasa are now using the L4(red) filter for selectively released images instead of the L2(near infra-red) filter. It is good to know that now we have a chance to see any suprise areas of colour that the previous method would probably have missed (if/when objects with subtle huges of blue an green occur they are more likely to be seen).

Not only did we get them to admit what was going on;
Nasa admits colour inaccuracies

It will be interesting to see if images that include the sky will now be shown using the same method. We know from the pathfinder mission that blue sky/clouds are possible on Mars and using the L4 filter we may well capture some of the amazing scenes of blue, blue/red and other combinations that Mars can offer us.

It is very pleasing to see Nasa react to public opinion in this way.

Phobos

You started a thread before about the "real" colors on mars, and you try to bring it up again - I particulary dont like the way you mention here NASA admits color inaccuracies, yet if you would have read the article you linked, you would see that there is no reference to _any_ NASA person saying anything about the image colors at all ! Actually they say they are "very happy" with the images.

The only thing your link proves is that some journalist did a 1:1 copy from some rumours on the web, and the _journalist_ expresses some thoughts on the color. There is no quote from any nasa person mentioning image colors - Not even an indirect assumption you could make out of it.


The only reaction NASA ever gave on this issue, was done by a respectable nasa lead scientist, in an email conversation with someone trying to clear up the color issue - and he provided that person with verifieable scientific data describing the way the rover captures the image data, and how it should be interpreted - this article is quite lengthy, you can find it here :

http://www.atsnn.com/marscolors.html

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