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Originally Posted by Ian Goddard
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)