Rick Woods
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Reged: 01/27/05
Posts: 4448
Loc: Inner Solar System
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I've seen a Viking photo of Mars, as initially released by NASA. The lander was in the foreground. An American flag was painted on the lander, and the flag colors were true. The sky was also blue, and the sand was normal sand red (not the deep red we're accustomed to in Mars surface pictures). There are plainly visible patches of green on the ground.
Next to it was the "corrected" version of the same picture. The ground is the brick-red we usually see. The sky is orange-pink. And the American flag is various shades of purple. The green patches are no longer visible.
There are NASA people here. What do you know about these things? Why are the officially released photos revised to make everything more red?
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- Rick
14" LX200GPS
8" Meade 826C
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jayscheuerle
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Reged: 01/16/06
Posts: 3096
Loc: S. Philadelphia, PA
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Links?
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12" Green Goblin (trusser w/Protstar secondary and OWL refigured primary)• 6" f/5 Eero2 ball-scope • 6" f/5 Frankenscope • Garrett Optical 10x50 binos • Edmund 8" yoke-mounted red-tube reflector • Edmund 6" GEQ red-tube reflector (on loan to Dad)
Gone, but with lessons learned:
Skyquest XT8 • NexSTar 8i • Eeroscope 6" f/5 ball(sacrifice was not in vain) • Vixen ED80sf • Edmund red-tube 4.25" f/10 • Edmund Astroscan
Facts are stubborn things.
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jayscheuerle
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Reged: 01/16/06
Posts: 3096
Loc: S. Philadelphia, PA
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After looking around via some Google links, it seems that a lot of the early Viking pictures were not properly calibrated before being released.
It also appears that many of the "corrected" versions out there were not corrected by people who understand color correcting and simply hit the "auto levels" button in Photoshop, which doesn't necessarily give a true representation of the real scene, but merely makes the darkest point pure black and the lightest pure white.
Color correcting is an art and a skill and it's obvious that NASA hadn't put much importance on it. I'm guessing that these were adjusted by some engineers or the "computer guys" instead of the proper professionals.
The officially released photos weren't revised to make everything more red, they just were that way before fixing them. Rushed to release in the excitement. - j
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12" Green Goblin (trusser w/Protstar secondary and OWL refigured primary)• 6" f/5 Eero2 ball-scope • 6" f/5 Frankenscope • Garrett Optical 10x50 binos • Edmund 8" yoke-mounted red-tube reflector • Edmund 6" GEQ red-tube reflector (on loan to Dad)
Gone, but with lessons learned:
Skyquest XT8 • NexSTar 8i • Eeroscope 6" f/5 ball(sacrifice was not in vain) • Vixen ED80sf • Edmund red-tube 4.25" f/10 • Edmund Astroscan
Facts are stubborn things.
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llanitedave
Humble Megalomaniac
Reged: 09/26/05
Posts: 10908
Loc: Amargosa Valley, NV, USA
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Funny, but yesterday I had just gotten around to reading Carl Sagan's "Pale Blue Dot", and he explained that incident directly.
Seems that those who did the initial color calibration on the first images were TV technicians, essentially, and they calibrated colors as they did because they expected to see a blue sky. The planetary scientists later recalibrated it -- and even though the colors on the American Flag logo seemed to match, the colors on the calibration scale didn't. So it was recalibrated specifically using the proper calibration scale.
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"S.O.E." (Sauron's Other Eye) 16" Royce conical mirror: A permanent work in progress.
10" Homebuilt dob, old Coulter mirror
Next Project: The "Eye of Sauron" Observatory!
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Rick Woods
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Reged: 01/27/05
Posts: 4448
Loc: Inner Solar System
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Quote:
Links?
No links, it was in a book.
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- Rick
14" LX200GPS
8" Meade 826C
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Rick Woods
Post Laureate
Reged: 01/27/05
Posts: 4448
Loc: Inner Solar System
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Quote:
Funny, but yesterday I had just gotten around to reading Carl Sagan's "Pale Blue Dot", and he explained that incident directly.
Seems that those who did the initial color calibration on the first images were TV technicians, essentially, and they calibrated colors as they did because they expected to see a blue sky. The planetary scientists later recalibrated it -- and even though the colors on the American Flag logo seemed to match, the colors on the calibration scale didn't. So it was recalibrated specifically using the proper calibration scale.
Well, that's what I'd always heard, too. But it seems odd that properly calibrating the colors to the scale caused the flag to become wildly off-color in the red.
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- Rick
14" LX200GPS
8" Meade 826C
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Kobayashi
sage
Reged: 07/10/08
Posts: 291
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Quote:
But it seems odd that properly calibrating the colors to the scale caused the flag to become wildly off-color in the red.
The color of a picture depends on the color of the object and the color of the light.
Say you have a US flag in a room, lit by incandescent lights. If you use slide film to take a picture of it, the white stripes would look orange. If you use a digital camera with auto white balance, the camera would correct for the reddish tint of the light, and the stripes would come out white. Which do you consider correct?
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-- Ken Kobayashi
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Rick Woods
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Reged: 01/27/05
Posts: 4448
Loc: Inner Solar System
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Interesting point.
How could the lander color scale be used, then, to correct the photo, given that the ambient light was changing the apparent color of things? Shouldn't the scale have been off too? And once it was adjusted to be correct, wouldn't the flag also be correct at that point? How could you possibly know what was correct?
Add to that the fact that spacecraft approaching Mars, the HST, and my telescope all show a Mars with a surface of the same red as that shown in the surface image with the blue sky - not the burnt brick color we see in most surface images. I wonder what we would really see were we actually standing on Mars, and not looking at images that have been color-corrected.
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- Rick
14" LX200GPS
8" Meade 826C
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jayscheuerle
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Reged: 01/16/06
Posts: 3096
Loc: S. Philadelphia, PA
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The one thing you DO know is the lighting source color in this case. When the Sun's directly above and the atmosphere is 1% of ours, you know it's a fairly pure white. Sunsets are problematic, but probably not nearly as much with Mars' thin atmosphere. I'd bet that Martian sunsets are blue instead of red... - j
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12" Green Goblin (trusser w/Protstar secondary and OWL refigured primary)• 6" f/5 Eero2 ball-scope • 6" f/5 Frankenscope • Garrett Optical 10x50 binos • Edmund 8" yoke-mounted red-tube reflector • Edmund 6" GEQ red-tube reflector (on loan to Dad)
Gone, but with lessons learned:
Skyquest XT8 • NexSTar 8i • Eeroscope 6" f/5 ball(sacrifice was not in vain) • Vixen ED80sf • Edmund red-tube 4.25" f/10 • Edmund Astroscan
Facts are stubborn things.
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David Knisely
Postmaster
Reged: 04/19/04
Posts: 6880
Loc: Beatrice, Nebraska
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Well, again, what was stated was correct. The first "blue sky" images were not properly calibrated using the target, and it took a while to get the color right. Indeed, the response of the Viking cameras was not the same as the eye. Here is an account of the difficulties involved from the viewpoint of "astro-artist" Don Davis:
http://www.donaldedavis.com/PARTS/MARSCLRS.html
Here is a more recent attempt to get the Viking colors right:
http://www.astrosurf.com/nunes/explor/explor_vik.htm
They do agree more closely with that of the MER and Pathfinder color CCD images. Clear skies to you.
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David W. Knisely
Hyde Memorial Observatory
http://www.hydeobservatory.info
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Rick Woods
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Reged: 01/27/05
Posts: 4448
Loc: Inner Solar System
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Very interesting sites. But, did you see the difference in the flag images on earth and on Mars? Davis even says: "Notice the purple cast of the blue pigments in the flag and the color chart, an apparent idiosyncrasy of that camera system". This is saying to me that the image from Mars is not accurate with regards to the true colors of the landscape. I suspect the first image on the page is closer to the truth. It looks similar to the blue-sky image I saw in the book, where the flag colors showed true.
I guess what it comes down to is that I'm being shown a picture containing a flag that's various shades of purple, and being told that it is a faithful rendition of the true color of Mars. And I just don't believe it.
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- Rick
14" LX200GPS
8" Meade 826C
Edited by Rick Woods (08/27/08 05:58 PM)
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David Knisely
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Reged: 04/19/04
Posts: 6880
Loc: Beatrice, Nebraska
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Quote:
Very interesting sites. But, did you see the difference in the flag images on earth and on Mars? Davis even says: "Notice the purple cast of the blue pigments in the flag and the color chart, an apparent idiosyncrasy of that camera system". This is saying to me that the image from Mars is not accurate with regards to the true colors of the landscape. I suspect the first image on the page is closer to the truth. It looks similar to the blue-sky image I saw in the book, where the flag colors showed true.
I guess what it comes down to is that I'm being shown a picture containing a flag that's various shades of purple, and being told that it is a faithful rendition of the true color of Mars. And I just don't believe it.
Well, the blue-sky image is just plain wrong, as it was the initial attempt to do the color without properly calibrating it. Rayleigh scattering (the mechanism that makes Earth's sky blue) is not very effective in the thin Martian atmosphere, which is why much of the time, the sky color is more determined by the fine suspended dust in the atmosphere, and thus is more pinkish or brownish than blue. The other images Don does show has one which has a sort of pinkish-brown sky and the flag looking fairly close to the way it should (but not quite right for reasons stated earlier). However, the filters on the Viking cameras are not quite right for doing a true visual image with perfect color balance. As stated on Ricardo Nunes' page:
"Viking's Red filter is shifted towards the IR part of the spectrum and this affects the final images by introducing a purple cast to the image, specially visible on the blue target and on the lander itself. The Green is close to the human eye, but still a little off towards the yellow. The Blue filter is too "short" and covers the cyan part of the spectrum. This shifts are reflected on the "Filter" text colors on the "Viking Landers" table."
He then goes on to explain how to approximately correct for this, but still adds, "Unfortunately the blue channel is still a little off but this cannot be corrected, because we lack a "violet" or UV channel with a shorter wavelength range. His final results are quite close to the colors shown in the final Pathfinder, MER, and Phoenix CCD camera images, so that is probably about as close as we are likely to get. The only images that do show some blue in the Martian sky are those taken of the area around the sun near sunset. Then, there is enough atmosphere in the way of the sunlight to allow Rayleigh scattering to really contribute (but only in the area immediately around the sun). Clear skies to you.
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David W. Knisely
Hyde Memorial Observatory
http://www.hydeobservatory.info
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Rick Woods
Post Laureate
Reged: 01/27/05
Posts: 4448
Loc: Inner Solar System
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So the initial pictures that show a blue sky (and the flag, the correct color) are wrong; but the corrected pictures are shifted too far into the red because they are unable to provide the correct blue? Something about that seems odd. I agree that the dust will affect the sky color; but there's not dust in the air all the time.
Whatever the cause, it still ends up with us not seeing an accurate color representation of the Martian surface. I think the original, where the control colors were correct (and there were green patches visible on rocks and on the ground), is likely to be closer to correct. I've read the explanations for the color corrections, but I'm unconvinced.
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- Rick
14" LX200GPS
8" Meade 826C
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jayscheuerle
Post Laureate
Reged: 01/16/06
Posts: 3096
Loc: S. Philadelphia, PA
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Why would there be green patches on the ground? That makes no sense to me. If my color correcting brought that out, it would be a big red flag that something was off. - j
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12" Green Goblin (trusser w/Protstar secondary and OWL refigured primary)• 6" f/5 Eero2 ball-scope • 6" f/5 Frankenscope • Garrett Optical 10x50 binos • Edmund 8" yoke-mounted red-tube reflector • Edmund 6" GEQ red-tube reflector (on loan to Dad)
Gone, but with lessons learned:
Skyquest XT8 • NexSTar 8i • Eeroscope 6" f/5 ball(sacrifice was not in vain) • Vixen ED80sf • Edmund red-tube 4.25" f/10 • Edmund Astroscan
Facts are stubborn things.
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Rick Woods
Post Laureate
Reged: 01/27/05
Posts: 4448
Loc: Inner Solar System
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Jay,
Off? Why is that?
Now mind you, I'm not talking blazing, lime-green patches; they were dull greenish stains. The book suggests some sort of desert varnish as a possibility. But they were greenish, and entirely absent from the "corrected" version.
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- Rick
14" LX200GPS
8" Meade 826C
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jayscheuerle
Post Laureate
Reged: 01/16/06
Posts: 3096
Loc: S. Philadelphia, PA
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To me green=life and there's no life like that up there, so if I was showing green, it would mean that something's wrong with the picture I'm creating.
Regardless of that, because the filters used in the Viking landers were not tuned to represent human vision, an accurate color representation just isn't possible with the data available. It's kind of like counting to 10, but in place of the 4 and the 7, we get an 11 and 12. If counting to 10 smoothly if what you want to do, it's not going to happen. In terms of the science they wanted to do, it made sense to have filters that captured information outside of the scope of human vision, even if it meant sacrificing accurate visual reproduction. That's why you need someone who understands what the specific filters did so that they can take it into account while coming up with the best possible approximation. Without filters that are tuned to human vision, it's impossible to accurately represent a scene. - j
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12" Green Goblin (trusser w/Protstar secondary and OWL refigured primary)• 6" f/5 Eero2 ball-scope • 6" f/5 Frankenscope • Garrett Optical 10x50 binos • Edmund 8" yoke-mounted red-tube reflector • Edmund 6" GEQ red-tube reflector (on loan to Dad)
Gone, but with lessons learned:
Skyquest XT8 • NexSTar 8i • Eeroscope 6" f/5 ball(sacrifice was not in vain) • Vixen ED80sf • Edmund red-tube 4.25" f/10 • Edmund Astroscan
Facts are stubborn things.
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Rick Woods
Post Laureate
Reged: 01/27/05
Posts: 4448
Loc: Inner Solar System
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Quote:
To me green=life and there's no life like that up there, so if I was showing green, it would mean that something's wrong with the picture I'm creating.
Well, it appears to me that you're making at least two unjustified assumptions:
1) "Green=life". I don't know of any reason this is necessarily so. There are any number of minerals that are green. Serpentine, for one. Life is, of course, one possibility; but certainly not the only one.
2) "There's no life like that up there". You must have information nobody else has, to make this assumption. Last time I checked, it was an open question.
And, I agree about the correction. But not that it was done in the best possible way. Otherwise, we wouldn't be seeing a purple flag.
When I'm told something that is directly contradicted by my senses (e.g. "This is the real color of Mars"), I can't just accept it blindly without convincing proof; which, in this case, I have yet to see.
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- Rick
14" LX200GPS
8" Meade 826C
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jayscheuerle
Post Laureate
Reged: 01/16/06
Posts: 3096
Loc: S. Philadelphia, PA
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Yes, if there was a Martian "Emerald City" it would be green, but there's nothing up there that's been found to be remotely green. Life like a moss or algae? I can't disprove it, but it's pretty unlikely. We have no evidence for greens.
Regarding the purple-flag. The problem is that when you're applying a color space to one it's not meant for is that you end up with colors that don't make sense. It may leave you with some colors that are very close to their visual equivalent and others that are shifted quite a bit. You can't fix it by globally shifting the hue or adjusting the color balance because you change the colors that are close as well. So in order to represent the ground colors most accurately, they sacrificed other parts of the image. Blue is touchy. Less than 10° color shift will take you from royal blue into purple territory.
If you look in the imaging forums, and RGB image looks different than a HaGB or an RGSii. When you apply data outside of the visual spectrum to a channel in an RGB image, you're going to get something that has no visual equivalent and you won't be able to adjust the image to get it to match what you'd see visually, no matter how good you are with color.
You cannot create a completely visually accurate RGB image from Viking's data.
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12" Green Goblin (trusser w/Protstar secondary and OWL refigured primary)• 6" f/5 Eero2 ball-scope • 6" f/5 Frankenscope • Garrett Optical 10x50 binos • Edmund 8" yoke-mounted red-tube reflector • Edmund 6" GEQ red-tube reflector (on loan to Dad)
Gone, but with lessons learned:
Skyquest XT8 • NexSTar 8i • Eeroscope 6" f/5 ball(sacrifice was not in vain) • Vixen ED80sf • Edmund red-tube 4.25" f/10 • Edmund Astroscan
Facts are stubborn things.
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llanitedave
Humble Megalomaniac
Reged: 09/26/05
Posts: 10908
Loc: Amargosa Valley, NV, USA
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Zeolites -- usually volcanic ash altered in the presence of water -- can be green as well. If we saw that we would definitely take notice as geologists.
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"S.O.E." (Sauron's Other Eye) 16" Royce conical mirror: A permanent work in progress.
10" Homebuilt dob, old Coulter mirror
Next Project: The "Eye of Sauron" Observatory!
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Rick Woods
Post Laureate
Reged: 01/27/05
Posts: 4448
Loc: Inner Solar System
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Then, we're in agreement that the images we've been shown are not accurate. This being the case, I'll still put my bet on the ones that show known objects in their true colors. Anything else is just someone's idea of what it should be, right?
And, nowhere did I say life, algae, moss, or emerald cities. I only pointed out that life is one possibility out of many. If you want to interpret that as little green men, that's your choice and not mine.
I have to disagree with your "no evidence for greens", though. They were quite plain in the picture I saw.
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- Rick
14" LX200GPS
8" Meade 826C
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jayscheuerle
Post Laureate
Reged: 01/16/06
Posts: 3096
Loc: S. Philadelphia, PA
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That's not quite right Rick. You can have the reds and oranges being close and the blues and purples off, even if your white is pure for both. It's possible that in order to get the ground close to what was expected, other colors on the opposite side of the spectrum (greens, blues and purples) may have shifted significantly. In other words, the greens may not have been green, even if the ground color was right. Shifts are not global in a case where data is inserted where it doesn't belong. - j
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12" Green Goblin (trusser w/Protstar secondary and OWL refigured primary)• 6" f/5 Eero2 ball-scope • 6" f/5 Frankenscope • Garrett Optical 10x50 binos • Edmund 8" yoke-mounted red-tube reflector • Edmund 6" GEQ red-tube reflector (on loan to Dad)
Gone, but with lessons learned:
Skyquest XT8 • NexSTar 8i • Eeroscope 6" f/5 ball(sacrifice was not in vain) • Vixen ED80sf • Edmund red-tube 4.25" f/10 • Edmund Astroscan
Facts are stubborn things.
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Pess
(Title)
Reged: 09/12/07
Posts: 1910
Loc: Toledo, Ohio
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This is an interesting discussion and hinges on the question of what 'is' is.
the light on the surface of Mars is quite different than the light hitting the surface of the Earth.
On Earth is goes through a thick blanket of nitrogen/oxygen with significant water vapor.
On Mars you have a tiny bit of carbon dioxide and little else.
So standing on Mars you would see the American Flag 'look' quite different then you see it standing on Earth.
The first TV guys gave you a correction that brought it to an "Earth-atmosphere normal" look, The technicians brought it to 'Mars-normal' look...or how it would look to an astronaut standing there.
Pesse (Which 'is' is normal?) Mist
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Rick Woods
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Reged: 01/27/05
Posts: 4448
Loc: Inner Solar System
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This is one reason someone needs to go there and see what it really looks like!
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- Rick
14" LX200GPS
8" Meade 826C
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llanitedave
Humble Megalomaniac
Reged: 09/26/05
Posts: 10908
Loc: Amargosa Valley, NV, USA
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But what if he/she's wearing a tinted visor?
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"S.O.E." (Sauron's Other Eye) 16" Royce conical mirror: A permanent work in progress.
10" Homebuilt dob, old Coulter mirror
Next Project: The "Eye of Sauron" Observatory!
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jayscheuerle
Post Laureate
Reged: 01/16/06
Posts: 3096
Loc: S. Philadelphia, PA
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You'd probably get an accurate color shot from a cheap digital camera with the white balance set to "sunlight".
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12" Green Goblin (trusser w/Protstar secondary and OWL refigured primary)• 6" f/5 Eero2 ball-scope • 6" f/5 Frankenscope • Garrett Optical 10x50 binos • Edmund 8" yoke-mounted red-tube reflector • Edmund 6" GEQ red-tube reflector (on loan to Dad)
Gone, but with lessons learned:
Skyquest XT8 • NexSTar 8i • Eeroscope 6" f/5 ball(sacrifice was not in vain) • Vixen ED80sf • Edmund red-tube 4.25" f/10 • Edmund Astroscan
Facts are stubborn things.
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David Knisely
Postmaster
Reged: 04/19/04
Posts: 6880
Loc: Beatrice, Nebraska
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Quote:
So the initial pictures that show a blue sky (and the flag, the correct color) are wrong; but the corrected pictures are shifted too far into the red because they are unable to provide the correct blue? Something about that seems odd. I agree that the dust will affect the sky color; but there's not dust in the air all the time.
Whatever the cause, it still ends up with us not seeing an accurate color representation of the Martian surface. I think the original, where the control colors were correct (and there were green patches visible on rocks and on the ground), is likely to be closer to correct. I've read the explanations for the color corrections, but I'm unconvinced.
Well, first of all, I think that the images on Ricardo Nunes' page are probably fairly close to what would be seen visually (as are some of the more properly calibrated images from Pathfinder, the MER rovers, and Phoenix). They cannot be perfectly accurate for the reasons stated earlier, but they are probably about as good as we are likely to get from the raw images the lander took. The 'blue sky' image was not seen with the first color images from Viking-2, as they knew enough from Viking 1's results to get at least an attempt to properly balance and correct the color:
http://www.msss.com/mars/pictures/viking_lander/12a168corr.jpg
As for dust, the finer dust in the Martian atmosphere is indeed *always* present. The material is incredibly fine (particles as small as one micrometer in diameter), so it has little difficulty in getting lofted into the atmosphere by surface winds. Once up there, it tends to say there for a very long time, and this largely accounts for the pinkish or brownish tints to the martian sky. The amount of fine dust in the atmosphere varies and some does settle out, but more is lofted in its place, so the atmosphere is never really free of it.
On the so-called "green patches", there can be greenish hues to rocky materials without it being linked to life. The problem here is discerning what may be life and what is just geology (my bet is on the geology). Clear skies to you.
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David W. Knisely
Hyde Memorial Observatory
http://www.hydeobservatory.info
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Rick Woods
Post Laureate
Reged: 01/27/05
Posts: 4448
Loc: Inner Solar System
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Quote:
The 'blue sky' image was not seen with the first color images from Viking-2, as they knew enough from Viking 1's results to get at least an attempt to properly balance and correct the color:
http://www.msss.com/mars/pictures/viking_lander/12a168corr.jpg
That image has almost the entire skyline cut off. But what it does show, appears pale blue, as a blue sky might on the horizon.
Quote:
On the so-called "green patches", there can be greenish hues to rocky materials without it being linked to life. The problem here is discerning what may be life and what is just geology (my bet is on the geology).
And you may well be right! But it's sure exciting to speculate, isn't it?
I'm not betting one way or the other on the nature of the green patches: but I'm convinced that indigenous life in some form will be found somewhere on Mars. There are too many places that are potentially hospitable. The 29% of the surface that could support liquid water; under the polar ice; underground; etc etc.
I do wonder, though, that the color "correction", in addition to turning the flag purple, also completely eliminated the green areas. This, on the same mission where the labled release experiment indicated the presence of life; but this was hurriedly discarded. One might be forgiven for sensing a determined effort not to recognize signs of possible life.
I say, let's all go and see for ourselves!
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- Rick
14" LX200GPS
8" Meade 826C
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jupiterzkool
Pooh-Bah
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