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Explaining the Mars Photo Colorization
TaddyPorter writes "I've seen stories going around the 'net in regards to NASA editing photos of mars. Mainly, the sundial used for calibration showed different colors than the dial on mars. While a wide range of explanations were taking shape, the Pancam Payload Element Lead for the mission, Jim Bell of Cornell University, was kind of enough to explain the color differences."
3 minutes and already slashdotted. anyone has a mirror?
If Yoda so strong in Force is, why words in right order he cannot put?
So the moon landing was real but the Mars Landing was faked? That'd explain why one newspaper saw fit to dedicate a double spread to how much the Mars landscape looked like a section of the Australian Outback. Presmably Beagle is being used as a barbie stand in Paul Hogan's back yard. Crocodile Dundee 4 anyone?
Ya know, this whole mars thing... What if the pictures they are capturing show up with these little green martian men just like in the cartoons... I mean.. do you really think they would tell us? No, of course not - so then whats the point of the whole mission?
Don't Tread on Me
Posted by: Kano
On: Sun January, 18 2004 @ 03:34 GMT
This article is a brief summarised explanation of how the PanCam on the Mars Spirit Rover operates, in relation to the strange appearance of the calibration sundial in some pictures. The question was first raised by ATS member AArchAngel, and has been discussed at length in this AboveTopSecret forum thread and ATSNN story:
thread
Mars Spirit Rover Picture analysis.
In this thread I will attempt to summarise my posts to the larger thread.
What are you talking about?
Ok, the initial alarm was raised after it was noticed that the color-calibration sundial mounted on the rover, looked quite markedly different in the Mars-Panorama shots compared to its regular appearance.
Image here
Immediately wide-ranging theories began to pop up. At this stage I knew very little of the particulars of the PanCam so I decided to go and see what the Horses mouth had to say. I sent out a swag of emails to the NASA marsrover team, the Athena Instrument team at Cornell University, and the long shot, an email to Assoc. Professor James Bell. Who is the Pancam Payload Element Lead for the mission.
Now, getting no response from the Athena team, and an automated response from the NASA team. I was amazed and delighted to see that Dr. Bell had indeed taken the time out of his busy schedule to help explain this quirk in the panorama pictures. His email response is below:
quote:
Sorry, I don't have anywhere to mirror this with images and all (anywhere that would survive an /. that is ;) )
TOP STORY: NASA Is Not Altering Mars Colors.
Posted by: Kano On: Sun January, 18 2004 @ 03:34 GMT This article is a brief summarised explanation of how the PanCam on the Mars Spirit Rover operates, in relation to the strange appearance of the calibration sundial in some pictures. The question was first raised by ATS member AArchAngel, and has been discussed at length in this AboveTopSecret forum thread and ATSNN story: thread
Mars Spirit Rover Picture analysis.
In this thread I will attempt to summarise my posts to the larger thread.
What are you talking about?
Ok, the initial alarm was raised after it was noticed that the color-calibration sundial mounted on the rover, looked quite markedly different in the Mars-Panorama shots compared to its regular appearance.
Immediately wide-ranging theories began to pop up. At this stage I knew very little of the particulars of the PanCam so I decided to go and see what the Horses mouth had to say. I sent out a swag of emails to the NASA marsrover team, the Athena Instrument team at Cornell University, and the long shot, an email to Assoc. Professor James Bell. Who is the Pancam Payload Element Lead for the mission.
Now, getting no response from the Athena team, and an automated response from the NASA team. I was amazed and delighted to see that Dr. Bell had indeed taken the time out of his busy schedule to help explain this quirk in the panorama pictures. His email response is below:
quote:
--------
Thanks for writing. The answer is that the color chips on the sundial have different colors in the near-infrared range of Pancam filters. For example, the blue chip is dark near 600 nm, where humans see red light, but is especially bright at 750 nm, which is used as "red" for many Pancam images. So it appears pink in RGB composites. We chose the pigments for the chips on purpose this way, so they could provide different patterns of brightnesses regardless of which filters we used. The details of the colors of the pigments are published in a paper I wrote in the December issue of the Journal of Geophysical Research (Planets), in case you want more details...
All of us tired folks on the team are really happy that so many people around the world are following the mission and sending their support and encouragement...
Thanks,
Jim Bell
Cornell U.
-------
Now, as far as the pink tab where the blue one should be, that email is infact the complete answer. But its not easily understandable to the layman. Below I will attempt to explain why this occurs.
Click here to read comments or post your own.
Displaying the first 12 replies to this news story...
Posted by: Kano
On: Sun January, 18 2004 @ 03:35 GMT
Digital Cameras
Firstly, we need to understand how the PanCam, and indeed digital photography in general works.
Luckily for us we have our good friends at http://www.howstuffworks.com to turn to.
How Digital Cameras Work
It would be worthwhile to read the entire article on howstuffworks, for a fuller understanding of the processes at work. But because I know you are all busy (lazy?) I will summarise.
Basically, the heart of a digital camera is the charge coupled device or CCD. This CCD converts light hitting it into electrical impulses, the brighter the light, the stronger the impulse. Now, CCD's are color-blind. All they do is signal how bright the light hitting them is. All well and good for black and white photography. But for color we need to do more. To get a color-picture. We need to record images via the CCD using a series of 3 filters. A Red filter, a Green filter, and a Blue filter. These are then recombined afterwards to give a color-representation of the picture. (Note, cheaper options
---- Take the Space Quiz!
Posted by: Kano
On: Sun January, 18 2004 @ 03:40 GMT
Thats It?
In a simplified way, yes. That is the explanation for the blue pigment showing as pink. There is a lot more to this story though. Firstly, we have to remember what the mission is for Spirit. It is a geological one, not a sightseeing one. More than half of the filters on the pancam are outside the visible spectrum. The way the filters and sundial are set up is to try and decrease the discoloration of the surface by the atmosphere, as it is better for the geological mission to see the colors of the rocks and ground as it would be when white-lit. Not all with a pink/red filter over it.
To most of us though, color pictures from Mars are much more satisfying than any data regarding the planets geological history. Athena and NASA have purpose built some high-end image processing software to re-create the images as close as they can get to what it would actually look like from the surface.
Posted by: Kano
On: Sun January, 18 2004 @ 03:41 GMT
Not Quite it.
That is obviously a shortened explanation of the reasons behind the blue pigment appearing pink. As shown earlier we can re-create this effect ourselves.
I also mentioned in that post that the simple equal mix of the RGB color plates (from the Spirit Raw Images hosted by NASA) is only equivalent for some pictures.
Why not all?
To explain this we need to look a little more at the PanCam and how it transmits the data. From our Pancam Technical brief, we discover that the onboard computer on the rover (which controls PanCam) has the ability to perform a limited set of image-processing tasks, one of which is:
quote:(4) rudimentary automatic exposure control capability to maximize the SNR of downlinked data while preventing data saturation
Channels Normalized
This means that the brightness of all three color plates has been amplified to give the highest range of brightness for each plate. I don't know the graphical term for it, but an equivalent Audio term would be something like Hard limiting. So I'll use that.
Basically, in each of the three filter pics. The exposure has been set so the brightest part of the picture from each filter, correlates with the absolute maximum brightness for that channel. For example the brightest part of the red channel is FF0000, green is 00FF00, and blue is 0000FF. (Obviously they all come in as b/w pics so in each black and white plate there is a perfect range from 000000 (absolute black) to FFFFFF (absolute white).
You can test this by opening one of the black and white plates (photoshop again sorry). Select either 000000 or FFFFFF as the working color. Then go to the select menu and color range. Set fuzziness to zero and OK. For each extreme you will find at least a few pixels of each.
On Earth
You can test the counter to this theory with a photo taken on Earth. Choose any photo taken on earth, (A good one to try is that Autumn road looking one that comes with Windows XP). Open it in photoshop and set its blending options so only the blue channel is showing. Its very dark, and there are no 0000FF pixels at all. In fact there are only a few 0000AA pixels, and they are in the whiteish parts. You can try this with any picture taken on earth. Try to avoid pictures with solid black and white in them however. Or something silly like a rainbow. White requires bright amounts of all RG and B to show. The rainbow is self-explanatory
Reason
By sending each plate of colors spread across each extreme, you gain the maximum amount of data from each plate. Once you know the calibration information it is easy to amplify each channel back down to its correct setting, and get the images looking as they should. If you were to send the images at equal exposure levels, the signal to noise ratio would be lower, and any slight error in one of the blue/green channels would be more noticeable.
Now, this only throws out the color-balance on images where th
Make even shorter URLs - 8LN.org
Well, if you zoom in even further, you'll find that everything is made up of tiny squares of different colors. The odd thing about it is that they are COMPLETELY square, as if the moon was built from Lego bricks or something. Clearly there is something going on here.
I for one welcome our new Pixelian overlords.
Table-ized A.I.