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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."
They could have used a Foveon Sensor if they didn't want Bayer interpolation.
Mirror here...
Here!
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 like the Bayer filter pattern are often used in commercial digital cameras, but they use interpolation and are subsequently less accurate than 3-filter methods.
Never True Color
Quite a big deal has been made o
Make even shorter URLs - 8LN.org
By your same logic, subliminal messages in movies should be allowed
Subliminal messages in movies are allowed. There's no law against it.
The only reasons they don't do it is because a) it doesn't work, and b) when audiences find out the theater is trying to brainwash them, they tend to stop going to movies. Negative publicity, you know.
Like woodworking? Build your own picture frames.
That's just an artifact of the JPEG compression that was used on the images.
For an interesting view on how colors shift when you use filters, see this item on the Color Rendering Process, "Digichromatography"
"It is a greater offense to steal men's labor, than their clothes"
Every single image taken by the rover (raw and not even combined into color images) is available for download from the mars rover website. Check here.
Mars Climate FAQ:
s as well.
- Why isn't the Martian sky blue like the Earth's?
That page includes images using colors-close-to-what-a-human-eye-would-see-them-a
Beware: In C++, your friends can see your privates!
If you look at one of the earlier panoramas (e.g., in grey or the partial ones in colour), it is pretty obvious why -- with the sun present, the range of brightness in the image is extreme, and it is difficult to get reasonable contrast from the ground unless you ignore the sky and over-stretch the contrast until the sky is almost white. It is worse when trying to make an image from a series of differently-exposed tiles. Because the sky is not the most interesting part of the image, and it just takes up extra space in the file, I think they just selected it, cropped it out, and set it to an even shade so it would compress well and not look messy with lots of seams between tiles.
I'm sure they will make some more full-res colour panoramas that include the sky eventually.
A "standard RGB style camera" would a.) have the same problems; although they usually have the color correction built into the firmware b.) would fail because of the extreme conditions (cold, radiation, 10+G acceleration loads, ...)
The horizon line does show very strong evidence of digital image manipulation. However, the fact that the accompanying press release claims that this image was manually stitched together form 675 separate digital photographs might also indicate that the image has been digitally manipulated.
Here's a page on The Colors of Mars written by Don Davis, a "Space Artist and Animator" before the current beat up, which explains all the problems involved in trying to get a "true" colour image. He has examples of what he thinks a man on the spot might see. Elsewhere on his site he covers other planets and nebulae.
You seem not to understand the issue.
NASA has a broad spectrum of image data from Mars.
They could use this data to present a picture of
Mars as it actually appears, or they could use the
data to present a picture of Mars which does not
represent the actual appearance. By making the
latter choice, they misinform the public.
In this way, they put themselves in the same class
with persons who offer misinterpretations of image
data from the moon landings to argue that those
landings were hoaxed: Both publications serve to
misinform an already woefully misinformed public.
-I like my women like I like my tea: green-
The images are not recolored to "make them look pretty."
There are two main reasons for the color shifts.
Reason one, some of the images are taken lower in the IR spectrum, and the pigments on the sundail are desighned to react differently in that part of the spectrum.
Reason two, all the images sent back have their individual RGB channels normalized, which is similar to using "auto levels" in photoshop.
But the important factor is this: the sundail has a mirror which shows both the sky & the ground, and has full white & black reagions, meaning that even a normalized image will come through unscathed by color changes. These colors are then used to match colors for the rest of the images.
Bottom line, the colors we see are as accurate as can be gleaned, not just made up to look pretty.
(You can test this with digital camera images of your own. Run Auto Level on them (which equalizes the color channels). If there are images that full of color, but have no areas of pure white & pure black, you'll likely get some whacky colors. I have a picture of the Charles river with blue sky, green grass, and purple water)
What were you expecting?
http://www.midwinter.com/lurk/guide/037.html
divided into parallel channels by a strong surface wind. It's fairly evident by the even spacing that the formation has a uniform density. I believe the prevailing flow is SW to NE (assuming up is "north") because of a small, secondary ridge of accumulated material on the NE side of the formation. As wind blows particles from the slopes of the channel and down the backside, some is desposited and builds up upon itself on the plateau behind it.
You can tell its wind-based by the similar bottom-left to top-right streaks all over the landscape.
Very cool, but definitely not organic. You would see this kind of thing at the beach if we have hurricane force winds all the time.
THIS THING CAN TURN ON A DIME, MACROSSZERO STYLE ALSO FUCK BETA, ~NYORON