Slashdot Mirror
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."
Actually, now it makes alot of sense. But that still won't stop the conspiracy kooks from claiming otherwise.
No boom today. Boom tomorrow. There's always a boom tomorrow. - Cmdr. Susan Ivanova
If blue appears pink on Mars, what is the real color of the little green guys?
They could have used a Foveon Sensor if they didn't want Bayer interpolation.
I don't trust him.
His website was taken down immediatly after slashdot posted this.
His "truth" couldn't stand up to the slashdoting scrutiny!
Yo Grark
Canadian Bred with American Buttering
From end of article (yes, I skipped straight there... :))
There is simply no point in adding on their site "caution these images are not 100% precisely actual colors" when no digital image is really 'actual colors'.
Quite. In fact, I'd go as far as to say that NASA expected most of the people who were scrutinising these pictures to have some experience with astronomical imaging, where almost nothing is "true" colour in that sense.
Personally, I'm in favour of as much rebalancing as it takes to make the images pretty. If they don't make full use of my eye's ability to perceive them, then what was the point of spending all that money obtaining them in the first place? So long as the raw originals are available too, who cares?
These sigs are more interesting tha
I have a Sonly Clie' PDA with a digicam built in, and it can be used to demonstrate how digicams "see" color differently, especially in the near-infrared range.
If you go into the camera application and aim the Clie' at an infrared remote control (like a TV or stereo remote), and hit one of the buttons on the remote, the PDA camera will pick up the infrared and actually display it visibly!
The bizarre claims of conspiracy theorists just go on and on. If you go to their websites you can read more than any brain can handle. I have read literally dozens of things that ``prove'' the moon landings were faked, for example, and each one is rather easily shown to be wrong by anyone with experience in such things.
I think the problem here is twofold: we tend to want to believe (or at least listen to) conspiracy theories, particularly to do with space. Also, the evidence is presented in such a way that, if you are unfamiliar with the odd nature of the vacuum of space and of space travel, it sounds reasonable.
>>esr>>
...doesn't NASA throw the public a bone? This color correction controversy pops up everytime a probe successfully lands on Mars and sends pictures back. One would think that they would have a standard RGB style camera for publicity shots. Chances are they can only afford to put on cameras practical for the mission, but I still believe a better solution could be provided. It probably just wasn't important to them... ;) Perhaps next time a camera could be included that features lens that provide scentific data and that can double as a publicist for NASA - spitting out RGB standard images that require no color correction.
Fun with Inkwell | www.coo
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
The questions are, of course,
- if there is a tinted color light source, what would the color target display on a normal color target? What would it show via the camera with the tinted light source
- The sun is the same light source on mars as it is on earth, therefore it should be easy enough to take a solar spectrum and see what the degree of tinting is.
- With an atmosphere at 1% or less of the earth, the spectrum could nearly be the same spectrum as in a vacuum
- if the spectrums are essentially similar, then the color targets should be the same, say as on earth or in vacuum, given a clear day without dust and clouds, etc.
- Of course,there is also the matter of the end result of different photo filters getting mis interpreted. However, JPL has published some pictures with red skies, and some with blue skies, as this item from the tin foil hat crowd. This has contributed to the controversy.
See also this earlier slashdot story on the Mars SundialsSo it looks like this particular annoyance has been around for a while.
"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.
Not to do anything crazy like bring the artcle into the conversation, but the uncalibrated RGB raw data that the mars rover sends back, and the methods used to color correct it reminds me of this:
The Russian Record
This brilliant Russian photographer in the late 1800s/early 1900s took an amazing number of photographs, and he would photograph everything three times, with a red, blue and green filter.
He would then use a special triple projector with the appropriate color filters to show gorgeous color images, long before the invention of color film.
So today, we can put these images back together in Photoshop, but we have the same Mars problem, we have three color channels, but no clear idea how they relate to each other.
Lacking a color-calibration sundial, we have to rely on our knowledge of skin tone, sky color, etc to tweak these colors. The link above has a link to the raw files in the Library of Congress, for geeks who want to recomposite some of their own.
What were you expecting?