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The Real Reason why Spirit Only Sees Red

Posted by CmdrTaco on from the now-thats-interesting dept.

use_compress writes To produce a color photograph, the rover's panoramic camera takes three black-and-white images of a scene, once with a red filter, once with a green filter and once with a blue filter. Each is then tinted with the color of the filter, and the three are combined into a color image. In assembling the Spirit photographs, however, the scientists used an image taken with an infrared filter, not the red filter (NYTimes, Free Registration Required). Some blue pigments like the cobalt in the rover color chip also emit this longer-wavelength light, which is not visible to the human eye."

24 of 273 comments (clear)

  1. Why b/w & filter? by Lolaine · · Score: 5, Interesting

    Can anyone explain why 3 separate B/W images are taken? If it is because of bandwidth... 3 grayscale images weights (more or less) like one color image ... so why B/W and filters?

    --
    ------- The last Sig. got fired.
    1. Re:Why b/w & filter? by City+Jim+3000 · · Score: 1, Interesting

      Say you have a 3MP camera. That (roughly) means 1 million "triples" of R+B+G receptors. So essentially you get 1/3 of the resolution.

      Imagine NASA wants to see a spectra composed of red, green, blue, two kinds of infrared and two kinds of ultraviolet light. So that makes 7 "pixels-per-pixel" meaning you get 1/7 of the resolution. Not very good from a scientific point of view.

    2. Re:Why b/w & filter? by Sahib! · · Score: 2, Interesting

      On a slightly related note, a Russian photographer named Sergei Mikhailovich Prokudin-Gorskii pioneered this technique of obtaining color images using colored filters and monochromatic film in the early 1900's. He actually built his own camera with three vertically-oriented lenses, each with a red, green or blue filter. The camera took the three pictures at the same time, but some interesting distortions come through because of the slight differences in paralax.

      http://www.loc.gov/exhibits/empire/

      This was mentioned here on /. some time ago, but if you haven't seen his photos, they are definitely worth checking out.

      --

      I prayed about it, and God said, "Don't do it!" But I thought, "I know better."

    3. Re:Why b/w & filter? by SoupIsGoodFood_42 · · Score: 2, Interesting
      You're confusing near-IR and thermal-IR (not sure if they're techically correct terms). Most CCDs pick up IR very well. Infact, they do it so well that most digital cameras have an IR blocking filter or "hot mirror" in front of the CCD. If you want to see heat though, you will need a special sensor for that. most CCDs can't pick up IR that deep.

      IR filters are easy to obtain. But if you want decent exposure times, you'll need to remove the hot mirror first, and replace it with plain glass. Most people don't want to do that to their digital cameras. But since I'm an idiot, I've done exactly that. You can see the results here. The lack of IR blocking filter means I can take IR pics without a tripod in good light.

      IR is interesting. I have quite a few black cloths that come out bright white, while other black cloths still come out black.

  2. Re:prepare the servers for a nytimes-dotting... by arcanumas · · Score: 4, Interesting

    If they wanted to take their revange they would have made it a link. Now, it is just text and most people don't like copy-pasting.
    But they mention that "As Mars buffs have pointed out in recent weeks on Web sites like Slashdot.org" , i wonder if they read Slashdot because they like it or just to see why an ungodly amount of refferer logs says: slashdot.org

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    Slashdot Sig. version 0.1alpha. Use at your own risk.
  3. Why don't they release the RGB too? by Tsar · · Score: 2, Interesting

    They're taking images through blue, green, red and infrared filters. The color shift problem in the publicly released images is because they're blending in the infrared shot instead of the red shot, right? Why don't they just release the RGB images as well as the iRGB? They have all the images after all--why waste press conferences explaining the differences or lack thereof when they could just give us the pictures?

  4. Blue? Infrared? by Rufus88 · · Score: 2, Interesting


    Some blue pigments like the cobalt in the rover color chip also emit this longer-wavelength light, which is not visible to the human eye."
    If it's a *blue* pigment, why does it emit a *longer* (i.e. infrared) wavelength?

  5. Re:Why don't they... by Carl+T · · Score: 5, Interesting
    [...] just use a 4 megapixel digital camera that anyone can buy from Compusa

    Quite possibly because it wouldn't survive the conditions on Mars. Or on the way there. Try deep-freezing your digital camera, then put it in a vacuum chamber, then in a really dusty sandbox, and finally subject it to a potentially lethal (for a human) dose of radiation, and see if it still works. Oh, and don't forget simulating the landing; heat it, vibrate it, and toss it on the ground.

    Disclaimer: I wasn't there. I don't know exactly how the poor thing was treated. I'm not a member of the PETC (People for the Ethical Treatment of Cameras).

    --

    This signature is not in the public domain.
  6. Re:Why don't they... by Lumpy · · Score: 4, Interesting

    because that 4 megapixel camera from comp usa is a total piece of crap compared to the 1 megapixel B&W camera on the rover.

    I have a old 2 megapixel digital camera that will beat the Best 4-6 megapixel consumer camera you can buy today. because of optics and the design of the CCD. (mine is a TRUE 2 megapixel whereas almost ALL camera's today sold as a 4 megapixel are really a 1.3 megapixel camera as you need 3 pixels for each photographed pixel.. (I.E. one for red,green and blue.)) plus the resolution of each color captured is vastly different, green usually being the best resolution while blue suffer's the most..

    Nasa is not about to send the really low grade crap that is available to the cunsumer to another planet. they sent the real deal.

    I suggest you actually learn about digital photography and why consumer grade "cameras" are utter junk.

    --
    Do not look at laser with remaining good eye.
  7. before shooting comments off the hip about IR by WormholeFiend · · Score: 2, Interesting

    maybe you should try taking infrared photos?

    most of the digital cameras on the market dont have countermeasures to prevent IR exposures, so feel free to experiment with various infrared-transmitting, deep red and light red filters.

    from my non-scientific experience, ultraviolet photos of rocks is more interesting than infrared.

    1. Re:before shooting comments off the hip about IR by jandrese · · Score: 3, Interesting

      I don't know if my camera has a cheap filter or no filter at all, but it is more sensitive to infared than the naked eye. The easiest way to see this is to point a remote control at the camera, hold down a button and snap a picture. In the picture you can see the little bulb in the remote all lit up, even though it is invisble to the naked eye.

      --

      I read the internet for the articles.
  8. But what is this thing? by tjmcgee · · Score: 5, Interesting

    The martian crab http://homepage.mac.com/thomasmcgee/ I know, I know, go ahead, mod me off topic. The truth is out there. Would anyone like to start a petition that requests NASA to try to get one more photo of this thing before they drive away?

    1. Re:But what is this thing? by Anonymous Coward · · Score: 1, Interesting

      Much better images here: www.rense.com

      I know Rense is a bit of a tin-foil hat site, but NASA have been strangely silent on this.

      The original NASA picture is at: marsrovers.jpl.nasa.gov [large file]

      Even the mainstream press are (deliberately?) ignoring it.

      I don't think it's debris from the lander.

  9. I've often wondered by ajs318 · · Score: 3, Interesting

    I've often wondered exactly how rigid the "400-700nm is visible" rule applies. We know that some animals can see infra-red and ultra-violet. But just how well-defined is the wavelength range for human beings? I mean, our bodies are different shapes and sizes, our voices have different pitches, our ears have varying ranges, some of us are allergic to certain substances that others are not ..... but has anyone ever investigated the phenomenon of what wavelengths humans can see? Is it a person-to-person variable, or is it constant for everyone? Can some people see IR, red and green, for instance, instead of red, green and blue? Or green, blue and UV, for that matter ..... and what would it look like?

    --
    Je fume. Tu fumes. Nous fûmes!
    1. Re:I've often wondered by sugar+and+acid · · Score: 4, Interesting

      A way of dealling with blindness from cataracts (the lens of the eye turning opaque), is to remove the lens of the eye and replace it with an artificial lens. An interesting side effect is that without the lens people can see further into the UV region of light.

      Interestingly the work of Claude Monet demonstrates this. Starting with his early work which is clear and in the normal colour range, then he develops cataracts and his work is more undefined swirls of colour, often dark and dim. Then he has cataract surgery and the new work is bright and vibrant, but with a deep purple/blue hue to many things because of the now increased presence of UV light in his vision.

  10. color problems on ordinary digital cameras by jms · · Score: 2, Interesting

    This problem is not unique to the Mars rovers.

    As a hobby and as income, I make borosilicate lampwork beads and sell them on ebay. This requires me to take digital pictures of my beads, which I do with a Nikon Coolpix 885.

    Every once in a while I run into a color combination that simply cannot be photographed correctly. One bead set I have looks brown/butterscotch/caramel to the eye, but when photographed using that particular camera, some of the brown features in the bead come out electric red.

  11. Re:Why not just give NEW pictures! by lcsjk · · Score: 2, Interesting

    As I understand it, the explanation is simply that the public was given pictures using filters intended for scientific research. This alters the printed colors. At this point NASA should have given more pictures that produce colors closely matching what the human eye sees. With color chips and photoshop(tm), along with a picture taken on earth before the mission, even I could come up with a presentable picture.

  12. JPL says by __aagmrb7289 · · Score: 2, Interesting

    This isn't what JPL said. They said they were using a full color, basic digital camera. Damn, where's that link?

  13. Re:Why not just give NEW pictures! by BiggyP · · Score: 3, Interesting

    so, i threw this one together the other day, is it anywhere close do you guys reckon?

    Spirit-pano-rgb-compose.jpg

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    Software Freedom Day!.
  14. Umm... by KewlPC · · Score: 2, Interesting

    I think people are also forgetting that, on Mars, white light is probably not reaching the surface. The dust in Mars' atmosphere is probably tinting the sunlight a little bit red, which certainly doesn't make getting the "correct" color easy.

    But a comparison of the Mars Pathfinder images against the MER images shows that the colors in the MER images are too red. In the MPF images the rocks aren't all the same color.

    It's pretty obvious that NASA's been doing a lot of Photoshopping on these images. While some Photoshop'ing is necessary (to merge the 3 grayscale images and to eliminate the seams in the panoramic images), I think they're overdoing it this time. I can't find the link right now, but there's one image in particular where it's blatantly obvious that they've replaced the sky with a single, solid color (you can see jaggies along the horizon in the high-resolution version).

    I'm not trying to be all conspiracy theorist or anything. I certainly don't think they're faking the landings, nor do I think the Martian sky is bright blue as some have suggested.

  15. Re:Why not just give NEW pictures! by daina · · Score: 5, Interesting
    It is a misconception that you can use Photoshop or some other image processing program to produce a "true colour" or RGB image when one channel represents infrared data. Here's why:

    If you use an infrared filter like the L2 filter on Sprit's Pancam, you get data that represents only things which reflect or emit light in that particular region of the spectrum. Anything that emits light ONLY in the red will be absent from the data set. It is possible for something that appears as a fairly monochromatic red to be entirely invisible. How can you use Photoshop to put back something that is invisible? You cannot.

    You can adjust an individual colour in the image using a reference image taken with the appropriate filters, and that colour will then appear correct. Other colours, however, will remain distorted.

    Worse, you cannot possibly know the emission/reflectivity spectrum of things on Mars, so any image you produce that appears to show the sundial colour chips correctly may distort terribly the Mars components of the image. It is not really very interesting to see a colour corrected photo of the sundial, is it? We could have achieved that without sending the rover all the way to Mars.

    Nope, using a relatively narrow-band-pass infrared filter like the L2 simply leaves out information about the red part of the spectrum, and extrapolation only goes so far in recreating that data. Non-linear data - discontinuities within the missing portion of the spectrum - are simply gone, never to be retrieved.

    Also, NASA is lying. Perhaps 'lying' is too strong a word, but they are either deceiving us or they are operating under a serious misconception.

    "We just made a mistake," said Dr. James F. Bell III, the lead scientist for the camera. "It's really just a mess-up." Well, NASA claims to be releasing the raw data from Spirit on its web site, but the raw data does not contain any image sets for the panoramas taken with the L4, L5, L6 filters. They have almost never used the L4 filter.

    So either the "mess up" is that they have forgotten to use the L4 filter from day one (unlikely, since each photograph taken presents another opportunity to switch to the L4) or that they have L4 images but they are not releasing them, in which case they really are not releasing the raw data.

    The argument about the L2 being better for science is bogus. There's no way that NASA scientists are doing serious mineral analysis with a pretty, stitched-together wide view panorama. That's just rubbish. they would be looking at detail images, and possibly comparing between detail-level images. The panoramas are strictly for public consumption, and maybe office posters at JPL.

    It's probably not a conspiracy, but it is a mystery.

  16. And you are right. by rk · · Score: 2, Interesting

    I have it on pretty good authority that it is part of the airbag.

    Just wait for more images from MER-B (Opportunity). You're about to see some really cool stuff in the next few days. No Martian crabs or bunnies, I'm afraid, but still some awesome stuff.

  17. Pancam Details/Specs by dekashizl · · Score: 2, Interesting
    Here is a collection of links from the MER2004 Rovers and their Instruments Technical Info section of the page listed below, with specs and details of the Pancam and its filters. Interesting reading:

    --
    For news, status, updates, scientific info, images, video, and more, check out:
    (AXCH) 2004 Mars Exploration Rovers - News, Status, Technical Info, History.
  18. Dust? by Fantastic+Lad · · Score: 2, Interesting
    Mars has an atmosphere thick and windy enough to kick up dust to prevent sunlight from reaching the surface?

    Hm. I'm no meteorologist, but I wasn't seeing any evidence of a dusty atmosphere in any of those rover images. --Details at distance seemed as clear as near objects. There's WAY more crap in Earth's much more robust atmosphere, and we get plenty of white light.


    -FL