The post below concerned NASA released images that show deviations in the colors of a color calibration device meant to ensure correct color representation in the Spirit rover images. A detailed examination of the issue is presented here: SCI/TECH: NASA Is Not Altering Mars Colors. http://www.abovetopsecret.com/forum/viewthread.php?tid=30048 The author presents the view that the released color images are relatively accurate representations of the Martian sky and surface. However, his analysis doesn't justify how the colors can be considered accurate when the green and blue color tags on the calibration device appear brown and red in the released color images that show Martian sky and surface. I attached an image I produced by combining Red, Green, Blue filter images into a single color image. It contains some bluish areas in the image I attached as well the image of the same area released by NASA. It does not contain the bluish areas. There is a JPL logo on the rover that is visible in the image. This might be able to be used to determine which of these images is more accurate by comparing to the color of this logo as appears in images of the rover taken on Earth. Bob Clark ======================================================== From: Robert Clark (rgregoryclark@yahoo.com) Subject: Re: More Mars color controversies. Newsgroups: sci.astro, alt.sci.planetary, alt.astronomy, sci.astro.amateur, sci.bio.misc Date: 2004-01-16 17:00:56 PST I found out the reason for the change in color in the calibration target in the NASA released color images is that in the images showing the Martian surface they used a near-infrared filter instead of the usual red filter. This is from a conversation on slashdot.com: ======================================= Re:If ya don't like their colors, then do it yours (Score:1) by tommy_teardrop (228273) on Saturday January 10, @09:44AM (#7937278) I've done a bit of experimenting with these files, comparing the colour wheel to the images taken on Earth, and in order to get a reasonable approximation of the 'true colours', you need the L4, L5, and L6 filters, for red, green and blue respectively. Ironically, the main problem is that there aren't yet pictures using the red filter. A lot of the images triplicated with the blue green and infrared images. (L6, 480; L5 530; L2 750) The use of the L2 infrared filter means that the blue colours are oversampled (at least on the colour chart). Once the L4 filter images are used on the planet, full colour images will be ours. -- IANAL, BIPOOTV ======================================= Re:If ya don't like their colors, then do it yours (Score:1) by rgclark (314480) on Tuesday January 13, @12:59PM (#7964175) "I've done a bit of experimenting with these files, comparing the colour wheel to the images taken on Earth, and in order to get a reasonable approximation of the 'true colours', you need the L4, L5, and L6 filters, for red, green and blue respectively. Ironically, the main problem is that there aren't yet pictures using the red filter. A lot of the images triplicated with the blue green and infrared images. (L6, 480; L5 530; L2 750) The use of the L2 infrared filter means that the blue colours are oversampled (at least on the colour chart). Once the L4 filter images are used on the planet, full colour images will be ours. -- IANAL, BIPOOTV" This still doesn't explain why the image of the sundial has the colors looking perfectly fine including the green and blue. It's only the images that also show the surface or sky that wind up with the wrong colors for the calibration targets on the sundial. Are you saying this image of the sundial was taken without using the red filter: http://marsrovers.jpl.nasa.gov/gallery/press/spiri t/20040108a/PIA05018_br.jpg Bob Clark ======================================= Re:If ya don't like their colors, then do it yours (Score:1) by tommy_teardrop (228273) on Wednesday January 14, @07:33AM (#7972065) No - these calibration images are taken with the L4, L5, L6 filters. There are images of the color wheel in all the filters (L1-7, R1-7), but very limited ones of the surface/sky in anything but L2, L5 and L6. In fact, there are now L4 images available. The true colour sky looks white, but does seem to have a greenish tinge to it. You can try this yourself if you have an imaging program that lets you use RGB colour channels. If you put color wheel images using L2 in red, L5 in green and L6 in blue, and move back to full colour, it looks nothing like the images you linked to. Blue looks bright pink-purple. If you use L4, L5, and L6, the colours come out just like that image you showed. Most of the posted colour images are colourised using the three main imaging filters (L2, L5, and L6), because those are the mainly used ones. It makes sense, the image quality is better, but one down side is that it doesn't give you as close a real colour as the L4 filter does. I urge you to try it, as it's great fun... but then I'm a dork. -- IANAL, BIPOOTV ======================================= I can understand that with scientific observations the near-infrared might be very useful, but it seems to me for an image to be released to the news media for public relations the red filter would be used to give the most accurate color rendition of the surface. I've also read that it's impossible to get a true color rendition even by altering the color ratios when this near-infrared filter is used. In the last post copied above, the fellow suggests there are now some images that use the correct L4 filter for the RGB color combination. Perhaps he is referring to images like the one visible here during this Spirit press conference: http://apnews.myway.com/image/20040110/MARS_ROVER.sff_RS103_20040110150347.html You'll notice the sky is a very pale blue. Actually if you look at the mirrored sky in the calibration target image, you'll see that when the Sun is high in the sky the sky color is light grey to pale blue, similar to the way it looks in this image. This to me is itself a very interesting scientific fact, the sky looks light grey to pale blue when the Sun is high in the sky. It is only when the Sun is low in the sky does the mirrored sky look pale orange in the calibration image. This is quite analogous to what we see on Earth during sunsets. In short, I think it was a poor decision to use the near-infrared filter instead of the correct visual light filter in composing the color images to be released to the press to give an idea of the actual colors on the Martian surface. (As I write this it occurs to me how strange that sounds, "You use an infrared filter instead of a visual light filter to give a VISUAL light image of the scene?") Bob Clark rgregoryclark@yahoo.com (Robert Clark) wrote in message news:<832ea96d.0401130558.45745a55@posting.google.com>... > Found this on slashdot.com: > > Colorization of Mars Images? > Posted by michael on Friday January 09, @02:15PM > from the technicolor dept. > ares2003 writes "There is no scientific reason, why JPL is colorizing > Mars in that dull red tint as in their press release images. In the > latest panorama image, there is a hint, that they deliberately altered > the colors, as the blue and green spots on the color calibration > target (the sundial) suddenly converted to bright red and brown. > Source of original images: 1, 2 - (for highres replace "br" with > "med"). At normal weather conditions, as we have at the moment, there > should be a blue sky on Mars and earthlike colors. Furthermore the sky > looks overcasted on the pictures as it cannot be considering the sharp > shadows on the sundial. If the sky was overcast, then because of > diffuse lighting, there would be no shadows. A few years ago, I did an > investigation about that very same topic for the Viking and Pathfinder > missions." > http://science.slashdot.org/article.pl?sid=04/01/09/1724246&tid= > > > As you can see in this image there are blue and green tabs on the > sundial calibration target: > > http://marsrovers.jpl.nasa.gov/gallery/press/spirit/20040108a/PIA05018_br.jpg > > But in the released public image the blue and green has inexplicably > changed to red and brown: > > http://marsrovers.jpl.nasa.gov/gallery/press/spirit/20040108a/color_panorama_sol6-A6R1_br.jpg > > One obvious way where color would be important is if there were > observed green patches on rocks. Since both the temperatures and > pressures within Gusev are within the range to permit liquid water > during the daytime AND the gamma ray spectrometer on Mars Odyssey > showed it to be an area of high water content, this would have > important implications for the life issue. One notes then that the > green target on the sundial has been turned brown in the released > color image. > It is notable also that Gil Levin has argued there were green patches > on rocks at the Viking lander sites: > > Color and Feature Changes at Mars Viking Lander Site. > GILBERT V. LEVIN AND PATRICIA ANN STRAAT > Biospherics Incorporated, 4928 Wyaconda Road, Rockville, MD 20852, > U.S.A. > AND > WILLIAM D. BENTON > Jet Propulsion Laboratory, 4800 Oak Grove Drive, Pasadena, CA 91103, > U.S.A. > Journal of Theoretical Biology, (1978) 75, 381-390. > http://mars.spherix.com/color/color.htm > > Levin and his son Ron, a physicist, also propose methods for resolving > the question of the correct colors of Mars: > > Solving the color calibration problem of Martian lander images > Ron L. Levin*a, Gilbert V. Levinb > a46 Washington Avenue, Burlington, MA USA 01803 > bSpherix Incorporated, 12051 Indian Creek Court, Beltsville, MD USA > 20705 > http://mars.spherix.com/spie2003/SPIE_2003_Color_Paper.htm > > > > Bob Clark ========================================================
The explanation here is pretty detailed: SCI/TECH: NASA Is Not Altering Mars Colors. http://www.abovetopsecret.com/forum...d.php?tid=30048 I understand why the colors have changed in the calibrations tags: it's because in the Red, Green, Blue composed color image, they used a near-infrared filter in place of the Red one. What I'm saying is that if they used the correct Red, Green, Blue filters to produce the color image of the calibration sundial and it showed the colors on the sundial looked the same in the Martian light as they do on Earth, why suddenly used a near-infrared filter to produce a VISUAL light image? Especially when this winds up distorting the colors? At this date NASA still has not released a color image showing the Martian sky and surface using the correct Red, Green, Blue filters that also shows the reference color chart so we can be confident of the color combination. They either show the reference color sundial and the Martian sky but use the near-infrared filter thereby distorting the color, or they use the correct RGB filters but only show the reference sundial not any part of Mars, or they use the correct RGB but only show Martian sky not the reference chart so we're not sure of the color combinations. Bob Clark
There's no conspiracy here Exo, the reason they're using the filters they're using is that they're doing science, not tourism. And even if they take an L4/L5/L6 shot, the camera's normalisation will still mess up the color somewhat - and then you have the reproduction of the image down here. Anyone that's ever tried to arrange their monitor to display a digital photo with accurate colour reproduction will tell you it's a pain in the ass and you never get it perfect.... With luck, they'll sort out the current problems and we'll get a few decent L4/L5/L6 shots over the next few weeks.
I Still would like some pictures of the martian night,...with any visible stars on the sky, or a sun-down, sinking in the zenith,... Anyone know some dude at NASA? Please Register or Log in to view the hidden image! I think this would also yield a potential sientific contribution...to the romantic image we've got from Mars, no? As a matter of fact: wouldn't it be great to have a few like that? Oh, I'm shure they already did some overnight photo-shoots,...but we'll never see them,...is that it? *sigh* will we ever know?
