Voyager 2 Saturn Revisited, Still a lot to be processed and reprocessed |
Voyager 2 Saturn Revisited, Still a lot to be processed and reprocessed |
Jan 20 2007, 02:36 AM
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IMG to PNG GOD Group: Moderator Posts: 2256 Joined: 19-February 04 From: Near fire and ice Member No.: 38 |
Emily recently mentioned in her blog the availability of calibrated and geometrically corrected Voyager images. Actually I had 'discovered' this dataset several months earlier but then managed to completely forget about it. Now I decided to do something so I downloaded volume 37 and decided to do some quick-and-dirty processing, mainly to check if it was feasible to do a very high resolution map (probably 25 degrees/pixel to match my Cassini map of the southern hemisphere) of Saturn's entire northern hemisphere by colorizing green filtered images using lower resolution color data I processed several years ago - at the resolution I want only green filtered images are available.
This was successful, opening the door to a new 'monster project': A very high resolution full color map of Saturn's entire northern hemisphere. First a color composite made from wide angle orange, green and blue images: This one was made from images C4386547_GEOMED.IMG, C4386554_GEOMED.IMG and C4386608_GEOMED.IMG. I adjusted the color to something more realistic than I initially got and removed some reseau marks in Photoshop that were visible, especially near ring edges and Saturn's limb. Some color fringing was also visible on Saturn's disk due to Saturn's rotation while the three images were obtained; I removed this by cloning the color of adjacent areas. The spokes in the rings presented similar problems. I then colorized a green filtered image obtained at a similar time as the wide angle images above. This was the result: The image should be fairly realistic and I was happy with the result, especially because I didn't do this very carefully - something better should be possible. Finally the same image sharpened with an unsharp mask: Lots of small scale details are visible, especially near the pole. I will probably post several additional Voyager Saturn images in the next several weeks. As previously mentioned, the plan now is to do a very high resolution map of Saturn's entire northern hemisphere based on these calibrated and rectified images. This means reprojecting the images to simple cylindrical projection. To do this I need to know the viewing geometry. Does anyone know if this information is available somewhere (or if not, if it's likely to ever become available)? I have some SPICE kernels which give me Voyager 2's location relative to Saturn. These are probably fairly accurate. However, the limited instrument pointing information I have is very inaccurate so it's useless to me. I can reverse engineer the viewing geometry/pointing but it's a lot of extra work. |
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Jun 27 2007, 02:02 AM
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Administrator Group: Admin Posts: 5172 Joined: 4-August 05 From: Pasadena, CA, USA, Earth Member No.: 454 |
Hi Chris, I'd be happy to add instructions regarding netpbm to the page -- if someone will compose some instructions describing how to use it. (Hint, hint.)
Yes, if you convert directly from 16-bit to 8-bit without adjusting contrast first, you'll find only pixel values up to (at most) 64. It's better to stretch the images while they're 16-bit, before converting to 8-bit, then you have more dynamic range to work with. Bjorn, if there aren't links to stuff you haven't forgotten about on the space imaging pages (hope you can follow the multiple negatives there), I'd appreciate suggestions for more links! --Emily -------------------- My website - My Patreon - @elakdawalla on Twitter - Please support unmannedspaceflight.com by donating here.
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Jun 28 2007, 12:34 AM
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Newbie Group: Members Posts: 19 Joined: 17-June 07 From: Near Southampton, UK Member No.: 2430 |
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