Global True Color View Of Venus? |
Global True Color View Of Venus? |
Aug 8 2005, 06:53 PM
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#1
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Administrator Group: Admin Posts: 5172 Joined: 4-August 05 From: Pasadena, CA, USA, Earth Member No.: 454 |
I'm creating a website with views of the worlds of the solar system, to scale with each other (it'll march up and down the few orders of magnitude necessary), and I am having a terrible time finding a global view of Venus to include in it that fits the criteria I'm trying to apply. To the extent possible, I am searching for:
- Full-disk, global view - Minimum phase angle available - Approximate true color, as would be perceived by a human observing the globe from space For Venus, the only global views I am finding are either based on Magellan data (radar views, nothing like what a human would see) or are colorized ultraviolet views (which greatly overemphasize the visibility of cloud patterns in the Venusian atmosphere). I've seen the lovely partial global view of Venus on Don Mitchell's website -- that's the sort of thing I'm looking for, but I need a full disk. Does anybody have any suggestions? Anybody done any work with Mariner 10 or Galileo data that produces a nice, realistic view? -------------------- My website - My Patreon - @elakdawalla on Twitter - Please support unmannedspaceflight.com by donating here.
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Dec 29 2008, 01:08 PM
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#2
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Member Group: Members Posts: 378 Joined: 21-April 05 From: Portugal Member No.: 347 |
Hi all,
I've updated my webpage with some Venus Express images processed in approximate real color. The images seem to show the Venusian atmosphere extending from the limb with a bluish color. The general tone of the planet is yellowish, in accordance to similar processing I've done with Mariner 10 images, available on this site. The brightest clouds are bluish, given that they reflect strongly on the UV parts of the spectrum. RGB channels were computed from NIR1, VIS and UV images using the following averages: Red = 0.3 x NIR1 + 0.7 x VIS = 0.3 x 965 + 0.7 x 513 = 649 Green = VIS = 513 Blue = 0.5 x VIS + 0.5 x UV = 0.5 x 513 + 0.5 x 365 = 439 Here's one image, you can see more at http://www.astrosurf.com/nunes/explor/explor_vex.htm -------------------- _______________________
www.astrosurf.com/nunes |
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Jun 1 2009, 06:48 PM
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#3
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Senior Member Group: Members Posts: 3648 Joined: 1-October 05 From: Croatia Member No.: 523 |
I've been messing around with the MESSENGER calibrated data and even though it's not a complete global view, I thought I'd share it here. From the filter choice standpoint, it's the closest we get to a RGB image for the time being. I already posted a few of those in the MESSENGER PDS threads, but those were quick-n-dirty versions.
Below is the familiar inbound view by the wide-angle camera, but this time I approached it somewhat differently. Instead of the typical E/D/C "red/green/blue" filter combo, I used E/D/F. Even though the "F" filter is labeled as violet, at 430 nm central wavelength it's actually much closer to the peak sensitivity of the blue light-sensitive cones in the human eye (437 nm). The "C" filter is shifted way too much toward green at 480 nm and also much more narrowband. Venus composites using the "blue" filter as a result fail to capture the bright clouds that reflect strongly in the UV, while the "F" filter does exactly that while still being inside human vision boundaries, i.e. not being UV. I used the ground calibration tables when calibrating the data as the inflight-derived results look inconsistent across filters to me. Next, I took the central filter wavelengths and compared them to the sRGB colospace central wavelengths. I calculated approximate channel mixes to bring the "average" wavelength in all 3 RGB channels to sRGB, this is what I used: red = 0.72*E + 0.28*D grn = 0.93*D + 0.07*F blu = 0.73*F + 0.27*D Finally, I boosted saturation by +15 to compensate for a slight loss of saturation by above mixing. Here is the resulting composite: It looks as it's in the same ballpark as some other versions here. This one is not gamma-corrected because absolutely all contrast would be washed out and you'd end up with a shiny white billiard ball. Here's a high-pass enhancement to bring the clouds out a bit: -------------------- |
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Jun 2 2009, 09:55 AM
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#4
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Member Group: Members Posts: 378 Joined: 21-April 05 From: Portugal Member No.: 347 |
... I calculated approximate channel mixes to bring the "average" wavelength in all 3 RGB channels to sRGB... ...This one is not gamma-corrected because absolutely all contrast would be washed out and you'd end up with a shiny white billiard ball. .... Nice results. I think that the channel mixing to average center wavelenght works very very well and can be used with almost any filter set. I'm not shure it saturation suffers that much, because that would have more to do with each filter bandwidth. Nevertheless, results are consistent. I think that you could include a gamma corrected version, because that would show exactly why the details are dificult to see at the telescope. It would also be closer to what we might see if in orbit of the planet. -------------------- _______________________
www.astrosurf.com/nunes |
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Jun 2 2009, 10:15 AM
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#5
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Senior Member Group: Members Posts: 3648 Joined: 1-October 05 From: Croatia Member No.: 523 |
I think that you could include a gamma corrected version, because that would show exactly why the details are dificult to see at the telescope. It would also be closer to what we might see if in orbit of the planet. Well, you asked for it: This was done on the 8 bit PNG above, not the 16 bit one I worked with as I'm at work now, but this only induces a slightly higher noise near the terminator. I continue to be amazed at just how sharply defined the planet's limb is. It really looks like someone put a solid ball in space - no limb brightening or other Rayleigh scattering effects. -------------------- |
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