Voyager and Galileo Images of Ganymede, The Ganymede images and mosaics thread |
Voyager and Galileo Images of Ganymede, The Ganymede images and mosaics thread |
May 18 2007, 09:43 PM
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#31
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IMG to PNG GOD Group: Moderator Posts: 2254 Joined: 19-February 04 From: Near fire and ice Member No.: 38 |
I've been processing some of the high resolution Galileo Ganymede images recently. As far as I know the two mosaics below have not appeared at the official websites (at least not in this form) so in a sense they are 'new'.
The first one was obtained during the G1 flyby in 1996. It covers a part of Memphis Facula which is centered at roughly 15°N, 132°W. The images were obtained at a distance of approximately 5000 km from Ganymede's center. The second one was obtained during the G28 flyby in May 2000. It is centered near 14.5°S, 319.7°W. The images making up the mosaic were obtained at a distance of roughly 4500 km from Ganymede's center. I will probably post more Ganymede mosaics later this month or next month. |
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Oct 20 2010, 07:49 AM
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#32
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Junior Member Group: Members Posts: 74 Joined: 9-October 10 From: Victoria, BC Member No.: 5483 |
The next attempt is actually as close to true colour as we're going to get here - a colour mosaic using Orange/Green/Blue in the R/G/B channels. Unfortunately I only could find a strip of Green filter images so the central part of Ganymede is the only part that's in (nearly true) colour. I really like how this one looks, it's just a shame that more of Ganymede wasn't covered by all three channels.
All this talk of filters makes me wonder - why did they not include a red filter in the ISS, so at least we could get some true colour pictures? (that said, looking at the filters here - http://pds-rings.seti.org/voyager/iss/inst...a1.html#filters - it looks like Orange extends into the red a bit too. Though "Green" actually seems to be more like yellow?) |
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Oct 20 2010, 08:13 AM
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#33
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Senior Member Group: Members Posts: 3648 Joined: 1-October 05 From: Croatia Member No.: 523 |
All this talk of filters makes me wonder - why did they not include a red filter in the ISS, so at least we could get some true colour pictures? The vidicons were blind to longer wavelengths. Even with the "orange" filter (which does sample some red color), the dropoff curve is most likely driven by detector sensitivity, not filter bandpass. Potentially a bigger problem with using Voyager OGB images directly as RGB is that the "green" filter actually skirts close to orange color (slightly less the case with Cassini). Since most objects are spectrally red, this causes their color in the direct RGB representation to have an excessive green tint if you don't compensate with channel mixing or interpolation. See for example some of the Voyager OGB Jupiter images. -------------------- |
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Oct 20 2010, 05:22 PM
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#34
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Interplanetary Dumpster Diver Group: Admin Posts: 4404 Joined: 17-February 04 From: Powell, TN Member No.: 33 |
Potentially a bigger problem with using Voyager OGB images directly as RGB is that the "green" filter actually skirts close to orange color (slightly less the case with Cassini). I often try to compensate when possible by mixing green with blue (or, if I must, violet). -------------------- |
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