Juno at Jupiter, mission events as they unfold |
Juno at Jupiter, mission events as they unfold |
Jul 5 2016, 07:53 PM
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Merciless Robot Group: Admin Posts: 8785 Joined: 8-December 05 From: Los Angeles Member No.: 602 |
This topic will consist of discussion of Juno operations post-JOI until end of mission, currently anticipated in Feb 2018.
-------------------- A few will take this knowledge and use this power of a dream realized as a force for change, an impetus for further discovery to make less ancient dreams real.
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Aug 2 2016, 08:28 PM
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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 have been experimenting with the color in the Juno images by multiplying the green and blue values with correction coefficients >1. Here is the last image (JNCE_2016181_00C1588_V01.png) that shows the GRS without any color correction:
North is up and the image has been enlarged by a factor of 4. It is obviously too yellowish. Here the color balance has been adjusted to make the average color of the bright zones approximately white. This is common practice when processing Earth-based images of Jupiter. This is much more realistic than the version above. And here is a sharpened version. This image shows hints of various familiar features. And here is yet another version which has been processed to make the global color match Jupiter's global spectrum. This is only approximate, both because the viewing geometry is very differenet from the viewing geometry of Earth based instruments and because Jupiter's global color varies slightly with time. This may be slightly more realistic than the version processed to make the zones whitish. I also get acceptable results if I correct the color balance using the parameters that work well for correcting the EFB images (like the Jupiter images they are also too yellowish if the color is not corrected). Of course this raises some questions: (1) Are there any 'official' color correction/calibration coefficients that are used to get correct color? I have been using ~1.1 for green and 1.4 to 1.7 for blue. (2) If these coeffcients exist, are they constant or do they vary with things like exposure, gain etc.? |
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Aug 2 2016, 09:08 PM
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Senior Member Group: Members Posts: 2346 Joined: 7-December 12 Member No.: 6780 |
I have been experimenting with the color in the Juno images by multiplying the green and blue values with correction coefficients >1. Here is the last image ... Of course this raises some questions: (1) Are there any 'official' color correction/calibration coefficients that are used to get correct color? I have been using ~1.1 for green and 1.4 to 1.7 for blue. (2) If these coeffcients exist, are they constant or do they vary with things like exposure, gain etc.? I've been hesitating to use factors >1 in order to avoid saturation, but this might be unnecessarily conservative. There exists a radiometrically corrected version as linearized RDRs of the EFBs. That's probably what comes closest to "official". By calibrating Earth's moon to grey vs. Earth's clouds to grey/white I got different results for the factors. I doubt, that there exists a perfect color calibration, since the spectral characteristics of the JunoCam color filters and the human color receptors differ significantly. And it's not quite clear, whether extinction by Earth's atmosphere should be included in the calibration; the latter seems to vary pretty much particularly for the blue color band. As I've mentioned in some other post, there doesn't seem to exist a common convention of how to color-calibrate Jupiter images. The approach to set the mean color to grey would make best use of the color space in some way, but then one can't expect, that the color looks "natural" at the same time. |
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