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Processing VIMS cubes, An attempt at "true" color
ugordan
post Sep 10 2006, 07:51 PM
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Right, a suggestion I made here in another topic made me wonder why not try that myself. A bunch of data was sitting on the PDS, after all. After a hassle figuring out just how the image cubes are organized and trying to read them, finally I was able to produce some results. This is all very rough work, can be considered first-iteration only and not particularly accurate.
Basically, I used the cubes to extract the visible spectrum in the 380-780 nanometer range which was then input to color matching code I found here by Andrew T. Young.
The code integrates over 40 10-nm steps to produce CIE XYZ color components. I then converted these to RGB values.

I'm aware of at least three inaccuracies in my code as of yet: one is the above sampled code apparently uses Illuminant C as the light source, not true solar spectra so the color turns out bluish (has a temp. of 9300 K instead of 6500 K, AFAIK). I tried to compensate at the moment by changing the final RGB white balance, but this is probably an inaccurate way to go. Another inaccuracy is I don't do bias removal from the cubes. This likely affects the outcome. Also, I don't use the precise wavelengths the code requires, but use the closest one in the cube. I intend to fix this by interpolating between nearest wavelengths.

All images are enlarged 4x.

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The leftmost image is a 4-cube mosaic. The colors in all four frames turned out identical which gives me at least some confidence. The image in the middle shows Dione's disc creeping in front of Saturn. Dione's disc appears elongated probably because as the lines were readout, it moved considerably in its orbit. The rightmost image shows a very overexposed Saturn image, the part below the ring shadows got overexposed. From what I've seen browsing through the PDS, a lot of the cubes are badly overexposed at some wavelengths.

Here's a couple of Jupiter images. I'm not very satisfied with them as they seem to look somewhat greenish, but overall the color looks believeable:
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Lastly, two Titan composites. They turned out way more reddish than I thought they would.
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It'll be interesting to see how much the results will change once I do a more proper processing pipeline working.


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edstrick
post Sep 26 2006, 09:49 AM
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It probably boils down to too-much-to-do, not-enough-techies, not-enough-grad-students...

The sort of thing that pennypinching does to a live mission. They'll have time for a systematic beginning-to-end calibration effort when the mission is over.
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ugordan
post Sep 26 2006, 02:27 PM
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To reiterate what you said, on my asking if updated calibration data will be provided, he said that will happen at the end of Cassini mission. An earlier update may be possible, but not likely.

Guess that means I'm stuck with homebrewn dark current models <sigh>...


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Posts in this topic
- ugordan   Processing VIMS cubes   Sep 10 2006, 07:51 PM
- - Malmer   its a really great "realitycheck" for th...   Sep 12 2006, 09:48 PM
|- - ugordan   QUOTE (Malmer @ Sep 12 2006, 10:48 PM) it...   Sep 13 2006, 08:56 AM
|- - Malmer   QUOTE (ugordan @ Sep 13 2006, 10:56 AM) I...   Sep 13 2006, 03:04 PM
- - dilo   Very nice work, gordan... now we see the colors...   Sep 12 2006, 10:21 PM
|- - ugordan   QUOTE (dilo @ Sep 12 2006, 11:21 PM) To m...   Sep 13 2006, 06:56 AM
|- - dilo   QUOTE (ugordan @ Sep 13 2006, 06:56 AM) T...   Sep 13 2006, 04:17 PM
- - CAP-Team   It looks as if the colors match Voyager's colo...   Sep 13 2006, 02:16 PM
- - Malmer   QUOTE (ugordan @ Sep 10 2006, 09:51 PM) I...   Sep 13 2006, 02:49 PM
- - DonPMitchell   How do you convert XYZ to RGB? Are you making sRG...   Sep 13 2006, 04:55 PM
|- - ugordan   Yes, I'm using that XYZ to RGB matrix. I had t...   Sep 13 2006, 08:33 PM
- - DonPMitchell   Very good. Gamma 2.2 is technically what should b...   Sep 14 2006, 04:07 AM
|- - ugordan   The pixels are linear as far as I know, a 12 bit A...   Sep 14 2006, 07:09 AM
|- - Malmer   QUOTE (DonPMitchell @ Sep 14 2006, 06:07 ...   Sep 14 2006, 09:30 AM
|- - Malmer   The pixels in the ISS images are not linearly save...   Sep 14 2006, 09:43 AM
||- - ugordan   I am very well aware of the ISS data specifics. Wh...   Sep 14 2006, 10:47 AM
||- - Malmer   QUOTE (ugordan @ Sep 14 2006, 12:47 PM) I...   Sep 15 2006, 12:50 PM
||- - ugordan   QUOTE (Malmer @ Sep 15 2006, 01:50 PM) On...   Sep 15 2006, 06:26 PM
||- - Malmer   it would be fun to paint spheres in the colors you...   Sep 15 2006, 11:40 PM
|- - DonPMitchell   QUOTE (Malmer @ Sep 14 2006, 02:30 AM) co...   Sep 14 2006, 03:39 PM
|- - Malmer   I think the strange piecewise funktion has its ben...   Sep 15 2006, 12:33 PM
|- - ugordan   QUOTE (Malmer @ Sep 15 2006, 01:33 PM) I ...   Sep 15 2006, 06:10 PM
- - DonPMitchell   One concept is to make an image that resembles wha...   Sep 16 2006, 01:56 AM
|- - Malmer   QUOTE (DonPMitchell @ Sep 16 2006, 03:56 ...   Sep 16 2006, 09:42 AM
|- - ugordan   A mosaic of Saturn's northern latitudes: App...   Sep 16 2006, 03:39 PM
||- - john_s   Just checked out your gallery, ugordan- your proce...   Sep 16 2006, 04:54 PM
||- - ugordan   QUOTE (john_s @ Sep 16 2006, 05:54 PM) Ju...   Sep 16 2006, 05:56 PM
|- - DonPMitchell   QUOTE (Malmer @ Sep 16 2006, 02:42 AM) so...   Sep 16 2006, 06:47 PM
|- - Malmer   QUOTE (DonPMitchell @ Sep 16 2006, 08:47 ...   Sep 16 2006, 09:02 PM
- - DonPMitchell   I also really like what you are doing. I hope you...   Sep 16 2006, 07:01 PM
|- - ugordan   QUOTE (DonPMitchell @ Sep 16 2006, 08:01 ...   Sep 16 2006, 09:37 PM
|- - DonPMitchell   QUOTE (ugordan @ Sep 16 2006, 02:37 PM) H...   Sep 17 2006, 04:17 AM
|- - ugordan   A couple of rough Saturn mosaics: The blob in the...   Sep 17 2006, 04:44 PM
|- - Malmer   I think it looks great. Very subtle beautiful colo...   Sep 17 2006, 07:17 PM
|- - ugordan   A few Jupiter images, fixed the greenish hue. It w...   Sep 19 2006, 05:21 PM
|- - Malmer   QUOTE (ugordan @ Sep 19 2006, 07:21 PM) A...   Sep 19 2006, 07:23 PM
|- - ugordan   The vertical stripes (most noticeable is a blue li...   Sep 19 2006, 07:37 PM
|- - Malmer   I guess you have to make an additional flatfield r...   Sep 19 2006, 08:16 PM
||- - ugordan   QUOTE (Malmer @ Sep 19 2006, 09:16 PM) I ...   Sep 20 2006, 07:24 AM
||- - Malmer   it was a typo. i actually ment darkcurrent. mixed ...   Sep 20 2006, 08:48 AM
||- - ugordan   Although the noise stays fixed, it changes intensi...   Sep 20 2006, 09:22 AM
||- - ugordan   Not particularly related to my processing, but her...   Sep 20 2006, 11:34 AM
||- - Malmer   QUOTE (ugordan @ Sep 20 2006, 11:22 AM) W...   Sep 20 2006, 03:23 PM
||- - ugordan   Here are a couple of... hm... questionable(?) resu...   Sep 20 2006, 07:38 PM
|- - tedstryk   Great work! As for the calibration data, it c...   Sep 19 2006, 08:18 PM
- - slinted   UGordon, first off, this is an amazing project you...   Sep 20 2006, 11:00 PM
|- - ugordan   Thanks, Slinted! I'll certainly have a loo...   Sep 21 2006, 07:46 AM
|- - JRehling   QUOTE (ugordan @ Sep 21 2006, 12:46 AM) I...   Sep 21 2006, 06:06 PM
|- - ugordan   JRehling, those are all valid, good points. I said...   Sep 21 2006, 07:16 PM
- - DonPMitchell   It is true that Judd and Vos made improvements to ...   Sep 21 2006, 12:55 PM
|- - ugordan   QUOTE (DonPMitchell @ Sep 21 2006, 01:55 ...   Sep 21 2006, 02:25 PM
- - DonPMitchell   Reflectance is independant of the illuminant. It ...   Sep 21 2006, 02:43 PM
- - DonPMitchell   There's a brown Moon for you, taken by Galil...   Sep 21 2006, 07:03 PM
- - slinted   Good points made by all, Part of my confusion on...   Sep 21 2006, 08:52 PM
|- - ugordan   VIMS cubes, their raw form, capture the brightness...   Sep 21 2006, 09:14 PM
|- - JRehling   QUOTE (slinted @ Sep 21 2006, 01:52 PM) I...   Sep 21 2006, 10:32 PM
|- - ugordan   QUOTE (JRehling @ Sep 21 2006, 11:32 PM) ...   Sep 22 2006, 08:07 AM
|- - ugordan   I can understand the reasoning of not touching the...   Sep 22 2006, 06:41 PM
|- - DonPMitchell   QUOTE (ugordan @ Sep 22 2006, 11:41 AM) Y...   Sep 22 2006, 07:06 PM
||- - ugordan   Be my guest. For starters, here's a dump of th...   Sep 22 2006, 07:45 PM
|- - tedstryk   For Jupiter and Saturn, I am biased toward the rig...   Sep 22 2006, 09:12 PM
|- - ugordan   I've been experimenting with cleaning up the V...   Sep 25 2006, 08:02 PM
|- - ugordan   Sure enough, I got a response from the VIMS team. ...   Sep 26 2006, 07:33 AM
- - edstrick   It probably boils down to too-much-to-do, not-enou...   Sep 26 2006, 09:49 AM
|- - ugordan   To reiterate what you said, on my asking if update...   Sep 26 2006, 02:27 PM
|- - ugordan   Here are a few quick results from the new PDS rele...   Oct 4 2006, 05:55 PM
- - Indian3000   First test to process VIMS cube ( gamma 2.2 ) v1...   Oct 11 2006, 11:53 AM
- - elakdawalla   Hey folks, the Rings Node has generated preview im...   Feb 18 2011, 10:20 PM
- - ngunn   A superb piece of work at TPS but we have to have ...   Apr 28 2011, 09:27 PM


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