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30th Anniversary of the Voyager 1 Flyby of Jupiter
machi
post Mar 21 2010, 04:08 PM
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Thanks! tongue.gif
What a pity, that most images from Voyager 1 are badly smeared. It's interesting how good work engineers made in other flybys (especially Uranus and Neptune flybys).


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tasp
post Mar 21 2010, 05:40 PM
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I am thinking the color Voyager pictures must have an additional complication over those shot on subsequent missions with solid state imaging devices.

With the vidicon technology they had in the seventies, the actual size of the pixels across the image varies slightly with brightness (due to complex technical reasons in how the electron beam pics off the accumulated charges) and for an object that was noticeably colorful, each filtered picture in the mosaic would have, in addition to varying pixel size from the images being taken at slightly different distances, and pixels slightly askew due to object rotation and motion and the spacecraft flight path diverging from a straight line during imaging, pixels of different size across each image itself.

That this can all be allowed for in the processing is amazing, especially in regards to maintaining the very fine detail in each image as we so often see here at UMSF. It would seem that each pixel in the final product might have had some influence from up to 9 pixels in the raw data.

If there is a quick and digestible short version of how the image processing can do this (that Callisto pic is truly amazing!!) I think it would be interesting to know.

Have any cameras been flown that do some/all of this processing as the images are taken, or is this something the compression software sometimes used does in the course of doing what it does ?

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Ian R
post Mar 21 2010, 06:08 PM
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That is just a beautiful example of image processing you've achieved there Machi. Nice one!


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machi
post Mar 22 2010, 10:13 AM
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Thanks!
Tasp:
If my memory is right, so different pixels size because of brightness isn't such problem. But vidicon cameras have always bigger geometrical distorsion than CCD cameras. Especially in corners. But CCD cameras also have faults, for example bleeding.
And yes, what you said about difficulties with color processing, all is true. Same problem is with Cassini or Galileo images, but in this case, images are taken more quickly and in lower flyby velocities, so changes aren't so prominent.
I overcome these problems in different ways. Actually most easy way (and case of this Callisto image) is using wide angle images. Then color information has much lower resolution (in this case 8). It's no problem with detail preservation. In some graphics programs you can combine two images in such way, that you have full details from BW image and color information from color image (ImageJ, PaintShop Pro).
Or you can use narrow angle images taken with different filters, but these were taken only at beginning of flybys. Color information in these images has higher resolution, but it's difficult to remove differences between them. Then you can remapping all images on sphere or apply warping techniques.
Another way is using color maps from another missions or different part of the same mission (for example Jupiter's combined LORRI + HST images).
Last resort is color from photometry. This is badly usefull in some cases (Io, Jupiter, Earth), but usable in others (Uranus moons, asteroids etc.).
Last question: Actually I don't know about scientific framing cameras with this processing. But monitoring camera on Mars Express is actually color camera with multicolor CCD (with Bayer pattern). And we have multicolor push-broom imagers with linear CCD's like HRSC, HiRISE or MVIC (functioning in same way as PC scanner).


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ugordan
post Jul 24 2010, 06:48 PM
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I've been experimenting with CIE XYZ colorspace calculations recently with various spacecraft data. This is the same approach I use with Cassini VIMS to generate color, except with camera filters you get many fewer wavelength datapoints so the end result is less accurate. I currently just linearly interpolate the spectral curve between missing points, but it still works pretty well.

As official Voyager images of Jupiter are known to be all kinds of funky colors ranging from greenish, to deeply red I decided to give it a whack. Unfortunately, I don't know how to properly calibrate Voyager images (if anyone has any pointers I'd be glad to hear) so I used raw images off the shelf. The images are c1524909.imq, c1524907.imq and c1524905.imq, OGB frames. Here's a crop of what the straight-up substitution for RGB image channels looks like:

Attached Image


Notice the uncalibrated dark current/bias in the upper left corner, also some color shifting near Europa. The colors are similar to some Photojournal images (albeit they are at a higher contrast stretch) suggesting I at least got the relative channel brightnesses right. Here's the image passed through the code that compensates for the differing wavelengths, and cleaned up in Photoshop:

Attached Image


Compare to a Cassini image processed the same way:


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Bjorn Jonsson
post Jul 24 2010, 08:37 PM
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The cleaned up/color compensated version looks great. The color in many of the ancient, 'official' color images is really bad and they really need to be reprocessed.

QUOTE (ugordan @ Jul 24 2010, 06:48 PM) *
I've been experimenting with CIE XYZ colorspace calculations recently with various spacecraft data. This is the same approach I use with Cassini VIMS to generate color, except with camera filters you get many fewer wavelength datapoints so the end result is less accurate. I currently just linearly interpolate the spectral curve between missing points, but it still works pretty well.

As official Voyager images of Jupiter are known to be all kinds of funky colors ranging from greenish, to deeply red I decided to give it a whack. Unfortunately, I don't know how to properly calibrate Voyager images (if anyone has any pointers I'd be glad to hear)

I really found out 'by accident' how to calibrate Voyager images several years ago: I installed ISIS and following that I suddenly had the Voyager calibration files. I then used information from these files (and possibly some of ISIS' source code - I don't remember) to incorparate Voayger calibration into my software. To simplify things I converted most of the calibration files (flatfields etc.) to 800x800 'raw files' containing 4 byte floating point numbers.

By the way - wasn't there a thread somewhere describing in detail the approach you used for generating Cassini (VIMS) color images? I'm just starting a major Voyager image processing project of mine and I'm currently deciding exactly how to process the color images. I might use a similar approach for the first time.
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Bjorn Jonsson
post Jul 24 2010, 08:57 PM
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Here are two files containing some information (in particular, voylin.sav contains the equation for the non-linearity correction):

Attached File  voycal.zip ( 3.87K ) Number of downloads: 101

Attached File  voylin.zip ( 1.84K ) Number of downloads: 89


As can be seen from voycal.sav there lots of files are needed for calibrating the Voyager images.

And a link just to be on the safe side:

http://isis.astrogeology.usgs.gov/document...UserRights.html
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ugordan
post Jul 24 2010, 09:09 PM
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Thanks for those files, Bjorn. I'll have to give calibration a shot one of these days. The VIMS thread you're probably thinking of is this old one.


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Bjorn Jonsson
post Jul 25 2010, 08:12 PM
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This is certainly extremely interesting. I tried recomputing the color balance of a Voyager 2 GRS mosaic I did back in 2001 ago but I now used calculations similar to those used above by Gordan and described in more detail in the VIMS thread. I think the color is significantly more realistic in the new version but beware that there might still be some bugs in my code so this might change slightly. Anyway, this is what it now looks like:

Attached Image


A smaller image showing the color in the old version of the mosaic:

Attached Image


The new version definitely looks more realistic in my opinion. It should be noted that I haven't done any gamma corrections.

By the way these are images of the Great Red Spot obtained by Voyager 2 on 6 July 1979 at a range of 3.8 million km. We are viewing the GRS from directly above in this mosaic so it shows the GRS' true shape better than the original images which were obtained with the spacecraft about 5 degrees north of the equatorial plane.
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Ian R
post Jul 26 2010, 08:35 AM
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As so often happens, Bjorn and Gordan, your work has yet again inspired me to crack out Paint Shop Pro and have a fiddle with some of the raw data.

Here's a relatively un-scientifically adjusted view of the GRS, taken by Voyager 2 (30th June 1979):

Attached Image


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Ian R
post Jul 26 2010, 11:52 AM
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Here's another view from Voyager 2, taken on May 28th, 1979:

Attached Image


I've used a rudimentary 'recipe' to reach this result, using the three filtered images: Orange, Green and Violet:

CODE
ORANGE == Add Violet, Dodge 4%
GREEN == Add Violet, 48%
VIOLET == Add Orange, Negative, Burn 14%

Grey World Color Balance
Curves adjustment




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Ian R
post Jul 26 2010, 12:03 PM
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Now, this certainly would be a mammoth undertaking, but just imagine what a cleaned-up and properly processed version of this movie would look like:

http://www.youtube.com/watch?v=BosvP4CLz9o


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Stu
post Jul 26 2010, 02:26 PM
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*****y hell...!!! ohmy.gif ohmy.gif ohmy.gif

That's like having a whole new mission to Jupiter!!! ohmy.gif


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ElkGroveDan
post Jul 26 2010, 04:09 PM
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Ah nostalgia. as I watch this I can almost smell the smoldering celluloid fragments inside the whirring projector as someone in the corner mutters, "Hey, pull the curtains closed tighter!"


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machi
post Jul 26 2010, 06:48 PM
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Ian, Bjorn, Ugordan: Very nice images! Very provocative smile.gif

Jupiter movie: I was trying this, but it's work for weeks sad.gif


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