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Voyager and Galileo Images of Ganymede, The Ganymede images and mosaics thread
DrShank
post Oct 18 2010, 11:46 PM
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its about as close to natural color (at high resolution) that we can get right now. kind of a pale milk chocolate. The moons not made of green cheese after all. we could sell land parcels on the chocolate moon!


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EDG
post Oct 19 2010, 08:10 AM
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Hooray! I just managed to find all my old Galileo and Voyager image mosaics and notes (I thought I'd lost them all)! I even have the scripts I used to make some of them in ISIS too (complete with matchpoints)!

So I may be posting a few more mosaics here, if they'll fit (and the scripts, if people want them) smile.gif.
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tasp
post Oct 19 2010, 05:32 PM
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Thanx!!
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elakdawalla
post Oct 19 2010, 06:26 PM
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Since the scripts are just text files and shouldn't take up too much space, I say post 'em. I have fantasies that I'll get back into using ISIS for image processing but I'll have to get myself a Mac first...


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Bjorn Jonsson
post Oct 19 2010, 06:48 PM
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Great mosaic, especially when keeping in mind that it was made more than 10 years ago. Reminds me of when I made my first 'real' (and big) planetary map towards the end of the 20th century - it was of Ganymede. My computer was completely swamped, a lot of time was spent on calculation runs and it crashed several times. Now I could make a *much* bigger map with ease and much more quickly.

Needless to say, seeing the scripts would be interesting. There are some ISIS users here.
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EDG
post Oct 19 2010, 07:10 PM
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QUOTE (elakdawalla @ Oct 19 2010, 11:26 AM) *
Since the scripts are just text files and shouldn't take up too much space, I say post 'em. I have fantasies that I'll get back into using ISIS for image processing but I'll have to get myself a Mac first...


Yeah, me too (well, the getting back into ISIS part, not the Mac part!). Unfortunately I then remember how horribly painful installing Linux and trying to get ISIS to work with it is... I had a quick look for the (old) versions of Linux that ISIS claims to be compatible with and I can't even find the installers for those anywhere anymore (and it sounds like it has problems running in the newest versions of SuSE).

So, the attached zipfile contains the script for the mosaic I posted. The "colourRAND.txt" in the zip file is the script itself - I'd advise that you have a look through it and check that it's all good, as I'm not sure if it's still compatible with the current version of ISIS. I also do some housekeeping in the script (deleting files) so make sure that's OK too. The zipfile also contains three input.txt files which are used in the "noseam" step of the processing. And there's also the RANDganymede.rmb file, which is a SPICE file that I got from Tim Colvin at RAND used in the "spicelab" step - I'm not sure if this is still necessary, but at the time it was better than the SPICE data in ISIS.

The script will take the original Voyager 2 IMQ format images, turn them into .cub format, update the labels with the SPICE data, remove the reseau marks (lvl 1), reproject them to sinusoidal (lvl 2) centred on 170 longitude with a resolution of 2.3 km, run noseam to make global orange, blue, and violet mosaics, output raw files of the mosaics, and then make global mosaics centred on the leading, trailing, and antijovian hemispheres.

You'll need the following Voyager images, available from http://pds-rings.seti.org/vol/VG_0025/GANYMEDE/C2063XXX/ :

c2063105.imq
c2063113.imq
c2063121.imq
c2063123.imq
c2063131.imq
c2063101.imq
c2063109.imq
c2063111.imq
c2063119.imq
c2063127.imq
c2063129.imq
c2063059.imq
c2063107.imq
c2063115.imq
c2063117.imq
c2063125.imq
c2063133.imq

I'd be interested to see if this works on other peoples' machines smile.gif

(EDIT: Oh yeah, and make sure all the imqs and the text files are in the same folder, and that you are running the script from the same folder too).
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Attached File  globalcolour.zip ( 12.76K ) Number of downloads: 83
 
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EDG
post Oct 19 2010, 07:11 PM
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QUOTE (Bjorn Jonsson @ Oct 19 2010, 11:48 AM) *
Great mosaic, especially when keeping in mind that it was made more than 10 years ago. Reminds me of when I made my first 'real' (and big) planetary map towards the end of the 20th century - it was of Ganymede. My computer was completely swamped, a lot of time was spent on calculation runs and it crashed several times. Now I could make a *much* bigger map with ease and much more quickly.


Funnily enough, I still have some email correspondence with you about making those maps wink.gif.
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EDG
post Oct 19 2010, 07:17 PM
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This is the global mosaic of Ganymede's trailing hemisphere that the script makes (at least I hope it's trailing, I get leading and trailing mixed up!) - note that this doesn't include any other images, it's just a reprojection of the antijovian mosaic:

And here's the leading hemisphere mosaic (huh. Interesting. I thought I did this in a separate post but it seems to have combined them - the one on the left is the trailing hemisphere, the one on the right is leading):
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EDG
post Oct 20 2010, 07:37 AM
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I was going to start a new thread for this but I think for now I'll keep posting my stuff here.

I also made a global colour mosaic of the sub-jovian hemisphere of Ganymede from the Voyager 1 images, but that proved more problematic, largely because some of the blue filter images were blurry. I made global mosaics using orange, green, blue, violet and UV filters, and here's what I came up with (details are all in the captions within the images).

The OBV (Orange/Blue/Violet) is the same filter combination as my Voyager 2 mosaics posted above, but you can see the issue with the blurry blue filters in the top left part of the image.
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EDG
post Oct 20 2010, 07:40 AM
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To correct the blurriness (aesthetically anyway), I cheated a bit - I took the Orange mosaic, fiddled with the brightness/contrast a bit (went into Photoshop > Adjust Brightness/Contrast, and set -10 Brightness, -5 Contrast) so it looked kinda like the Blue one, and put the modifed orange mosaic in the Green channel of the image to replace the blue one that was there. So technically this mosaic is Orange/Modified Orange/Violet in the R/G/B/ channels.

The result is that the blurriness isn't there anymore, but it's no longer accurate in appearance. Still, it doesn't look too bad IMO.
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EDG
post Oct 20 2010, 07:49 AM
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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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EDG
post Oct 20 2010, 07:52 AM
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And finally, just for kicks I tried an OGU image (Orange/Green/Ultraviolet), which wouldn't really look like true colour at all and doesn't actually have that much overlap between all three filters (the only part that does is a thin strip on the left of the Green, but it blends in somewhat with the yellow overlap so it's hard to make out).

I'll see if I can dig up the scripts for these. Anyone manage to get the Voyager 2 script working at all?
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ugordan
post Oct 20 2010, 08:13 AM
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QUOTE (EDG @ Oct 20 2010, 09:49 AM) *
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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tedstryk
post Oct 20 2010, 05:20 PM
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Cool. That looks like the set I used in this one.

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tedstryk
post Oct 20 2010, 05:22 PM
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QUOTE (ugordan @ Oct 20 2010, 09:13 AM) *
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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