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Galileo images and mosaics of Europa
paxdan
post Aug 22 2005, 07:49 PM
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nice work on europa guys. It is so cool to see the images being properly reproduced instead of horrid stuff you still see in text books.
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tedstryk
post Aug 22 2005, 08:08 PM
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QUOTE (scalbers @ Aug 22 2005, 07:35 PM)
Ted,

Your images are very nice as well, particularly the large gibbous view in post #1. One thing in particular I'd consider is comparing the hue and saturation realism to what I had used, namely the colors from Bjorn's map (that I may have tweaked a bit). Do you have a feel for the pros and cons of the color accuracy compared with Bjorn's? Both look pretty good to me - I wonder what new insights you have come up with. I'll reread your posts as well.
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Be careful of that image. The filter sets available were limited at best, and those used to produce the image vary throughout. Plus, some color data is from the actual set the grayscale image was made from, but a lot of it is from different orbits at different illumination angles. So the color, while processed to seem roughly realistic, is quite treacherous - a lot of guesswork went into it, and then I normed it a bit to fit the other images. As for the others, they are as accurate as I could make, but I can't directly compare them because I don't know how Bjorn's color was produced.


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Guest_Sunspot_*
post Aug 22 2005, 11:38 PM
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How about trying the same with images of Io?
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tedstryk
post Aug 22 2005, 11:45 PM
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I have thought of that. The only problem is that Io has much more color contrast than Europa (europa has some color contrast, but it is pretty predictable - Io's isn't). I am not sure if it would come out well or not. I may try.


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Decepticon
post Aug 23 2005, 12:37 AM
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Keep them coming! Europa really deserves an orbiter.
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tedstryk
post Aug 23 2005, 03:07 AM
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QUOTE (Decepticon @ Aug 23 2005, 12:37 AM)
Keep them coming! Europa really deserves an orbiter.
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Well, I might work on some other moons, or try some mosaics. This is the only other global view of Europa I could find in the Galileo set that was worth combining with some color data.



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Bjorn Jonsson
post Aug 23 2005, 11:14 AM
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Regarding my Europa map, the color there was taken from global Voyager images only. I used these to colorize higher resolution grayscale data (mainly clear filter). The reason I used Voyager and not Galileo data was higher resolution and IIRC Galileo had not imaged Europa globally in color at the time I made the map. I don't remember whether I used OGB or OGV (probably the latter) - I'm at work wink.gif and can't check it now.

I'm pretty sure the color is a bit too saturated in my map. It may too reddish as well, a common problem when the wavelength of the data used for colorizing is too short (e.g. O instead of R and/or V instead of B ).

I have been working on a much bigger Europa map (9000+ pixels in the horizontal direction) from time to time for more than two years. I have reprojected most of the high-res data I plan to use but haven't started working on the color. I plan to use Galileo images for color where possible, filling gaps (or very low-res areas) with Voyager data and/or synthetic color. I also expect to use synthetic B instead of V. The V images are more contrasty than the B images but mixing G and V should give a fairly good results (definitely better than using V only). One thing that complicates color work is Europa's photometric properties, limb darkening varies with wavelength and I prefer images as close to zero phase angle as possible.

Ted's images look fairly good, especially wrt sharpness but there are some saturation problems, caused both by saturation in the red images (this manifests itself as pinkish areas) and in all of the images in some cases (bright, white areas). I have some early 'test images' of Europa that look similar. And I should add that there is great color data at 1.4 km/pixel in the E14 data.

BTW Europa's color should be kid's stuff compared to Io. There is some information on Io's color on my experimental renderings page ( http://www.mmedia.is/bjj/3dtest/ ) and I will add more once I make my new map of Io available, I've been too swamped in data recently to update my website wink.gif. In particular, it is impossible to use 'unmodified' IR7560 as red without seriously messing up the color balance.
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4th rock from th...
post Aug 23 2005, 12:50 PM
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If you consider the Galileo filters and their wavelenghts, you have:

Violet - 404 : Green - 559 : Red - 671 : IR756 - 756 : IR968 - 968


The human color vision has a peak response of:

Blue - 440 : Green - 510 : Red - 650


So to "convert" the Galileo filters in to "human colors" we can mix images from different filters to get the proper wavelenghts.

I've calculated the ratios and corresponding wavelenghts:

75% Violet + 25% Green = blue (443)
70% Green + 30% Violet = green (513)
80% Red + 20% Green = red (649)
50% IR756 + 50% Green = red (658)
20% IR968 + 80% Green = red (641)


I've tried this on two Europa images and the results look good. Saturation is low, but that's expected when you mix the color data. Also, Europa looks white through a telescope anyway ;-)

Attached Image


Attached Image


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tedstryk
post Aug 23 2005, 03:45 PM
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I experimented with filter mixes. Realistically, the problem is that Galileo image quality varies wildly depending on compression used. Also, it is rare to get a color mosaic without some bad gaps. But I did use similar mixes.

Bjorn: I see the problem in my large mosaic, but could you point out what you are talking about in my other images? I am not sure which spots you are referring to, and would like to know so I can try to correct the problem. Some of what you are seeing may be due to the fact that I jacked the contrast up on the posted images.


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Bjorn Jonsson
post Aug 23 2005, 04:25 PM
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The pinkish areas are very prominent in the C10 image (the message dated yesterday at 05:29 PM), especially in the bright areas near the left limb and near Pwyll.
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tedstryk
post Aug 23 2005, 04:41 PM
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QUOTE (Bjorn Jonsson @ Aug 23 2005, 04:25 PM)
The pinkish areas are very prominent in the C10 image (the message dated yesterday at 05:29 PM), especially in the bright areas near the left limb and near Pwyll.
*



This is a tweaked version.



And another.



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Bjorn Jonsson
post Aug 24 2005, 12:01 AM
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These are better but still a bit pinkish. I'm not sure why - now that I'm at home and can have a look at what happened when I was processing these same images a few years ago I see I also had some problems with pinkish areas, especially near Pwyll. They were less pinkish but still pinkish.

Time to try to finish that 9816 x 4908 map of Europa I have been working on for two years, I should be able to get more realistic color for that map. I have now checked and seen that my current map of Europa was colorized using OGV as I thought. This means it is probably too reddish and saturated.

It is probably an interesting idea to check if there are any Cassini RGB (or CB1-GB) images of Europa near closest approach.
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scalbers
post Aug 24 2005, 05:14 PM
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If you try the CICLOPS site and use their new search feature for "Europa" a couple of nice (if small) color images will pop up.


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Decepticon
post Oct 1 2005, 05:37 PM
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Some "True Color" Images of Europa.

Somthing I found looking around. http://pirlwww.lpl.arizona.edu/HIIPS/EPO/gallery.html
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ljk4-1
post Oct 7 2005, 03:13 PM
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This could bode well for life on Europa (and Enceladus?):

Scientific American, 30 September 2005

http://www.sciam.com/article.cfm?chanID=sa...A8E83414B7F4945

Geologists have produced evidence of abundant marine life on the earth from a
period when others say a thick layer of ice gripped the entire planet. The find lends
considerable support to one side of a scientific controversy that has been widely debated for
decades.

The hullabaloo is over a glacial period dating to about 750 million to 600
million years ago.

Experts agree about the presence of ice on the planet then--even at the
equator--but how much and to what extent is still up in the air. Theories range from a "snowball
Earth" hard packed in kilometer-thick ice to a "slush ball Earth" characterized by thin ice and
areas of open water. The range of conditions would have impacted the microorganisms present.

Thick ice would have made life difficult for plants and animals, one line of reasoning goes,
choking oxygen out of the sea and blocking sunlight needed for photosynthesis. Mass extinction
would ensue and after the thaw, give rise to an explosion of multicellular life.


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and feel as if I had done some wrong, and it is hard to forget the ugly circumstance.
I see that such intercourse long continued would make one thoroughly prosaic, hard,
and coarse. But the longest intercourse with Nature, though in her rudest moods, does
not thus harden and make coarse. A hard, sensible man whom we liken to a rock is
indeed much harder than a rock. From hard, coarse, insensible men with whom I have
no sympathy, I go to commune with the rocks, whose hearts are comparatively soft."

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