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Reprocessing Galileo Io Images
volcanopele
post Mar 27 2007, 07:59 AM
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The New Horizons images of Io that have come down over the last month have gotten me interested in Io again, and with Galileo images of Io. So I've decided to go back through and reprocess some of the color views of Io, particularly global views. I will post some of the more interesting ones here with the goal of rebuilding at least some of my Io website to host them in the long term.

The first view I'd like to present has a bit of a mystery. This is a two-frame, three-color mosaic of the Prometheus volcano from I27. The filters used are violet (in the blue channel), green (in the green channel), and IR-7560 (in the red channel). This mosaic has a resolution of 170 meters per pixel. I'm still working on the color registration (I'm doing all the present processing in Photoshop, so I hope no one minds).

Attached Image


Okay, so what's this mystery? Well, as I was attempting registration, I noticed something funny. I noticed this odd rainbow-colored patch to the southwest of Prometheus Patera. When you flip through the individual color frames, as you can see in the animation linked to below, you can see that this feature is actually a dark feature that moves from southeast to northwest from frame to frame. So what is this feature? The frames are separated in time by about 17 seconds. Could it be an optically thick...chunk in the plume? Any other...sane thoughts? Just thought I would throw this up there.

Attached Image


Well, I hope to post additional Io images over the next few days.

EDIT: I have uploaded a new version of the Prometheus mosaic and have updated the version in this post.


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volcanopele
post Mar 27 2007, 08:44 AM
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Here are some random Io images before I head off to bed. I'll post details in the morning.

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ugordan
post Mar 27 2007, 09:35 AM
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Regarding the mystery question, it might be a dark plume patch. Are you using calibrated images? If so we can rule out flatfield effects on the CCD especially if the dark feature actually isn't static on the CCD but follows the ground features. I assume parallax effect would be sufficient to explain movement of a high plume here?

Regarding the images, nice composites, are you maybe thinking about producing some "true" color ones? They'd be dull, I know, but I'm always interested in an accurate color look.
You mentioned IOs color showed high phase angle dependency, is this the effect of the much more pronounced bluish (violet?) regions at higher phases, while otherwise it's a more subdued appearance?


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Bjorn Jonsson
post Mar 27 2007, 12:21 PM
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Io's brightness and color is highly variable with phase angle. There are areas near the equator that appear whitish at low phase angles and much brighter than the areas at higher latitudes. At higher phase angles they get much darker and and appear grayish (they can even get darker than the polar areas). And at least some of the dark/black spots (e.g. Loki Patera) brighten a lot at high phase angles.

I remember a paper in Icarus or JGR several years ago that had rather interesting global maps of Io showing the Henyey-Greenstein g parameter. Many of Io's major albedo/color features were easily recognizable in the maps.
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JRehling
post Mar 27 2007, 03:55 PM
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QUOTE (volcanopele @ Mar 27 2007, 12:59 AM) *
So what is this feature? The frames are separated in time by about 17 seconds. Could it be an optically thick...chunk in the plume? Any other...sane thoughts? Just thought I would throw this up there.


I had a sane thought, but it didn't check out. I wondered if it might be the shadow of a smaller jovian satellite moving across in eclipse. Racing to the solar system simulator, I found that Io was on the sunward side of Jupiter at the time of I27, so it couldn't be Metis, Adrastea, Amalthea, or Thebe. The shadow explanation would only work if a small satellite had an orbit between Io and Europa. Not only is no such body known, but I suspect such an orbit would not be stable (?).

So, I've given up on sane ideas; back to the asylum.
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volcanopele
post Mar 27 2007, 07:27 PM
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Unfortunately I haven't had a chance to calibrate the images. The program I use for that, ISIS, seems to have developed problems with Galileo images since the last time I processed Galileo images (almost 3 years now). However, I fairly confident the dark patch is real, and not a flat field artifact.

In terms of creating "true" color images, I don't really intend on doing that. The filters used don't really support that and I'm not going finagle with the images beyond what I already have done.


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belleraphon1
post Mar 28 2007, 01:48 AM
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Beautiful, volanopele!!!!!

Always loved the Prometheus imaging. Correct if I am wrong, but is the plume caused by silicate lava flowing over fields of sulphur dioxide ice dunes and causing them to explode into vapor?

Love the textures of the dunes in this image.... tryng to imagine in my minds eye what it would be like to hike these deposits.... THAT would also make a great visual simulation....

thanks for these ...

Craig
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PhilHorzempa
post Mar 28 2007, 03:53 PM
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Thank you for those Io images. However, I do recall that
one member of the UMSF had a GIANT image of Io on his website
about a year ago. I do not remember his name. So could he step
forward and post either his web image page address or a link to that
incredible Io image. As I recall, the Io image in question was the one
in which the background is the surface of Jupiter itself.


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Malmer
post Mar 30 2007, 04:16 PM
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Could be me... I have stitched together one really big one:

really big IO picture

its not the best processing in the universe but its ok.





QUOTE (PhilHorzempa @ Mar 28 2007, 05:53 PM) *
Thank you for those Io images. However, I do recall that
one member of the UMSF had a GIANT image of Io on his website
about a year ago. I do not remember his name. So could he step
forward and post either his web image page address or a link to that
incredible Io image. As I recall, the Io image in question was the one
in which the background is the surface of Jupiter itself.
Another Phil
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MizarKey
post Mar 30 2007, 04:52 PM
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Malmer - that's a sweet image of IO. Thanks for posting that.


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4th rock from th...
post Mar 30 2007, 05:48 PM
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QUOTE (volcanopele @ Mar 27 2007, 08:27 PM) *
In terms of creating "true" color images, I don't really intend on doing that. The filters used don't really support that and I'm not going finagle with the images beyond what I already have done.


The best approach with these filters would be to create an appropriate color space (something like an extra extra wide-sRGB) and then convert the final balanced result to a normal sRGB JPG. That way proper color hues can be generated, while getting a good approach to the correct saturation. If I can, I'll do it and post the results here.


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tedstryk
post Mar 30 2007, 06:35 PM
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QUOTE (4th rock from the sun @ Mar 30 2007, 05:48 PM) *
The best approach with these filters would be to create an appropriate color space (something like an extra extra wide-sRGB) and then convert the final balanced result to a normal sRGB JPG. That way proper color hues can be generated, while getting a good approach to the correct saturation. If I can, I'll do it and post the results here.

Why a jpeg? I almost always work in png mode. The problem is that when I process an image, I compulsively go back and rework it at some point. Each time, the jpeging loss would build. Also, I like to work in 16-bit mode - it is more forgiving.


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4th rock from th...
post Mar 30 2007, 07:40 PM
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I mentioned JPG as the format to upload the final image to this forum, for example. While working on a image, I prefer 16bit TIF files biggrin.gif


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elakdawalla
post Mar 30 2007, 09:34 PM
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QUOTE (4th rock from the sun @ Mar 30 2007, 10:48 AM) *
The best approach with these filters would be to create an appropriate color space (something like an extra extra wide-sRGB) and then convert the final balanced result to a normal sRGB JPG. That way proper color hues can be generated, while getting a good approach to the correct saturation. If I can, I'll do it and post the results here.

Wow. blink.gif That is hard core, but that's clearly a rigorous way to do things. Is this something that you could explain to a moderately educated person (i.e., me) how to do, or does it require software that I'm not likely to have access to? Or, once you had developed your Galileo color space, would you be able to produce a "recipe" of the appropriate proportions to use to mix common sets of available filters to produce approximate true color images?

--Emily


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volcanopele
post Mar 30 2007, 09:48 PM
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Bjorn has a good write-up on how to create "true" color images of Io:

http://www.mmedia.is/bjj/3dtest/io/index.html

I never really like the results this produces and far prefer my false color images...

Basically, the quick and simple way of doing this is to use "Channel Mixer" in Photoshop, and for the output channel select blue, then set the percentages as 61% Green, 39% Blue.


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