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Deep Impact camera data, Messing about with images from the PDS
elakdawalla
post Dec 28 2009, 07:06 PM
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I'm wondering if anybody here has spent any time working on the Tempel 1 images from Deep Impact. The data are available at the Small Bodies Node (see e.g. http://pdssbn.astro.umd.edu/holdings/dif-c...0/dataset.html), and Version 2 of the PDS archive (which appears to have been published 3 years ago) includes versions of the data that have been calibrated, cleaned of instrument artifacts, and converted to units of radiance and also I/F. The HRI data have not been deconvolved to remove the blur: a bit of playing shows that without deconvolution, HRI images look pretty similar to MRI images. Attached is a color composite I made of the highest-resolution full-globe shots of Tempel 1 captured by the MRI before the impact. The image isn't big but there's more variety in color than I expected. This is made from the I/F images and is an RGB composite of red, green, and violet continuum filter images, overlaid over a clear image that I sharpened slightly. It's very red, but I think that's real.

Has anybody else worked with these?
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ugordan
post Dec 28 2009, 07:28 PM
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Haven't worked with Tempel 1 data yet because I'm not really inclined to download gigabytes not knowing what I'll find inside, I prefer the PDS Atlas search approach. As for the redness, part of it could be due to the "red" and "violet" filters (the other part would be due to no gamma correction). I'd suggest "orange" and "blue" filters instead and if you really want to split hairs, you could do some channel mixing to bring the wavelengths to sRGB colorspace spec.

The central wavelengths originally chosen for the filters allow for a fairly simple channel mix. Here's what I used on some EPOXI Earth data (OGB filters):

R = 60% red + 40% green
G = 100 % green
B = 80% blue + 20% green

I suspect the very act of replacing the "red" (actually bordering on near IR) with "orange" would give you a more brownish result. Assuming there is such filter data, ofc.

EDIT: Ahh, only now I see the MRI instrument lacks those other filters and only the RED is common.


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ugordan
post Dec 28 2009, 07:54 PM
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Right, here's what playing with RED, GREEN_CONT and VIOLET_CONT channel mixes instead produces:

Attached Image


Your image with the following mixes and brightened 2x:

R = 0.36R + 0.64G
G = 0.11R + 0.89G
B = 0.68G + 0.32B

It would be nice to compare this with HRI ORANGE/GREEN/BLUE filter mixes as in my previous post, if available, especially since these continuum filters are very narrowband. And of course, this mixing business assumes the source spectra is fairly linear, otherwise it starts to fall apart, especially when your source filters are so off-base (like these). The HRI filters are much closer to standard RGB wavelengths and are wideband so aren't likely to miss any spectral features.


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elakdawalla
post Dec 28 2009, 07:57 PM
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Yeah, with the Tempel 1 data especially I wish they had provided tar-balls of just the July 4 data, because that's all that resolves the comet. I used the browse pages to pick out a sequence of interest then just downloaded the few images from that sequence. Here's the relevant browse pages:

MRI: http://pdssbn.astro.umd.edu/holdings/dif-c...5_185/index.htm
HRI: http://pdssbn.astro.umd.edu/holdings/dif-c...5_185/index.htm
ITS: http://pdssbn.astro.umd.edu/holdings/dii-c...5_185/index.htm

Looks like the sharpest full-globe view is from the ITS.

The MRI has very different filters to the HRI, and there's really nothing corresponding exactly to RGB. Attached is a description.
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elakdawalla
post Dec 28 2009, 08:02 PM
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Cross-posting smile.gif Thanks for your version. Guess I'll go dig up those HRI images and see what they produce!


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machi
post Dec 28 2009, 08:10 PM
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Just old images, but nothing perfect.
First is mosaic from ITC, second and third are from HRI.
This treasure still wait for digging.
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elakdawalla
post Dec 28 2009, 08:18 PM
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Hooray -- just discovered that IMG2PNG handles these images just fine (Bjorn added FITS conversion when he wanted to use IMG2PNG to open New Horizons files). However the resultant images are mirror-flipped top-for-bottom. To convert these, you don't need to download the LBL files. If you're going to use the I/F files, you need to instruct IMG2PNG to stretch them all the same way. To do that, use this command:

img2png *.fit -ctstretch.txt

And have a file named stretch.txt that contains the following text:
QUOTE (stretch.txt)
-0.00001 0.1
- -
- -


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tedstryk
post Dec 28 2009, 08:35 PM
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I have worked with a few images.

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elakdawalla
post Dec 28 2009, 09:19 PM
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Nice, is that one of the lookback frames?

Funny story...I was at Von Karman for the DI impact event. During the Q and A session following the briefing where they showed the lookback images for the first time, some random TV reporter chick asked A'Hearn whether he could "explain what was going on in that tunnel image." Everyone on the panel, and everyone in the room, looked confused for a few seconds as they tried to figure out what the hell she was talking about. Then you could feel a mix of contempt and horror wash across the room as everyone realized she was talking about the lookback image, and had had absolutely no idea what she was looking at; trying to make sense of it, her brain had matched it to the view through a dark tunnel. Contempt -- what was she doing in this room, how could she have no idea what she was seeing? And horror, especially on the part of the panel -- does anybody out there in the public have any understanding of what we just accomplished? A'Hearn stammered some sort of basic answer describing that photo. Afterward, I think all the other reporters asking questions worked harder to sound like they were smart and knew what was going on.

--Emily


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tedstryk
post Dec 28 2009, 09:31 PM
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It is a large stack of deconvolved lookback frames.


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elakdawalla
post Dec 28 2009, 09:55 PM
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OK, here's the HRI O-G-B combo. Pretty blurry, and the blur seems to be wavelength-dependent. Doesn't look too different from your modified version of the MRI image, Gordan.
Reason for edit: Corrected channel identification

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elakdawalla
post Dec 28 2009, 10:10 PM
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OK, here's a pretty fictional image -- it's the OGB color I posted above, over an ITS frame captured shortly before. There is significant rotation between the HRI and ITS images and I don't know how to deal with that. I'm also attaching the ITS image without adjustment. Anybody got any advice on anything I can do within Photoshop or GIMP to match the two points of view a bit better?
Reason for edit: Corrected channel identification

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machi
post Dec 28 2009, 10:28 PM
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Not best, but quickest is probably "per partes" method.
Here is colorised ITC image (color from your O-G-V image).
It's made in Paintshop and slightly improved in GIMP.
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ugordan
post Dec 28 2009, 10:33 PM
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QUOTE (elakdawalla @ Dec 28 2009, 10:55 PM) *
OK, here's the HRI O-G-B combo. Pretty blurry, and the blur seems to be wavelength-dependent. Doesn't look too different from your modified version of the MRI image, Gordan.

To be compared in an apples-to-apples comparison to that mixed image, this one should be channel mixed as well (I assume you didn't mix the channels?).
R = 0.6R + 0.4G
B = 0.2G + 0.8B
Attached Image


EDIT: Fixed blue channel mix as it turns out it was in fact blue, not violet channel.


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elakdawalla
post Dec 28 2009, 11:09 PM
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Sorry, Gordan, I meant OGB! I fixed that in my posts above.

Machi, your version looks nice. What do you mean by "per partes"?


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