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Data Discolsure, SRC of HSRC on MEX
Phil Stooke
post Dec 14 2005, 04:12 AM
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We're looking at the north pole. Stickney is off the top. Roche, very near the north pole, is deep in shadow at bottom. There are three SRC images from this orbit spread left to right, but giving no new coverage. The HRSC image which matches this has a data gap but does show the full disk (except that gap) including Stickney at lower resolution. I'll post it tomorrow. There are Viking images of this general area, and the previously released Phobos images from Mars Express (a release early this year, if I recall) also overlap it a lot.

The only publicly released SRC image I can think of is one of those from the earlier Phobos set. My Deimos images (above in this thread) show that SRC has a slight double exposure-type defect. In this Phobos image it seems to add to the perception of there being a zillion grooves.

Phil


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Guest_BruceMoomaw_*
post Dec 14 2005, 04:56 AM
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The HRSC scientists are still reluctant to talk about the SRC, but one photo of a dust devil taken by it was shown at the AGU. The resolution was still listed as 5 meters/pixel, implying that they haven't been able to correct the focusing problem.
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mcaplinger
post Dec 14 2005, 05:24 AM
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QUOTE (elakdawalla @ Dec 13 2005, 03:32 PM)
And, for this picture in specific: would it be a valuable activity to try any of those focus-correcting or deconvolution tools on these blurry SRC images?


*


Despite what's been said in other discussions in this forum, you need knowledge of a system's point-spread function to do deconvolution. Anything you do without knowledge of the PSF is just regular high-pass filtering, and you can do that with Photoshop perfectly well.


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tedstryk
post Dec 14 2005, 10:32 AM
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QUOTE (mcaplinger @ Dec 14 2005, 05:24 AM)
Despite what's been said in other discussions in this forum, you need knowledge of a system's point-spread function to do deconvolution.  Anything you do without knowledge of the PSF is just regular high-pass filtering, and you can do that with Photoshop perfectly well.
*


If you can find images of point sources from a camera, you can reconstruct the PSF.


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Phil Stooke
post Dec 14 2005, 02:49 PM
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Here's the HRSC image of Phobos from MEX orbit 1163 to match the SRC image above. I want to emphasize that there is a (minimal) improvement in resolution going from HRSC to SRC, even with the flaw. See my next post.

Stickney is at the top. The north pole is at the bottom near the terminator. And this is a left-right mirror image. I didn't correct it because it's important to illustrate the fact that the raw images can be flipped in that way.

Phil

Attached Image


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Phil Stooke
post Dec 14 2005, 03:09 PM
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I said there was an increase in resolution, and thought I'd make a direct comparison image to prove it. The results were not promising so I edited my comment above! Here's the comparison:

Attached Image


The HRSC-nd2 image is a 100 by 100 pixel detail from the previous post, enlarged two times. The SRC image was cropped to match this and had to be shrunk slightly to match the scale, but that is not making any significant difference to the resolution because it is already degraded. The double exposure (or jitter) effect is visible on every sharp edge here. Here the nd2 image is flipped to match SRC and the view you would see.

If you just sharpen the SRC image you are sharpening the double exposure! That won't help. A custom-written routine to subtract the ghost image might be possible, but such things are never perfect.

Phil


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mcaplinger
post Dec 14 2005, 04:05 PM
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QUOTE (tedstryk @ Dec 14 2005, 02:32 AM)
If you can find images of point sources from a camera, you can reconstruct the PSF.
*


Certainly. In fact, I might say that this is the only way to reliably determine the PSF, though it's complicated by the fact that you are limited by the sampling frequency of the system's detector and you would usually not oversample the PSF as much as you'd like to if you were just trying to measure the PSF, not take useful images.

However, I haven't seen anyone on this forum going through the PSF determination process, and without doing that, you can't do deconvolution, you can only do filtering.

Just a pedantic nitpick, perhaps, but I think it's important to be precise about these things.


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Guest_BruceMoomaw_*
post Dec 15 2005, 01:12 AM
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One possible additional problem: since SRC's focusing problem seems to be due to the fact that they can't adequately regulate the camera's temperature, the degree of defocusing may keep changing, making reliable deconvolution almost impossible. (ESA has implied that they knew this was a risk when they decided to add the lightweight SRC to Mars Express' payload at the last minute.)
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edstrick
post Dec 15 2005, 10:28 AM
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mcaplinger: "Just a pedantic nitpick, perhaps, but I think it's important to be precise about these things."

Anyway, it's fun for us pedantic nitpickers to beat the plebians over the head with our leaden erudition!
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Phil Stooke
post Dec 15 2005, 02:23 PM
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edstrick said:

"Anyway, it's fun for us pedantic nitpickers to beat the plebians over the head with our leaden erudition!"

Yes, and it makes the beatees feel superior too, though in a slightly different way...


Phil


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lyford
post Dec 15 2005, 05:35 PM
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Eschew Obfuscation!


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Lyford Rome
"Zis is not nuts, zis is super-nuts!" Mathematician Richard Courant on viewing an Orion test
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Phil Stooke
post Dec 15 2005, 05:46 PM
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Done!
Phil


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Phil Stooke
post Dec 15 2005, 05:50 PM
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I've just noticed that I made a mistake in my Phobos postings. To clarify, the SRC image is from MEX orbit 1163, but the HRSC-nd2 image is from orbit 1212. If I recall, the SRC missed Phobos on the later orbit.

Phil


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