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machi
post Nov 25 2009, 06:51 PM
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Wow! Especially the last one looks very cool. Maybe with some destripping technique that can be even better.


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elakdawalla
post Nov 25 2009, 07:04 PM
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Getting rid of the stripes would be nice. Can you suggest any specific workflow in GIMP or Photoshop that would reduce that effect? Or any other software out there?

--Emily


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elakdawalla
post Nov 25 2009, 07:16 PM
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Here's what that same channel-mixing algorithm as in "version 4" above does to a half-phase photo containing the Tharsis Montes.
Attached Image


And heres's that same image, except this time I subtracted 20% each of red and blue channels from the green. I think I'm beginning to get too cute with all this channel mixing though. I differenced the two and found almost no difference between them.
Attached Image


--Emily


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ElkGroveDan
post Nov 25 2009, 07:29 PM
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What the heck is that angular smudge shape in the lower right quadrant?


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djellison
post Nov 25 2009, 07:42 PM
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It's a camera artefact, there's some funky internal reflections and god knows what else going on with it.
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ElkGroveDan
post Nov 25 2009, 07:48 PM
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QUOTE (djellison @ Nov 25 2009, 11:42 AM) *
It's a camera artefact, there's some funky internal reflections and god knows what else going on with it.

It reminds me of an emulsion tear on the old Cibachrome photo paper, (1970s before you kids were born.)


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ugordan
post Nov 25 2009, 08:41 PM
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I've long been contemplating a flatfield for the camera, but the trouble is it's not trivial to generate one from non-blank images such as we get. I wasn't also sure if it would make much difference. Turns out it does help, as an exercise I stacked 6 or so recent frames and selected a (small!) portion of the resulting image that provided best noise reduction as a makeshift flatfield. Here's a comparison of an image without this section multiplied out (though in photoshop which does not do proper multiplication AFAIK). See if you can figure out which bit was flatfielded:

Attached Image


The "flatfield" still has some residual surface details from the original image and is obviously not spatially uniform. If I pursue this further and it turns out good, I may add automatic flatfielding to the vmc2rgb tool.


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djellison
post Nov 25 2009, 09:23 PM
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I wonder if there's an observation we could request that could emulate a flat-field.

This is my post VMC2RGB efforts for a few 2009 sequences.

Just realised some of the movies are stupidly long - but the motive behind making them .movs was that in quicktime you can scrub backwards and forwards really easily.
Attached thumbnail(s)

Attached Image
 

Attached File(s)
Attached File  09_324.mov ( 196.56K ) Number of downloads: 633
Attached File  09_182.mov ( 249.14K ) Number of downloads: 537
Attached File  09_186.mov ( 189.45K ) Number of downloads: 486
Attached File  09_187.mov ( 198.89K ) Number of downloads: 500
Attached File  09_191.mov ( 186.29K ) Number of downloads: 497
Attached File  09_192.mov ( 171.21K ) Number of downloads: 521
Attached File  09_200.mov ( 181.24K ) Number of downloads: 526
Attached File  09_322.mov ( 362.73K ) Number of downloads: 531
 
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JohnVV
post Nov 25 2009, 09:51 PM
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QUOTE
Can you suggest any specific workflow in GIMP

about the only thing in gimp 2.6.7 would be the gimc "graystrastion"

there is an isis3 way
run a highpas with something like 301x 3
and a lowpas with 3x33 and add then together in algebra
play with the two boxcar sizes
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elakdawalla
post Nov 25 2009, 10:36 PM
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QUOTE (ugordan @ Nov 25 2009, 12:41 PM) *
Here's a comparison of an image without this section multiplied out (though in photoshop which does not do proper multiplication AFAIK). See if you can figure out which bit was flatfielded...

If I pursue this further and it turns out good, I may add automatic flatfielding to the vmc2rgb tool.

It's a definite improvement. The area most affected by the flatfielding also appears smoother -- I thought that was all noise, but does the success of the flatfield suggests it would be something that could be flatfielded out?

Please please add into vmc2rgb! smile.gif

--Emily


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djellison
post Nov 25 2009, 10:44 PM
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Why have I not been playing with this stuff more. There's a lot of crescent obs that i just don't think are recoverable to being particularly attractive - but some stuff earlier in the year was awesome smile.gif

Attached - rolled-out action of my saturation + channel tweaking post vmc2rgb
Attached thumbnail(s)
Attached Image
 
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elakdawalla
post Nov 25 2009, 11:04 PM
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What logic led you to that channel math, I'm curious? Or was it just the result of fiddling? My thinking was that if there was bleeding from one channel to another, then I ought to subtract the extreme channels from each other...


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djellison
post Nov 25 2009, 11:06 PM
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Pure artistic tweakery.
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ugordan
post Nov 25 2009, 11:13 PM
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QUOTE (elakdawalla @ Nov 25 2009, 11:36 PM) *
The area most affected by the flatfielding also appears smoother -- I thought that was all noise


It's noise, but it's static noise for the most part, indicating it's down to individual pixel sensitivities. Which can easily be corrected given an adequate flatfield. I don't think other noise sources even begin to matter in such a simple, 8 bit camera.

The difficult bit is not adding an algorithm for this into the tool, it's creating a flatfield in the first place.


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djellison
post Nov 25 2009, 11:26 PM
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I wonder if by virtue of imaging far closer to mars, on more featureless areas, possibly during dust storms - we might be able to generate a flatfield of some sort.

I'm also wondering if it's worth suggesting to the VMC team that they could well avoid the four different exposure settings, stick with the 2nd of the 4, typically, and either quarter the downlink, quadruple the frame rate, or quadruple the observation duration. There seems to be a pattern of one under exposed, one slightly over exposed and one saturated image for every well exposed image. It's not like we're going to be pulling HDR images out of this stuff.

If we can then constrain observations to that one exposure setting - then we can have just one dark field image, one flat field image, and be much better equipped to process the images.
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