Clouds? |
Clouds? |
Jul 8 2008, 01:38 AM
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#1
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Senior Member Group: Members Posts: 1465 Joined: 9-February 04 From: Columbus OH USA Member No.: 13 |
Was looking at some MGS imagery:
Kind of a low-contrast scene with some darker splotches here and there. Running that through an equalizing filter gives this image: Some surprising detail brought out there--it looks to me like there are small clouds casting shadows on the surface. Can that be right? They could be little hills I suppose. -------------------- |
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Jul 8 2008, 01:49 AM
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#2
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Member Group: Members Posts: 128 Joined: 10-December 06 From: Atlanta Member No.: 1472 |
QUOTE Some surprising detail brought out there--it looks to me like there are small clouds casting shadows on the surface. Can that be right? They could be little hills I suppose. Likely JPEG lossy-compression artifacts. |
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Jul 8 2008, 01:55 AM
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#3
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Senior Member Group: Members Posts: 1465 Joined: 9-February 04 From: Columbus OH USA Member No.: 13 |
Likely JPEG lossy-compression artifacts. The original images are from IMG files (256 pixels per degree MGS images http://www.msss.com/mgcwg/mgm/), only converted to JPG in the final step. I believe IMG files are lossless. -------------------- |
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Jul 8 2008, 11:42 AM
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#4
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Member Group: Members Posts: 128 Joined: 10-December 06 From: Atlanta Member No.: 1472 |
The original images are from IMG files (256 pixels per degree MGS images http://www.msss.com/mgcwg/mgm/), only converted to JPG in the final step. I believe IMG files are lossless. I'm not sure. I agree, IMG per se is lossless, but MOC had the ability to compress images on board using Walsh-Hadamard or Discrete Cosine techniques, which are lossy. I wonder whether you can see the same low-contrast, semi-regular patterning in other MOC wide-angle images. |
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Jul 8 2008, 11:59 AM
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#5
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Senior Member Group: Members Posts: 3648 Joined: 1-October 05 From: Croatia Member No.: 523 |
I don't see these as compression artifacts, the features very much look like real fuzzy bright objects with corresponding darker shadows in the right places. DCT doesn't do that, it just produces blocky artifacts more or less.
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