MSL Images & Cameras, technical discussions of images, image processing and cameras |
MSL Images & Cameras, technical discussions of images, image processing and cameras |
Aug 16 2012, 11:05 PM
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Senior Member Group: Members Posts: 2228 Joined: 1-December 04 From: Marble Falls, Texas, USA Member No.: 116 |
I'm still trying to figure out a number of things about the new images we are trying to work with. Assuming others are likewise trying to learn, I thought I would open this thread to create a place for such discussions.
I'd like to start out with a comment about raw image contrast. There have been several postings in the main threads about whether or not the MSL raw images have been stretched like those from the MER missions. I am certainly no expert on this, but it looks to me as if the MSL images have not been stretched at all. I haven't tried to analyze all of the image types, but the hazcams and navcams have pixel brightness histograms that are very different from their MER counterparts. This attached image compares MER and MSL navcams along with their luminosity histograms. The MSL images clearly are not using the entire, available range of brightness values, whereas the MER raws do. For this reason, the MSL raw images can usually be nicely enhanced by simply stretching the distribution of brightness across the full 256 value range. -------------------- ...Tom
I'm not a Space Fan, I'm a Space Exploration Enthusiast. |
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Aug 28 2012, 04:17 PM
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#2
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Member Group: Members Posts: 408 Joined: 3-August 05 Member No.: 453 |
Ugordan,
But photon shot noise is less of an issue with larger number of photons (i.e. higher CCD signal levels) and that is exactly where a square root compander "does its thing" the most, so I don't see how photon shot noise would be relevant to my original question? I could understand it if the CCD read noise was a dominant factor, and thus the 12 bits of data are really only "effectively" worth around 8 bits, but that would imply a huge noise contribution! Airbag |
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Aug 28 2012, 04:22 PM
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#3
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Senior Member Group: Members Posts: 2542 Joined: 13-September 05 Member No.: 497 |
But photon shot noise is less of an issue with larger number of photons... shot noise = sqrt(signal), so shot noise is higher at higher signal levels. The square root encoding is coarser at higher levels, finer at lower levels. You could have a philosophical debate about what this means, but that's the way our cameras work. -------------------- Disclaimer: This post is based on public information only. Any opinions are my own.
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Aug 28 2012, 06:30 PM
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#4
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Member Group: Members Posts: 408 Joined: 3-August 05 Member No.: 453 |
I was looking at shot noise from a S/N point of view but I get the hint and will skip any debates - thanks for the clarifications everybody!
Airbag |
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