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, 10:08 AM
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Senior Member Group: Members Posts: 1465 Joined: 9-February 04 From: Columbus OH USA Member No.: 13 |
I wonder what the effective bits per pixel of the MASTCAM raw images is. The cameras use the KODAK KAI-2020CM sensor. Is it sampled with a 12-bit ADC like MARDI and NAVCAM? One reference for NAVCAM gives an SNR of >200 for certain conditions. So that would mean effectively 7-8 bits per pixel for that camera anyway?
It was interesting that yesterday Mike Malin referred to stacking images. -------------------- |
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Aug 28 2012, 01:48 PM
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#3
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Senior Member Group: Members Posts: 2542 Joined: 13-September 05 Member No.: 497 |
I wonder what the effective bits per pixel of the MASTCAM raw images is. The MAHLI paper I've referred to several times before is an excellent source of this kind of information. From section 7.5.1: "Acquired as 12-bit images, MAHLI data are converted onboard the instrument, without loss of information, to 8-bit images using a square-root companding look-up table." -------------------- Disclaimer: This post is based on public information only. Any opinions are my own.
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Aug 28 2012, 02:39 PM
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#4
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Member Group: Members Posts: 408 Joined: 3-August 05 Member No.: 453 |
"Acquired as 12-bit images, MAHLI data are converted onboard the instrument, without loss of information, to 8-bit images using a square-root companding look-up table." I read that a while back and was puzzled by how one could do any such conversion without a loss of information unless the original data already fit in 8 bits? Any non-trivial processing operation results in a loss of information somewhere (usually with the purpose of increasing apparent information somewhere else). I understand companding and all that, but that is not a two-way operation without loss of information. The resulting 8 bit data cannot be converted back into the original 12 bit data, surely, as multiple values in the 12 bit sample get mapped to the same 8 bit value? Just trying to understand what exactly was meant in the MAHLI document. Airbag |
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