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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Sep 15 2012, 07:36 PM
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Senior Member Group: Members Posts: 4256 Joined: 17-January 05 Member No.: 152 |
For the navcams, here's my guess. We've discussed before (image thread?) that the MSL public navcams appear to be stretched/lut'ed/delut'ed differently from the MER navcams. In practice it looks like the histograms are typically concentrated into the lower half (0-128 or so) of the full 8 bit range. So there's less information to begin with than in MER navacams. But then the details on MSL navcams tend to be dark with low contrast, so maybe jpeg doesn't capture the details as well. Then you need to stretch them to show the detail, and you end up enhancing the jpeg artifacts. You could test this by jpegging an original image, and then halving the intensity of the original, jpegging, and then doubling the intensity, and comparing the two.
Or they may be compressed more heavily on MSL. MER uses various compression levels depending on the need. |
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