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 25 2012, 08:54 PM
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Senior Member Group: Members Posts: 4256 Joined: 17-January 05 Member No.: 152 |
Here's the FFT of the jpeged Bayer patterns, upper two are a patch of smooth sky, and lower two a patch of ground:
In the ground image, you only see 2-pixel-scale (rough) periodicity, corresponding to the Bayer pattern, which shows up as broad peaks at the edges of the FFT. In the sky image, you also see peaks at the 2-pixel scale at the edges of the FFT, but sharp now since the sky is smooth. And you can also see FFT peaks halfway and quarter way to the edges, corresponding to 4- and 8-pixel periodicity. But of course there should be no 4 or 8 pixel periodicity in a smooth Bayer image! So clearly those peaks are the result of jpegging. So I tried to filter out those peaks in the power spectrum. Here's the result on the same image as ugordan used: Very similar result! The Fourier space filtering beautifully gets rid of the blotchy pattern on large smooth areas, but breaks down at the edges of those areas since the periodicity breaks down there. But there was no need to make the algorithm adaptive here - it works in one simple step. Here's the horizon shot: Again, a great job on the sky, but very little improvement on the not-so-periodic blotches over the mound. |
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