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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Oct 14 2012, 10:40 PM
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Martian Photographer Group: Members Posts: 352 Joined: 3-March 05 Member No.: 183 |
I tend to be more on the side of expecting the sky to color the terrain, and wanting to see what the scene looks like with a context appropriate white balance (i.e., using the cal target). Under current dust loads, diffuse sky light exceeds direct sun light throughout the sol. That's never true under a blue sky on Earth--but rarely true for other sky colors and frequently true for gray skies. And, on Earth, the blue sky results in a yellowed Sun. On Mars, the dust slightly reddens (oranges?) the Sun as well as being colored by mineral absorption. That said, I doubt astronauts will come back talking about how much the sky changed their color perception--it's well within adaptability (but that's another debate).
Another small effect that can change the appearance of the same image as interpreted by different people is just that, while the broad filters sorta match the eye's response, the processing (e.g., companding to 8 bits vs. gamma=2.4 vs. perhaps expanding the bits without applying a gamma [?], no accounting for eye vs. monitor color) does not match the sRGB standard, and will not show up as the right color on typical monitors. These differences are small, I think--but can result in slight variations of color balance, even between white balanced images. |
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Oct 14 2012, 11:39 PM
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Senior Member Group: Members Posts: 1583 Joined: 14-October 05 From: Vermont Member No.: 530 |
That said, I doubt astronauts will come back talking about how much the sky changed their color perception--it's well within adaptability (but that's another debate). It's always fun to get accustomed to ski goggles or tinted sunglasses and then remove them. Pretty easy to become unaware of the weird lighting. |
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