MSL Images & Cameras, technical discussions of images, image processing and cameras Options

[CosmicRocker]

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.

[Art Martin]

I hope this is the right section for this. I'm actually replying to a post in another thread but, since it's about image processing, thought it better to put it here.

Amazing comparing the Hirise anaglyph to what we actually see on the ground. One thing that seems to be obvious to me though is that there is a real exaggeration of relief in the Hirise 3D effect (mesa are taller, canyons are deeper) most likely created because the left and right images are taken a great deal farther apart than the human eyes. If I understand they are simply images taken at different points in the orbit and not by two cameras side by side as on the rovers. While that relief is stunning and produces this amazing view of surface from above, it is not really a true representation as to what a human observer would see from orbit. In these days of phenomenal image and video processing software, where a program can build intermediate frames of a video by analyzing the pixels of each surrounding frame, I wonder if someone hasn't devised a way of correcting the relief of a 3D anaglyph if one knows the actual separation of the two images. I can certainly picture the code process in my mind and it doesn't seem complicated if one works with image comparison coding. I'm a computer programmer but it's been years since I did anything where I was manipulating pixels and my relearning curve would be extensive or I'd tackle something myself.

Sure seems that anaglyphs have been around long enough that someone would have figured this out by now. Any thoughts?

I borrowed Fred's excellent rendition to compare with HiRISE anaglyph of the prime science region around the inverted riverbed. It's a very narrow angle of view. If I marked some features wrong, please let me know.

[attachment=27716:msl_science_target.jpg]

[ngunn]

I wonder if someone hasn't devised a way of correcting the relief of a 3D anaglyph

We've discussed this here a while ago, but rather than try to dig back for that here are a couple of salient points. Anaglyphs don't have a constant intrinsic exaggeration factor. The apparent relief you see depends on the size of the image and the distance you view it from. Adjust those and you could in theory view any anaglyph without line-of sight exaggeration. It's true that in many cases you'd have to enlarge the image enormously and sit very close to it!!

One solution I've suggested is the inclusion of a small virtual cube in the corner of each anaglyph to serve as a three dimensional scale bar, so if the cube looks too tall you know you're seeing the scene exaggerated by the same amount.

[john_s]

It's true that in many cases you'd have to enlarge the image enormously and sit very close to it!!

Actually, does enlarging the image have any effect on the apparent vertical exaggeration? I wouldn't expect so, because there should be no vertical exaggeration when the convergence angle of your eyes matches the convergence angle of the original image pair [convergence angle = angle between the two lines of sight in the stereo pair, measured at the surface location being viewed]. The convergence angle of your eyes depends on their distance from the image, but doesn't depend on the image magnification.

John