Mars Rover Picture Analysis Discussion, page 1

Opening this thread for any questions regarding the analysis of the analysis of the pictures from the spirit rover.

The full thread is here:

www.abovetopsecret.com...

I know its long, but please don't ask any dumb questions without reading the lot to make sure they arent contained within.

www.atsnn.com... Kano's excellent work has been upgraded to an ATSNN story. The code running the ATSNN.com site is much better optimized for high traffic and especially search engines (notice the lack of ".php" and "?tid=30048" in the URL which causes Google to look at pages a little differently). This will help his work get a much higher visibility on the Internet.

I enjoyed the article at www.atsnn.com... but two things occur to me.

1) It would be nice if NASA could tell the parameters of the "hard limiting" algorithm for each exposure. If they could give us the actual low and high values (in any convenient units) they map to 0x00 and 0xFF, it would allow us to composite them in ways we can't now.
Does NASA even have this data? If not, I guess it would be unreasonably to hope they would share it with us.

2) It seems to me that it wouldn't be too hard to take the RGB data from an image captured with 750/530/480 filters and translate it to one approximating what it would look like if it had been captured with 600/530/480 filters. It wouldn't be perfect, of course, since the real data from a 600nm filter could theoretically be anything.
But if you take a look at the two triangles in the "But Why?" section [the second one, btw, lists 700nm in place of 750nm--a typo??] it would be easy to map 24-bit RGB values in the 750/530/480 space into values in the 600/530/480 space, with the proviso that we'd have to map values that lie outside the target triangle to values on the edge. So we gain kind-of-more-accurate hues at the expense of throwing away some bits.


[Edited on 19-1-2004 by tuc]

I enjoyed the article at www.atsnn.com... but two things occur to me.

1) It would be nice if NASA could tell the parameters of the "hard limiting" algorithm for each exposure. If they could give us the actual low and high values (in any convenient units) they map to 0x00 and 0xFF, it would allow us to composite them in ways we can't now.
Does NASA even have this data? If not, I guess it would be unreasonably to hope they would share it with us.

2) It seems to me that it wouldn't be too hard to take the RGB data from an image captured with 750/530/480 filters and translate it to one approximating what it would look like if it had been captured with 600/530/480 filters. It wouldn't be perfect, of course, since the real data from a 600nm filter could theoretically be anything.
But if you take a look at the two triangles in the "But Why?" section [the second one, btw, lists 700nm in place of 750nm--a typo??] it would be easy to map 24-bit RGB values in the 750/530/480 space into values in the 600/530/480 space, with the proviso that we'd have to map values that lie outside the target triangle to values on the edge. So we gain kind-of-more-accurate hues at the expense of throwing away some bits.

Originally posted by tuc
I enjoyed the article at www.atsnn.com... but two things occur to me.

1) It would be nice if NASA could tell the parameters of the "hard limiting" algorithm for each exposure. If they could give us the actual low and high values (in any convenient units) they map to 0x00 and 0xFF, it would allow us to composite them in ways we can't now.

Does NASA even have this data? If not, I guess it would be unreasonably to hope they would share it with us.

AFAICT, you can't truly know these high and low luminance values because they probably depend on the exposure, and MER sends it back already modified. I don't see that as a bug, though. You have to realize that some colours, like bright sunlight, can't ever be reproduced on your monitor, much less on paper. The best we can do is approximate a balanced image within the limits of the RGB medium.

What Kano refers to as "hard limiting" is called equalizing in the image processing world. Or at least that's what Adobe calls it. You can see for yourself what this does to an image by selecting Image/Adjustments/Levels... and then clicking on "Auto." You can see how the histogram levels stretch to fit the 0x00 to 0xFF scale. The Auto Levels function in the Adjust menu does the same thing, just one less step.

2) It seems to me that it wouldn't be too hard to take the RGB data from an image captured with 750/530/480 filters and translate it to one approximating what it would look like if it had been captured with 600/530/480 filters. It wouldn't be perfect, of course, since the real data from a 600nm filter could theoretically be anything.

True. This could be done using something like the Channel Mixer (Image/Adjustments/Channel Mixer), although the slider settings in there aren't the least helpful to do it scientifically. It's also only linear, while in this case you'd want to apply it on a curve.

In theory, basically, you'd want to remove red from the red channel (darken it), and add some of green to it (to lighten it and bring it higher on the spectrum). Like you said, it's not real data, however. It's an interpolation. Also knowing the specific frequency responses of the calibration targets would be a big help to balance out the result.

All that said, I think that the images that NASA is putting up are a pretty decent approximation.

I noticed that NASA has updated the panorama image. The 'old' image that showed the sundial is no longer on the press release page, although the link for it still works.

In the new image THE SUNDIAL IS CUT OUT!

30KB image:
origin.mars5.jpl.nasa.gov...

12MB image:
origin.mars5.jpl.nasa.gov...

Dr. Mark Adler (Spirit Mission Manager) was kind enough to drop by today and clear up a few things for us.

www.abovetopsecret.com...

Included is confirmation that the 'little pole' is indeed the Low-Gain antenna, and an explanation of how the images from Spirit are assigned filenames. The "image file name decoder ring" as it were.

If anyone is interested I just came across this image posted at Rense.com which still argues that Mars has a slight blue sky.

www.rense.com...

The sky-color issue is one that will be resolved sooner or later. This issue here, and Kano's excellent work helping to get the team leader from NASA involved, is focused on the color attributes of the images taken by Spirit. BTW: the URL given in the picture on Rense, cass.jsc.nasa.gov... is non-functioning... so it's hard to know if we're looking at an image that hasn't been enhanced.

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