Mars Rover Picture Analysis Discussion

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.

I would like to see blue skies, and green fields on Mars, but I am willing to settle for less.

What is the closest to a true color image available now?

The ones NASA is releasing, basically.

Kano, if you weren't a moderator, I'd be pressing the vote button. Thanks for posting this article. I have been reading up on this myself, and your links were a definite help. I work with earthbound image analysis, and I've been wondering about mars colors for a long time.


[Edited on 18-1-2004 by Zzub]

Now, In the first series the Red component is from filter L4, (600nm) and in the second the filter is L2, (750nm). The green and blue filters are the same for both at L5 (530nm), and L6 (480nm) respectively.

If I understand this correctly images compiled from L4, L5, and L6 filters would be the closest to 'true color'.

The sundial image in this section that you created from L2, L5, and L6 looks very much like the sundial in the Panorama. This explains the pink but then raises the questions:

Is the Panorama image created from these filters?

How can we tell which filters NASA used in the images they publish?

Which of the ones at NASA's rover site are L4, L5, and L6 RGB?

Kano, if you weren't a moderator, I'd be pressing the vote button.

I too must compliment you on the quality, and depth of your work. And no paycheck for it....

Well done.

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.

AArchangel, in the Raw image directory the filenames have the filter in them. You just have to find which 3-part series corresponds to which image. (Usually not that hard, though I imagine it will be as the raw image folders begin to fill up).

There really isn't that much of a difference between the L2 and L4 redpoints as far as the landscape goes, as mentioned the L2 gives a slightly less-red look.

why don't they just use normal RGB colored images? Today's technology would make that possible. They could beam them back to earth with lasars instead of radio emissions.

And that calibration tool they have added to their sundial is just about the silliest thing Ive ever seen. To use four colors (and those four colors) to calibrate an image is just bogus. Hey. When I calibrate a screen, a scanner or a TV monitor we use a screen with many optimally the whole spectrum. NASA doesn't manage to turn me into a believer just like that.

Blessings,
Mikromarius

[Edited on 19-1-2004 by mikromarius]

That shiny metal pole you've been wondering about is the lander's low-gain X-band antenna. it's used for direct lander-earth communications when the high-gain X-band antenna (the round paddle) isn't pointed at earth. The low-gain antenna doesn't need to be pointed, but its data transmission speed is very limited compared to the high-gain antenna.

Just as a little note: We won't be able to do our own calibration once the sundial gets red dust all over it...

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.

And came up with this result:


The pictures on the top are originals (and the referance calibration are also untouched). The ones below are calibrated images. Well calibrated. I used like two minutes in PS. If I had larger pictures I could have done a good job with them. But you "get the picture" don't you?

This means: By reverse "engeneering" these images, you can say that what is blue becomes red. And what's green becomes yellow. Hmmmm......

Below is an attempt at "bringing the image back" to it's original state. I only looked at the colors on the sundial, I didn's look at the photos. Startling.....



Blessings,
Mikromarius

[Edited on 19-1-2004 by mikromarius]

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...

Originally posted by avit

Originally posted by tuc
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.

I was thinking of actually writing a program, rather than using photoshop. But if photoshop can do it I guess it would be dumb to reimplement it by hand.

I'm not sure I undersand what you're saying about linear vs. curve. To map a point from the 750/530/480 triangle to a point in the 600/530/480 would pretty much be a linear, no? (Converting to/from CIE cooridinates might not be linear but, if I remember my color theory correctly, can be done.)

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

agreed

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.