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MSL Images & Cameras, technical discussions of images and cameras
CosmicRocker
post Aug 16 2012, 11:05 PM
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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.
Attached Image


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.


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fredk
post Aug 17 2012, 02:52 PM
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I've noticed the same thing. It means for some of these images, we're effectively getting 7 bit images. But on the other hand, the MSL images don't seem to loose detail in the whites the way MER images do.

I don't know if the MSL images have had any nonlinear pixel value transformations done, such as a logarithmic lookup table. I am curious what the images would look like with pixel value linearly related to the true scene intensity, and with the zero point correct.
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CosmicRocker
post Aug 18 2012, 05:53 AM
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I'm curious about something I am seeing in the mastcam color images (M-34) and hope someone here can explain it. I'm not sure if this is the correct term, but I am seeing what appears to be color banding in most of the color mastcams. It is more apparent in some than others, and if you split the color image into it's red, green, and blue channels it becomes even more apparent.

In the attached example I have put the red channel greyscale alongside the color image. I have contrast stretched both images to make the banding effect more apparent.
Attached Image


My best guess is that this may be caused by the raw images having had their bit depth reduced at some point. Or, could this be caused by some kind of image compression?


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um3k
post Aug 18 2012, 06:00 AM
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That's the JPEG compression having an aneurysm. smile.gif
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Cargo Cult
post Aug 18 2012, 10:45 PM
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QUOTE (um3k @ Aug 18 2012, 07:00 AM) *
That's the JPEG compression having an aneurysm. smile.gif

Something I've been wondering about - are the Mastcam, MARDI and MAHLI JPEG images being recompressed on Earth, or is this JPEG data originally produced on Mars?

(I read somewhere on these fine forums that the Navcams use some fancy wavelet compression, but the colour cameras use good old JPEG. I'd love it if some of the raw images were literally that - identical data to that produced on another planet. Being repackaged and recompressed into a more web-friendly form is much more likely, alas...)

Pointlessly, I did check an image for EXIF tags, just in case - unsurprisingly there's nothing exciting.

CODE
Spiral:Desktop afoster$ jhead 0003ML0000124000E1_DXXX.jpg
File name : 0003ML0000124000E1_DXXX.jpg
File size : 132864 bytes
File date : 2012:08:18 15:35:06
Resolution : 1200 x 1200
Comment : NASA/JPL-Caltech/Malin Space Science Systems


Transmitting data like the manufacturer's name, camera serial number, focal length and whatever, over and over again, could be deemed an unnecessary use of interplanetary bandwidth? Shame. I imagine useful metadata takes a different route. wink.gif
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um3k
post Aug 18 2012, 10:50 PM
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QUOTE (Cargo Cult @ Aug 18 2012, 06:45 PM) *
Something I've been wondering about - are the Mastcam, MARDI and MAHLI JPEG images being recompressed on Earth, or is this JPEG data originally produced on Mars?

At least some of the images are compressed in-rover, but I suspect these glaring artifacts are the result of recompression for the web. Especially since the data is almost certainly transmitted as a grayscale image with an intact bayer pattern. It'd be rather silly to debayer it on Mars and triple the amount of data that needs sent.
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ugordan
post Aug 18 2012, 11:04 PM
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QUOTE (um3k @ Aug 19 2012, 12:50 AM) *
It'd be rather silly to debayer it on Mars and triple the amount of data that needs sent.

... except that's pretty much exactly what the cameras do onboard, de-Bayer is applied and JPEG-compressed as that's the lossy compression scheme of choice. Probably every single color image returned so far used this approach. It's not 3x the amount of data because its compressed in a lossy way and the chrominance channels are subsampled. In fact, this approach of exploiting visual similarity between what would otherwise be 3 similar b/w images encoded separately might by itself reduce bits-per-pixel requirement for a given image quality, even with no chrominance subsampling.


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um3k
post Aug 18 2012, 11:16 PM
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I suppose that sort of makes sense. It makes the photographer in me cringe, and explains the sub-par demosaicing, but I understand the logic behind it. As someone who frequently deals with video encoding, I'm well aware of the relative compression efficiency of redundant data.
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mcaplinger
post Aug 18 2012, 11:48 PM
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QUOTE (um3k @ Aug 18 2012, 04:16 PM) *
I suppose that sort of makes sense. It makes the photographer in me cringe, and explains the sub-par demosaicing, but I understand the logic behind it.

Gee, thanks for the ringing endorsement. smile.gif ugordan has it all correct. A complete description of MMM compression can be found in the Space Science Reviews paper on MAHLI -- http://rd.springer.com/article/10.1007/s11214-012-9910-4 -- see section 7.5 "Image Compression".

We can return uninterpolated frames if we want to pay the downlink volume penalty.

I haven't verified this but I suspect that the web release images are going through a decompress/recompress cycle.


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um3k
post Aug 18 2012, 11:55 PM
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I mean no offense, in fact I greatly admire you and the rest of the MSSS team. You've (collectively and individually) accomplished some amazing things. I just have a rather negative gut reaction to lossy compression. tongue.gif

EDIT: Also, about the demosaicing: I'm quite certain you know what you're doing. I'm referring to the anomalous horizontal lines in the MARDI images, which I assume (perhaps mistakenly) have to do with the demosaicing, the quality of which I (again) assume is limited by the limited processing power/time of the rover. I also fully realize that more complex, non-linear interpolation algorithms aren't very conducive to scientific analysis. Perhaps my excessive assumptions are correlated with the fact that the MSSS team has cameras in space, while I have a desk cluttered with scavenged optics and a spectrograph made of LEGO bricks and a mutilated DVD-R. tongue.gif
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Winston
post Aug 19 2012, 02:51 PM
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The signal to noise ratio and information content of this forum is outstanding. Let me contribute a small bit by providing links to technical documents about some of the MSL cameras, documents I found in the process of researching the MSL's computer system and internal network (about which I found virtually nothing):

The Mars Science Laboratory Engineering Cameras
http://www-robotics.jpl.nasa.gov/publicati...ne/fulltext.pdf

THE MARS SCIENCE LABORATORY (MSL) NAVIGATION CAMERAS (NAVCAMS)
http://www.lpi.usra.edu/meetings/lpsc2011/pdf/2738.pdf

THE MARS SCIENCE LABORATORY (MSL) HAZARD AVOIDANCE CAMERAS (HAZCAMS)
http://www.lpi.usra.edu/meetings/lpsc2012/pdf/2828.pdf

THE MARS SCIENCE LABORATORY (MSL) MARS DESCENT IMAGER (MARDI) FLIGHT INSTRUMENT
http://www.lpi.usra.edu/meetings/lpsc2009/pdf/1199.pdf

THE MARS SCIENCE LABORATORY (MSL) MARS HAND LENS IMAGER (MAHLI) FLIGHT INSTRUMENT
http://www.lpi.usra.edu/meetings/lpsc2009/pdf/1197.pdf

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Some interesting heat shield documents:

MEDLI System Design Review Project Overview
http://www.mrc.uidaho.edu/~atkinson/Senior...ct_Overview.pdf

Advances in Thermal Protection System Instrumentation for Atmospheric Entry Missions
http://www.mrc.uidaho.edu/~atkinson/ECE591...ntations/Fu.ppt

A relatively short but very interesting document about the engineering challenges of landing on Mars which discusses the advantages and disadvantages of the various possible methods:
http://www.engineeringchallenges.org/cms/7126/7622.aspx

As I said, I found virtually nothing about the Mars Compute Element (MCE) and the network(s) used within the lander to control MSL hardware (anyone know a good source, the more technical the better?), but I did find a tiny bit within this document starting on p41 where the electronics architecture is discussed. The bus used is redundant 2Mbps RS-422. The SAM uses BASIC keywords for its command language!:

The Sample Analysis at Mars Investigation and Instrument Suite
http://www.springerlink.com/content/p26510...08/fulltext.pdf

Excerpt:
The (SAM) CDH (Command and Data Handling) module (Fig.16) includes a number of functions. The CPU is the Coldfire CF5208 running at 20 MHz. The CDH (module) communicates with the Rover via redundant 2 Mbps high speed RS-422 serial bus along with a discrete interface (NMI).

In the SAM software description starting on p47, I found this interesting tidbit:
SAM’s command system is a radical departure from prior spaceflight instrumentation. SAM is a BASIC interpreter. Its native command language encompasses the complete set of BASIC language constructs—FOR-NEXT, DO-WHILE, IF-ENDIF, GOTO and GOSUB—as well as a large set of unique built-in commands to perform all the specific functions necessary to configure and operate the instrument in all its possible modes.

SAM’s commands, which are BASIC commands with SAM-specific commands built in, are transmitted in readable ASCII text. This eliminates the need for a binary translation layer within the instrument command flow, and makes it possible for operators to directly verify the commands being transmitted. There are more than 200 commands built in to the SAM BASIC script language.


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And even though this is just a NASA Press Kit, it is satisfyingly detailed technically on various MSL systems:
Mars Science Laboratory Landing
http://mars.jpl.nasa.gov/msl/news/pdfs/MSLLanding.pdf

And just for the heck of it, here's NASA's Viking Press Kit. How very far we have come, even with press kits:
http://mars.jpl.nasa.gov/msl/newsroom/presskits/viking.pdf
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nprev
post Aug 19 2012, 04:29 PM
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Welcome, Winston, and thanks for a terrific first post! smile.gif We may archive some of those links in the MSL FAQ thread; much appreciated!


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mcaplinger
post Aug 24 2012, 08:02 PM
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QUOTE (Holger Isenberg @ Aug 24 2012, 11:48 AM) *
Now the question is: Which is the actual transmissin curve of the IR cutoff filter? The one (black dotted line) in the 2541.pdf or the one (thick dark green line) on the JPL-Mastcam web page?

The plot in 2541.pdf is not a transmission curve, it's a response curve and thus modulated by the detector QE. The JPL web page looks pretty close.


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Holger Isenberg
post Aug 24 2012, 08:30 PM
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QUOTE (mcaplinger @ Aug 24 2012, 10:02 PM) *
The plot in 2541.pdf is not a transmission curve, it's a response curve and thus modulated by the detector QE. The JPL web page looks pretty close.


Thanks for pointing that out! So the overall effect is like adding a strong UV filter to a normal digital camera, like a LP 420, which is actually helping to reduce visual haze. However, what explains then the decrease of the blue response function maxima at 470nm to almost 30% with the green response being the 100% reference on the black dotted line in 2541.pdf?
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mcaplinger
post Aug 24 2012, 09:25 PM
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QUOTE (Holger Isenberg @ Aug 24 2012, 01:30 PM) *
However, what explains then the decrease of the blue response function maxima at 470nm to almost 30% with the green response being the 100% reference on the black dotted line in 2541.pdf?

I'm not sure what the dashed line is really supposed to mean. The IR-cutoff response is shown in blue, green, and red, but all the filters have been normalized to their peaks, so you can't, for example, compare the R2/L2 narrowband response to the IR-cutoff blue response, or the IR-cutoff blue to the red. This plot was just intended to give an outline of where the bandpasses are.


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