How Spirit Takes Pictures

Some Clown writes "MSNBC has a great article on the details of the camera system on the Mars Rover titled How Sprit makes great photos. Apparently the high resolution images are all done with a 1-megapixel camera. All the money is in the CCD and Lens. The hardcore digital photographers in the crowd will probably find the article to be only a teaser on the technical specs, but the rest of us in the unwashed masses should find it interesting."

Comments

Original

[Gherald]

Why not link directly to the original article?

Re:I was honestly surprised.

[froody]

It's important to note that in a color digicam each "pixel" only senses 1 color. The NASA cam is a black and white, and to make color they take 3 shots with different filters. This makes it equivalent to a consumer 3MP camera.
They also have a nice lens and a large sensor which helps as well.

Tim

It's All About The Optics

[raider_red]

Resolution in cameras (both digital and film) is really determined by optics. By taking pictures of a smaller area and stitching them together, they can probably get better pics than most pros get with their high end Digital SLRs, because they've put more money into the optics than the sensor. Also, the higher density CCDs and CMOS sensors going into digital cameras now tend to be more prone to noise than some of the very high quality, lower density models.

Also, remember that the cameras in the rover had to go through a lot more testing than a typical consumer camera, so it's probably using three, four, or even five year old components in the imaging systems.

Re:It's All About The Optics

[Anonymous Coward]

You can also do cunning tricks with moving the camera fractions of a pixel to generate 'super-resolution' images - I'm almost afraid to think what the images from Spirit could be like with this technique.

They've talked about using it to take pictures of the hills a few kilometres away - even if the rover doesn't reach them, they should still get some very impressive images of them.

Re:$400,000,000?

[nairnr]

Well, it isn't like you can head down to Radio Shack and pick up a functional interplanetary robot now can you? You are talking about one off ( or two off in this case) The second rover will cost half to make more than likely due to parts being already made for the first one. I mean think about how much R&D has to go into building a craft capable of surviving and thriving after being blasted off from earth, traveling through the radiation of space, hit a spot on a planet after many months of travel. After that you have to go through reentry and hit the ground at 60MPH, with all sorts of high precision instruments functional.

Quality is expensive, the survival rate of craft going to Mars is less than 1/3. They tried to cut costs, but that leads to failure. Build them with enough attention that you don't throw $3-400MM away after years of effort...

if (!ie){......}

[ExileOnHoth]

"Sorry, your browser is not compatible with this feature!"

@%**! MSnbc

Click on the "Interactive feature" if you don't know what I mean,

then curse microsoft,

then go straight to http://marsrovers.jpl.nasa.gov to see the images without paying the microsoft tax. I vowed a long time ago to stop clicking on msnbc links.... sucker that I am to keep coming back for more...

And it runs Java

[bradyh]

Here's a story about some of the software involved.

Brady

Nonsense...

[Anonymous Coward]

I am not very surprised that no journalist understand that, I am more surprised that /. readers missed the point: it is simply nonsense to say that the camera is 1M pixels.

Indeed, the CCD has 1 million pixels, but look at the published pictures: they are assembled from a great number of small 1 megapixels squares!! Simply have a look at the raw pictures on marsrovers.jpl.nasa.gov: some of them are not fully transmitted yet, consequently parts of the pictures are black.

To make a "normal" picture, like one you would naturally do with your 5M pixels camera, the pancam needs to take shots from, say, 20 different angles. And it is even worse than that: each pictures must be taken 4 times with each filters to get colors. Do not even dream of taking photographs of moving subjects!

There is another drawback: there is two cameras, for stereo. But if you look at the tech specifications on Cornell website, you'll see that each camera has filters that can cover only one half of the color spectrum. Hence, to get color pictures, you have to combine the photographs taken by both the left and right cameras. That's why there is some weird colored patterns on big objects: to put it simply, the left camera sees the red, the right one sees the blue! But both cameras do not see exactly the same thing! /. readers, please, if you are geeks, always read the small lines. Do not expect NASA or a journalist to do that for you. It is not the interest of the former, and the latter is just stupid.

And nonetheless, there was a hint: do you really expect 1M pixels raw pictures to weight 7MB? Huuh?

Re:Specs

[angst_ridden_hipster]

It is also interesting to see how it produces color photos.

This is how virtually all consumer digital cameras work (more or less). They paint a pattern of color filters over the CCD. Then they use interpolation, based on the relative intensities, to figure out the most likely color of each pixel.

Different vendors use different masks, and there is a lot of debate about the best approach. See DP Review's Glossary section for more information.

Re:Specs

[cgenman]

It's in the interpolation stage that most consumer cameras turn to junk. The fact that the mars rover takes a picture using an identical array (rather than a very-similar-array) with 3 different filters is what makes the image crisp. It's totally impractical in the consumer arena, however, because people would need to stand exactly still while their camera took 3 pictures.

Multi-layered sensors are in the works, however, one of which has been slashdotted. This would provide true image color with no interpolation, but failed to materialize in the year promised (last one).

If anyone has the slashdot link from a few years back, I'm sure it would be relevant to this discussion.

Re:Interesting, but..

[jmh_az]

It extracts data by looking at the return levels at the various wavelenghts of the filters, among other things. With image processing software like IRAF you can get an amazing amount of information out of an image. Also, conventional comsumer CCD cameras use one CCD device with a RGB patterned color filter literally painted onto the face of the CCD to get red, green and blue. High-end cameras use three CCD's with seperate filters in front of each imaging device and splitter prisms to direct the light. Since things like weight and complexity are issues when building spacecraft, they accomplish the same thing as the high-end cameras here on earth by using one CCD and a filter wheel. This approach also allows them to do other things, such as take images through polarizers, or have magnification if they need it, and all in one camera package. And, last but not least, these cameras are tested and calibrated to within an inch of their lives before they ever leave the ground, so the researchers know exactly what the dark current (electronic noise), flat field (pixal responsiveness across the entire CCD) and defect characteristics for the CCD are. This information is then used to subtract out a lot of the noise and imperfections, leaving as much of the original data for analysis as possible. That analysis is the stuff of research papers like this one.

Hope that was useful.

Multiple exposure explained

[dargaud]

For those not familiar with it, the multiple exposure they talk about in the article has been long used in the darkroom and can be done easily with modern scanners with good software. It brings out extreme details in parts of images that are normally burnt out.

Take a single slide that you scan. With a program like VueScan, you can set the exposure of the scanner, so you can do a dark scan (thus exposing properly the light part of the image), a normal scan and a light scan (exposing the dark part of the image).

Import all 3 into a graphic program, superimpose them and cancel the parts that you don't like (which is the creative part and not as easy as it seems).

Note that you can also do that taking 3 pictures with various exposure with the camera on a tripod, and it's the way the Mars rover does it.

Re:I was honestly surprised.

[jovlinger]

huh? To get stereo, you need separation. You could do this with a couple of prisms, or maybe the biggest fresnel lens you ever saw, but why not just move the camera sideways between shots?

If your camera can take several pix in a row, use that, and simply move the camera laterally during the shooting (assumes you have fast shutter time).

Lastly, no. As I understand it, a CMOS sensor cut into 1000x1000 pixels will give you "better" pixels than the same die at 2000x2000 pixels, and coupling the pixels 2x2. This has several causes:

1) you can only average your combined pixels after sampling: thus you get quantisation noise (and hypothetically phase interferernce, although I've never heard anyone comment on this)

2) if you couple 2x2 pixels, you will get 1xR + 2xG + 1B pixels. Most pixels will be predominantly one of these colors, removing the other 3(2 for G) from the picture. This also means that a blue photon heading towards the 2x2 metapixel must hit the 1/4 area which can see it, else it is lost.

3) (I don't quite get this one. As close as I understand it:) The size of the sensor feature size is coming close to the wavelength of light: Sony's new 8mp sensor is 0.008 m long, with 3000 pixels. That makes each pixel 2.6e-6 m. Compare with Red light, at a wavelength of 0.7e-7 m. Each sensor is three wavelengths wide(!). This apparently means that you can't usefully use an fstop higher than 11ish on the new sony f828. Search photo.net for a technical discussion.

4) I guess that we also get effects from the fact that each pixel sensor is basically in a well, and the smaller the pixel becomes, the harder it becomes for a photon to hit the sensor, rather than the well wall. I never hear this discussed either