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A Single Pixel Camera
BuzzSkyline writes "Scientists at Rice University have developed a one pixel camera. Instead of recording an image point by point, it records the brightness of the light reflected from an array of movable micromirrors. Each configuration of the mirrors encodes some information about the scene, which the pixel collects as a single number. The camera produces a picture by psuedorandomly switching the mirrors and measuring the result several thousand times. Unlike megapixel cameras that record millions of pieces of data and then compress the information to keep file sizes down, the single pixel camera compresses the data first and records only the compact information. The experimental version is slow and the image quality is rough, but the technique may lead to single-pixel cameras that use detectors that can collect images outside the visible range, multi-pixel cameras that get by with much smaller imaging arrays, or possibly even megapixel cameras that provide gigapixel resolution. The researchers described their research on October 11 at the Optical Society of America's Frontiers in Optics meeting in Rochester, NY."
It would be indeed impractical, and that makes this method quite useless in most applications. The researchers asked themselves "what if that single pixel receptor is good and expensive" while most modern answers are quite opposite to that - it's easier to make plenty of medium quality sensors than one good sensor. Not even counting the micro-mechanics needed. Solid state already gives you several megapixels for a few dollars, and the cost is only going down.
within a certain wavelength range (down to where actual atomic structures break up the smoothness), a perfectly flat material with no resistance has perfect reflection (that's why the silver back on a glass mirror is so reflective, is very flat and conductive
Instead of using micro mirrors, the Los alamos team used an LCD which were more mature at the time. And Instead of using random modulation they used a progression of zenike polynomials and thus achieved much more control over the data compression.
Some drink at the fountain of knowledge. Others just gargle.
Actually a less fancy version of this technique was already used on mars pathfinder where several images were taken of the same objective and then combined to obtain better resolution.
"Superresolution image processing is a computational method for improving image resolution by a factor of n[1/2] by combining n independent images. This technique was used on Pathfinder to obtain better resolved images of Martian surface features."
Taken from the abstract of this article:
A patent for "A single element detector acts as an array"
The technique in use for years for infra-red cameras involves the use of a single (Peltier-cooled) pixel and a scanner, but scanners have numerous problems one of which is that there is always vibration caused by the two frequency components of the line end switching of the horizontal and vertical scans. This technique, by using pseudo-random switching, should eliminate vibration.
So the ultimate long term goal would appear to be the ability to produce 3-D images with focus throughout the entire scene, low light capability and an absence of blur due to vibration. IANAOR (I am not an optical researcher) but it seems a good line of investigation.
Pining for the fjords
Is it really cheaper to manufacture micromirror arrays that CCD or CMOS sensors?
Not likely. And it certainly doesn't sound mechanically robust to have moving parts replace a purely electronic chip. Cameras need to be rugged.
Also, what degree of photon loss do you have from the arrays? No mirror is perfect...
Imperfection in the reflectivity is probably secondary to diffraction, which will be a big problem for these small mirrors - and they would have to shrink even further for reasonable (multi-Mpixel) image resolutions. Diffraction is the biggest limiting factor for contrast in DMD projectors.
There are other problems with this design. First off, it is a time-sequential acquisition. The reconstruction algorithm assumes that all measurements are taken from the exact same scene. God knows what garbage it produces if you have moving objects or camera shake.
I guess their biggest motivation is to do the image sensing directly in compression space. Unfortunately, their compression space is vastly inferior to the compression space of, say JPEG. You see, JPEG is very cleverly designed in that it doesn't actually zero out certain frequencies directly - it just quantizes higher frequencies more agressively than lower ones, and that results in data that compresses better with a lossless compression algorithm (Huffman). By contrast, this compressive camera thing essentially directly zeroes out certain frequencies that have low amplitude. Not a very good idea perceptually.
This kind of thing has been used for a long time: Nipkow Disk, Drum Scanner. The combination with micromirror arrays is new.
However, there's a reason we "acquire first, ask questions later", as the article talks about current systems: electronics is much better at "asking questions" than mechanical hardware.
That's vive la différence. Difference is a girl in French. :)
No real French speaker would make this kind of mistake...
The durability of a micromirror array is actually very high. It's counterintuitive, but not hard to understand. The reason is the mirrors are so tiny. They have very little mass which means they transfer very little stress to their mechanical structure, even under large G force loading.
Think about the normal operating conditions of a micromirror in a DLP TV -- each of those mirrors is designed to flap at 100 kHz. They're already subject to extreme G forces in their everyday operations. Bouncing a chip off the ground is not much force compared to actually using it.
A good question would be the efficiency of light transmission. There's a clear shield mounted over the mirror array, which will attenuate the light both on the way in and on the way out. And the mirrors themselves can not be 100% efficient reflectors. But I suppose with a single pixel detector, you can invest more in making it very sensitive to low light conditions.
John
Like a lot of people who do not know any optics, I suspect you think that the light at the scene is somehow concentrated by the lens to form the image. It isn't; the lens doesn't suck in any extra light other than what impinges on it.
A single pixel is effectively approx f/1.
Oh yes, and you are arrogant, rude, and stupid. Perhaps you really do have a job with Microsoft.
Pining for the fjords
I refer, of course, to the flying-spot scanner of early (and sometimes late) television.
it was very difficult to make a working early camera tube with lame phosphors, flaky passive components, and nightmare wiring. but it was pretty simple to paint a raster on a screen by comparison. so the object to be scanned was put in front of the raster and a single photodiode vacuum tube picked up the changes in brightness, and modulated the "spot" created by the line and position sweep signals.
old hat by the end of the 1920s, but used as late as the 1980s in super-quaity scanners to encode 35mm and 16mm film for network-quality television. the indian-head generators that took two racks of tubes, and provided the best signal reference at the start of a broadcast day and the best calibration signal for TV repairmen in the field, were all flying-spot scanners.
no patent forrrrr YOU.
if this is supposed to be a new economy, how come they still want my old fashioned money?
No camera system is perfect... but I think you might be selling this one short a little too soon.
The idea behind the average consumer camera is to gather photons from a large area in a reasonably short amount of time. Usually we do this with film or with a CCD or CMOS array. However, film is going out of vogue, and CCDs and CMOS arrays can have dead spots. From a scientific standpoint, arrays are problematic for this very reason... plus, who has time to calibrate several thousand detector elements per camera? Using a single element detector helps mitigate this problem.
In this ScienceDaily article, it is revealed that the system works best with higher frequency information that can appear to be white noise. While it may produce images that are unappealing to the human eye, from a scientific standpoint it might be just the thing needed for a given application. I'd be very careful stating that it "essentially directly zeroes out certain frequencies that have low amplitude"... a more appropriate description of what it is doing is recording less information for fields that contain little or no change. Change is often edges, and edges are approximately generated through the summation of many high-frequency sinusoids.
From an imaging standpoint, this is some intriguing stuff. I would have gone to the presentation, but I had class at the time.
Low-orbit weather satellites work this way too. They have a rotating mirror that scans the image on to a single-pixel sensor, then the spacecraft's motion provides the Y dimension. These things take really cool pictures. I use a modified Radio Shack scanner and my computer (with its sound card) to receive them.
I've toyed with mechanical scanning for a couple of applications: making a high speed camera, and turning an infrared thermometer into a FLIR imager. The price tags on real FLIR cameras (like the one they used on Mythbusters when they were screwing with infrared alarms) have too many digits. :-(
...laura
Lots of the satellites like GOES, etc. use a single sensor and a spinning mirror. So the horizontal is scanned by the mirror, and the vertical is scanned by the satellite motion. That gives you raster data with a single "pixel" sensor and it is already serialized in the correct order for transmission to the ground.
Intron: the portion of DNA which expresses nothing useful.
I have often thought that it would be really neat if you could get a visual image of radio waves like around for example 2.4ghz and be able to see exactly how your surroundings block/absorb/reflect those wave - in addition to seeing sources of the waves.
People do this all the time. It's called radar. Some recent developments along the line you are interested in are SAR (synthetic aperture radar) and terahertz radar.