Using Heat to Defeat Blur
One unexpected way to fix blurry images involves heaters. Spacecraft instruments undergo large temperature swings, depending on their place in orbit and the angle of the sun. As a result, they tend to be kept under careful thermal control. Using our algorithm, we can figure out how to operate a nearby heater to change the optics to correct wavefront error.
Imagine, for example, that some component in an optical system changes its shape over time—a primary mirror warps under mechanical strain, causing light to bend in unintended ways and producing unfocused images. We could apply heat to expand the support structures, changing the distance between two mirrors in a space telescope.
We could also use heaters mounted to a particular mirror to bend it in a desirable way. We actually did this on the 1992 Mars Observer mission prior to its unfortunate demise; we are now building mirrors with heaters deliberately placed so that we can use them to control the wavefront.
But there's more. Our own eyes may one day also become beneficiaries of the software. Prescription eyeglasses correct for focus and perhaps astigmatism, but those are just two ways that wavefronts can be distorted. In reality, there are many other subtle, higher-order effects that can degrade your vision. Correcting these effects will lead to what vision science researchers have termed superhuman vision, the enhancement of visual acuity beyond normal 20/20 vision.
Vision scientists already use techniques for wavefront sensing and control. Most modern LASIK procedures, for example, use Shack-Hartmann wavefront sensors to determine eye aberrations. But as we discussed earlier, the sensor's resolution is limited by the density of its lenslet array. The modified Gerchberg-Saxton algorithm, by contrast, is limited only by the resolution of the camera used to capture the points of light, which is in the realm of tens of millions of pixels. Some vision scientists have proposed the possibility of replacing their aberration-measuring equipment with our computations for the human eye.
We're also working on cutting down the amount of time the algorithm needs to complete the complex calculations. Our software performs a massive number of calculations, which can take a long time on a regular microprocessor. By translating these computations into a graphics-processing problem, we can offload much of the work from the CPU to run on high-performance graphics cards, in effect turning our desktop PCs into supercomputers. Now we can generate wavefront-error results in seconds, down from about 5 minutes. Evolving graphics technology will help the software come closer to running in real time.
Ultimately, our dream is to be able to correct astronomical images "on sky," with the software running in real time and using only camera imagery to continuously determine and correct wavefront error. On Earth, our goal is for crisp, unprecedented visual clarity. In all, we're helping to write a new legacy for Hubble, and we're turning a boondoggle into a boon for the entire electromagnetic spectrum.
The authors would like to thank their collaborators, especially Scott Basinger, Joseph Green, Catherine Ohara, and Fang Shi.
This article originally appeared in print as "The End of Blur".
About the Author
Sidd Bikkannavar and David Redding, work at NASA's Jet Propulsion Laboratory. Bikkannavar first encountered IEEE Spectrum's staff in the Australian outback, where he was helping to run a solar-car race the magazine was covering. Both authors say they stumbled into careers in optics. Redding did so while working on control systems for positioning laser beams and "discovered we didn't really know how to point mirrors." He got curious and, as he puts it, "one day I woke up an optical engineer".
