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HP on Mars

Labs technology used to send most accurate images possible

January 2004


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"Lossless compression is mandatory in cases where the images are very precious." An HP Labs image-compression algorithm is partly to thank for some of the spectacular, high-resolution images of Mars now being transmitted by NASA's roving spacecraft. The method is used in cases where images must be transmitted without quality loss.

Just hours after it landed, NASA's Spirit Rover began sending stunning black-and-white photographs of Mars' rocky surface back to Earth, 106 million miles away. These and other color images will be used to help scientists select the most promising targets to explore for signs of water that might once have sustained life on Mars.

To send the most accurate images possible, the NASA is relying on the LOCO-I algorithm (LOw COmplexity LOssless COmpression for Images) developed by HP Labs.

Image preservation essential

The algorithm is the basis for the JPEG-LS lossless/near-lossless compression standard for continuous-tone images. But NASA didn't use JPEG-LS; scientists "went right to the source," says Gadiel Seroussi, director of the Information Theory Research group at HP Labs.

"This lossless compression is mandatory in cases where the images are very precious, as in the case of space imagery, where data is very costly to obtain and must be accurately preserved for scientific exploration," he says.

Scientists at the Jet Propulsion Laboratory (managed for NASA by the California Institute of Technology), who modified LOCO for their purposes, credit HP Labs researchers Marcelo Weinberger, Gadiel Seroussi and Guillermo Sapiro (now with the University of Minnesota) in their technical papers, saying that LOCO-I helps to "maximize data return within stringent mission download links."

"NASA and the Jet Propulsion Laboratory have traditionally been strongholds in imaging technologies," Seroussi says. "In this case, they chose LOCO-I for its superior compression performance and low complexity implementability."

Together with LOCO-I, NASA used the JPL-developed ICER, a lossy image compression scheme. The mission uses a mixture of lossless and lossy image compression to optimize bandwidth, human visual perception, and scientific precision requirements.


Searching for water

Spirit landed on January 3 near the center of Gusev Crater, which may have once held a lake.Three weeks later, a second craft will reach the Meridiani Planum, a region containing exposed deposits of a mineral that usually forms under watery conditions.

In addition to the cameras, these "robotic geologists" each carry several spectrometers, an infrared instrument, a microscope and other tools that allow them to identify and study the rocks that appear most promising.

by Jamie Beckett

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