Painting by Number: From Ones and Zeros to Pictures of Mars

When Spirit sends pictures back from Mars, they aren't finished products by any means. Each pixel in the image is coded in zeros and ones, and sent across 120 million miles of cold, dark space back to Earth. Once they are received by the Deep Space Network antennas here, the zeros and ones are translated into pixel color and brightness.

"We're basically doing a more sophisticated version of ‘Paint by Numbers' when we reconstruct the images," laughs Eric De Jong, who rarely leaves the glow of his high-end computer screens. As one of the team members who is responsible for processing the images from Mars, he has barely a moment to spare with all of the data coming in.

A sequence of zeros and ones means a certain color/brightness, so it's just a matter of translating each sequence into the right visual information. "It works a lot like your digital camera, which registers pixels in a similar way," he relates. "It just takes a little longer to create the final picture since we have to wait for the information to reach us from Mars."

	The "black box" is an example of a temporary drop-out of data from a raw Pancam image. Each rover can retransmit data to gain the information lost in the first transmission due to communication hiccups. Large Image

Black Boxes of Data

To complicate matters, the pieces of the picture don't always make it back to Earth all at once. The images streaming down from Mars are sent in data "packets" that are delivered either directly from the rovers or through their sister spacecraft orbiting Mars – Mars Odyssey and Mars Global Surveyor. Sometimes all of the data does not make it through the 120-million-mile journey all at once, leaving a temporary black box or hole in the image.

"If there is rain in Spain near the Deep Space Network station, or some other communications problem, a packet of information can get distorted mid-stream and not show up at the Jet Propulsion Laboratory in Pasadena, California," explains Jim Bell, the lead scientist for the Panoramic Camera, which captures 360-degree views of the martian surface at a higher resolution than any camera previously sent to the surface of another planet.

"Just like you can get "holes" in your conversation when talking on cell phones that temporarily drop out of range, we can get holes in our pictures from Mars," Jim says a bit ruefully, since he and his team are especially eager to study the full data as soon as possible. When that happens, though, the mission team quickly identifies the missing packets and asks Spirit to resend the missing zeros and ones to complete the picture.

Historical photo of an engineer coloring by numbers sent down by the Mariner spacecraft in the 1960s, when the first digital images were transmitted through space from Mars. Large Image

After a day or two, the missing packets are resent to complete the picture, and the science team intensively pores over them, looking for unique rocks and surfaces that might give clues about the history of water, wind, and other processes at the landing site.

"My whole team spends all their waking hours gazing at Mars," Jim comments. "We don't want to miss a thing!"

Eric couldn't agree more. "We've come such a long way," he says with great enthusiasm and an appreciation for historical accomplishments. "Early astronomers used sketches, paintings, and photographic plates to share their visions of other worlds, and as late as the 1960s, engineers literally used a handful of crayons to color in numbers that represented a few hues on Mars. Today, we have the most realistic, clearest view of Mars ever."

This view of the "real Mars" is due to the modern, highly sophisticated "paint by number" image processing techniques that Eric and his fellow image-processing team members use. Racks of servers hum in the cool, darkened environment of the Multi-Image Processing Laboratory where they work, which is lit largely by plasma and other computer screens bearing the latest images from Mars.

Unlike the laborious processes of the past, which could take as long as weeks, images are in the hands of the science team within a minute after they hit the ground at the Deep Space Network Station. "It's awesome!" Eric smiles. "We were only expecting 50 megabits per downlink, but now we're receiving five times that. It doesn't stop us at all—high speed computers do the work and shoot out the data through the pipeline to everyone."

"It's exciting to have all of this technology - digital cameras, image processing, and digital communications – at hand," says De Jong. "It gives us an unprecedented opportunity to share the images with everyone on Earth. They can share in our exploration of Mars the moment it is happening."