Image calibration chart flies to Mars

Researchers have created a unique calibration target to help calibrate images captured by the Mars Hand Lens adjustable-focus, color Imager (MAHLI) at the end of the robotic arm on NASA's Mars Rover Curiosity.

The MAHLI calibration target includes color chips, a metric standardized bar graphic, a penny, and a stair-step pattern for depth calibration. The chart is attached to the Rover at the robot arm's shoulder joint.

Patches of pigmented silicone on the upper portion of the MAHLI target serve as aids for interpreting color and brightness in images. Five of them -- red, green, blue, 40-percent gray and 60-percent gray -- are spares from calibration targets for the Panoramic Camera on NASA's Mars rovers Spirit and Opportunity. The sixth contains a fluorescent pigment that glows red when an ultraviolet light source shines on it.

The target's bar graphic is adapted from a standardized US Air Force chart for testing camera resolution. The penny is from 1909, the first year Lincoln pennies were minted and the centennial of Abraham Lincoln's birth. Including it on the calibration target is a nod to geologists' tradition of placing a coin as a size reference in close-up photographs of rocks. One of the graphics, just above the left edge of the penny, is a tiny cartoon figure called "Joe the Martian."

MAHLI can provide 3-D information by taking a series of images at different focal ranges or by moving the camera between two images to yield stereo-pair images. The stair-step pattern at the bottom of the target and the penny help with three-dimensional calibration.

NASA's Mars Science Laboratory mission was launched on November 26, 2011, and will deliver the rover Curiosity to Gale Crater on Mars in August 2012. With MAHLI and nine other science instruments, Curiosity will investigate whether the area has ever offered environmental conditions favorable for microbial life.

-- by Dave Wilson, Senior Editor, Vision Systems Design