NASA converted an image of the Mona Lisa into a black and white, 152-by-200 pixel image. After that, they signaled to the orbiter how bright to make each pixel by delaying the message (or "pulse) to one of 4,096 slots in a very small time-frame. In other words, instead of a continuous stream of pulses in regular intervals, the laser varied the time between intervals. Depending on the length of that variation, the pixel appeared one of 4,096 shades of gray. Rinse and repeat with each pixel until you have the Mona Lisa.