From greg.org: In 1965, after the Mariner 4 probe had possibly transmitted its first closeup images of Mars and in the many hours before JPL computers would finish processing that image, mission scientists were concerned about what, if anything the data would reveal.
So Richard Grumm and his fellow mission managers came upon the idea of printing out the brightness values onto vertical strips, taping them up on the office divider, and coloring each number in with pastels. Thus it was that the world’s first transmitted, televised image of Mars was drawn by hand.
Clarification by Dan Goods, who curated the Data + Art exhibition and interviewed Grumm: The story is that mangers for the mission were unsure if the tape recorder on Mariner 4 was working correctly. It turns out that the one used was a spare not originally intended for use, but because of previous failures it was used. After the flyby of the planet it would take several hours for the computers to process a real image. There had been some anomalous errors pointing towards the tape recorder so everyone was a little freaked out that they were not going to get any images. So Mr. Grumm, who oversaw the tape recorder, and his crew decided to prove one way or the other.
The engineers thought of different ways of taking the 1’s and 0’s from the actual data to create an image and decided that printing out the digits and coloring over them was the most efficient. So Mr. Grumm went to a local art store and was looking for a set of chalk in different grays. The art store replied that they “did not sell chalk” (as that was too low for them, only convenience stores sold “chalk”), but they did have colored pastels. Richard did not want to spend a lot of time arguing with them, so he just picked them up, printed out the 1’s and 0’s and his team colored them by their brightness level. Though he used a brown/red color scheme the thought that mars was red did not enter his mind. He really was looking for the colors that best represented a grey scale, since that was what they were going to get anway. It is uncanny how close to the actual colors of mars he was as they look like they came right out of current images of the planet. I’ve seen some of the other color schemes he tried and it could have been green or purple!