Nearly every studio film at the multiplexes this summer will have been created, at least partly, by a computer. The digital origins of some effects will be easy enough to guess: starships and rocket-suited men in flight, giant fighting robots, ancient naval battles. Vastly more of them will be subtle enough to pass by the average moviegoer—casual, dialogue-driven scenes shot in front of green screens and placed into digital streetscapes, or wires and buildings digitally removed.

These bread-and-butter effects are everywhere. Even “Amour,” last year’s Palme d’Or-winning drama set within a Paris apartment, relied on green-screen work.

The rise of the pixel in cinema may feel like a recent development, but this year actually marks its fortieth anniversary. It began in 1973, with the release of a low-budget science-fiction film, Michael Crichton’s “Westworld.” The movie’s use of a digital effect for a total of two minutes—a now-routine process called pixelization, commonly deployed on Gordon Ramsay cooking shows to obscure a contestant’s cursing mouth—was the unlikely launching point of this revolution.

Crichton both wrote the script and directed the film. Inspired by the Disney theme parks, he imagined an adult vacation spot called Delos, made up of three resorts: Medieval World, which offered a fantasy version of life in thirteenth-century Europe; Roman World, which promised the “decadent” morality of the Roman Empire at its peak; and Westworld, which re-created the lawless frontier of 1880. For a thousand dollars a day, visitors lived their fantasies, interacting with characters of the period—in reality, robots programmed only to serve. As the film begins, two professional men in their mid-thirties, played by James Brolin and Richard Benjamin, are heading to Westworld for a bachelors’ adventure. A recorded female voice assures the new arrivals that the technology of Delos is “highly reliable.” Of course, it isn’t. Partway through the visit, the robots turn on the guests; the staff in the control room tries to halt the mayhem, but is rendered helpless by a power shutdown. A robot gunslinger, played by Yul Brynner, kills one of the men and coolly, relentlessly stalks the other to a final showdown. (If the plot sounds clichéd, it is only because its ideas were later excavated by the “Terminator” films and Crichton’s “Jurassic Park.”)

Crichton was concerned from the outset with how to give a distinct look to the gunslinger’s point of view when the audience saw events through its eyes. Five years earlier, Stanley Kubrick had used a wide-angle lens to show the perceptions of HAL 9000, the troubled computer of “2001: A Space Odyssey.” Crichton, however, wanted his villain’s perspective to look like that of an electronic machine. His script described it as “a bizarre, computerized image of the world” with “flashed-up calculated figures” and “shifting green tones which apparently represent shifts in the Gunslinger’s concentration.”

The question was how to make it work. “There were no effects houses around that knew what to do,” said Paul Lazarus, the film’s producer. “It wasn’t like giving it to Industrial Light & Magic and having it come back.”

Compounding the problem was the modest budget of $1.25 million imposed by M.G.M. “Westworld” had been turned down by every other studio, perhaps because Crichton’s directing credentials were limited to making an ABC movie of the week and hanging around the set of “The Andromeda Strain,” the 1971 thriller based on a novel he had written as a Harvard medical student. Crichton got a quote for generating the computer imagery from the Jet Propulsion Laboratory in Pasadena. He was told that the two minutes of footage would cost two hundred thousand dollars and require nine months—both prohibitive. He turned to a maker of abstract films, John Whitney, Sr., famed in art and film circles for his work creating animation with military-surplus analog electronics and motor assemblies. Whitney referred Crichton to his son, John Whitney, Jr., who was eager to follow in his father’s footsteps as an experimental filmmaker, but using computers. He agreed to do the effects in four months for twenty thousand dollars. (Whitney wasn’t the only one who worked cheaply: Yul Brynner, down on his luck, took the role of the gunslinger for seventy-five thousand dollars and wore the costume he had used in “The Magnificent Seven.”)

Whitney proposed the simpler effect that ultimately appeared in the film, dividing each image into small squares and calculating the average color in each area. In essence, the effect turned a high-resolution film image into a blocky low-resolution one. Still, he wasn’t certain how to get it done. “I was playing a confidence game,” said Whitney, now sixty-seven.

Machines that could scan film into a computer or record computer images onto film were rare. Whitney knew of a Los Angeles-based company, Information International, Inc., that made such equipment. He struck a deal in which the company supplied a programmer and access to a scanner and recorder. From there, it was trial and error; he spent two months creating test footage and projecting it onto theatre screens to determine the best contrast and resolution for the pixelated effect, and to figure out what kind of raw footage would be easiest to understand once it was pixelated. In the process, he also learned that the digitally created colored areas needed to start as rectangles so they would appear square when projected in Panavision.

Based on Whitney’s test results, the shots of the gunslinger’s point of view—the footage destined for computer processing—were filmed in an idiosyncratic manner. To insure that audiences could make out the hunted character at low resolution, the actor on the run wore solid white to stand out in a dark interior: white costume, white shoes, white gloves, white makeup, white hair. For shots on horseback, his stunt double was red from head to toe, to stand out against the sky.

Because Whitney didn’t have a color scanner, the workload was tripled: M.G.M.’s optical department made color separations of the film—one set of black-and-white footage for each of the three primary colors—that he needed to process separately, image by image. The computer processing itself took about eight hours per ten-second sequence. “What made it hard was that it took a lot of computing power just to do a single frame,” said Brent Sellstrom, who supervised Whitney’s work and the film’s other effects.