Now they're using computers to color black-and-white movies

In the early 1900s, before the advent of color film, some movie companies nonetheless had a way of splashing color on the screen. Tapping the abundance of cheap, and apparently patient, labor of the day, they would enlist teams of women to hand-dab individual frames of black-and-white film with dye. The results were crude but colorful.

Today the process is being revived, albeit in a way compatible with an age that puts seven people simultaneously in space and produces talking dishwashers. Electronics is now being used to transform old black-and-white film into color.

A number of old television stalwarts are already being changed (episodes of the ''The Twilight Zone,'' for instance), as are several cinematic classics (''Yankee Doodle Dandy,'' Laurel and Hardy features, and the original 1937 version of the Gary Grant classic ''Topper''). Other cinematic history is also being tinted in the lab.

The product of all this is not a film but a ''colorized'' videocassette. (It is possible, though, to transfer the images back to film for theater viewing.) And the result is proving both intriguing and irksome to the industry:

Irksome - to purists who worry about some black-and-white artistic monument like ''Citizen Kane'' being reissued in color. ''There's a line there: You don't color black-and-white Picassos,'' says Gene Allen, president of the Academy of Motion Picture Arts and Sciences.

Intriguing - because many in the industry have long sought a way to revive interest in the great black-and-white films and TV shows of the past. More than 17,000 such feature films now sit in Hollywood vaults, not to mention thousands of hours of TV programming. To viewers in the age of color TV, the oldies usually appear dull, so many stations won't show black-and-white features.

Two companies, working independently, have come up with colorization processes: Color Systems Technology of Los Angeles and Colorization of Toronto. Although the methods are slightly different, they work on the same principle. Computer technology lies at the core of both. First, the film is electronically scanned and each frame broken down into a grid of 525,000 dots. Then an art director looks at the first frame of a scene (the first and last frames with Color Systems), picks colors for each object, and indicates on the computer screen where they should go. The computer takes over from there, shading the rest of the scene by comparing each new frame with the one behind it.

It's not too tough for the computer to keep track of the movements from frame to frame: There's usually about a 2-percent change in movement from one to another. If there is a rapid motion, however, or another element or person added to the scene, the art director makes the adjustments. The companies can choose colors at their whim. But they usually dig into archives and try to use authentic colors where appropriate. This can't be carried across the board, though. In the early days, directors often had actors wear brightly colored clothing on the set to heighten the contrast in black and white. Re-creating the true colors would produce something more like a kaleidoscope than Cinemascope.

This freedom, however, can also be a boon. When tinting a version of the 1936 favorite, ''San Francisco,'' with Clark Gable and Jeanette MacDonald, Color Systems added sparkles to a dark gown worn by the actress in one scene to make it stand out against the background.

The process can be complex and time-consuming, though. Colorization says it might take five months to redo a full-length film, between the research and processing. Color Systems claims its process takes less time.

Both companies see a pot of gold at the end of their rainbow-coloring. Hal Roach Studios, 35 percent owner of Colorization and producer of ''Topper,'' is coloring more of its stock, including the Laurel and Hardy features. MGM/UA has contracts with Colorization and Color Systems to revise some of its movie classics, such as the 1935 version of ''Mutiny on the Bounty,'' ''Yankee Doodle Dandy,'' and ''Dr. Jekyll and Mr. Hyde.'' Episodes of the TV series ''Sea Hunt'' are also being redone. ''We would not be investing money and going to this kind of trouble unless we felt there was a market,'' says Roger Mayer, a senior vice-president of MGM/UA.

Backers of the concept optimistically envision color versions of everything from early ''I Love Lucy'' shows to ''Casablanca'' - with viewers tuning in by cable, commercial TV, and their videocassette machines. ''We're adding a dimension that will bring them back to all generations,'' says Victor White, president of Hal Roach Studios. But there's no guarantee the idea will catch on. The current cost of coloring can be high ($180,000 for a 90-minute feature). Greater demand, however, could reduce the tab. There are also questions about the depth of the appetite for old programming, color or not. And what about those purists?

''You always have the option of turning off the color on your TV set,'' rejoins Charles Powell, executive vice-president of Color Systems Technology. ''I predict that when we color 'Casablanca,' the movie buffs will crucify us, but a major network will buy it, and it will be one of the biggest hits of the year.''