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With 25 years of hindsight, Jurassic Park marks a pivotal point in the history of visual effects in film. It came 11 years after 1982's Star Trek II: The Wrath of Khan debuted computer-generated imagery for a visual effect with a developed by George Lucas's Industrial Light and Magic to animate a demonstration of a life-creating technology called Genesis. And Tron, also in 1982, included 15 minutes of fully computer-generated imagery, including the notable sequence.

Yet Jurassic Park stands out historically because it was the first time computer-generated graphics, and even characters, , drawing the audience into the illusion that the dinosaurs' world was real. Even back then, upon seeing the initial digital test shots, George Lucas was stunned: He's often quoted as saying ", like the invention of the light bulb or the first telephone call … A major gap had been crossed and things were never going to be the same."

Since then, computer graphics researchers have been working to constantly improve the realism of visual effects and have achieved great success, scholarly, commercial and artistic. Today, nearly every film contains computer-generated imagery: Explosions, tsunamis and even the are , and detailed 3-D models and green-screen backgrounds have .

Years of progress

I have been for nearly two decades and witnessed the transition from practical to virtual effects; it didn't happen overnight. In 1993, the film industry didn't really trust computer graphics. For decades, filmmakers had relied on physical models, stop motion and , many of them provided by ILM, which was founded to create the effects in the and, notably, provided effects for . When he made Jurassic Park, therefore, director Steven Spielberg approached computer-generated sequences with caution.

By some counts, were of the two-hour movie. They were supplemented with physical models and animatronics. This juxtaposition of computer-generated and real-world imagery gave audiences the illusion of realism because the computer-generated images were on screen along with real footage.

The 3-D animated movies that followed in the late 1990s – like series and – were stylized, cartoonish films limited even by the era's best computing power, lighting models, and geometric modeling and animation packages.

The bar for realism is much higher when computer-generated images are mixed with live-action footage: that mapping an actor's face onto a younger virtual body didn't work well in 2010's "Tron: Legacy." (Even the director .) In fact, when they look quite close but just a little bit off.

Early successes of computer special effects – such as , and – focused on adding events like explosions and other large-scale destruction. Those can be less true to real life because most of the audience hasn't experienced similar events in person. Over the years, though, computer graphics researchers and practitioners tackled , , , and .

Learning to use the innovations

There were important practical advances as well. Consider the evolution of . In the early days, live actors would have to imagine their interactions with computer-generated characters. The people playing the computer-generated characters would stand nearby, describing their actions out loud, as the human actors pretended to see it happening. Then the virtual-characters' actors would record their performance in a motion capture lab, supplying data to 3-D animators, who would refine the performance and render it to be incorporated in the scene.

The process was painstaking and especially difficult for the live-action actors, who couldn't interact with the virtual characters during filming. Now, more allow virtual characters to be interactive on the set, even on locations, and provide much richer data to the animators.

With all this technological ability, directors have to make big choices. Michael Bay is famous – among fans and critics – for . True masters remember Spielberg's lesson and skillfully combine the virtual and real worlds. In the Lord of the Rings movies, for example, it would have been easy to use computer graphics techniques to make the hobbit characters seem smaller than their human counterparts. Instead director Peter Jackson used to achieve this effect. Similarly, the barrel escape scene from The Hobbit: The Desolation of Smaug with computer-generated liquids.

More recently, makeup and computer magic were combined to in The Shape of Water. Looking toward the future, as synthetic images and video become , people will need to be on guard that those techniques can be used not just for entertainment but to .