Twinkle twinkle...

2019-03-07 07:03:01

By Catherine Zandonella in Los Angeles SIMULATED diamonds and other transparent objects will soon twinkle more seductively in computer-generated photographs, thanks to a gem of a technique developed by researchers at the University of Washington in Seattle. Computers are often used to lift objects from one photo and place them in the background of another, but transparent objects are tricky. They cannot be inserted into a new background without losing their surface reflections, because these depend on light sources in the original background. But the Washington researchers have worked out a way to transplant transparent objects while keeping their ability to accurately reflect and refract light. The first step is to determine how each of the object’s surfaces affects light. So the researchers first photograph the object in front of a series of 20 different striped green and magenta screens that let the computer calculate the origin of the light in each pixel on the screen. The computer also calculates the colour of reflected light, and something called the alpha value, which tells you whether the pixel is part of the background or of the object in the foreground. Once the researchers know how an object reflects and refracts light, they can paste its image onto a new background. The computer draws each pixel individually based on all the information it has collected. Graduate students Douglas Zongker and Dawn Werner presented the technique, which is called “environment mapping”,