Nvidia GeForce GTX 980 White Paper page 14

MAXWELL: ENABLING THE NEXT
GeForce GTX 980 Whitepaper FRONTIER IN PC GRAPHICS
Figure 4: Scene rendered with direct lighting only
Figure 5: Same scene with GI enabled, note the indirect light and specular reflections on the floor
Because it's a computationally expensive lighting technique (particularly in highly detailed scenes), GI
has been primarily used to render complex CG scenes in movies using offline GPU rendering farms.
While some forms of GI have been used in many of today's most popular games, their implementations
have relied on pre-computed lighting. These "prebaked" techniques are used for performance reasons;
however, they require additional artwork, as the desired lighting effects must be computed beforehand.
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