mental ray Architectural and Design Visualization Shader Library

94 4 Camera- and Exposure EffectsThe “Sunny 16” resultThe settings we used abide by the “Sunny 16” rule in photography; for an aperture of f/16,setting the shutter speed (in fractional seconds) equal to the film speed (as an ISO number)generates a “good” exposure for an outdoor sunny scene. As we can see, indeed, the outdoorarea looks fine, but the indoor area is clearly underexposed.In photography, the “film speed” (the ISO value), the aperture (f number) and shutter timeall interact to define the actual exposure of the camera. Hence, to modify the exposure youcould modify either for the “same” result. For example, to make the image half as bright, wecould halve the shutter time, halve the ISO of our film, or change the aperture one “stop” (forexample from f/16 to f/22, see page 91 for more details).In a real world camera there would be subtle differences between these different methods, butwith this shader they are mathematically equivalent.f/8 f/4Clearly the f/4 image is the best choice for the indoor part, but now the outdoor area isextremely overexposed. This is because we have the burn highlights parameter at 1.0,which does not perform any compression of highlights.burn highlights = 0.5 burn highlights = 0.0