We describe an automated three-axis gonioreflectometer, which can help increase the physical realism of computer graphics renderings by providing light scattering data for the surfaces in a scene. The gonioreflectometer performs rapid measurements of the bidirectional reflectance distribution function (BRDF) for flat, isotropic, sample surfaces over the complete visible spectrum and over most of the incident and reflection hemispheres. The instrument employs a broadband light source and a detector with a diffraction grating and linear diode array. Validation is achieved by comparisons against reference surfaces and other instruments. The accuracy and spectral and angular ranges of the BRDFs are appropriate for computer graphics imagery, while reciprocity and energy conservation are preserved. Measured BRDFs on rough aluminum, metallic silver paint, and a glossy yellow paint are reported, and an example rendered automotive image is included.