1. An image processing apparatus for generating a computer graphics image, comprising: a first input section configured to input light source characteristic data representing a spectral characteristic and light distribution characteristic of at least one light source which illuminates a scene; a second input section configured to input object characteristic data representing a spectral property of at least one object contained in the scene; a trace section configured to perform ray tracing for respective rays having different wavelengths, and calculate a spectral radiance in each pixel of a computer graphics image which represents the scene based on the light source characteristic data and the object characteristic data; and a generator configured to calculate color signal values of each pixel from the spectral radiance in the each pixel, and generate the computer graphics image of the scene, wherein at least one of the first and second input sections, the trace section, and the generator is implemented using a processor.