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 the trace section sets a maximum crossing count for each of at least two wavelengths of rays to be traced based on reflectance or transmittance at each wavelength indicated by the object characteristic data of an object first crossing the rays and wavelengths of the rays indicated by the light source characteristic data, and performs the ray tracing in each of the at least two wavelengths of rays to be traced so that a crossing count of the ray and objects does not exceed the maximum crossing count, and wherein at least one of the first and second input sections, the trace section, and the generator is implemented using a processor.