1. An image processing apparatus for generating an image of a scene, the image processing apparatus comprising: a first calculation unit configured to calculate, for each pixel of an image of a scene, based on light source characteristics and object information in the scene, spectral radiance data by performing ray tracing from a viewpoint; a determination unit configured to determine, during performing of the ray tracing, whether contents to be confirmed by a user by a preview indicate a shape of an object; a generation unit configured to, in a case that the determination unit determines that the contents to be confirmed by the user by the preview indicate the shape of the object, (1) acquire, before completion of the calculation by the first calculation unit, the spectral radiance data that the first calculation unit calculates and temporarily saves before completion of the calculation by the first calculation unit, and (2) generate preview data of the image of the scene by performing a wavelength-based collection of the acquired spectral radiance data that the first calculation unit calculates and temporarily saves before completion of the calculation by the first calculation unit; a display control unit configured to display, on a display unit, a preview image represented by the generated preview data; and a second calculation unit configured to acquire all pieces of the spectral radiance data after the completion of the calculation by the first calculation unit, and to calculate color signal values of pixels of the image of the scene based on the acquired all pieces of the spectral radiance data to generate the image of the scene, wherein the preview image represented by the generated preview data is different from the image of the scene generated by the second calculation unit, and wherein at least one of the first calculation unit, the determination unit, the generation unit, the display control unit, or the second calculation unit is implemented using a processor.