Spectral Image Rendering of Fluorescent Objects Using a Conventional Renderer

We propose a practical spectral image rendering method for fluorescent objects using a renderer that does not natively support wavelength-shifting transport. For scenes composed of matte fluorescent and non-fluorescent surfaces, the illumination incident on a target fluorescent object is classified into three types: (1) direct illumination from a light source, (2) indirect illumination reflected from other reflective objects, and (3) luminescent illumination emitted from other fluorescent objects. We express the radiance observed on a fluorescent surface as a linear combination of five terms: reflection and fluorescence under direct illumination, reflection and fluorescence under indirect illumination, and reflection induced by luminescent illumination emitted by other fluorescent surfaces. Assuming isotropic emission and single-bounce fluorescence, the fluorescent shading terms reuse the diffuse-reflection shading produced by the renderer, while measured Donaldson matrices provide the wavelength conversion. Mitsuba is used as the underlying conventional rendering system. Experiments conducted with a physically built Cornell Box validate the proposed method through comparisons with direct measurements and an existing fluorescence-capable renderer. Finally, we demonstrate an extension to non-planar fluorescent objects via sparse emitter discretization.