When it comes time to render a dynamic object, the Volumetric Lightmap is interpolated to each pixel being shaded, providing precomputed indirect lighting. Lightmass places lighting samples throughout the level and computes indirect lighting for them during the lighting build.
How It Worksįrom a high-level, the Volumetric Lightmaps system works in the following manner: ( b) Simplified schematic of optics showing imaging and illumination rays formed by MLA1 and MLA2 for the case that the sample (SAM) is a surface mirror.Sparse Volume Lighting Samples determined leaking amounts and lighting accuracy. The marginal rays for one imaging microlens (green) and one illumination microlens (yellow) are shown. Light from the sample (SAM) passes through the objective (OBJ), the filter cube (BS and EM) and the tube lens (T1) (focal length: 200 mm) to the imaging microlens array (MLA1), which focuses it at the back focal plane of MLA1, where it is collected by the 1:1 relay lens system (R1, 2× Nikon AF Nikkor with nose-to-nose mounting, focal length: 50 mm) and imaged by the camera (CAM). The illumination light field is focused by the objective (OBJ) on the sample (SAM). For fluorescence applications, the excitation (EX) and the emission filters (EM) are placed in the standard Nikon microscopic filter cube, together with the beam splitter (BS). Integration of light-field illumination into the standard microscope light port is achieved with the mirrors M1 and M2 and the tube lens T2 (focal length: 200 mm). The image of the DMD is focused on the back focal plane of the illumination microlens array MLA2 by a 1:1 telecentric relay lens R2 (Brilliant Technologies).
( a) Light from the light source is conducted by a light guide and concentrated through an integrator rod and a TIR prism on the DMD-SLM (not shown in the figure, but explained by Levoy et al.22). Thus, N regions at the top of the volume (i.e., x, xiv, xv and xvi) are not excited while regions at the bottom of the volume (i.e., ix, xi, xii and xiii) receive light. S3 ( i) avoids unwanted excitation of non-occluded non-excitation regions. S2 ( h) avoids any unwanted excitation of N by sacrificing excitation light at E (e.g., regions ii and vi receive less light than in S1). S1 ( g) illuminates E (i–viii) while ignoring unwanted excitation of N, thus a high number of N (ix–xvi) is excited.
( g– i) Optical axial-slice simulation of illumination strategies S1, S2 and S3 for eight excitation regions ( E) and eight non-excitation regions ( N). For illustration reasons, we applied 100 μm microspheres and a dry 20×/0.75 NA objective (see Table 1 for details) in the experiment for ( a–f). The corresponding light-field masks are shown inset (approximated and optimized by solving Eq. ( d, f) Strategies S2, S3 cause no incorrect excitations, but-due to occlusion-they reduce the level of correct excitations. ( a, b) Two occluding microspheres i and ii ( c, d) i is to be excited, while ii is to remain unexcited ( e, f) ii is to be excited, while i is to remain unexcited ( c, e) Masking strategy S1 leads to maximal correct excitation but-due to occlusion and transparency-also to a small amount of incorrect excitation.