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4.2.4 Image-based measurement
Further, physically correct parameters can be determined for volumetric materials
by image-based measurement. Lensch et al. captured an object’s response to
illumination using a high dynamic range camera from multiple points [LGB + 03].
In this work, the highly scattering homogeneous materials are represented by the
four-dimensional diffuse BSSRDF.
The algorithm is subdivided into two parts. The first is a large preprocessing
step to compute and store the impulse response to incident light for each surface
point under subsurface scattering. The responses are divided into local and global
effects. Local effects are modeled as a per-texel filter kernel that is applied as a
texture map representing the incident illumination. The global response is stored
as vertex-to-vertex throughput factors for the object’s triangle mesh. During the
rendering stage, two responses are combined using the current light situation to
form the final image.
The work builds on subsurface scattering research, as it is unique in attempt-
ing to handle interactive image synthesis. The advantage is that the model is
able to handle rendering of translucent materials at roughly interactive rates (ap-
proximately 5 frames per second), while including dynamic camera movement and
changes in illumination.
Goesele et al. extended this work by presented a technique (denoted as the
DISCO acquisition technique) that can derive the necessary input data for real
translucent materials with spatially-varying properties [GLL + 04]. This work is the
first to acquire the subsurface light transport behavior for arbitrary heterogeneous
materials.
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The model utilizes the previous method of interactive rendering of highly-