GPU Pro 6

4. Physically Based Light Probe Generation on GPU 253

0.0 0.25 0.5

Roughness

0.75 1.0

(a)

(b)

Figure 4.5. (a) The preintegrated specular BRDF for different roughness with 1024

samples per pixel. (b) The ground truth integration using 100,000 samples without the

importance sampling.

Number of Preintegrated Cube Map Face Size

samples 128 × 128 64 × 64 32 × 32 16 × 16 8 × 8

64 2.8 0.8 0.2 0.04 0.02

128 6.2 1.6 0.5 0.1 0.08

512 25 6.5 1.7 0.4 0.3

1024 - 13.5 3 1 0.7

4096 - 53.8 15 5 3

Table 4.1. BRDF importance sampling preintegration on GTX 760.

The main problem with BRDF importance sampling (and importance sam-

pling in general) is that a large number of samples ...