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- Postscript of paper, minus color images and Figure 8 (490K)
- Postscript of full paper, with low-resolution grayscale images (2200K)
- Figure 2: Glossy highlights from area light sources
- Figure 6: An area light source adjacent to a diffuse surface
- Figure 9: Bidirectional path tracing for global illumination
- (a) The weighted contribution that each bidirectional sampling technique makes to image (b) (JPEG, 197K)
- (b) Combines samples from all the bidirectional techniques shown in (a) using the power heuristic (JPEG, 53K, 25 samples per pixel)
- (c) Standard Monte Carlo path tracing using the same amount of work (JPEG, 92K, 56 samples per pixel)

A false-color image showing the weights used to compute Figure 2(c). Green represents samples from Figure 2(a), red from Figure 2(b). Yellow indicates that both types of samples are assigned a significant weight. Notice that some of the highlights are yellow in the center and green around the edges---the weights are not just a function of the light source size and surface roughness.

Figure 9(x) (JPEG, 312K)

This is an extension of Figure 9(a). Each image shows the weighted
contribution made by one of the bidirectional sampling techniques
to Figure 9(b), using the power heuristic with $\beta=2$. In this
case, paths of up to length $k=6$ were sampled.

Row $i$ shows techniques that sample transport paths of length $i+1$. The $m$-th image in the $i$-th row uses the distribution $p_{i+1,m-1}$ described in Sec. 4.3 (this distribution chooses $m-1$ vertices using the light subpath, and the other $i+3-m$ vertices using the eye subpath). Images in row $i$ have been overexposed by $i$ f-stops so that details can be seen.

Relative to Figure 9(a), we have added one extra column to the left of each row (these images are nearly black, as mentioned in the text), and one row along the bottom (showing transport paths of length 6). We have still omitted one image from the right side of each row, corresponding to the sampling distribution $p_{i+1,i+2}$ (zero vertices in the light subpath). These images are truly black, since this particular scene has a pinhole lens.

Figure 9(y) (JPEG, 530K)

This image shows what the various bidirectional sampling
techniques look like when used alone. This is similar to
Fig. 2(a) and Fig. 2(b), where we used two different sampling
techniques in attempting to compute the same image. In this case,
the $m$-th image of row $i$ uses the distribution $p_{i+1,m-1}$
to make an image of the light flowing on paths of length $i+1$.
Standard path tracing is equivalent to summing the second image
from the left on each row (except for caustic paths, which get
their contribution from the first image on each row).

Last modified: May 16, 1995