Grain and Edge Blending By using the beach ball element, two more useful elements are created for integrating the ball into the background scene: a grain element and an edge-blending element. The grain element is created with a noise field matching the noise existing in the background element. In this instance, a small bit of the background sand is added in with the grain to provide additional break up (see Figure 44). The elements in Figure 44 are enlarged to better show the detail. The new grain element is then placed inside the alpha of the beach ball and combined with an add function to the beach ball element. The second element, shown on the bottom of Figure 44, is an edge element. This element is created by applying an edge detection filter on the beach ball element. Most compositing software packages provide an edge detection filter. It is important to note that the edge filter’s utility depends heavily upon the contrast level of the element involved. Edge detection algorithms are based on contrast, so it is frequently necessary to boost the contrast on an element before using such a filter. Once the edge matte is created, it can be used for a number of final compositing tweaks. In this case, it will be used for a slight edge blur on the final composite.

[Figure 44] Beach ball grain element and edge element.

[Figure 45] Rough comp of beach ball over beach background.

Color Adjustments
These elements can now all be layered together to help place the beach ball on the beach. The first step in the process is placing the beach ball over the background plate and making a simple A over B composite (see Figure 45). The beach ball does not exactly blend in seamlessly with the background. The render itself is extremely bright and high in contrast with anti-aliasing problems around the edges, and no shadow to tie it to the ground. It needs help, and that’s exactly what the shadow, grain, and edge elements will do. Adding those elements, along with color corrections to the beach ball, makes this scene much less offensive to the eye. This rough comp provides direction and clearly illustrates the problems with the element. Before the additional layers are added, the beach ball saturation is reduced, and the specular highlight is attenuated to 60% of its original value. These values are adjusted using trial and error to select values for each operator until the ball blends more closely with the background. This can be evaluated by taking pixel readings from the background to determine saturation and brightness values. The beach ball values can be adjusted to put them in the same range as the background. Once the numbers are fairly close, look at the ball and see if it looks right. This is one point where it benefits the compositor to take a step back, and look outside the numbers. If it still looks too saturated, even if the numbers match with the background, reduce the saturation. The eye of the viewer is the final judge, and even with precise value matching, a shot can still look wrong.