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Shadows and Occlusion

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Shadow Size and Perspective

The location of a light source relative to the object casting shadows determines the size of the shadows. For example, a light that is far away from your subject will cast a shadow similar in size to your subject, as shown on the left in Figure 3.10. Alternatively, moving the light closer to the subject will enlarge the shadow, making the shadow much bigger than the subject itself, as shown on the right side of the figure.

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Figure 3.10 What size do you want your shadow to be? Move the light farther away for a smaller shadow (left) or up close for a larger shadow (right.)

Adjustable shadow size works only with shadows coming from a point source, such as a spotlight. If you were using directional or infinite lights, they would always make shadows the same size as the object casting them, regardless of position.

Shadows look different, and even take on different shapes, when cast from different perspectives. For example, there is something visibly wrong with the sunbeams on the left side of Figure 3.11. They were produced by putting one spotlight directly outside of each window in the room. You can see how they splay outward, aiming away from the nearby lights. Moving the lights much farther back, as shown on the right side of the figure, makes the shadows appear parallel. On the right side of the figure, the left and right sides of the sunbeams appear parallel, as they would in real life. Using an infinite or directional light instead of a spotlight could also create parallel sunbeams.

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Figure 3.11 Sunbeams that spread out from an unnaturally close perspective (left) give away that sun lights were placed too close to the windows. Moving lights farther away (right) creates parallel sunbeams.

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