[Figure 8] A 360-degree view pieced together from multiple photographs.

The other elements in the scene may require more attention, because they are typically at eye level and more clearly in the camera’s view (depending on the angle of the camera), but still do not require extremely detailed texture maps. Because reflections are distorted by both the shape of the object they reflect off, as well as the roughness of that surface, complete precision when creating reflection texture maps is not necessary. A 360-degree panorama, created by piecing together many shots from the position of the subject in a scene can be used without the necessity of exactly matching and blending every seam between images (see Figure 8). The images used for the environment map in Figure 8 have been reduced in scale in the x direction to make a more manageable image file (at actual size, the image is more than 10,000 pixels wide) and to display more easily on the page. If the portions of the reflection map showing up on the subject appear incorrect, the environment texture can be scaled during the texture-mapping phase in the shader. Unless viewed in a perfect, flat mirror, the reflections are distorted and faint on most surfaces and any inaccuracy is not noticeable.

CG Environment Types
To project the environment texture onto a subject, a choice is made in the shader for the shape defining the environment. This shape is most commonly a sphere, a cube or a cylinder. Each type creates a slightly different reflection and has advantages and disadvantages. The spherical projection method most closely recreates the real-world environment, but warps standard rectilinear images to fit to its shape. To provide an accurate map, this method requires a texture recorded with a fisheye lens. These lenses are expensive and not always readily available. A cube environment shape lends itself for use as the walls, ceiling and floor of a room containing reflective objects. In the example presented here, a beach ball is placed into the scene in Figure 8. The reflection map in this case uses cylindrical mapping and is shown at full intensity in the image on the left of Figure 9. The reflection is completely independent of lights in the scene, so even with no lights or each light’s intensity set to zero, the reflection is still evident. The amount of reflection is controlled in the surface shader, and is typically a percentage or a normalized value between zero and one. When the amount of reflection is reduced to an appropriate level for the surface material, the effect offers another touch of realism for blending the computer graphics element into the shot (see Figure 9, right).

[Figure 9] A beach ball with full reflection on the left, and a beach ball with reflection dialed in to match the background on the right.

Specific Reflections
In some cases, the reflection is vital to the scene, and the director asks for a specific image to be clearly defined. In Terminator 2: Judgment Day, the liquid metal Terminator taking control of a helicopter looks at the pilot and tells him to get out. For this scene, it is important to the story that the pilot’s frightened face be clearly shown in the reflections on the Terminator’s head. In such a case, the most reliable way to attain the desired result is recording a clear shot of the image required for the reflections. This image can then be manipulated or placed over an appropriate background to fit with the scene, and then be used as the reflection texture. The image can simply be another texture added to the appropriate area of the object. The other reflections are non-descript, simply matching the color and value of the surrounding scene. When using reflections, identify the important element, and make the remaining areas of the reflection map unobtrusive, even if not entirely accurate.

Additional data for creating environment maps is found in the reference shots of a chrome sphere. The chrome sphere offers precise data for creating reflections in a scene from the camera’s point of view. If the camera is zoomed in on the chrome sphere to capture enough detail, this image can be used as an environment texture. This method creates accurate and believable reflections, and it is a valuable tool in a digital production pipeline.