| 摘要 |
In a system for combining foreground video images with background video images, using the so-called "blue-screen" (or special background color) technique, a comprehensive control system is provided which accommodates a broader range of foreground objects, permits the careful coordination of control of the blue of the foreground with the level of the background signals, and also permits precise shadow control in accordance with the artistic requirements of the scene to be produced. To properly control the level of the blue from the foreground and to properly distinguish between situations where the video signal arises from solid or partially transparent actual foreground objects and where it originates from the blue screen, various electrical adjustments are provided for accommodating different types of foreground objects. One of the adjustments for controlling the blue foreground has three terms, one limiting the level of blue to the amount of green present in the signal, the second permitting an increase in the blue signal in accordance with a function of the positive value of green minus red, and a third term permitting increase of the amount of blue signal in accordance with a function of the positive value of red minus green present in the signal. As will be described in greater detail below, these electronic circuits will handle the more difficult color situations involving, for example, blue eyes which present a difficult problem because of the similarity to the blue background screen; and purple objects which include high red and blue content but little green. The background control signal may also be switched to three different types of control depending on the type of foreground which is being reproduced and included in the composite scene. If desired, the background control signal switch may be mechanically coupled to the switch which limits the blue of the foreground. As in the case of the control of foreground blue, the background control signal may have several terms. In addition to the color terms which may be included in the background control signal, electronic circuitry is provided for both accommodating variations in brightness of the "blue screen" background, and also to control desired shadow effects, from completely eliminating shadows to intensifying them, with the additional capability of providing shadow effects. Special switches are also being provided to switch from composite foreground and background video signal generation to (1) foreground only with background blacked out, (2) foreground complete with blue screen signals (3) background only, and (4) background only with foreground blacked out. These switches permit the achievement of various special effects.
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