| 摘要 |
A light source for providing controllable illumination having the red, green, and blue components in selected intensity proportion, uses a lamp/filter assembly which projects light through a diffusing plate into a mixing chamber from the output end of which mixed light is emitted for illuminating photographic paper through a negative. The chamber is rectilinear, and the red and green lamps project toward opposite corners while the blue lamp projects along the axis of the chamber. A light pipe which has an input end facing the output end of the chamber extends into the chamber and extracts light which is processed in red, green, and blue channels having temperature stabilized phototransducer circuitry and control circuitry wherein signals corresponding to the intensity of the color components are processed in the channels and are modified by control signals which can be produced in the photo printer control computer. The control signals, as they may be modified, are compared in each channel with a time-variant, repetitive waveform synchronized to the AC line, which varies in accordance with an anti-log function and which provides control pulses. The control pulses are applied to switching circuitry which controls the power to each lamp. This circuitry thereby compensates for the nonlinearity in the transfer characteristic of the system. The illumination of the photographic paper is therefore accurately controlled.
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