| 摘要 |
A projection television display apparatus comprises a display device with an image formed for projection and a display screen for receiving the projected image. A plurality of photo sensors are located adjacent to edges of the display screen and each generates an output signal responsive to an intensity of illumination by the projected image. A detector with controllable detection threshold is coupled to the photo sensors for generating a signal having a first state when the output signal generated by each of the plurality photo sensors is greater than the detection threshold, and a second state when the output signal generated by each of said plurality photo sensors is less than the detection threshold. A controller is coupled to the display device and to the detector for setting the detection threshold for the output signal generated by each one of the plurality of photo sensors. In response to the signal having the first state, the controller moves the image on the display device to sequentially illuminate another one of the plurality of photo sensors.
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