| 摘要 |
PURPOSE:To detect an image suitable for auto-focusing with a high probability by using the output signal of a line sensor for an area a certain length or longer distant from the peripheral edge of an image projection face to detect the image and making it difficult that dust and flaws have an influence when the line sensor is moved to detect the image. CONSTITUTION:The slice level for image detection is changed on the basis of the output of a specified picture element of a line sensor 40 while moving the line sensor 40, and the image detecting operation to discriminate the presence or the absence of a proper image is performed in parallel with this slice level change. A control means 50 discriminates the in-focus state on the basis of the output signal of the line sensor, and the auto-focusing operation to move a projection lens 20 to the in-focus position by a motor 51, the control of a printer 34, movement of reflection mirrors 22, 24, and 30, etc., are performed. A CPU 52 sends a signal (a), which commands a proper frequency, to a clock generator 54, and a driving pulse (b) having this commanded frequency is sent to the line sensor 40 to successively send an output signal (c) of respective picture elements to an amplifier 56. Thus, the image suitable for auto-focusing is detected with a high probability to reduce the malfunction.
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