| 摘要 |
PROBLEM TO BE SOLVED: To quickly adjust a luminous quantity without causing hunting in response to a change in the lightness of a screen on which an object is displayed. SOLUTION: A processor 10 of an endoscope is provided with a histogram processing circuit 16, an aperture control circuit 17, an aperture 18, a light source 19 and a stepping motor 26. A luminance is periodically calculated on the basis of histogram data obtained by the histogram processing circuit 16 and a moving amount (moving angle) of the aperture 18 is obtained depending on a difference between the luminance value and a reference value. The aperture control circuit 17 gives number of pulses in response to the obtained moving amount to the stepping motor 26. Then the aperture is driven for each prescribed period in matching with the step motion of the stepping motor 26 to adjust a luminous quantity led from the light source 19 to an object. When the moving amount of the aperture 18 is larger than the prescribed moving amount, the aperture 18 is driven at next adjustment of the luminous quantity.
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