| 摘要 |
PURPOSE:Not to be influenced by unevenness of sensitivity of an ITV camera and uneveness of illumination, by constituting so that a standard level at each display point can have a constant level difference against the video signal level in the condition of light is turned off. CONSTITUTION:At first, an indicator is made a state that a light is turned off, and a video signal is generated. This signal is held in order in the latch circuit LATCH through the sample holding circuit S/H and the A/D converting circuit A-D, and after that, it is stored through the gate B in the memory Mo for storing a data when a light is turned off. Subsequently, the image signal is formed again in the researchable state by closing the gate B and opening the gate A. In this case, a data from the LATCH is input to the subtracter SUB through the gata A. This SUB reads out a data formerly stored from the memory Mo, and derives the difference between both the input data. The comparator COMP of the next stage compares the input signal with the threshold level, and if the former is large, it outputs ''1'' by regarding as a light is turned on, and if the former is small, it outputs ''0'' by regarding as a light is turned off. |
