| 摘要 |
PROBLEM TO BE SOLVED: To determine the presence or the absence of an input video signal by a composite synchronizing signal generated by compositing the horizontal synchronizing signal and the vertical synchronizing signal of the input video signal. SOLUTION: The number of edges of the composite synchronizing signal of a video signal inputted from an input terminal 1 is counted with an input signal counter 3 for a period (T<SB>1</SB>) set with a period setting part 2. A counter value (X) is outputted. A value (A) which is based on a calculated value of the horizontal synchronizing signal in the period (T<SB>1</SB>) set with a range setting part 5, a value (B) in consideration of a calculated value of the composite synchronizing signal and a noise component caused by a weak electric field, and the counter value (X) are counted with a counter (Y<SB>1</SB>) when it is A≤X≤B, and otherwise counted with a counter (Y<SB>2</SB>) in a counter value comparison processor 4. An up/down counter is subjected to up-processing when the counter value of the (Y<SB>1</SB>) reaches an upper limit value (C) set with an upper limit setting part 7 in an up/down counter 8. When the counter value of the (Y<SB>2</SB>) reaches an upper limit value (D), the up/down counter is subjected to down-processing. The presence or the absence of the input video signal is determined by using an up/down counter value with a signal presence/absence determining part 10. COPYRIGHT: (C)2006,JPO&NCIPI
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