Patent ID: 8023037

Claim:
A focus-adjustment signal generating apparatus comprising: a filter configured to extract a high-frequency component at a specific frequency or higher from a luminance signal of an input video signal; a comparator configured to compare an absolute value of the high-frequency component with a specific reference value, to output a first detection signal when the absolute value is equal to or larger than the reference value whereas a second detection signal is output when the absolute value is smaller than the reference value; an extender configured to extend an output period of the first detection signal according to a period indicated by a period-length setting signal, to output an extended first detection signal; and a selector configured to select a first chrominance difference signal that indicates a specific color in response to the extended first detection signal whereas a second chrominance difference signal is selected to indicate an achromatic color in response to the second detection signal, the first or the second chrominance difference signal being output as a focus-adjustment signal; wherein the extender includes: a shift resister configured to shift at least the first chrominance difference signal and output the shifted chrominance difference signal as first N-bit output signals (N being an integer of 2 or more), each first output signal having a specific level that continues for a specific period; an AND logic unit configured to perform an AND operation to the period-length setting signal and the first N-bit output signals and output second N-bit output signals, each of a specific number of consecutive second output signals having the specific level, the number depending on the period-length setting signal; and an OR logic unit configured to perform an OR operation to the second N-bit output signals, to obtain an ORed output signal having the specific level that continues for a period that is the specific number times the specific period, the ORed output signal being output as the extended first detection signal.