Focus-adjustment signal generating apparatus and method, and imaging apparatus and method with manual focus adjustments

1. 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.

2. An imaging apparatus comprising:

a video signal generator configured to take an image of an object and generate a video signal carrying the image;

a filter configured to extract a high-frequency component at a specific frequency or higher from a luminance signal of the 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;

a selector configured to select a first chrominance difference signal that indicates a specific color in response to the 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;

a down converter configured to down-convert the focus-adjustment signal by decreasing at least either the number of lines in a vertical direction or the number of pixels in a horizontal direction of the focus-adjustment signal;

a display configured to display an image of the object with the specific color at an edge portion of the image; and

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;

wherein the extender includes:

a shift resister configured to shift 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.

3. A focus-adjustment signal generating method comprising the steps of:

extracting a high-frequency component at a specific frequency or higher from a luminance signal of an input video signal;

comparing 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;

extending 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

selecting 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 extending step includes the steps of:

shifting at least the first chrominance difference signal and outputting 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;

performing an AND operation to the period-length setting signal and the first N-bit output signals and outputting 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

performing 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.

4. An imaging method comprising the steps of:

taking an image of an object and generating a video signal carrying the image;

extracting a high-frequency component at a specific frequency or higher from a luminance signal of the input video signal;

comparing 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;

selecting a first chrominance difference signal that indicates a specific color in response to the 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;

down-converting the focus-adjustment signal by decreasing at least either the number of lines in a vertical direction or the number of pixels in a horizontal direction of the focus-adjustment signal;

displaying an image of the object with the specific color at an edge portion of the image; and

extending 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;

wherein the extending step including the steps of:

shifting the first chrominance difference signal and outputting 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;

performing an AND operation to the period-length setting signal and the first N-bit output signals and outputting 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

performing 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.