Pull-down signal detecting apparatus, pull-down signal detecting method, and video-signal converting apparatus

1. A pull-down signal detecting apparatus comprising:

a difference-calculating circuit which finds a difference between the present field signal of an input video signal and a signal delayed by one field with respect to the present field signal;

an inter-field correlation determination circuit which compares the difference output from the difference-calculating circuit, with a first comparison value, adds the result of the comparison for each field, compares the result of the addition with a second comparison value and determines an inter-field correlation level;

a first determination circuit which determines whether the input video signal is one of a first pull-down signal and a second pull-down signal for each field period, on pattern of consecutive inter-field correlation levels obtained by the inter-field correlation determination circuit;

a second determination circuit which comprises a first counter configured to count the number of times the first determination circuit determines that the input video signal is the first pull-down signal, and which determines that the input video signal is the first pull-down signal, when the count of the first counter exceeds a first preset value; and

a resetting unit which resets the count of the first counter to “0” when the first determination circuit determines that the input video signal is a signal other than the first and second pull-down signals, and which maintains the count of the first counter

when the first determination circuit determines that the input video signal is the second pull-down signal,

the first pull-down signal is a signal generated by converting a 24-frame-per second progressive-scan video signal representing an image composed of different frame images, to one of a 2-3 pull-down signal and a 2-2 pull-down signal, and the second pull-down signal is a signal generated by converting a 24-frame-per second progressive-scan video signal representing an image composed of frame images including consecutive identical images, to a 2-3 pull-down signal or a 2-2 pull-down signal.

2. The pull-down signal detecting apparatus according to claim 1 , further comprising:

a first flag unit configured to set a flag when the first determination circuit determines that the input video signal is the first pull-down signal and to supply data representing the state of the flag, as the first flag information, to the first determination circuit,

wherein the first determination circuit determines that the input video signal is the second pull-down signal when the input video signal is not the first pull down signal and the first flag is set.

3. The pull-down signal detecting apparatus according to claim 2 , further comprising a third determination circuit which comprises a second counter configured to count the number of times the first determination circuit determines that the input video signal is the second pull-down signal, and which determines that the input video signal is a signal other than the first and second pull-clown signal and resets the counts of the first and second counters to “0,” when the count of the third counter exceeds a second preset value.

4. A video-signal converting apparatus comprising:

a field delaying circuit which provides a one-field-delayed signal generated by delaying the present field of an input video signal by one field, and a two-field-delayed signal generated by delaying the one-field-delayed signal by one field;

an interpolated signal generating circuit which generates a first interpolated signal from at least one of the present field signal, the one-field-delayed signal and the two-field-delayed signal;

a pull-down signal detecting circuit which detects a pull-down signal from the present field signal, the one-field-delayed signal and the two-field-delayed signal;

a first selector which selects one of the first and second interpolated signals on the basis of the result of detection performed by the pull-down signal detecting circuit and which provides the selected signal as a pair-field signal;

a second selector which selects one of the first interpolated signal and the pair-field signal on the basis of the result of detection performed by the pull-down signal detecting circuit and which provides the selected signal as a second interpolated signal; and

a conversion circuit which synthesizes the one-field-delayed signal and the second interpolated signal, thereby providing a progressive-scan signal,

the pull-down signal detecting circuit comprising:

a difference-calculating circuit which finds a difference between the present field signal and the one-field-delayed signal;

an inter-field correlation determination circuit which compares a first difference value output from the difference-calculating circuit, with a first comparison value, adds the result of the comparison for each field, compares the result of the addition with a second comparison value for each field and determines an inter-field correlation level;

a first determination circuit which determines whether the input video signal is one of a first pull-down signal and a second pull-down signal for each field period, on the basis of a pattern off consecutive inter-field correlation levels obtained by the inter-field correlation determination circuit;

a first flag unit which sets a flag when the first determination circuit determines that the input video signal is the first pull-down signal, and which supplies data representing the state of the flag, as the first flag information, to the first determination circuit;

a second determination circuit which comprises a first counter configured to count the number of times the first determination circuit determines that the input video signal is the first pull-down signal, and which determines that the input video signal is the first pull-down signal, when the count of the first counter exceeds a first preset value; and

a resetting unit which resets the count of the first counter to “0” when the first determination circuit determines that the input video signal is a signal other than the first and second pull-down signals, and which maintains the count of the first count when the first determination circuit determines that the input video signal is the second pull-down signal,

the first pull-down signal is a signal generated by converting a 24-frame-per second progressive-scan video signal representing an image composed of different frame images, to one of a 2-3 pull-down signal and a 2-2 pull-down signal, and the second pull-down signal is a signal generated by converting a 24-frame-per second progressive-scan video signal representing an image composed of frame images including consecutive identical images, to a 2-3 pull-down signal or a 2-2 pull-down signal.

5. The video-signal converting apparatus according to claim 4 , further comprising:

a first flag unit configured to set a flag when the first determination circuit determines that the input video signal is the first pull-down signal and to supply data representing the state of the flag, as the first flag information, to the first determination circuit,

wherein the first determination circuit determines that the input video signal is the second pull-down signal when the input video signal is not the first pull down signal and the first flag is set.

6. The video-signal converting apparatus according to claim 5 , wherein the first pull-down signal is a signal generated by converting a 24-frame-per second progressive-scan video signal representing an image composed of different frame images, to one of a 2-3 pull-down signal and a 2-2 pull-down signal, and the second pull-down signal is a signal generated by converting a 24-frame-per second progressive-scan video signal representing an image composed of frame images including consecutive identical images, to one of a 2-3 pull-down signal and a 2-2 pull-down signal.

7. A pull-down signal detecting method comprising:

providing a difference between the present field signal of an input video signal and a signal delayed by one field with respect to the present field signal;

comparing the difference output from the difference-calculating circuit, with a first comparison value, adding the result of the comparison for each field, comparing the result of the addition with a second comparison value, determining an inter-field correlation level and providing the inter-field correlation level;

determining whether the input video signal is one of a first pull-down signal and a second pull-down signal for each field period, on the basis of a pattern of the consecutive inter-field correlation levels, and providing the result of the determination as a result of signal determination;

setting a flag when the input video signal is determined to be the first pull-down signal, and providing data representing the state of the flag, as the first flag information;

counting the number of times the input video signal is determined to be the first pull-down signal, and finally determining that the input video signal is the first pull-down signal, when the counted number of times exceeds a first preset value; and

resetting the number of times counted to “0” when the input video signal is determined to be a signal other than the first and second pull-down signals, and maintaining the count of the first count when the first determination circuit determines that the input video signal is the second pull-down signal,

wherein the first pull-down signal is a signal generated by converting a 24-frame-per second progressive-scan video signal representing an image composed of different frame images, to one of a 2-3 pull-down signal and a 2-2 pull-down signal, and the second pull-down signal is a signal generated by converting a 24-frame-per second progressive-scan video signal representing an image composed of frame images including consecutive identical images, to a 2-3 pull-down signal or a 2-2 pull-down signal.