Scene change detector for detecting a scene change of a moving picture

1. A scene change detector for detecting a scene change of a moving picture reproduced by a series of frames of pictures, comprising:

activity calculating means for calculating an activity of each of the frames of pictures, the activity of a frame of picture denoting a sum of absolute values of digital picture signals which indicate the picture, and a second activity ACT2 of a current frame of picture being calculated after a first activity ACT1 of a preceding frame of picture is calculated;

first activity storing means for storing the second activity ACT2 calculated by the activity calculating means;

second activity storing means for storing the first activity ACT1 calculated by the activity calculating means; and

scene change judging means for judging whether or not a scene change of the moving picture occurs in the current frame of picture by comparing the second activity ACT2 stored in the first activity storing means and the first activity ACT1 stored in the second activity storing means, the occurrence of the scene change being detected in cases where the first activity ACT1 greatly differs from the second activity ACT2.

2. A detector according to claim 1 in which the activity calculating means includes:

bandpass filter means for extracting frequency components in a predetermined band from digital picture data composing each of the frames of pictures;

absolute value calculating means for calculating absolute values of the frequency components extracted by the bandpass filter means; and

accumulating means for accumulating the absolute values calculated by the absolute value calculating means to obtain a summed value denoting the activity of each of the frames of pictures.

3. A detector according to claim 2 in which the scene change judging means includes:

a calculator for calculating a degree of difference between the first activity ACT1 and the second activity ACT2 according to a scene change judging equation (1),

RC=.vertline.ACT1-ACT2.vertline./(ACT1+ACT2) (1)

where the symbol RC denotes a judging value indicating the degree of the difference; and

a judging circuit for judging that a scene change of the moving picture occurs in the current frame of picture in cases where the judging value RC is equal to or larger than a threshold value.

4. A scene change detector for detecting a scene change of a moving picture reproduced by a series of frames of pictures, comprising:

picture dividing means for dividing each of the frames of pictures into a plurality of divided pictures, a current frame of picture being divided into a plurality of divided current pictures after a preceding frame of picture is divided into a plurality of divided preceding pictures;

activity calculating means for calculating activities of the divided pictures obtained in the picture dividing means each time a frame of picture is divided in the picture dividing means, an activity of a divided picture denoting a sum of absolute values of digital picture signals which indicate the divided picture, and second activities ACT2(n) (n is a natural number) of the divided current pictures being calculated after first activities ACT1(n) of the divided preceding pictures are calculated;

first activity storing means for storing the second activities ACT2(n) calculated by the activity calculating means;

second activity storing means for storing the first activities ACT1(n) calculated by the activity calculating means; and

scene change judging means for judging whether or not a scene change of the moving picture occurs in the current frame of picture by comparing the second activities ACT2(n) stored in the first activity storing means and the first activities ACT1(n) stored in the second activity storing means, the occurrence of the scene change being detected in cases where the first activities ACT1(n) greatly differ from the second activities ACT2(n).

5. A detector according to claim 4 in which the activity calculating means includes:

bandpass filter means for extracting frequency components in a predetermined band from digital picture data composing each of the divided pictures;

absolute value calculating means for calculating absolute values of the frequency components extracted by the bandpass filter means; and

accumulating means for accumulating the absolute values calculated by the absolute value calculating means to obtain a summed value denoting the activity of each of the divided pictures.

6. A detector according to claim 5 in which the scene change judging means includes:

a calculator for calculating degrees of differences between each of the first activities ACT1(n) and each of the second activities ACT2(n) according to a scene change judging equation (1),

RC(n)=.vertline.ACT1(n)-ACT2(n).vertline./(ACT1(n)+ACT2(n))(1)

where the symbol RC(n) denotes judging values indicating the degrees of the differences; and

a judging circuit for judging that a scene change of the moving picture occurs in the current frame of picture in cases where a ratio of the number of judging values RC(n) equal to or larger than a threshold value to the number of judging values RC(n) is greater than a predetermined value.

7. A scene change detector for detecting a scene change of a moving picture reproduced by a series of frames of pictures in which a plurality of rows each consisting of an I-frame or P-frame of picture and one or more B-frames of pictures are arranged in series, comprising:

frame storing means for storing a frame of picture one after another from among the frames of pictures;

switching means for switching on to pass an I-frame or P-frame of picture in cases where the I-frame or P-frame is stored in the frame storing means and switching off not to pass a B-frame of picture in cases where the B-frame is stored in the frame storing means;

activity calculating means for calculating an activity of each of the I-frames and P-frames of pictures passing through the switching means, the activity of an I-frame or P-frame of picture denoting a sum of absolute values of digital picture signals which indicate the picture, and a second activity ACT2 of a current P-frame of picture being calculated after a first activity ACT1 of a preceding I-frame or P-frame of picture is calculated;

first activity storing means for storing the second activity ACT2 calculated by the activity calculating means;

second activity storing means for storing the first activity ACT1 calculated by the activity calculating means;

scene change judging means for judging whether or not a scene change of the moving picture occurs in the current P-frame of picture by comparing the first activity ACT1 stored in the second activity storing means and the second activity ACT2 stored in the first activity storing means and outputting a judging flag indicating the occurrence of the scene change, the occurrence of the scene change being detected in cases where the first activity ACT1 greatly differs from the second activity ACT2; and

interframe predictive coding means for predicting the current I-frame or P-frame of picture with the preceding P-frame of picture stored in the frame storing means to encode the current P-frame of picture predicted in cases where the judging flag indicating the occurrence of the scene change is not output from the scene change judging means, and encoding the current P-frame of picture without any prediction in cases where the judging flag indicating the occurrence of the scene change is output from the scene change judging means.

8. A detector according to claim 7 in which the activity calculating means includes:

bandpass filter means for extracting frequency components in a predetermined band from digital picture data composing each of the I-frames and P-frames of pictures;

absolute value calculating means for calculating absolute values of the frequency components extracted by the bandpass filter means; and

accumulating means for accumulating the absolute values calculated by the absolute value calculating means to obtain a summed value denoting the activity of each of the I-frames and P-frames of pictures.

9. A detector according to claim 8 in which the scene change judging means includes:

a calculator for calculating a degree of difference between the first activity ACT1 and the second activity ACT2 according to a scene change judging equation (1),

RC=.vertline.ACT1-ACT2.vertline./(ACT1+ACT2) (1)

where the symbol RC denotes a judging value indicating the degree of the difference; and

a judging circuit for judging that a scene change of the moving picture occurs in the current P-frame of picture in cases where the judging value RC is equal to or larger than a threshold value.