JP3168723B2 - Video signal encoding device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video signal encoding apparatus for compressing an inter-frame difference signal of a moving image video signal such as a television signal, and more particularly to a video signal encoding apparatus capable of preventing an adverse effect when a scene change occurs. The present invention relates to a video signal encoding apparatus.

[0002]

2. Description of the Related Art Various encoding methods are known as methods for encoding a moving image video signal such as a television signal with high efficiency.
A hybrid coding scheme that combines orthogonal transform such as T (discrete cosine transform) is promising.

FIG. 3 shows an example of a specific configuration for explaining a hybrid coding system combining such motion compensation prediction and orthogonal transform. In FIG. 3, a moving image video signal such as a television signal is supplied to an input terminal 11. The input video signal is temporarily stored (delayed) in an image memory 12 such as a frame memory, and then sent to a motion detection circuit 13 and a subtractor 14. The output from the subtractor 14 is sent to an orthogonal transform circuit 15 where it is subjected to an orthogonal transform such as DCT (discrete cosine transform) and quantized by a quantizer 16 to be an inverse quantizer 17 serving as a local decoder. And an inverse orthogonal transform (for example, IDCT) circuit 18. The output from the inverse orthogonal transform circuit 18 of the local decoder is sent to an image memory 20 such as a frame memory via an adder 19. The output read from the image memory 20 is sent to the motion detection circuit 13 and the motion compensation circuit 21, and the motion detection information (such as a motion vector) from the motion detection circuit 13 is sent to the motion compensation circuit 21. The output from the motion compensation circuit 21 is sent to the subtractor 14 and the adder 19, respectively.

Here, the input video signal is transmitted to the image memory 12
, And are read out in blocks of a predetermined size (for example, 8 × 8 pixels) and processed. The motion detection circuit 13 compares the pixel value of the delayed input video signal block from the image memory 12 with the pixel value of the locally decoded video signal from the image memory 20 and determines that the pixel value of the input video signal block is A motion vector is detected based on a block in the locally decoded video signal that becomes smaller. The motion compensation circuit 21 outputs a reference block based on the motion vector, and the subtractor 14 calculates a difference between the input video signal block and the reference block. The difference output is orthogonally transformed by the orthogonal transformation circuit 15, quantized by the quantizer 16, sent to, for example, a variable length encoder 23 and subjected to variable length encoding.

[0005] Further, the output from the variable length encoder 23 is sent to, for example, a transmission frame construction circuit 24, combined with the motion vector from the motion detection circuit 13, and sent to a transmission memory 25. The transmission memory 25 temporarily stores codes to be transmitted, and controls the quantization by the quantizer 16 and the encoding by the variable-length encoder 23 so that the data amount per unit time becomes constant, for example. An output from the transmission memory 25 is taken out through an output terminal 26, transmitted through a communication line or the like, or recorded and reproduced on a recording medium.

[0006]

However, in such a hybrid encoding apparatus, adverse effects such as image degradation occur at the time of a scene change at which image contents are switched. In other words, if a motion vector is calculated between frames and corrected irrespective of a scene change, a motion vector is calculated using images of different scenes over two fields after the scene change, and an erroneous vector is generated. However, there is a disadvantage that a sufficient motion vector correction effect cannot be obtained. If processing corresponding to a scene change is not performed, it is necessary to reduce the compression ratio so that the amount of information generated at the time of the scene change does not exceed the transmission path capacity. However, there is a disadvantage that sufficient image quality cannot be obtained.

Here, in Japanese Patent Application Laid-Open No. 2-222388, during a certain frame period immediately after the start of the encoding process or a certain frame period after the scene change, the quantization step width is converted into a predetermined value, and Moving picture coding that reduces the number of generated codes for each block and reduces the number of times the coding process is stopped for each block to increase the number of blocks to be coded as a whole screen and reduce image quality degradation A method is disclosed. However, this technique does not devise the calculation of the motion vector at the time of a scene change, and does not solve the drawback that an erroneous vector is generated and a sufficient vector correction effect cannot be obtained.

[0008] The present invention has been made in view of such circumstances, and it is possible to obtain an appropriate motion vector when a scene change occurs, and to obtain a sufficient vector correction effect. It is an object of the present invention to provide a video signal encoding device.

[0009]

According to the video signal encoding apparatus of the present invention, a video signal for transmitting a current frame signal of a video signal and an inter-frame prediction signal to a difference means to encode a difference output signal. In the encoding apparatus of the above, a scene change detecting means for detecting a scene change of a video signal, and a switching means for switching between an inter-frame prediction signal and an inter-field prediction signal and sending the signal to the difference means, are provided. The above-mentioned problem is solved by switching the changeover switch when a scene change is detected and switching from the inter-frame prediction signal to the inter-field prediction signal for the second field after the scene change. I do.

[0010] Here, a motion detecting means for detecting the motion of the current frame signal, and a signal delayed by one frame or one field in accordance with the output from the motion detecting means, compensates for the motion between the frames or fields. It is preferable to provide a motion compensation unit that sends the prediction signal to the difference unit. In addition, the output video signal from the difference means is output after being orthogonally transformed and then quantized. The output is inversely quantized by the local decoding unit and then inversely orthogonally transformed and delayed by one frame or one field. It is preferable that the signal is sent to the difference means as the inter-frame or inter-field prediction signal.

[0011]

When a scene change is detected, switching from inter-frame prediction to inter-field prediction is performed.
Vector correction of the second field after the scene change can be performed, and vector correction is performed on the previous field that is the same scene, thereby suppressing generation of an information amount.

[0012]

FIG. 1 is a block circuit diagram showing a schematic configuration of an embodiment of a video signal encoding apparatus according to the present invention. In FIG. 1, the same reference numerals are given to portions corresponding to the respective portions in FIG. 3 described above. In FIG. 1, a moving image video signal such as a television signal is supplied to an input terminal 11. This moving image signal is output to the pre-processing unit 31.
Is sent to the scene change detection circuit 32 via The scene change detection circuit 32 can have various configurations. For example, a video signal input from the pre-processing unit 31 and
A comparison result (absolute value or square value, etc.) of each pixel by comparing the input video signal with a video signal delayed by one frame, for example
The scene change is detected by, for example, integrating the image data in units of frames. The scene change detection circuit 32 outputs the video signal delayed by one frame, for example, and the scene change detection output signal, and the output video signals are sent to the motion detection circuit 13 and the subtractor 14, respectively. The signal is sent to a changeover switch 34 described later as a changeover control signal.

The output from the subtractor 14 is supplied to the orthogonal transform circuit 1
5 and subjected to an orthogonal transform such as DCT (Discrete Cosine Transform), quantized by a quantizer 16, and an inverse quantizer 17 serving as a local decoder and an inverse orthogonal transform (for example, IDC).
T) is sent to a series circuit with the circuit 18. The output from the inverse orthogonal transform circuit 18 of the local decoder is supplied via an adder 19 to
The data is sent to the series circuit of the two field memories 20a and 20b corresponding to the image memory 20 of FIG. The one-field delayed output video signal read from the field memory 20a is supplied to the selected terminal a of the changeover switch 34,
The one-frame-delayed output video signal read from b is sent to the selected terminal b of the changeover switch 34, respectively. As described above, the changeover switch 34 is controlled to be switched in accordance with the scene change detection output signal from the scene change detection circuit 32. When a scene change is detected, the changeover switch 34 is set to the selected terminal a side. Connected to select terminal b side. The output video signal from the changeover switch 34 is sent to the motion detection circuit 13 and the motion compensation circuit 21, respectively. The motion vector information detected by the motion detection circuit 13 is sent to the motion compensation circuit 21. Motion compensation circuit 2
1, the inter-field prediction signal is output when the changeover switch 34 is connected to the selected terminal a, and the inter-frame prediction signal is output when the changeover switch 34 is connected to the selected terminal b. Alternatively, the inter-frame prediction signal is supplied to the subtractor 14 and the adder 1
9 respectively.

Here, the motion detection and the motion compensation operation for the input video signal, the orthogonal transform and the quantization process, etc. are performed as follows.
Since the configuration is the same as that of the video signal encoding device of FIG. 3 described above, the description is omitted. The output signal from the quantizer 16 is sent to, for example, the variable-length encoder 23 to perform variable-length encoding, and further, for example, is transmitted to the transmission memory via the transmission frame configuration circuit in the same manner as described with reference to FIG. You can send it.

Next, the operation of the embodiment shown in FIG. 1 will be described with reference to FIG. In this FIG. 2,..., N-1, N, N + 1,...
It is assumed that it is occurring at the boundary with one field.

FIG. 2A shows an output video signal from the pre-processing unit 31. The signal A is delayed by, for example, one frame (two fields) by passing through the scene change detection circuit 32, and becomes as shown in a signal B of FIG. This is time t _{1 at} the boundary between the field and the (N + 1) th field. The output video signal from the field memory 20a is as shown in FIG. 2C in which the signal B is delayed by one field, and the output video signal from the field memory 20b is that the signal C is further delayed by one field. The result is as shown in FIG. Further, the above-mentioned scene change detection output signal from the scene change detecting circuit 32, the field corresponding to the output video signal C from the memory 20a, the period of one field from the time t ₂ is a scene change timing of the signal C ( time t ₂ ~t ₃ between) only becomes "1" or "H" (high level). Changeover switch 34, the period (between times t ₂ ~t ₃₎ only switches to the selected terminal a, the motion to select one field delayed output video signal C from the field memory 20a detection circuit 13 and the motion compensation circuit 21 Send to That is, the output video signal from the changeover switch 34, as shown in F of FIG. 2, until the time t ₂ outputs a frame delayed output video signal D from the field memory 20b, the time t ₂ ~
only during t ₃ and outputs one field delayed output video signal C from the field memory 20a. This changeover switch 3
The output video signal F from 4 is motion-compensated and sent to the subtractor 14.

Therefore, in the subtractor 14, the time t ₂
2, the difference between the video signal B from the scene change detection circuit 32 and the inter-frame predicted video signal (corresponding to the timing of the signal D) delayed by one frame with respect to the signal B is calculated. An output signal N-1 'as shown in FIG.
N ′, etc., but when a scene change is detected (time t ₂
Between) is ~t _3, taking the difference between the one field delayed field predictive signal with respect to the signal B (corresponding to the timing of the signal C), the time t ₂ ~t ₃ in G of FIG. 2 That is, the signal N + 2 ″ is obtained from the signal of the Nth field by subtracting the signal of the (N−2) th field from the signal of the Nth field, and the signal N + 2 ″ is the signal of the N + 2th field. 3 shows an inter-field difference signal obtained by subtracting the signal of the (N + 1) th field from the signal of the first field.

[0018] From the above, in one field period immediately after the scene change detection time t _2, the same as the first field of the image after the scene change (the N + 1 field) and the next field (the N + 2 field) scenes Since an inter-field difference output is obtained, the occurrence of an information amount can be suppressed more favorably than a frame difference signal between different scenes. Therefore, since motion compensation using the field motion vector is performed for the second field after the scene change, erroneous motion vector correction can be reduced, and a sufficient vector correction effect can be obtained. In addition, since the previous field, which is the same scene, is vector-corrected, it is possible to reduce the amount of information generated, thereby improving the coding efficiency except for scene changes, and as a result, performing high-quality coding processing.

The present invention is not limited to the above embodiment. For example, the processing after obtaining the frame difference is not limited to the configuration shown in FIG. it can. In addition, it goes without saying that various changes can be made without departing from the spirit of the present invention.

[0020]

As is clear from the above description, according to the video signal encoding apparatus of the present invention, the current frame signal and the inter-frame prediction signal of the video signal are sent to the difference means to output the difference output signal. In a video signal encoding device that encodes, when a scene change of the video signal is detected,
Since the inter-frame prediction signal is switched from the inter-frame prediction signal to the inter-field prediction signal for the second field after the scene change, false detection of a motion vector in the second field of the scene change can be reduced, and erroneous motion vector correction can be performed. Can be reduced. In addition, since vector correction is performed in a field in the same scene, the amount of generated information can be reduced. Further, since the amount of information generated in the second field after the scene change is suppressed, the overall encoding efficiency can be increased, and as a result, high-quality encoding processing can be realized.

[Brief description of the drawings]

FIG. 1 is a block circuit diagram showing a schematic configuration of an embodiment of a video signal encoding apparatus according to the present invention.

FIG. 2 is a time chart for explaining the operation of the embodiment.

FIG. 3 is a block circuit diagram showing a general configuration of a video signal encoding device.

[Explanation of symbols]

 11 video signal input terminal 13 motion detection circuit 14 subtracter 15 orthogonal transform circuit 16 quantizer 17 · Inverse quantizer 18 ··· Inverse orthogonal transform circuit 19 ··· Adder 20 ··· Image memories 20a and 20b ··· Field memory 21 ··· Motion compensation circuit 31 pre-processing circuit 32 scene change detection circuit 34 changeover switch

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-59-128881 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H04N ^7/ 24-7/68

Claims (3)

(57) [Claims] 1. A video signal encoding device for transmitting a current frame signal of a video signal and an inter-frame prediction signal to a difference unit and encoding a difference output signal, wherein a scene change detection unit for detecting a scene change of the video signal. when, by switching the prediction signal and the inter-field predictive signal between frames is provided and switching means for sending to said difference means, and switching control of the changeover switch when a scene change is detected by the scene change detecting means, Sea
A video signal encoding apparatus for switching from the above-mentioned inter-frame prediction signal to the above-mentioned inter-field prediction signal for a second field after the change. 2. A motion detecting means for detecting a motion of the current frame signal; and a motion compensation for a signal delayed by one frame or one field in accordance with an output from the motion detecting means, thereby performing the inter-frame or inter-field prediction. 2. The video signal encoding apparatus according to claim 1, further comprising a configuration for transmitting the signal to the difference unit. 3. An output video signal output from the difference means is orthogonally transformed and then quantized, and the output is dequantized by a local decoding unit and then inversely orthogonally transformed.
2. The video signal encoding apparatus according to claim 1, further comprising a configuration in which a frame or an inter-field delay signal is sent to the difference means after a delay of one frame or one field.