JP4561701B2 - Video encoding device - Google Patents

Description

  The present invention relates to a moving image encoding apparatus, and more particularly to a moving image encoding apparatus that divides image data related to a moving image into blocks having a predetermined number of pixels and performs compression encoding using motion compensated prediction in units of the blocks.

  Currently, a number of compression coding standards that efficiently compress and encode image data related to moving images have been standardized, and storage media such as magnetic tape, DVD (Digital Versatile Disc), semiconductor memory, satellite digital broadcasting, the Internet, etc. Widely used in the broadcasting and communication field.

  In a typical MPEG (Moving Picture Experts Group) among the above compression coding standards, moving image data obtained by interlace scanning is encoded by switching between an interlace structure and a frame structure in a predetermined block unit. This is because the field structure moving image data is compared with the frame structure moving image data, and the vertical pixel spatial correlation (spatial resolution) is low because the vertical pixels are thinned out. Since the pixel time correlation (temporal resolution) is high because it is expressed in two fields, in the case of image data with little temporal change and little motion, encoding with a frame configuration with high spatial resolution will improve efficiency. On the contrary, in the case of image data with a large temporal change and a lot of movement, it is because efficiency is improved if encoding is performed with a field configuration with a high temporal resolution.

  In view of this, there has been disclosed a moving image encoding apparatus that compares the pixel correlation values in the vertical direction of the frame structure and the field structure and encodes the structure having the higher correlation (see, for example, Patent Document 1).

Japanese Patent No. 3125145

  However, the moving picture encoding apparatus described in Patent Document 1 has the following problems. In general, in a moving image encoding apparatus that compresses and encodes moving image data in units of blocks, an I frame that performs only intra-coding on moving image data, a P frame that performs unidirectional inter-image predictive encoding, There are a total of three frame types (picture type as a prediction type) of B frames that perform bidirectional inter-picture prediction encoding. In the I frame, all blocks are intra-coded, in the P frame, intra-frame coding and unidirectional inter-picture prediction coding are switched on a block basis, and in the B frame, intra-frame coding and unidirectional inter-picture coding on a block basis. Predictive coding and bidirectional inter-picture predictive coding are switched. In the above-described moving picture encoding apparatus, regardless of the frame type, the pixel correlation value in the vertical direction of the frame structure and the field structure in one image is compared, and the structure having the higher correlation is encoded.

  When performing intra-picture coding, it can be expected that the coding efficiency will be improved by selecting a highly correlated structure obtained from the activity. However, when performing inter-picture prediction coding, the inter-picture prediction efficiency is improved. Therefore, the selection of a highly correlated structure obtained from the activity in one image does not necessarily lead to an improvement in coding efficiency. Therefore, the encoding efficiency is further improved by considering the inter-picture prediction efficiency in addition to the activity in one image.

  That is, as shown in FIG. 6 (a), the inter-picture prediction distance in the frame structure in which the display is switched every frame of 1/30 seconds in the order of F0, F1, and F2 is 1/30 seconds, while FIG. As shown in b), the top field fT0 and the bottom field fB0 of the frame 0, the top field fT1 of the next frame 1, the bottom field fTB1, the top field fT2 of the next frame 2, and the bottom field fTB2 in this order are 1/60 seconds. The predicted distance between images in the field structure in which the display is switched for each field is 1/60 seconds. Since moving images are correlated in the time direction, the prediction efficiency increases as the inter-image prediction distance is shorter.

  Therefore, for frame types (P frames and B frames) for which inter-picture prediction encoding is performed, it is possible to improve inter-picture prediction efficiency by increasing the selection rate of the field structure. In particular, the effect can be expected for a moving image having a complicated and detailed movement with a feature in which field / frame determination tends to be ambiguous.

  The present invention has been made in view of the above points. By changing the selection rate of the frame structure and the field structure according to the frame type, the inter-picture prediction efficiency is improved, and an encoded signal having a suitable image quality is obtained. It is an object of the present invention to provide a moving image encoding device that can be generated.

  In order to achieve the above object, the present invention comprises a plurality of first blocks, with an incoming moving image signal obtained by interlace scanning as a minimum encoding unit of a first block having a predetermined first number of pixels. In a moving image encoding apparatus that obtains an encoded image signal by performing intra-image encoding or inter-image predictive encoding for each predetermined image unit, an incoming moving image signal having a second number of pixels smaller than the first number of pixels. A first calculation means for calculating a block frame activity indicating a vertical inter-pixel energy of a frame structure in a second block unit; and an incoming moving image signal for a vertical inter-pixel energy of a field structure in a second block unit. A second calculating means for calculating the indicated block field activity, and a prediction indicating whether each image unit of the moving image signal is encoded by intra-picture encoding or inter-picture predictive encoding. A type signal and a block frame activity and a block field activity are supplied, and based on the block field activity, an FI that is a value related to the field activity in the first block to be encoded is generated, and the current encoding target When the prediction unit signal of the image unit including one block indicates intra-picture encoding, FR1 that is a value related to the frame activity in the first block to be encoded is generated based on the block frame activity; When the prediction type signal for each image including the first block to be encoded indicates inter-picture prediction encoding, a value related to the frame activity in the first block to be encoded based on the block frame activity In , Generating means for generating FR2 having a value greater than FR1, and when FI is greater than FR1 or FI is greater than FR2, control is performed so that the first block to be encoded is encoded in a frame structure. When FI is smaller than FR1 or FI is smaller than FR2, control is performed so that the first block to be encoded is encoded with a field structure. When FI is equal to FR1 or FI is equal to FR2 And coding structure determining means for controlling to encode the first block to be coded with either the field structure or the frame structure.

  In the present invention, when intra-picture encoding is performed, the FI generated based on the block field activity is compared with FR1 generated based on the block frame activity, and when performing inter-picture predictive encoding, the above-described FI and block frame are compared. Compared with FR2 having a value greater than FR1 generated based on the activity, and when FR1 or FR2 is greater than FI, an encoded image signal encoded with a field structure is output, but FR2 is more than FR1. Therefore, when inter-picture predictive coding is performed, a coded image signal coded with a field structure can be output with higher probability than when intra-picture coding is performed.

  According to the present invention, by making the selection rate of the frame structure and the field structure variable according to the frame type, in particular, a moving image with a lot of complicated and fine motion having a characteristic that field / frame determination is likely to be ambiguous. Therefore, it is possible to provide a moving image coding apparatus having a suitable image quality, and when performing inter-picture predictive coding, a coded image signal coded with a field structure is higher than when performing intra-picture coding. Since output is performed with a probability, a field structure with high prediction efficiency can be prioritized in inter-picture prediction encoding, and an optimal encoded image signal more suitable for the frame type can be selected and output.

  Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a configuration diagram of an embodiment of a moving picture encoding apparatus according to the present invention. FIG. 2 is a flowchart for explaining the overall operation of an embodiment of the moving picture coding apparatus according to the present invention. The configuration and operation of the embodiment of FIG. 1 will be described with reference to FIG. First, an input image signal a which is an interlace scanning moving image signal to be encoded is a prediction type signal indicating whether each image unit of the image signal a is encoded by intra-picture encoding or inter-picture predictive encoding. It is input to the coding structure determiner 11 together with the frame type signal b. The coding structure determiner 11 determines whether to encode the input image signal with a frame structure or a field structure for each basic block in accordance with the frame type signal b with the configuration described later (step S100). An encoded structure signal c indicating the structure and an encoding target image signal d are output.

  Here, the encoding target image signal d is an image signal in which the input image signal a is arranged in the frame structure if the encoding structure signal c indicates the frame structure, and the encoding structure signal c indicates the field structure. For example, the input image signal a is an image signal arranged in a field structure. The basic block uses a macroblock unit (16 horizontal pixels × 16 vertical pixels). Note that the basic block may be a macroblock pair unit (horizontal 16 pixels × vertical 32 pixels).

  The encoded structure signal c and the encoding target image signal d are given to the motion detector 13. The motion detector 13 obtains a motion vector from the encoding target image signal d and the reference image signal from the image memory 23 according to the encoding structure signal c (step S101). The motion compensation predictor 14 generates a prediction signal from the motion vector from the motion detector 13 and the reference image signal from the image memory 23 (step S102), and sends it to the subtractor 12. The subtracter 12 subtracts the prediction signal from the motion compensated predictor 14 from the encoding target image signal d to generate a prediction error signal (step S103).

  The orthogonal transformer 15 performs orthogonal transformation processing of the prediction error signal from the subtracter 12 (step S104), and gives the obtained coefficient to the quantizer 16. The quantizer 16 quantizes the coefficients with a predetermined quantization step width (step S105), and supplies the quantized coefficients to the entropy encoder 17 and the inverse quantizer 19. The entropy encoder 17 performs entropy encoding on the quantized coefficient according to a predetermined method (step S106). The multiplexer 18 multiplexes the header information together with the frame type signal b, the encoded structure signal c, the motion vector, the entropy-encoded code string, and the like (step S107), and generates and outputs a moving image code signal e.

  On the other hand, the inverse quantizer 19 inversely quantizes the quantized coefficient from the quantizer 16 (step S108), and the inverse orthogonal transformer 20 applies the inverse quantized signal from the inverse quantizer 19 to the inversely quantized signal. Then, a process reverse to the orthogonal transform is performed to reproduce the prediction error signal (step S109). The adder 21 adds the prediction error signal from the inverse orthogonal transformer 20 and the prediction signal from the motion compensation predictor 14 (step S110), and generates a locally decoded reproduced image signal. The reproduced image signal is supplied to and stored in the image memory 23 (step S112) after deblocking processing for reducing block distortion occurring at the time of encoding is performed by the loop filter 22 (step S111). The reproduced image signal stored in the image memory 23 is read as necessary and supplied to the motion detector 13 and the motion compensation predictor 14 as a reference image signal.

  Next, the configuration and operation of the coding structure determiner 11 that is a characteristic component of the moving picture coding apparatus according to the present embodiment will be described in more detail. FIG. 3 shows a block diagram of an embodiment of a coding structure determiner 11 which is a characteristic component of the moving picture coding apparatus according to the present invention. As shown in FIG. 3, the coding structure determiner 11 includes a frame activity calculator 111, a field activity calculator 112, and a determiner 113.

  As shown in FIG. 5A, the frame activity computing unit 111 is an activity block unit (horizontal 8 pixels) among the top field (odd field) pixels indicated by white circles and the bottom field (even field) pixels indicated by black circles. The block frame activity is calculated for each of (vertical 8 pixels) according to the formula (1) described later. This block frame activity is the sum of energy between two lines of pixels adjacent in the vertical direction.

  In addition, as shown in FIG. 5B, the field activity calculator 112 is an activity block unit among the pixels in the top field (odd field) indicated by white circles or the pixels in the bottom field (even field) indicated by black circles. For each (8 horizontal pixels × 8 vertical pixels), a block field activity is calculated according to equation (2) described later. This block field activity is the sum of energy between two adjacent pixels in the vertical direction.

ここで、（１）式及び（２）式はエネルギーを垂直画素間絶対差分とみなしたアクティビティ算出方法の一例である。また、（１）式、（２）式中、Ｐ（ｘ，ｙ）はフレーム画像における水平座標ｘ、垂直座標ｙにおける画素値であり、Ｐ（ｘ，ｙ＋１）は画素値Ｐ（ｘ，ｙ）の画素より異なるフィールドの１ライン下側に隣接する画素の画素値であり、Ｐ（ｘ，ｙ＋２）は画素値Ｐ（ｘ，ｙ）の画素と同じフィールドの１ライン下側に隣接する画素の画素値である。

Here, equations (1) and (2) are examples of an activity calculation method in which energy is regarded as an absolute difference between vertical pixels. In the expressions (1) and (2), P (x, y) is the pixel value at the horizontal coordinate x and the vertical coordinate y in the frame image, and P (x, y + 1) is the pixel value P (x, y). ) Is a pixel value of a pixel adjacent to one line below the different field, and P (x, y + 2) is a pixel adjacent to one line below the same field as the pixel having the pixel value P (x, y). Pixel value.

  In FIG. 3, the determiner 113 receives the frame type signal b and the output signals of the frame activity calculator 111 and the field activity calculator 112 as inputs, and encodes each basic block with a frame structure or a field structure. The coding structure signal c indicating the frame / field structure and the coding target image signal d are output.

  Next, the operation of the embodiment of FIG. 3 will be described with reference to the flowchart of FIG. In FIG. 3, an input image signal a is input to a frame activity calculator 111 and a field activity calculator 112. The frame activity calculator 111 calculates and outputs a block frame activity (Block Frame Activity) based on the equation (1) for each activity block (horizontal 8 pixels × vertical 8 pixels) for the input image signal a. In parallel with this, the field activity calculator 112 performs block field activity on the input image signal a based on the equation (2) for each activity block (horizontal 8 pixels × vertical 8 pixels). Is calculated and output.

  The determiner 113 receives the frame type signal b and the output signals of the frame activity calculator 111 and the field activity calculator 112 as inputs. First, the frame type of the input image signal a to be encoded is determined from the frame type signal b. Is an I frame, a P frame, or a B frame (step S201).

  Further, the determiner 113 calculates the frame activity (FrameActivity) of the basic block from the block frame activity (Block Frame Activity) from the frame activity calculator 111 and at the same time the block field activity (Block Field Activity) from the field activity calculator 112. ) To calculate the basic block field activity (FieldActivity). Here, the frame activity (FrameActivity) of the basic block is the sum of the four block frame activities (Block Frame Activity) included in the basic block, and the field activity (FieldActivity) of the basic block and 4 included in the basic block. It is the sum of two block field activities and is represented by the following equation.

FrameActivity = ΣBlock Frame Activity (3)
FieldActivity = ΣBlock Field Activity (4)
The method for calculating the basic block frame (field) activity is not limited to the sum of the four block frame (field) activities. The minimum value, maximum value, average value, etc. of the four block frame (field) activities can also be used.

If the determination unit 113 determines in step S201 that the frame type signal b is an I frame, the following expression FR = FrameActivity (5)
FI = FieldActivity (6)
To calculate the frame activity FR and the field activity FI, respectively (step S203).

If the determination unit 113 determines in step S201 that the frame type signal b is a P frame, the following expression FR = FrameActivity + Op (7)
FI = FieldActivity (8)
To calculate the frame activity FR and the field activity FI, respectively (step S202). If the determination unit 113 determines in step S201 that the frame type signal b is a B frame, FR = FrameActivity + Ob (9)
FI = FieldActivity (10)
Thus, the frame activity FR and the field activity FI are calculated respectively (step S204). That is, when the frame type is P frame or B frame, the determiner 113 has positive offset values Op, Ob (that is, Op> 0, so that the value of the frame activity FR is larger than that of the I frame. Ob> 0) is added.

  Subsequently, the determiner 113 determines whether or not the frame activity FR and the field activity FI calculated in step 202, 203, or 204 satisfy FR ≦ FI (step S205). When FR ≦ FI, The field structure is determined (step S206). If FR> FI, the field structure is determined (step S207). This is because, among FR and FI, the smaller the value, the higher the correlation. When FR = FI, the field structure may be determined (if the equal sign holds, either coding structure may be selected).

  The determiner 113 generates and outputs an encoded structure signal c indicating the frame structure / field structure determined in this way. The determination unit 113 controls the subsequent encoding so that the input image signal a is encoded as a frame structure if the encoding structure signal c indicates a frame structure, and the encoding structure signal c indicates a field structure. Then, the subsequent encoding is controlled so that the input image signal a is encoded as a field structure.

  As described above, in the present embodiment, in the P frame and the B frame, which are frame types for performing inter-picture predictive coding, the positive value offset is set so that the value of the frame activity FR is larger than that in the I frame. The values Op and Ob are added because the P frame and the B frame are not related to the coding efficiency as much as the I frame in which the frame activity of the P frame or the B frame performing the inter-picture prediction performs the intra-picture coding. This is because priority is given to a field structure with high prediction efficiency.

  As described above, according to the present embodiment, by making the selection rate of the frame structure and the field structure variable according to the frame type, the field / frame determination is particularly complicated with the characteristic that the field / frame determination tends to be ambiguous. It is possible to provide a moving image encoding device having a suitable image quality for moving images with many fine movements.

  The present invention is not limited to the above embodiment, and 0 <Op <Ob is set, and the B frame is set to give priority to the field structure with higher prediction efficiency than the P frame. May be. In this embodiment, the offset value is controlled according to the frame type signal as the prediction type signal. However, it is also possible to control this according to the slice type signal as the prediction type signal (for example, a frame or The prediction type [intra-image prediction, unidirectional prediction, bidirectional prediction] may be set in slice units, which are image units smaller than the field, in order to cope with this).

  The present invention also includes a moving image encoding program that causes a computer to execute the configuration shown in FIGS. Here, the moving picture encoding program may be taken into a computer from a recorded recording medium, distributed via a communication network, taken into the computer, or further incorporated into the computer as firmware. It may be.

It is a block diagram of one embodiment of a moving picture coding apparatus of the present invention. It is a flowchart for operation | movement description of one Embodiment of the moving image encoder of this invention. It is a block diagram of one Embodiment of the encoding structure determination device of the principal part of the moving image encoder of this invention. It is a flowchart for operation | movement description of the encoding structure determiner of FIG. It is a figure explaining the frame activity and the field activity in the Example of the moving image encoder of this invention. It is a figure explaining a frame structure and a field structure.

Explanation of symbols

a input image signal b frame type signal c encoding structure signal d encoding target image signal e moving image code signal 11 encoding structure determiner 12 subtractor 13 motion detector 14 motion compensation predictor 15 orthogonal transformer 16 quantizer 17 Entropy Encoder 18 Multiplexer 19 Inverse Quantizer 20 Inverse Orthogonal Transformer 21 Adder 22 Loop Filter 23 Image Memory 111 Frame Activity Calculator 112 Field Activity Calculator 113 Determinator

Claims (1)

Intra-picture coding is performed for each predetermined image unit including a plurality of the first blocks, with the first block having a predetermined first number of pixels as the incoming video signal by interlace scanning as a minimum coding unit. Alternatively, in a video encoding device that obtains an encoded image signal by performing inter-picture prediction encoding,
First calculation means for calculating a block frame activity indicating vertical inter-pixel energy of a frame structure in the second block unit having a second pixel number smaller than the first pixel number for the incoming moving image signal; ,
Second calculation means for calculating a block field activity indicating vertical inter-pixel energy of a field structure in the second block unit for the incoming moving image signal;
A prediction type signal indicating whether each image unit of the moving image signal is encoded by the intra-picture encoding or the inter-picture prediction encoding, the block frame activity, and the block field activity are supplied; Based on a block field activity, an FI that is a value related to a field activity in the first block to be encoded is generated, and the prediction type signal in units of images including the first block to be encoded is When intra-picture encoding is indicated, FR1 that is a value related to frame activity in the first block to be encoded is generated based on the block frame activity, and the first block to be encoded The prediction type signal in units of images including the image When showing the predictive coding, on the basis of the said block frame activity is a value for a frame activity in the first block of the current coded, a generating means for generating a FR2 large becomes than the FR1,
When the FI is larger than the FR1 or the FI is larger than the FR2, the first block to be encoded is controlled to be encoded in a frame structure, and the FI is smaller than the FR1 or the When FI is smaller than FR2, control is performed to encode the first block to be encoded with a field structure, and when FI is equal to FR1 or when FI is equal to FR2, A moving picture coding apparatus comprising coding structure determination means for controlling the first block to be coded as a field structure or a frame structure.

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