HK1225203B - Motion-video encoding apparatus and method and motion-video decoding apparatus and method - Google Patents

Description

Motion picture encoding device and method, motion picture decoding device and method

This application is a divisional application of application number 201180047243.5, application date July 21, 2011, and invention name “Motion image encoding device, motion image decoding device, motion image encoding method and motion image decoding method”.

Technical Field

The present invention relates to a moving picture encoding device and a moving picture encoding method for efficiently encoding a moving picture, and a moving picture decoding device and a moving picture decoding method for decoding an efficiently encoded moving picture.

Background Art

For example, in international standard image coding methods such as MPEG (Moving Picture Experts Group) and "ITU-TH.26x", the input image frame is divided into rectangular blocks (coding object blocks), and prediction processing using the encoded image signal is performed on the coding object block to generate a predicted image. The prediction error signal, which is the difference between the coding object block and the predicted image, is orthogonally transformed and quantized on a block-by-block basis to perform information compression.

For example, in AVC/H.264 (ISO/IEC 14496-10 | ITU-T H.264), which is an international standard, intra prediction is performed based on coded nearby pixels, or motion compensation prediction is performed between adjacent frames (see, for example, Non-Patent Document 1).

In MPEG-4 AVC/H.264, in the intra prediction mode of luma, one prediction mode can be selected from a plurality of prediction modes on a block-by-block basis.

FIG. 10 is an explanatory diagram showing intra prediction modes when the luma block size is 4×4 pixels.

In FIG10 , white circles are pixels in the block to be coded, and black circles are pixels used for prediction, which are pixels in adjacent blocks that have already been coded.

In FIG10 , nine modes 0 to 8 are prepared as intra prediction modes. Mode 2 is a mode for performing average value prediction, in which pixels in the encoding target block are predicted using the average value of adjacent pixels of the blocks above and to the left.

Modes other than Mode 2 perform directional prediction. Mode 0 is vertical prediction, generating a predicted image by vertically repeating adjacent pixels of the upper block. For example, Mode 0 is selected for a vertical stripe pattern.

Mode 1 is horizontal prediction, which generates a predicted image by repeating the adjacent pixels of the left block horizontally. For example, mode 1 is selected when a horizontal stripe pattern is used.

Modes 3 to 8 generate a predicted image by generating interpolated pixels in a predetermined direction (direction indicated by an arrow) using adjacent pixels of the block above or to the left.

The block size of luminance to which intra prediction is applied can be selected from 4×4 pixels, 8×8 pixels, and 16×16 pixels. In the case of 8×8 pixels, nine intra prediction modes are defined similarly to the case of 4×4 pixels.

In the case of 16×16 pixels, four intra prediction modes (average prediction, vertical prediction, horizontal prediction, and planar prediction) are specified.

Planar prediction is a mode in which pixels generated by interpolating adjacent pixels of an upper block and adjacent pixels of a left block in a diagonal direction are used as prediction values.

In the directional prediction mode when the block size is 4×4 pixels or 8×8 pixels, a prediction value is generated in a direction predetermined according to the mode, such as 45 degrees. Therefore, when the direction of the boundary (edge) of the target within the block is consistent with the direction indicated by the prediction mode, the prediction efficiency becomes higher and the amount of code can be reduced.

However, if there is a slight deviation between the direction of the edge and the direction indicated by the prediction mode, or even if the directions are consistent but the edge within the encoding target block is slightly distorted (wobbling, bending, etc.), a large local prediction error will occur, and the prediction efficiency will drop drastically.

In order to prevent such a decrease in prediction efficiency, in the directional prediction of 8×8 pixels, the result obtained by applying a smoothing filter to the encoded adjacent pixels is used as a reference image when generating the predicted image, thereby generating a smoothed predicted image, thereby reducing the prediction error that occurs when a slight deviation in the prediction direction or a slight distortion at the edge occurs.

Non-Patent Document 1: MPEG-4 AVC (ISO/IEC 14496-10)/ITU-T H.264 Standard

Summary of the Invention

Conventional image coding devices are configured as described above. By applying filtering to generate a smoothed predicted image, even if there are slight deviations in the prediction direction or slight distortion at edges, the resulting prediction error can be reduced. However, in Non-Patent Document 1, filtering is not performed except for 8×8 pixel blocks, and only one type of filter is used for 8×8 pixel blocks. In practice, even for blocks of sizes other than 8×8 pixels, the same problem exists: even if the predicted image and the target image have similar patterns, slight mismatches at edges can lead to large localized prediction errors, sometimes significantly reducing prediction efficiency.

In addition, there is the following problem: even in blocks of the same size, if the quantization parameters used when quantizing the prediction error signal, the positions of the pixels within the block, etc. are different, the filters suitable for reducing the local prediction error will be different, but only one filter is prepared, and the prediction error cannot be fully reduced.

The present invention is made to solve the above-mentioned problems, and its purpose is to obtain a motion picture encoding device, a motion picture decoding device, a motion picture encoding method and a motion picture decoding method that can reduce locally occurring prediction errors to improve image quality.

The image decoding device according to the present invention includes an intra-frame prediction unit. When the coding mode associated with a coding block is the intra-frame coding mode, the intra-frame prediction unit performs intra-frame prediction processing corresponding to the intra-frame prediction parameters used in each block, thereby generating a predicted image. The intra-frame prediction unit generates intermediate prediction values from reference pixels according to the intra-frame prediction parameters, and uses the value obtained by filtering the intermediate prediction value as the final prediction value only at specific positions within the block, and uses the intermediate prediction value as the final prediction value at other positions within the block.

According to the present invention, there is an intra-frame prediction unit, which, when the coding mode related to the coding block is the intra-frame coding mode, performs intra-frame prediction processing corresponding to the intra-frame prediction parameters used in the block for each block that serves as the unit of prediction processing for the coding block, thereby generating a predicted image. The intra-frame prediction unit generates an intermediate prediction value based on the reference pixels according to the intra-frame prediction parameters, and uses the value obtained by filtering the intermediate prediction value as the final prediction value only at a specific position within the block, and uses the intermediate prediction value as the final prediction value at other positions within the block. Therefore, it has the following effect: the prediction error that occurs locally is reduced, so that an intra-frame prediction image with high image quality that is the same as the intra-frame prediction image generated on the motion image coding device side can be generated on the motion image decoding device side.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a diagram showing the structure of a moving picture encoding apparatus according to Embodiment 1 of the present invention.

FIG2 is a diagram showing the configuration of the moving picture decoding apparatus according to Embodiment 1 of the present invention.

FIG3 is a flowchart showing the processing contents of the moving picture encoding apparatus according to Embodiment 1 of the present invention.

FIG4 is a flowchart showing the processing contents of the moving picture decoding apparatus according to Embodiment 1 of the present invention.

FIG. 5 is an explanatory diagram showing a case where a coding block of a maximum size is hierarchically divided into a plurality of coding blocks.

FIG6(a) is a diagram showing the distribution of partitions after division, and FIG6(b) is an explanatory diagram showing, in a quad-tree graph, the allocation of coding modes m( ^Bn ) to the partitions after hierarchical division.

FIG7 is an explanatory diagram showing an example of intra-frame prediction parameters ( ^intra -frame prediction modes) selectable in each partition _Pin within a coding block ^Bn .

FIG8 is an explanatory diagram showing an example of pixels used when generating predicted values of pixels in a ^block _Pin when _lin = _min = ^{4 .}

FIG. 9 is an explanatory diagram showing an example of reference pixel arrangement in the case of N=5.

FIG. 10 is an explanatory diagram showing intra prediction modes in a case where the block size of luminance is 4×4 pixels.

(Explanation of Symbols)

1: Coding control unit (coding control unit); 2: Block division unit (block division unit); 3: Switch (intra-frame prediction unit, motion-compensated prediction unit); 4: Intra-frame prediction unit (intra-frame prediction unit); 5: Motion-compensated prediction unit (motion-compensated prediction unit); 6: Subtraction unit (differential image generation unit); 7: Transformation/quantization unit (image compression unit); 8: Inverse quantization/inverse transformation unit; 9: Addition unit; 10: Intra-frame prediction memory; 11: Loop filter unit; 12: Motion-compensated prediction frame memory; 13: variable length coding unit (variable length coding unit); 51: variable length decoding unit (variable length decoding unit); 52: switching switch (intra-frame prediction unit, motion compensation prediction unit); 53: intra-frame prediction unit (intra-frame prediction unit); 54: motion compensation prediction unit (motion compensation prediction unit); 55: inverse quantization/inverse transformation unit (differential image generation unit); 56: addition unit (decoded image generation unit); 57: memory for intra-frame prediction; 58: loop filter unit; 59: motion compensation prediction frame memory.

DETAILED DESCRIPTION

Hereinafter, in order to explain the present invention in more detail, specific embodiments will be described with reference to the accompanying drawings.

Implementation method 1.

In this embodiment 1, the following motion image encoding device and motion image decoding device are described: the motion image encoding device inputs each frame image of the image, and generates a predicted image by performing intra-frame prediction processing based on the encoded nearby pixels or performing motion compensation prediction processing between adjacent frames, and after performing compression processing on the prediction error signal which is the differential image between the predicted image and the frame image through orthogonal transformation/quantization, variable-length coding is performed to generate a bit stream, and the motion image decoding device decodes the bit stream output from the motion image encoding device.

The moving picture encoding apparatus of this first embodiment is characterized in that it divides the video signal into regions of various sizes to perform intra-frame/inter-frame adaptive encoding in response to local changes in the spatial/temporal directions of the video signal.

In general, image signals exhibit local variations in signal complexity across space and time. When viewed spatially, within a given image frame, patterns with uniform signal characteristics across relatively wide image regions, such as the sky and walls, are mixed with patterns with complex textures within smaller image regions, such as figures and paintings with detailed textures.

When observed in time, for the sky and the wall, the changes in the local time direction pattern are small, but for moving people and objects, their outlines undergo rigid/non-rigid motion in time, so the changes in time are large.

In the encoding process, a prediction error signal with low signal power and entropy is generated through temporal/spatial prediction, thereby reducing the overall amount of code. However, if the parameters used for prediction can be evenly applied to the largest possible image signal area, the amount of code for the parameter can be reduced.

On the other hand, if the same prediction parameters are applied to an image signal pattern that varies greatly temporally and spatially, prediction errors increase, making it impossible to reduce the amount of code for the prediction error signal.

Therefore, it is preferable to reduce the prediction target region for image signal patterns that vary greatly temporally and spatially, thereby reducing the power and entropy of the prediction error signal even if the amount of parameter data used for prediction is increased.

In order to perform such encoding adapted to the general properties of the image signal, the moving picture encoding apparatus of this embodiment 1 hierarchically divides the image signal into regions starting from a predetermined maximum block size, and performs prediction processing and prediction error encoding processing on each divided region.

The motion image encoding device of this embodiment 1 processes, as image signals, color image signals of arbitrary color spaces such as YUV signals composed of a luminance signal and two color difference signals, and RGB signals output from a digital camera element, as well as arbitrary image signals whose image frames are composed of horizontal/vertical two-dimensional columns of digital samples (pixels), such as monochrome image signals and infrared image signals.

The grayscale of each pixel may be 8 bits, 10 bits, 12 bits, or the like.

However, in the following description, unless otherwise specified, the input video signal is assumed to be a YUV signal. In addition, the two color difference components U and V are assumed to be a 4:2:0 format signal subsampled with respect to the luminance component Y.

Furthermore, the unit of processed data corresponding to each image frame is referred to as a "picture." In this first embodiment, a "picture" is described as a signal of an image frame that is scanned sequentially (progressive scanning). However, if the image signal is an interlaced signal, a "picture" may also be a field image signal that constitutes a unit of an image frame.

FIG1 is a diagram showing the structure of a moving picture encoding apparatus according to Embodiment 1 of the present invention.

In Figure 1, the encoding control unit 1 implements the following processing: determines the maximum size of the coding block that serves as the processing unit when performing intra-frame prediction processing (within-frame prediction processing) or motion compensation prediction processing (inter-frame prediction processing), and determines the upper limit of the number of layers when the maximum-sized coding block is hierarchically divided.

Furthermore, the encoding control unit 1 performs processing for selecting an encoding mode suitable for each hierarchically divided encoding block from one or more available encoding modes (one or more intra-frame encoding modes and one or more inter-frame encoding modes).

The encoding control unit 1 also performs processing to determine, for each encoding block, the quantization parameter and transform block size used when compressing the differential image, and the intra-frame prediction parameters or inter-frame prediction parameters used when performing prediction processing. The quantization parameter and transform block size are included in the prediction error coding parameters and output to the transform/quantization unit 7, the inverse quantization/inverse transform unit 8, and the variable length encoding unit 13.

In addition, the encoding control unit 1 constitutes an encoding control unit.

The block division unit 2 performs the following processing: upon receiving an image signal representing an input image, the block division unit 2 divides the input image represented by the image signal into coding blocks of the maximum size determined by the coding control unit 1, and further divides the coding blocks hierarchically until the upper limit of the number of layers determined by the coding control unit 1 is reached. The block division unit 2 also constitutes a block division unit.

The switching switch 3 implements the following processing: if the encoding mode selected by the encoding control unit 1 is the intra-frame encoding mode, the encoding block divided by the block division unit 2 is output to the intra-frame prediction unit 4; if the encoding mode selected by the encoding control unit 1 is the inter-frame encoding mode, the encoding block divided by the block division unit 2 is output to the motion compensation prediction unit 5.

The intra-frame prediction unit 4 performs the following processing: if a coding block divided by the block division unit 2 is received from the switching switch 3, it uses the encoded image signal within the frame and implements intra-frame prediction processing for the coding block based on the intra-frame prediction parameters output from the encoding control unit 1 to generate a predicted image.

Among them, after generating the above-mentioned predicted image, the intra-frame prediction unit 4 selects a filter from one or more pre-prepared filters according to the state of various parameters related to the encoding of the filtering object block, and uses the filter to implement filtering processing on the above-mentioned predicted image, and outputs the filtered predicted image to the subtraction unit 6 and the addition unit 9.

The above filter is selected by taking into consideration at least one of the following four parameters.

Parameters (1)

The block size of the above predicted image

Parameters (2)

The quantization parameter determined by the encoding control unit 1

Parameters (3)

The distance between the coded image signal within the frame used to generate the predicted image and the pixel to be filtered

Parameters (4)

The intra-frame prediction parameters determined by the encoding control unit 1

The switch 3 and the intra prediction unit 4 constitute an intra prediction unit.

The motion compensation prediction unit 5 performs the following processing: when the inter-frame coding mode is selected by the coding control unit 1 as the coding mode suitable for the coding block divided by the block division unit 2, the motion compensation prediction processing is performed on the coding block based on the inter-frame prediction parameters output from the coding control unit 1 using one or more reference images stored in the motion compensation prediction frame memory 12, thereby generating a predicted image.

The switch 3 and the motion compensation prediction unit 5 constitute a motion compensation prediction unit.

The subtraction unit 6 performs processing to generate a difference image (= coded block - predicted image) by subtracting the predicted image generated by the intra prediction unit 4 or the motion compensation prediction unit 5 from the coded block divided by the block division unit 2. The subtraction unit 6 constitutes a difference image generation unit.

The transform/quantization unit 7 performs a transform process (e.g., a DCT (discrete cosine transform) or an orthogonal transform such as a KL transform with a pre-designed basis for a specific learning series) on the difference image generated by the subtraction unit 6 in units of the transform block size included in the prediction error coding parameters output from the encoding control unit 1. Furthermore, the transform coefficients of the difference image are quantized using the quantization parameters included in the prediction error coding parameters, and the quantized transform coefficients are output as compressed data of the difference image. Furthermore, the transform/quantization unit 7 constitutes image compression means.

The inverse quantization/inverse transform unit 8 performs the following processing: using the quantization parameter included in the prediction error coding parameter output from the encoding control unit 1, the compressed data output from the transform/quantization unit 7 is inverse quantized, and the inverse transform processing (for example, inverse DCT (inverse discrete cosine transform), inverse KL transform, and other inverse transform processing) of the inversely quantized compressed data is performed in units of transform block size included in the prediction error coding parameter, thereby outputting the compressed data after the inverse transform processing as a local decoded prediction error signal.

The adding unit 9 performs the following processing: adds the local decoded prediction error signal output from the inverse quantization/inverse transform unit 8 and the prediction signal representing the predicted image generated by the intra-frame prediction unit 4 or the motion compensation prediction unit 5, thereby generating a local decoded image signal representing the local decoded image.

The intra prediction memory 10 is a recording medium such as a RAM that stores the local decoded image represented by the local decoded image signal generated by the adder 9 as an image used by the intra prediction unit 4 in the next intra prediction process.

The loop filter unit 11 performs processing to compensate for coding distortion included in the local decoded image signal generated by the adder 9 and outputs the local decoded image represented by the local decoded image signal after coding distortion compensation to the motion compensation prediction frame memory 12 as a reference image.

The motion-compensated prediction frame memory 12 is a recording medium such as RAM that stores the local decoded image filtered by the loop filter unit 11 as a reference image to be used by the motion-compensated prediction unit 5 in the next motion-compensated prediction process.

The variable-length coding unit 13 performs variable-length coding on the compressed data output from the transform/quantization unit 7, the coding mode and prediction error coding parameters output from the coding control unit 1, and the intra-frame prediction parameters output from the intra-frame prediction unit 4 or the inter-frame prediction parameters output from the motion-compensated prediction unit 5, thereby generating a bitstream in which the compressed data, coding mode, prediction error coding parameters, and coded data of the intra-frame prediction parameters/inter-frame prediction parameters are multiplexed. The variable-length coding unit 13 constitutes a variable-length coding unit.

FIG2 is a diagram showing the configuration of the moving picture decoding apparatus according to Embodiment 1 of the present invention.

In FIG2 , the variable length decoding unit 51 performs the following processing: variable length decoding is performed on the coded data multiplexed on the bit stream to obtain compressed data, coding mode, prediction error coding parameters, and intra-frame prediction parameters/inter-frame prediction parameters related to each hierarchically divided coding block, and the compressed data and prediction error coding parameters are output to the inverse quantization/inverse transform unit 55, and the coding mode and intra-frame prediction parameters/inter-frame prediction parameters are output to the switch 52. The variable length decoding unit 51 constitutes a variable length decoding unit.

The switching switch 52 implements the following processing: when the coding mode related to the coding block output from the variable length decoding unit 51 is the intra-frame coding mode, the intra-frame prediction parameters output from the variable length decoding unit 51 are output to the intra-frame prediction unit 53; when the coding mode is the inter-frame coding mode, the inter-frame prediction parameters output from the variable length decoding unit 51 are output to the motion compensation prediction unit 54.

The intra prediction unit 53 performs a process of performing an intra prediction process on a coding block based on the intra prediction parameters output from the switch 52 using a decoded image signal within a frame, thereby generating a predicted image.

Among them, after generating the above-mentioned predicted image, the intra-frame prediction unit 53 selects a filter from one or more pre-prepared filters according to the state of various parameters related to the decoding of the filtering processing object block, uses the filter to implement filtering processing on the above-mentioned predicted image, and outputs the filtered predicted image to the addition unit 56.

The above filter is selected by taking into consideration at least one of the following four parameters.

Parameters (1)

The block size of the above predicted image

Parameters (2)

The quantization parameter obtained by variable length decoding by the variable length decoding unit 51 is

Parameters (3)

The distance between the decoded image signal within the frame used to generate the predicted image and the pixel to be filtered

Parameters (4)

The intra-frame prediction parameters obtained by variable-length decoding by the variable-length decoding unit 51 are

The switch 52 and the intra prediction unit 53 constitute an intra prediction unit.

The motion-compensated prediction unit 54 performs a motion-compensated prediction process on the coding block based on the inter-frame prediction parameters output from the switch 52 using one or more reference images stored in the motion-compensated prediction frame memory 59 to generate a predicted image.

The switch 52 and the motion compensation prediction unit 54 constitute a motion compensation prediction unit.

The inverse quantization/inverse transform unit 55 performs the following processing: using the quantization parameter included in the prediction error coding parameter output from the variable length decoding unit 51, it inversely quantizes the compressed data related to the coding block output from the variable length decoding unit 51, and performs inverse transform processing (for example, inverse DCT (inverse discrete cosine transform) or inverse KL transform) on the inversely quantized compressed data in units of the transform block size included in the prediction error coding parameter, thereby outputting the compressed data after the inverse transform processing as a decoded prediction error signal (a signal representing the difference image before compression). In addition, the inverse quantization/inverse transform unit 55 constitutes a difference image generation unit.

The addition unit 56 performs processing to generate a decoded image signal representing a decoded image by adding the decoded prediction error signal output from the inverse quantization/inverse transform unit 55 and a prediction signal representing a predicted image generated by the intra prediction unit 53 or the motion compensation prediction unit 54. The addition unit 56 constitutes a decoded image generation unit.

The intra prediction memory 57 is a recording medium such as a RAM that stores the decoded image represented by the decoded image signal generated by the adder 56 as an image to be used in the next intra prediction process by the intra prediction unit 53 .

The loop filter unit 58 performs processing to compensate for coding distortion included in the decoded image signal generated by the adder 56 , and outputs a decoded image represented by the decoded image signal after coding distortion compensation to the motion compensation prediction frame memory 59 as a reference image.

The motion-compensated prediction frame memory 59 is a recording medium such as RAM that stores the decoded image filtered by the loop filter unit 58 as a reference image to be used by the motion-compensated prediction unit 54 in the next motion-compensated prediction process.

In FIG. 1 , it is assumed that the components of the moving picture coding apparatus, namely, the coding control unit 1, the block division unit 2, the switch 3, the intra-frame prediction unit 4, the motion-compensated prediction unit 5, the subtraction unit 6, the transform/quantization unit 7, the inverse quantization/inverse transform unit 8, the addition unit 9, the loop filter unit 11, and the variable-length coding unit 13, are each formed of dedicated hardware (e.g., a semiconductor integrated circuit or a single-chip microcomputer having a CPU mounted thereon). However, if the moving picture coding apparatus is formed of a computer, a program describing the processing details of the coding control unit 1, the block division unit 2, the switch 3, the intra-frame prediction unit 4, the motion-compensated prediction unit 5, the subtraction unit 6, the transform/quantization unit 7, the inverse quantization/inverse transform unit 8, the addition unit 9, the loop filter unit 11, and the variable-length coding unit 13 may be stored in a memory of the computer, and the CPU of the computer may execute the program stored in the memory.

FIG3 is a flowchart showing the processing contents of the moving picture encoding apparatus according to Embodiment 1 of the present invention.

In FIG2 , it is assumed that the variable length decoding unit 51, the switching switch 52, the intra-frame prediction unit 53, the motion compensation prediction unit 54, the inverse quantization/inverse transform unit 55, the adding unit 56, and the loop filter unit 58, which are components of the motion picture decoding device, are each composed of dedicated hardware (for example, a semiconductor integrated circuit in which a CPU is mounted, or a single-chip microcomputer, etc.). However, if the motion picture decoding device is composed of a computer, a program describing the processing contents of the variable length decoding unit 51, the switching switch 52, the intra-frame prediction unit 53, the motion compensation prediction unit 54, the inverse quantization/inverse transform unit 55, the adding unit 56, and the loop filter unit 58 may be stored in a memory of the computer, and the CPU of the computer may execute the program stored in the memory.

FIG4 is a flowchart showing the processing contents of the moving picture decoding apparatus according to Embodiment 1 of the present invention.

Next, the operation will be explained.

First, the processing contents of the moving picture encoding apparatus in FIG. 1 will be described.

First, the encoding control unit 1 determines the maximum size of the coding block that serves as the processing unit when performing intra-frame prediction processing (within-frame prediction processing) or motion compensation prediction processing (between-frame prediction processing), and determines the upper limit number of layers when the maximum-sized coding block is hierarchically divided (step ST1 of Figure 3).

As a method for determining the maximum size of a coding block, for example, a method of determining a size corresponding to the resolution of an input image for all pictures may be considered.

Another possible method is to quantify the difference in complexity of local motion in the input image as a parameter, and to determine a small maximum size for a picture with intense motion and a large maximum size for a picture with less motion.

As a method for setting the upper limit of the number of layers, for example, the more intense the motion of the input image, the larger the number of layers to enable finer motion detection, and the smaller the number of layers to enable finer motion detection, the less motion there is.

Furthermore, the encoding control unit 1 selects an encoding mode suitable for each hierarchically divided encoding block from one or more available encoding modes (M intra-frame encoding modes and N inter-frame encoding modes) (step ST2 ).

The method for selecting the coding mode performed by the coding control unit 1 is a well-known technology, so detailed description is omitted, but there are also methods such as the following: using any available coding mode, implementing coding processing on the coding block to verify the coding efficiency, and selecting the coding mode with the best coding efficiency among the multiple available coding modes.

Furthermore, the encoding control unit 1 determines, for each encoding block, a quantization parameter and a transform block size used when compressing a differential image, and determines intra-frame prediction parameters or inter-frame prediction parameters used when performing a prediction process.

The encoding control unit 1 outputs prediction error coding parameters including quantization parameters and transform block size to the transform/quantization unit 7, inverse quantization/inverse transform unit 8, and variable length encoding unit 13. In addition, the prediction error coding parameters are output to the intra prediction unit 4 as needed.

When a video signal representing an input image is input, the block division unit 2 divides the input image represented by the video signal into coding blocks of the maximum size determined by the coding control unit 1, and divides the coding blocks hierarchically until the upper limit of the number of layers determined by the coding control unit 1 is reached.

Here, FIG5 is an explanatory diagram showing a case where a coding block of a maximum size is hierarchically divided into a plurality of coding blocks.

In the example of FIG. 5 , the coding block of the largest size is the coding block B ⁰ of the 0th layer, which has a size of (L ⁰ , M ⁰ ) in the luminance component.

In the example of FIG. 5 , the maximum-sized coding block B ⁰ is used as a starting point, and the coding block B ⁿ is obtained by hierarchically dividing the coding block B n to a predetermined depth determined separately using a quadtree structure.

At depth n, coding block ^Bn is an image region of size ( ^Ln , ^Mn ).

^Ln and ^Mn may be the same or different, but the example in FIG5 shows a case where ^Ln = ^Mn .

Hereinafter, the size of the coding block ^Bn is defined as the size ( ^Ln , ^Mn ) in the luma component of the coding block ^Bn .

Since the block division unit 2 performs quadtree division, (Ln ⁺¹ , Mn ⁺¹ ) = ( ^Ln /2, ^Mn /2) always holds.

However, in a color video signal (4:4:4 format) such as an RGB signal where all color components have the same number of samples, the size of all color components is ( ^Ln , ^Mn ). However, when processing the 4:2:0 format, the size of the coding block of the corresponding color difference component is ( ^Ln /2, ^Mn /2).

Hereinafter, the coding mode selectable in the coding block ^Bn of the nth layer is denoted as m( ^Bn ).

In the case of a color video signal composed of multiple color components, the coding mode m( ^Bn ) can be configured to use a separate mode for each color component. However, unless otherwise specified, the coding mode m(Bn) will be described as indicating the coding mode for the luminance component of a coding block in a YUV signal and 4:2:0 format.

In coding mode m( ^Bn ), there are one or more intra-frame coding modes (collectively referred to as "INTRA") and one or more inter-frame coding modes (collectively referred to as "INTER"). As described above, the coding control unit 1 selects the coding mode with the best coding efficiency for the coding block ^Bn from all coding modes or subgroups thereof that can be used in the picture.

As shown in FIG5 , the coding block ^Bn is further divided into one or more prediction processing units (partitions).

Hereinafter, the partitions belonging to the coding block ^Bn will be referred to as _Pin ⁽ i: partition number in the nth layer).

How to partition the ^blocks _P in the coding block B ⁿ is to be divided is included as information in the coding mode m(B ⁿ ).

For all blocks P _i ⁿ , prediction processing is performed according to the coding mode m(B ⁿ ), but individual prediction parameters can be selected for each block P _i ⁿ .

The encoding control unit 1 generates a block division state as shown in FIG. 6 , for example, for the maximum-sized encoding block, and determines the encoding block B ⁿ .

The shaded portion of FIG6(a) indicates the distribution of the divided blocks, and FIG6(b) shows, in a quadtree diagram, the allocation of the coding modes m( ^Bn ) to the hierarchically divided blocks.

In FIG6(b), the nodes surrounded by □ represent nodes (coding blocks ^Bn ) to which coding mode m( ^Bn ) is assigned.

When the encoding control unit 1 selects the optimal encoding mode m( ^Bn ) for the _block ^Pin of each encoding block ^Bn , if the encoding mode m( ^Bn ) is an intra-frame encoding mode (step ST3), the switching switch 3 outputs the ^block _Pin of the encoding block ^Bn divided by the block division unit 2 to the intra-frame prediction unit 4.

On the other hand, if the coding mode m(B ⁿ ) is the inter-frame coding mode (step ST3 ), the blocks _P ⁱⁿ of the coding block B ⁿ divided by the block dividing unit 2 are output to the motion compensation prediction unit 5 .

Upon receiving the ^{block Pin} _of the coding block ^Bn from the switching switch 3, the intra-frame prediction unit 4 uses the encoded image signal within the frame and, based on the intra-frame prediction parameters output from the encoding control unit 1, performs intra-frame prediction processing on the _block ^Pin of the coding block ^Bn , thereby generating an intra-frame predicted image _Pin ⁽ step ST4).

Among them, after generating the above-mentioned intra-frame prediction image P _i ⁿ , the intra-frame prediction unit 4 selects a filter from one or more pre-prepared filters according to the status of various parameters related to the encoding of the filtering processing object block, and uses the filter to perform filtering processing on the intra-frame prediction image P _i ⁿ .

After filtering the intra-frame prediction image _P ⁱⁿ , the intra-frame prediction unit 4 outputs the filtered intra-frame prediction image _P ⁱⁿ to the subtraction unit 6 and the addition unit 9. However, in order to enable the moving picture decoding apparatus in FIG. 2 to generate the same intra-frame prediction image ^{P in} _, the intra-frame prediction parameters are output to the variable-length coding unit 13.

The outline of the processing contents of the intra prediction unit 4 is as described above, but the detailed processing contents will be described later.

Upon receiving the ^{block Pin} _of the coding block ^Bn from the switching switch 3, the motion-compensated prediction unit 5 uses one or more reference frames stored in the motion-compensated prediction frame memory 12 and, based on the inter-frame prediction parameters output from the encoding control unit 1, performs motion-compensated prediction processing on ^the block _Pin of the coding block ^Bn , thereby generating ^an inter-frame predicted image _Pin (step ST5).

Note that the technology for generating a predicted image by performing motion compensation prediction processing is a well-known technology, and therefore detailed description thereof will be omitted.

If the intra prediction unit 4 or the motion compensation prediction unit 5 generates a prediction image (intra ^prediction image _Pin , inter ^prediction image _Pin ), the subtraction unit 6 subtracts the prediction image (intra prediction image Pin, inter prediction image _Pin ^{) generated by the intra prediction unit 4 or the motion compensation prediction unit 5 from the block Pin of} the coding _block ^Bn divided by the block division ^unit ₂ , thereby generating a difference image, and outputs a prediction error signal _ein representing the difference ^image to the transform/quantization unit 7 (step ST6).

Upon receiving the prediction error signal _e ^indicative of the differential image from the subtraction unit 6, the transform/quantization unit 7 performs a transform process (e.g., a DCT (discrete cosine transform), an orthogonal transform such as a KL transform whose basis is pre-designed for a specific learning series) on the differential image in units of a transform block size included in the prediction error coding parameters output from the encoding control unit 1, and quantizes the transform coefficients of the differential image using the quantization parameters included in the prediction error coding parameters, thereby outputting the quantized transform coefficients as compressed data of the differential image to the inverse quantization/inverse transform unit 8 and the variable-length coding unit 13 (step ST7).

If the inverse quantization/inverse transform unit 8 receives the compressed data of the differential image from the transform/quantization unit 7, it uses the quantization parameter included in the prediction error coding parameter output from the encoding control unit 1 to inverse quantize the compressed data of the differential image, and performs inverse transform processing (for example, inverse DCT (inverse discrete cosine transform), inverse KL transform, and other inverse transform processing) on the inverse quantized compressed data in units of transform block size included in the prediction error coding parameter, thereby outputting the compressed data after the inverse transform processing as a local decoding prediction error signal e _i ⁿ cap (due to the relationship of electronic application, the "^" attached to the alphabetical characters is recorded as cap) to the addition unit 9 (step ST8).

Upon receiving the local decoded prediction error signal _ein ^- hat from the inverse quantization/inverse transform unit 8, the adder 9 adds the local decoded prediction error signal _ein ^- hat and a prediction signal representing a predicted image (intra-frame predicted image _Pin , inter-frame predicted image ^{Pin )} generated by the intra-frame prediction unit 4 or the motion-compensated prediction unit 5, thereby generating a local decoded block image _Pin ^- hat or a locally decoded coded block image as a collection thereof, i.e., _a locally decoded image (step ST9).

When generating a local decoded image, the adder 9 stores a local decoded image signal representing the local decoded image in the intra prediction memory 10 , and outputs the local decoded image signal to the loop filter 11 .

The processes of steps ST3 to ST9 are repeatedly performed until the processes of all the hierarchically divided coding blocks ^Bn are completed. When the processes of all the coding blocks ^Bn are completed, the process moves to step ST12 (steps ST10 and ST11).

The variable length coding unit 13 performs entropy coding on the compressed data output from the transform/quantization unit 7, the coding mode (including information indicating the segmentation status of the coding block) and the prediction error coding parameters output from the coding control unit 1, and the intra-frame prediction parameters output from the intra-frame prediction unit 4 or the inter-frame prediction parameters output from the motion compensation prediction unit 5.

The variable-length coding unit 13 multiplexes the compressed data, which is the result of entropy coding, the coding mode, the prediction error coding parameter, and the coded data of the intra-frame prediction parameter/inter-frame prediction parameter to generate a bit stream (step ST12 ).

If the loop filter unit 11 receives a local decoded image signal from the adder 9, it compensates for the coding distortion contained in the local decoded image signal and saves the local decoded image represented by the local decoded image signal after coding distortion compensation as a reference image in the motion compensation prediction frame memory 12 (step ST13).

The filtering processing using the loop filter unit 11 can be performed on the maximum coding block or each coding block unit of the local decoded image signal output from the adder 9, or can be performed on the unit of multiple maximum coding blocks, or on the unit of one picture after the local decoded image signal of one picture is output.

Next, the processing contents of the intra prediction unit 4 will be described in detail.

FIG7 is an explanatory diagram showing an example of intra-frame prediction parameters ( ^intra -frame prediction modes) selectable in each partition _Pin within a coding block ^Bn .

In the example of FIG. 7 , intra prediction modes and prediction direction vectors indicated by the intra prediction modes are shown, and the design is such that the relative angles between the prediction direction vectors decrease as the number of selectable intra prediction modes increases.

The intra-frame prediction unit 4 performs intra-frame prediction processing on the block P _i ⁿ based on the intra-frame prediction parameters for the block P _i ⁿ and the selection parameters of the filter used in generating the intra-frame prediction image P _i ⁿ .

The following describes the intra-frame processing of generating an intra-frame prediction signal of ^a luminance signal based on the intra-frame prediction parameters (intra-frame prediction mode) of the luminance signal for the block _Pin .

Here, the size of ^the block _Pin is set to _lin × _min ^{pixels .}

FIG8 is an explanatory diagram showing an example of pixels used when generating predicted values of pixels in a ^block _Pin when _lin = _min = ^{4 .}

In Figure 8, the pixels (2× _lin +1) of the encoded upper block and the pixels ^(2×min ₎ of the ^left block adjacent to the _block ^Pin are used as pixels for prediction, but the pixels used in the prediction can be more or less than the pixels shown in Figure 8.

In addition, in FIG8 , pixels corresponding to one adjacent row or column are used for prediction, but pixels corresponding to two rows or two columns, or more, may be used for prediction.

When the index value of the intra-frame prediction mode for ^block _Pin is 2 (average value prediction), the average value of the adjacent pixels of the upper block and the adjacent pixels of the left block is used as the prediction value of the ^pixels within block _Pin to generate an intermediate prediction image.

When the index value of the intra prediction mode is other than 2 (average value prediction), the predicted values of the pixels in the ^block _Pin are generated based on the prediction direction vector _vp = (dx, dy) indicated by the index value.

Here, the relative coordinates within the block ^Pin of the _pixel that generates the prediction value (prediction object pixel) (with the upper left pixel of the block as the origin) are set to (x, y).

The position of a reference pixel used in prediction is the intersection of A and an adjacent pixel shown below.

where k is a positive scalar value.

When the reference pixel is at an integer pixel position, the integer pixel is used as the predicted value of the prediction target pixel.

On the other hand, when the reference pixel is not located at an integer pixel position, an interpolated pixel generated from integer pixels adjacent to the reference pixel is used as a prediction value.

In the example of FIG8 , since the reference pixel is not at an integer pixel position, the predicted value is calculated by interpolation based on two pixels adjacent to the reference pixel. However, the predicted value is not limited to being generated based on two adjacent pixels; an interpolated pixel may be generated based on two or more adjacent pixels to serve as the predicted value.

Next, a final predicted image is obtained by performing filtering processing on the intermediate predicted image (predicted value) generated by the above steps.

The following describes specific filtering processing.

A filter to be used is selected from at least one filter prepared in advance by a method described later, and filtering is performed on each pixel of the intermediate prediction image according to the following equation (1).

In the formula (1), a _n (n=0, 1, ..., N) is a filter coefficient composed of coefficients (a ₀ , a ₁ , ..., a _N-1 ) related to a reference pixel and an offset coefficient a _N .

p _n (n=0, 1, ..., N-1) represents reference pixels of a filter including the filtering target pixel p ₀ .

s(p _n ) represents the luminance value of each reference pixel, and s hat (p ₀ ) represents the luminance value after filtering at the filtering target pixel p ₀ .

However, the filter coefficients may be configured without the offset coefficient a _N . Note that N is an arbitrary number of reference pixels.

FIG. 9 is an explanatory diagram showing an example of reference pixel arrangement in the case of N=5.

When performing the above filtering processing, the larger the size of ^{the block} _Pin ⁽ _line × _minute ), the more likely it is that non-linear edges will exist in the input image, and the more likely it is that a deviation from the prediction direction of the intermediate prediction image will occur, so it is preferred to smooth the intermediate prediction image.

Furthermore, the larger the quantization value of the prediction error, the greater the quantization distortion generated in the decoded image, and the lower the prediction accuracy of the intermediate prediction image generated based on the encoded pixels adjacent to ^the block _Pin , so it is preferable to prepare a smoothed prediction image that roughly represents the ^block _Pin .

Furthermore, among the pixels within the same ^block _Pin , the farther away from the encoded pixels adjacent to the block _Pin used in generating the ^intermediate prediction image, the more likely it is that deviations such as edges will occur between the intermediate prediction image and the input image. Therefore, it is preferable to smooth the prediction image to suppress the sharp increase in prediction error when deviations occur.

Furthermore, not only the strength of the filter needs to be varied, but also the reference pixels of the filter need to be appropriately arranged according to the prediction direction of the intermediate prediction image to prevent the edges of the intermediate prediction image from being unnaturally distorted.

Therefore, in the filter selection process, the filter is selected in consideration of the following four parameters (1) to (4).

(1) Size of _Pin ^{block (l in} _{× min} ⁱⁿ )

(2) Quantization parameters included in the prediction error coding parameters

(3) The distance between the group of coded pixels used in generating the intermediate prediction image (“pixels used in prediction” shown in FIG8 ) and the pixel to be filtered

(4) Index value of the intra-frame prediction mode when the intermediate prediction image is generated

Specifically, as the size ^{(l in × m in} ₎ ^of _the ^block _Pin increases, as the quantization value determined by the quantization parameter increases, and as the distance between the pixel being filtered and the coded ^pixel group used to generate the intermediate prediction image to the left and above the block _Pin increases, a filter with a stronger smoothing strength is used. Furthermore, the filter strength and reference pixel arrangement in the prediction direction of the intra-frame prediction mode are taken into consideration. In other words, by associating appropriate filters from a pre-prepared filter group for each combination of the above parameters, adaptive selection of filters corresponding to the above parameters is achieved.

However, any number of filter strength types may be used, as long as there are at least two. As an expression of filter strength, the weakest filter may be defined as equivalent to no filtering. Therefore, it is possible to configure filtering such that only specific pixels within the intermediate prediction image are filtered, while all other pixels are filtered using the weakest filter, i.e., no filtering.

In the above description, it is assumed that a necessary number of filters are prepared in advance. However, the filter may be defined as a function of the filter selection parameter and calculated based on the value of the filter selection parameter.

Furthermore, in the above description, an example is shown in which a filter is selected by considering four parameters (1) to (4), but a filter may be selected by considering at least one of the four parameters (1) to (4). As an example, the following configuration can be cited: when considering (3) and (4) of the four parameters, a filter with a stronger strength is selected as the distance from the pixel used for prediction of each filtering target pixel (in the example of FIG. 8 , the distance from the "reference pixel" adjacent to the upper end of the block) increases according to the prediction direction of the intra-frame prediction mode.

Furthermore, since the four parameters (1) to (4) are already known to the video decoding apparatus, no additional information to be encoded due to the above-mentioned filtering process is generated.

Through the same steps, predicted pixels for all pixels of the luminance signal within ^the block _Pin are generated, and the generated intra-frame predicted ^image _Pin is output.

The intra-frame prediction parameters used to generate the intra- ^frame prediction image _Pin are output to the variable-length coding unit 13 in order to multiplex them into the bit stream.

For the color difference signal within the ^block _Pin , intra-frame prediction processing based on intra-frame prediction parameters (intra-frame prediction mode) is implemented through the same steps as the luminance signal, and the intra-frame prediction parameters used in generating the intra-frame prediction image are output to the variable length coding unit 13.

However, regarding the intra-frame prediction of the chrominance signal, the filtering process described above may be performed in the same manner as the luminance signal, or the filtering process described above may not be performed.

Next, the processing contents of the image decoding apparatus in FIG. 2 will be described.

If the variable length decoding unit 51 inputs the bit stream output from the image encoding device in Figure 1, it implements variable length decoding processing on the bit stream and decodes the frame size information according to the sequence unit or picture unit composed of more than one frame (step ST21 in Figure 4).

The variable length decoding unit 51 determines the maximum size of the coding block that serves as the processing unit when performing intra-frame prediction processing (within-frame prediction processing) or motion compensation prediction processing (between-frame prediction processing) through the same steps as the encoding control unit 1 in Figure 1, and determines the upper limit of the number of layers when the maximum-sized coding block is hierarchically divided (step ST22).

For example, when the maximum size of a coding block is determined according to the resolution of an input image in an image coding apparatus, the maximum size of the coding block is determined according to previously decoded frame size information.

Furthermore, when information indicating the maximum size of a coding block and the upper limit of the number of layers is multiplexed in a bitstream, the information decoded from the bitstream is referenced.

The coding mode m(B ⁰ ) of the maximum-sized coding block B ⁰ multiplexed in the bitstream includes information indicating the division state of the maximum-sized coding block B ^0. Therefore, the variable-length decoding unit 51 decodes the coding mode m(B ⁰ ) of the maximum-sized coding block B ⁰ multiplexed in the bitstream, thereby determining each hierarchically divided coding block B ⁿ (step ST23).

After determining each coding block B ⁿ , the variable length decoding unit 51 decodes the coding mode m(B ⁿ ) of the coding block B ⁿ and determines ^{the partition Pin} _belonging to the coding block B ⁿ based on the information of the partition _Pin belonging to the coding mode m(B ^{n )} .

When the variable-length decoding unit 51 determines the partition _Pin belonging to the ^coding block ^Bn , it decodes the compressed data, coding mode, prediction error coding parameters, and intra-frame prediction parameters/inter-frame prediction parameters for ^each partition _Pin (step ST24).

That is, when the coding mode m(B ⁿ ) assigned to the coding block B ⁿ is the intra coding mode, intra prediction parameters are decoded for each partition P _i ⁿ belonging to the coding block.

When the coding mode m(B ⁿ ) assigned to the coding block B ⁿ is the inter-frame coding mode, inter-frame prediction parameters are decoded for each partition P _i ⁿ belonging to the coding block.

The block that becomes the prediction processing unit is further divided into one or more blocks that become the transformation processing units according to the transformation block size information contained in the prediction error coding parameter, and compressed data (transformation/quantized transformation coefficients) are decoded for each block that becomes the transformation processing unit.

When the coding mode m( ^Bn ) of the partition _Pin belonging to the coding ^{block Bn} determined by the variable length decoding unit 51 is the intra coding mode (step ST25), the switching switch 52 outputs the intra prediction parameters output from the variable length decoding unit 51 to the intra prediction unit 53.

On the other hand, when the coding mode m(B ⁿ ) of the block P _i ⁿ is the inter-frame coding mode (step ST25 ), the inter-frame prediction parameters output from the variable-length decoding unit 51 are output to the motion compensation prediction unit 54 .

Upon receiving the intra-frame prediction parameters from the switching switch 52, the intra-frame prediction unit 53, like the intra-frame prediction unit 4 in FIG1 , uses the decoded image signal within the frame and performs intra-frame prediction processing on the block _P in the coding block ^B according to the ^intra -frame prediction parameters, thereby generating an intra-frame predicted image _P ⁽ step ST26).

Among them, when generating the intra-frame prediction image P _i ⁿ , the intra-frame prediction unit 53 selects a filter from one or more pre-prepared filters according to the status of various parameters related to the decoding of the filtering processing object block through the same method as the intra-frame prediction unit 4 in Figure 1, uses the filter to perform filtering processing on the intra-frame prediction image P _i ⁿ , and uses the filtered intra-frame prediction image P _i ⁿ as the final intra-frame prediction image.

In addition, in the above description, it is assumed that the necessary number of filters are prepared in advance. However, in the case where the intra-frame prediction unit 4 in Figure 1 defines the filter as a function of the above parameters in a manner of calculating the filter according to the state of the parameters used in filter selection, the intra-frame prediction unit 53 can also be configured to define the filter as a function of the above parameters in a manner of calculating the filter according to the state of various parameters related to the decoding of the above-mentioned filtering processing object block.

Upon receiving the inter-frame prediction parameters from the switching switch 52, the motion-compensated prediction unit 54 uses one or more reference frames stored in the motion-compensated prediction frame memory 59 to perform motion-compensated prediction processing on the block _Pin of the coding block ^Bn according to the inter-frame prediction parameters, thereby generating ^an inter ^- frame predicted image _Pin (step ST27).

The inverse quantization/inverse transform unit 55 uses the quantization parameter included in the prediction error coding parameter output from the variable length decoding unit 51 to inverse quantize the compressed data related to the coding block output from the variable length decoding unit 51, and performs inverse transform processing (for example, inverse DCT (inverse discrete cosine transform), inverse KL transform, and other inverse transform processing) on the inverse quantized compressed data in units of transform block size included in the prediction error coding parameter, thereby outputting the compressed data after the inverse transform processing as a decoded prediction error signal (a signal representing the differential image before compression) to the addition unit 56 (step ST28).

If the adding unit 56 receives the decoded prediction error signal from the inverse quantization/inverse transform unit 55, it adds the decoded prediction error signal and the prediction signal representing the predicted image generated by the intra-frame prediction unit 53 or the motion compensation prediction unit 54 to generate a decoded image, saves the decoded image signal representing the decoded image to the intra-frame prediction memory 57, and outputs the decoded image signal to the loop filter unit 58 (step ST29).

The processes of steps ST23 to ST29 are repeatedly performed until the processing is completed for all the hierarchically divided coding blocks ^Bn (step ST30).

Upon receiving the decoded image signal from the adder 56 , the loop filter 58 compensates for coding distortion included in the decoded image signal and stores the decoded image represented by the decoded image signal after coding distortion compensation as a reference image in the motion compensation prediction frame memory 59 (step ST31 ).

The filtering process by the loop filter unit 58 can be performed in units of the largest coding block or each coding block of the decoded image signal output from the adder unit 56, or can be performed collectively for one picture after the decoded image signal equivalent to one picture's macroblock is output.

As described above, according to the first embodiment, when the intra-frame prediction unit 4 of the motion image encoding device generates an intra-frame predicted image by performing intra-frame prediction processing using the encoded image signal within the frame, a filter is selected from one or more pre-prepared filters according to the states of various parameters related to the encoding of the filtering object block, and filtering processing is performed on the predicted image using the filter, thereby achieving the effect of reducing the prediction error that occurs locally and improving the image quality.

In addition, according to the first embodiment, the intra-frame prediction unit 4 selects a filter by considering at least one parameter among (1) the size of the ^block _Pin ( _l ⁱⁿ × ^{m in} ₎ , (2) the quantization parameter included in the prediction error coding parameter, (3) the distance between the encoded pixel group used when generating the intermediate prediction image and the filtering object pixel, and (4) the index value of the intra-frame prediction mode when the intermediate prediction image is generated. Therefore, the following effect is obtained: a local prediction error caused by a slight deviation between the direction of the edge of the encoding target image and the prediction direction in the intermediate prediction image having a high correlation with the encoding target image or a slight distortion of the edge is suppressed, thereby achieving the effect of improving the prediction efficiency.

According to this embodiment 1, when the intra-frame prediction unit 53 of the motion image decoding device generates an intra-frame prediction image by performing intra-frame prediction processing using the decoded image signal within the frame, a filter is selected from one or more pre-prepared filters according to the states of various parameters related to the decoding of the filtering processing object block, and the filtering processing is performed on the prediction image using the filter, thereby achieving the following effects: the prediction error occurring locally is reduced, and the intra-frame prediction image that is the same as the intra-frame prediction image generated on the motion image encoding device side can be generated on the motion image decoding device side.

In addition, according to the first embodiment, the intra-frame prediction unit 53 selects a filter by considering at least one parameter among (1) the size of the ^block _Pin ( _l ⁱⁿ × ^{m in} ₎ , (2) the quantization parameter included in the prediction error coding parameter, (3) the distance between the encoded pixel group used when generating the intermediate prediction image and the filtering object pixel, and (4) the index value of the intra-frame prediction mode when the intermediate prediction image is generated. Therefore, the following effect is achieved: in the intermediate prediction image having a high correlation with the encoding object image, a local prediction error caused by a slight deviation between the direction of the edge of the encoding object image and the prediction direction or a slight distortion of the edge is suppressed, so that the same intra-frame prediction image as the intra-frame prediction image generated on the motion image encoding device side can be generated on the motion image decoding device side.

Implementation method 2.

In the first embodiment described above, an example is shown in which the intra-frame prediction unit 4, when performing intra-frame prediction processing using an already encoded image signal within a frame to generate an intra-frame predicted image, selects a filter from one or more pre-prepared filters based on the states of various parameters related to the encoding of the target block to be filtered, and performs filtering processing on the predicted image using the filter. However, a Wiener filter may be designed to minimize the sum of squared errors between the target block to be encoded and the predicted image. If the prediction error is reduced more significantly when using the Wiener filter than when using the filter selected from the one or more pre-prepared filters, the Wiener filter may be used instead of the selected filter to perform filtering processing on the predicted image.

The following describes the details of the processing.

In the first embodiment described above, the intra-frame prediction units 4 and 53 select a filter from one or more pre-prepared filters based on the states of various parameters related to the encoding of the target block to be filtered. However, when selecting a filter based on the four parameters (1) to (4), an appropriate filter can be selected from among the selection candidates. However, if an optimal filter exists other than the selection candidates, "optimal filtering" cannot be performed.

In this embodiment 2, it is characterized in that, on the side of the motion image encoding device, an optimal filter is designed according to the picture unit to implement filtering processing, and the filter coefficients, etc. of the filter are encoded, and on the side of the motion image decoding device, the filter coefficients, etc. are decoded to implement filtering processing using the filter.

The intra prediction unit 4 of the moving picture coding apparatus generates ^an intra prediction image _Pin by performing an intra prediction process on the partition _Pin of ^the coding block ^Bn , similarly to the first embodiment.

In addition, the intra-frame prediction unit 4 selects a filter from one or more pre-prepared filters according to the status of various parameters related to the encoding of the filtering target block in the same way as in the above-mentioned embodiment 1, and uses the filter to filter ^the intra-frame prediction image _Pin .

After the intra-frame prediction unit 4 determines the intra-frame prediction parameters in all coding blocks ^Bn in the picture, it designs a Wiener filter for each area in the picture where the same filter is used (area with the same filter index) so that the sum of the square errors between the input image and the intra-frame prediction image in the area (the average square error in the object area) is minimized.

Regarding the Wiener filter, the filter coefficient w can be calculated using the autocorrelation matrix R _s's' of the intermediate predicted image signal s' and the cross-correlation matrix R _ss' between the input image signal s and the intermediate predicted image signal s' according to the following equation (4). The size of the matrices R _s's' and R _ss' corresponds to the calculated number of filter taps.

If the intra-frame prediction unit 4 designs a Wiener filter, the sum of square errors in the filter design object area when the Wiener filter is used to implement filtering processing is set to D1, the code amount when the information related to the Wiener filter (for example, the filter coefficient) is encoded is set to R1, and the sum of square errors in the filter design object area when the filtering processing is implemented using a filter selected by the same method as the above-mentioned embodiment 1 is set to D2, and confirm whether the following formula (5) is established.

D1+λ·R1<D2 (5)

Here, λ is a constant.

When equation (5) holds true, the intra prediction unit 4 performs filtering using the Wiener filter instead of the filter selected by the same method as in the first embodiment.

On the other hand, when the equation (5) does not hold, filtering processing is performed using a filter selected by the same method as in the first embodiment.

Although the evaluation is performed here using the sum of squared errors D1 and D2, the present invention is not limited thereto and the evaluation may be performed using another measure indicating the distortion of the prediction, such as the sum of absolute values of errors, instead of the sum of squared errors D1 and D2.

When the intra prediction unit 4 performs filtering processing using a Wiener filter, it requires filter coefficients of the Wiener filter and filter update information indicating which filter index is to be replaced with the Wiener filter.

Specifically, when the number of filters that can be selected through filtering processing using filter selection parameters is set to L and each filter is assigned an index of 0 to L-1, for each index, when using the designed Wiener filter, it is necessary to encode the value of "1" as filter update information, and when using a pre-prepared filter, it is necessary to encode the value of "0" as filter update information.

The variable-length coding unit 13 performs variable-length coding on the filter update information output from the intra prediction unit 4 and multiplexes the coded data of the filter update information into a bit stream.

Here, an example is shown of designing a Wiener filter so that the mean square error between the input image and the predicted image in each area where the same filter is used in a picture is minimized. However, the example may also be configured such that, for each area where the same filter is used, a Wiener filter is designed so that the mean square error between the input image and the predicted image in the area is minimized not by picture units but by other specific area units. The filter may also be designed only for a specific picture, or may be designed only for situations that meet specific conditions (for example, a scene change detection function is added and a picture in which a scene change is detected).

The variable length decoding unit 51 of the moving picture decoding apparatus obtains filter update information by variable length decoding based on the coded data multiplexed in the bit stream.

The intra prediction unit 53 performs intra prediction processing on the partition _P in ^the coding block B ⁿ in the same manner as in the first embodiment, thereby generating an intra prediction image P _in ^.

Upon receiving the filter updating information from the variable length decoding unit 51 , the intra prediction unit 53 refers to the filter updating information and checks whether or not the filter of the corresponding index has been updated.

When the result of the confirmation shows that the filter of a certain area is replaced by the Wiener filter, the intra-frame prediction unit 53 reads out the filter coefficient of the Wiener filter contained in the filter update information, determines the Wiener filter, and uses the Wiener filter to perform filtering processing on the intra-frame prediction image P _i ⁿ .

On the other hand, in the region not replaced by the Wiener filter, a filter is selected by the same method as in the first embodiment, and filtering processing is performed on the intra- ^frame prediction image _Pin using this filter.

As described above, according to this embodiment 2, a Wiener filter is designed in which the sum of the square errors between the block of the encoding object and the predicted image is minimized. When the degree of reduction in the prediction error is higher when using the Wiener filter than when using a filter selected from one or more pre-prepared filters, the Wiener filter is used instead of the selected filter to perform filtering processing on the predicted image, thereby achieving the effect of further reducing the locally occurring prediction error compared to the above-mentioned embodiment 1.

Furthermore, the present invention can freely combine the various embodiments, modify any components of the various embodiments, or omit any components in the various embodiments within the scope of the invention.

Industrial applicability

As described above, the motion image encoding device, motion image decoding device, motion image encoding method, and motion image decoding method of the present invention are configured such that, when the intra-frame prediction unit generates a predicted image by performing intra-frame prediction processing using an encoded image signal within a frame, a filter is selected from one or more pre-prepared filters according to the states of various parameters related to the encoding of the filtering target block, and filtering processing is performed on the predicted image using the filter, and the filtered predicted image is output to the differential image generation unit. Therefore, the motion image encoding device and motion image encoding method for efficiently encoding motion images, and the motion image decoding device and motion image decoding method for decoding efficiently encoded motion images, etc.

Claims (4)

1. A moving picture decoding device, characterized in that: An intra-frame prediction unit is provided for performing intra-frame prediction processing on each block serving as a unit of prediction processing to generate an intra-frame prediction image when the coding mode associated with the coding block is the intra-frame coding mode. The intra-frame prediction unit generates an intermediate prediction image based on reference pixels according to an intra-frame prediction mode, performs filtering processing on only a portion of pixels of the intermediate prediction image according to the intra-frame prediction mode to obtain the intra-frame prediction image, generates pixels at a specific position in the block of the intra-frame prediction image as a final prediction image, and generates pixels at other positions in the block of the intermediate prediction image as a final prediction image, The intra prediction mode includes a mode for performing average value prediction and a mode for performing directional prediction. 2. A moving picture encoding device, characterized in that An intra-frame prediction unit is provided for performing intra-frame prediction processing on each block serving as a unit of prediction processing to generate an intra-frame prediction image when the coding mode associated with the coding block is the intra-frame coding mode. The intra-frame prediction unit generates an intermediate prediction image based on reference pixels according to an intra-frame prediction mode, performs filtering processing on only a portion of pixels of the intermediate prediction image according to the intra-frame prediction mode to obtain the intra-frame prediction image, generates pixels at a specific position in the block of the intra-frame prediction image as a final prediction image, and generates pixels at other positions in the block of the intermediate prediction image as a final prediction image, The intra prediction mode includes a mode for performing average value prediction and a mode for performing directional prediction. 3. A motion picture encoding method, characterized in that: The method comprises an intra-frame prediction processing step, in which, when the coding mode associated with the coding block is the intra-frame coding mode, intra-frame prediction processing is performed on each block serving as a unit of prediction processing to generate an intra-frame prediction image. In the intra-frame prediction processing step, an intermediate prediction image is generated based on reference pixels according to an intra-frame prediction mode, filtering is performed on only a portion of pixels of the intermediate prediction image according to the intra-frame prediction mode to obtain the intra-frame prediction image, pixels at a specific position in the block of the intra-frame prediction image are generated as a final prediction image, and pixels at other positions in the block of the intermediate prediction image are generated as a final prediction image, The intra prediction mode includes a mode for performing average value prediction and a mode for performing directional prediction. 4. A motion picture decoding method, characterized in that: The method comprises an intra-frame prediction processing step, in which, when the coding mode associated with the coding block is the intra-frame coding mode, intra-frame prediction processing is performed on each block serving as a unit of prediction processing to generate an intra-frame prediction image. In the intra-frame prediction processing step, an intermediate prediction image is generated based on reference pixels according to an intra-frame prediction mode, filtering is performed on only a portion of pixels of the intermediate prediction image according to the intra-frame prediction mode to obtain the intra-frame prediction image, pixels at a specific position in the block of the intra-frame prediction image are generated as a final prediction image, and pixels at other positions in the block of the intermediate prediction image are generated as a final prediction image, The intra prediction mode includes a mode for performing average value prediction and a mode for performing directional prediction.