KR20140057518A - Method of decoding moving pictures - Google Patents

Abstract

The present invention relates to an image decoding method which adaptively generates reference pixels of a current block and filters the reference pixels to generate a prediction block close to an original image. According to the present invention, the image decoding method comprises following steps: an intra-prediction mode is reconstructed when an unavailable reference pixel of a current block exists; a reference pixel is generated using the available reference pixels; and whether the reference pixels of the current block are to be filtered is determined based on the reconstructed intra-prediction mode and the size of the current block. When it is determined that the reference pixels of the current block are to be filtered, a filter is selected using the size of the current block; and the difference in information between the reference pixels and the reference pixels of the current block are filtered using the selected filter. A prediction block is generated according to the reconstructed intra-prediction mode.

Description

[0001] METHOD OF DECODING MOVING PICTURES [

The present invention relates to a video decoding method, and more particularly, to a video decoding method for generating a prediction block close to an original video by adaptively generating and filtering reference pixels of a current block.

In general, various digital video compression techniques have been proposed to efficiently transmit moving image signals at a low data rate while maintaining a high image quality. Such video compression techniques include H.261, MPEG-2 / H.262, H.263, MPEG-4, and AVC / H.264. The compression techniques include discrete cosine transform (DCT), motion compensation (MC), quantization, entropy coding, and the like.

In order to maintain a high image quality, a large amount of data is required in coding a moving image. However, the bandwidth that is allowed to transmit the moving picture data is limited, so that the data rate applicable at the time of transmitting the encoded data can be limited. For example, a data channel of a satellite broadcasting system or a data channel of a digital cable television network generally transmits data at a constant bit rate (CBR).

Accordingly, a moving image encoding method has been proposed in order to obtain high image quality while reducing the complexity of the processing method and the transmission data rate, if possible.

For example, the H.264 / AVC standard performs intraprediction encoding in a spatial domain by using neighboring pixel values in intra coding. It is important to determine which pixel value is to be used. In this case, an optimal intra-prediction direction is determined and a predicted value of a pixel to be encoded is calculated using neighboring pixel values corresponding to the direction.

However, if the size of the prediction block is increased and diversified, there is a high possibility that a plurality of reference blocks adjacent to the current block exist. In this case, a step may be generated between the reference pixels located at both boundaries of the reference blocks. When intra prediction is performed using the reference pixels in the case where a step is generated, there is a high possibility that the residual blocks after generation of the prediction block contain a large amount of high-frequency components, which lowers the coding efficiency.

SUMMARY OF THE INVENTION The present invention provides a method of restoring an intra prediction block close to an original image. The present invention provides a method of reducing the amount of data while enhancing image quality by minimizing the amount of residual signal to be reconstructed when a reconstruction block is generated in an intra prediction mode.

According to an aspect of the present invention, there is provided an image decoding method comprising: restoring an intra prediction mode; Generating a reference pixel using an available reference pixel if there is a reference pixel that is not available in the current block; Determining whether to filter reference pixels of a current block based on the intra prediction mode and the size of the current block; Selecting a filter using the size of the current block and the step information between the reference pixels and filtering the reference pixels of the current block using the filter if it is determined to filter the reference pixels of the current block; And generating a prediction block according to the mode.

According to the present invention, a non-available reference pixel is generated from a usable reference pixel, and a reference block is adaptively filtered according to the current block size and intra-prediction mode, Can be generated. In addition, by predicting the prediction block similar to the original image, the residual signal at the time of encoding and decoding is minimized, thereby improving the compression performance of the image and maximizing the encoding and decoding efficiency.

1 is a block diagram showing a moving picture encoding apparatus according to an embodiment of the present invention;
2 is a block diagram illustrating an operation of an intra predictor according to an embodiment of the present invention;
3 is a diagram for explaining planner mode prediction according to an embodiment of the present invention;
4 is a block diagram illustrating a moving picture decoding apparatus according to an embodiment of the present invention;
FIG. 5 is a flowchart for restoring an intra block according to an embodiment of the present invention; FIG.

Hereinafter, various embodiments of the present invention will be described in detail with reference to exemplary drawings. It is to be understood that the invention is not to be limited to the specific embodiments thereof except as defined in the appended claims and all changes, Should be understood to include. Like reference numerals are used for like elements in describing each drawing.

1 is a block diagram illustrating a moving picture encoding apparatus according to an embodiment of the present invention.

1, a moving picture encoding apparatus includes a coding mode determination unit 110, an intra prediction unit 120, a motion compensation unit 130, a motion estimation unit 131, a transform coding / quantization unit 140, an entropy coding A dequantization / conversion decoding unit 160, a deblocking filtering unit 170, a picture storage unit 180, a subtracting unit 190, and an adding unit 200. The dequantization /

The encoding mode determination unit 110 analyzes an input video signal to divide a picture into a predetermined size of an encoding block, and determines a coding mode for the divided predetermined size of the encoding block. The encoding mode includes intraprediction encoding and inter prediction encoding.

The picture is composed of a plurality of slices, and the slice is composed of a plurality of maximum coding units (LCU). The LCU can be divided into a plurality of coding units (CUs), and the encoder can add information indicating whether or not to be divided to a bit stream. The decoder can recognize the position of the LCU by using the address (LcuAddr). The coding unit CU in the case where division is not allowed is regarded as a prediction unit (PU), and the decoder can recognize the position of the PU using the PU index.

The prediction unit PU may be divided into a plurality of partitions. The prediction unit (PU) may also be composed of a plurality of conversion units (TUs).

The encoding mode determination unit 110 sends the image data to the subtraction unit 190 in units of blocks of a predetermined size (for example, in units of PU or TU) according to the determined encoding mode.

The transform coding / quantizing unit 140 transforms the residual block calculated by the subtracting unit 190 from the spatial domain to the frequency domain. For example, two-dimensional discrete cosine transform (DCT) or discrete cosine transform (DST) -based transform is performed on the residual block. In addition, the transcoding / quantization unit 140 determines a quantization step size for quantizing the transform coefficient, and quantizes the transform coefficient using the determined quantization step size. The quantization matrix can be determined according to the determined quantization step size and encoding mode.

The quantized two-dimensional transform coefficients are transformed into one-dimensional quantized transform coefficients by one of the predetermined scanning methods.

The transformed one-dimensional sequence of quantization transform coefficients is supplied to the entropy encoding unit 150.

The inverse quantization / conversion decoding unit 160 dequantizes the quantization coefficients quantized by the transcoding / quantization unit 140. Further, the inverse quantization coefficient obtained by inverse quantization is inversely transformed. Accordingly, the residual block transformed into the frequency domain can be restored into the residual block in the spatial domain.

The deblocking filtering unit 170 receives the inverse quantized and inverse transformed image data from the inverse quantization / inverse transform coding unit 160 and performs filtering to remove a blocking effect.

The picture storage unit 180 receives the filtered image data from the deblocking filtering unit 170 and restores and restores the image in picture units. The picture may be a frame-based image or a field-based image. The picture storage unit 180 has a buffer (not shown) capable of storing a plurality of pictures. A plurality of pictures stored in the buffer are provided for intra prediction and motion estimation. The pictures provided for intra prediction or motion estimation are referred to as reference pictures.

The motion estimation unit 131 receives the at least one reference picture stored in the picture storage unit 180 and performs motion estimation to output motion data including an index indicating a motion vector and a reference picture and a block mode do.

In order to optimize the prediction precision, a motion vector is determined with a fractional pixel precision, for example, 1/2 or 1/4 pixel accuracy. Since the motion vector can have a fractional pixel precision, the motion compensation unit 130 applies the interpolation filter for calculating the pixel value of the fractional pixel position to the reference picture so that the pixel value of the fractional pixel position .

The motion compensation unit 130 is configured to perform motion compensation on a block to be coded from a reference picture used for motion estimation among a plurality of reference pictures stored in the picture storage unit 180 according to the motion data input from the motion estimation unit 131 And outputs the extracted prediction block.

The motion compensation unit 130 determines a filter characteristic of the adaptive interpolation filter necessary for motion compensation with a decimal precision. The filter characteristic is, for example, information indicating the filter type of the adaptive interpolation filter and information indicating the size of the adaptive interpolation filter. The size of the filter is, for example, the number of taps, which is the number of filter coefficients of the adaptive interpolation filter.

Specifically, the motion compensation unit 130 may determine either a separate type or a non-separable type adaptive filter as an adaptive interpolation filter. Then, the number of taps of the determined adaptive interpolation filter and the value of each filter coefficient are determined. The value of the filter coefficient can be determined differently for each position of the fractional pixel relative to the integer pixel. Also, the motion compensation unit 130 may use a plurality of non-adaptive interpolation filters with fixed filter coefficients.

The motion compensation unit 130 can set the characteristics of the interpolation filter in a predetermined processing unit. For example, it can be set in a fractional pixel unit, a coding basic unit (encoding unit), a slice unit, a picture unit, or a sequence unit. In addition, one characteristic may be set for one video data. Therefore, since the same filter characteristic is used in a predetermined processing unit, the motion compensation unit 130 has a memory that temporarily holds the filter characteristic. This memory maintains filter characteristics, filter coefficients, and the like as needed. For example, the motion compensation unit 130 can determine the filter characteristic for each I picture and determine the filter coefficient for each slice.

The motion compensation unit 130 receives a reference picture from the picture storage unit 180 and applies a filter process using the determined adaptive interpolation filter to generate a prediction reference picture of a decimal precision.

Then, based on the generated reference picture and the motion vector determined by the motion estimation unit 131, motion compensation is performed with a small number of pixels to generate a prediction block.

The subtractor 190 receives the block in the reference picture corresponding to the input block from the motion compensator 130 and performs a difference operation with the input macroblock in the case of performing inter picture prediction coding on the input block to be coded, and outputs a residue signal.

The intraprediction unit 120 performs intraprediction encoding using the reconstructed pixel values in a picture to be predicted. The intra prediction unit receives the current block to be predictively encoded and performs intra prediction by selecting one of a plurality of intra prediction modes preset according to the size of the current block. The intra predictor 120 determines the intra prediction mode of the current block using the previously coded pixels adjacent to the current block, and generates a prediction block corresponding to the determined mode.

The previously encoded region of the current picture is decoded again for use by the intra prediction unit 120 and stored in the picture storage unit 180. [ The intra prediction unit 120 generates a prediction block of a current block using pixels neighboring the current block or non-adjacent but applicable pixels in the previously coded area of the current picture stored in the picture storage unit 180. [

The intra prediction unit 120 may adaptively filter adjacent pixels to predict an intra block. For the same operation in the decoder, it is possible to transmit information indicating whether or not filtering is performed in the encoder. Or the intra-prediction mode of the current block and the size information of the current block.

The prediction type used by the image coding apparatus depends on whether the input block is coded in the intra mode or the inter mode by the coding mode determination unit.

The switching between the intra mode and the inter mode is controlled by the intra / inter selector switch.

The entropy encoding unit 150 entropy-codes the quantization coefficients quantized by the transcoding / quantization unit 140 and the motion information generated by the motion estimation unit 131. [ Also, an intra prediction mode, control data (e.g., quantization step size, etc.), and the like can be coded. Also, the filter coefficient determined by the motion compensation unit 130 is encoded and output as a bit stream.

2 is a block diagram showing the operation of the intra predictor 120 according to the present invention.

First, the encoding mode determination unit 110 receives the prediction mode information and the size of the prediction block (S110). The prediction mode information indicates an intra mode. The size of the prediction block may be a square of 64x64, 32x32, 16x16, 8x8, 4x4, or the like, but is not limited thereto. That is, the size of the prediction block may be non-square instead of square.

Next, the reference pixel is read from the picture storage unit 180 to determine the intra-prediction mode of the prediction block.

It is determined whether the reference pixel is generated by examining whether or not the unavailable reference pixel exists (S120). The reference pixels are used to determine the intra prediction mode of the current block.

If the current block is located at the upper boundary of the current picture, pixels adjacent to the upper side of the current block are not defined. In addition, when the current block is located at the left boundary of the current picture, pixels adjacent to the left side of the current block are not defined. It is determined that these pixels are not usable pixels. In addition, it is determined that the pixels are not usable even if the current block is located at the slice boundary and pixels adjacent to the upper or left side of the slice are not encoded and reconstructed.

As described above, if there are no pixels adjacent to the left or upper side of the current block, or if there are no pixels that have been previously coded and reconstructed, the intra prediction mode of the current block may be determined using only available pixels.

However, it is also possible to generate reference pixels at positions that are not available using the available reference pixels of the current block (S130). For example, if the pixels of the upper block are not available, the upper pixels may be created using some or all of the left pixels, or vice versa. That is, available reference pixels at positions closest to the predetermined direction from the reference pixels at unavailable positions can be copied and generated as reference pixels. When there is no usable reference pixel in a predetermined direction, the usable reference pixel at the closest position in the opposite direction can be copied and generated as a reference pixel.

On the other hand, even if the upper or left pixels of the current block exist, the reference pixel may be determined as an unavailable reference pixel according to the encoding mode of the block to which the pixels belong. For example, if the block to which the reference pixel adjacent to the upper side of the current block belongs is inter-coded and the reconstructed block, the pixels can be determined as unavailable pixels. In this case, it is possible to generate usable reference pixels by using pixels belonging to the restored block by intra-coded blocks adjacent to the current block. In this case, information indicating that the encoder determines available reference pixels according to the encoding mode must be transmitted to the decoder.

Next, an intra prediction mode of the current block is determined using the reference pixels (S140). The number of intra prediction modes that can be allowed in the current block may vary depending on the size of the block. For example, if the current block size is 8x8, 16x16, or 32x32, there may be 34 intra prediction modes. If the current block size is 4x4, 17 intra prediction modes may exist. The 34 or 17 intra prediction modes may include at least one non-directional mode and a plurality of directional modes. The one or more non-directional modes may be a DC mode and / or a planar mode. When the DC mode and the planar mode are included in the non-directional mode, there may be 35 intra-prediction modes regardless of the size of the current block. At this time, it may include two non-directional modes (DC mode and planar mode) and 33 directional modes.

The planner mode generates a prediction block of the current block using at least one pixel value (or a predicted value of the pixel value, hereinafter referred to as a first reference value) located at the bottom-right of the current block and the reference pixels .

The planner mode will be described with reference to Fig. FIG. 3 is a diagram for explaining planner mode prediction when the current block is 8x8 block.

A first reference value D located at the bottom-right of the current block and a pixel value C adjacent to the lowermost pixel of the current block adjacent to the left of the current block are used to determine the pixel Lt; / RTI > Similarly, by using the first reference value D and a pixel value B adjacent to the rightmost pixel of the current block among the pixels adjacent to the upper side of the current block, prediction pixels corresponding to the pixels located therebetween . A linear combination may be used to generate the prediction pixel. However, when the arrangement of the pixels is not linear, the prediction pixels can be generated by a predetermined non-linear combination.

Next, the generated predictive pixels (i.e., the pixels between the pixels C and D and the pixels between the pixels B and D) and the pixels adjacent to the current block (i.e., the pixels between A and B and the pixels A and C The remaining prediction pixels are generated. The prediction pixels can be generated by linearly combining two pixels adjacent to the upper side and the left side and two pixels generated at the lower side and the right side. In addition, the coupling does not necessarily have to be linear, but may be a nonlinear coupling considering the distribution of pixels. As described above, in the planar mode, the number of reference pixels used to generate the predictive pixel may vary depending on the position of the predictive pixel.

On the other hand, the left reference pixels of the current block can be used, but the upper reference pixels may not be available. At this time, the upper reference pixels may be generated using one of the first reference value and the left reference pixels. That is, when only the left reference pixels are available, the reference pixel located at the uppermost one of the left reference pixels can be copied to generate upper reference pixels, and the reference pixel located closest to the first reference pixel and the upper pixel To generate predicted pixels between B and D. [

Similarly, when the left reference pixels are not available, the left reference pixel may be generated by copying the leftmost reference pixel among the upper reference pixels, The prediction pixels between C and D can be generated using the pixel and the first reference value.

Meanwhile, the first reference value or information indicating the first reference value may be added to the bitstream and transmitted to the decoder, or the decoder may derive the first reference value.

When the first reference value or the information indicating the first reference value is transmitted to the decoder, the difference between the predicted value of the first reference value and the first reference value using at least one of the encoded and reconstructed pixels adjacent to the current block is transmitted Can reduce the number of bits. To this end, the predicted value of the first reference value may be any one of (1) an average value of reference pixels adjacent to the current block, (2) an average value of A, B and C, and (3) an average value of B and C. As another method, the difference value between A and C and the difference value between A and B may be compared with each other (B or C) indicating a direction in which the difference value is small.

When the first reference value is derived by the encoder and the decoder, the encoder and the decoder should be able to derive the same reference value. For this purpose, the encoder can use the reference pixels A, B, and C to generate the first reference value. Assuming that the screen changes smoothly, (1) the value obtained by adding the difference between B and A to C or the difference between C and A to B, ie, (B + CA) Can be set as the first reference value. In this case, instead of B and C, B adjacent reference pixels and C adjacent reference pixels may be used. In this way, since the encoder and the decoder can restore the first reference value in the same manner, it is not necessary to transmit the first reference value or information indicating the first reference value to the decoder, so that the number of transmitted bits can be reduced.

Next, when the intra-prediction mode of the current block is determined, a prediction block is generated (S150). The prediction block is generated using a reference pixel (including the generated pixel) or a linear combination thereof based on the intra-prediction mode of the current block.

The DC mode generates a prediction block of the current block using an average value of reference pixels adjacent to the current block. The reference pixels may include both a usable reference pixel and a generated reference pixel.

Next, when the intra prediction mode of the current block is determined, the intra prediction mode is encoded (S160). The intra-prediction mode encoding may be performed in the intra-prediction unit 120 or in an intra-prediction mode encoding apparatus (not shown) or an entropy encoding unit 150.

On the other hand, when the number of reference blocks adjacent to the current block is varied, a step may occur between the reference pixels located at the boundary of the reference blocks. In this case, the residual blocks after the prediction block generation are likely to contain a high frequency component. Thus, a problem arises that the blocking artifact between the reference blocks also affects the current block. The problem is that the larger the size of the current block, the higher the frequency. Conversely, if the size of the reference block is larger than the size of the current block, such a problem may not occur.

Therefore, one method to overcome the above problem is to adaptively filter the reference pixels to generate new reference pixels. This may be performed before determining the intra prediction mode. The reference pixels are adaptively filtered in advance according to the intra prediction mode and the size of the prediction block to generate new reference pixels and the intra prediction mode of the current block may be determined using the original reference pixels and the generated new reference pixels have. However, the above method may be performed after determining the intra prediction mode of the current block. Since the problem of the blocking artifact increases as the size of the block increases, the number of prediction modes for filtering the reference pixel may be equal to or greater than the size of the block in the range of the block of a specific size.

If the available reference pixels need to be filtered, two or more filters may be adaptively applied according to the difference in level difference between the reference pixels. The filter is preferably a low-pass filter. For example, when using two filters, the first filter may be a 3-tap filter and the second filter may be a 5-tap filter. The second filter may be a filter that applies the first filter twice. The filter coefficient of the filter is preferably symmetrical. Alternatively, only one filter may be used to reduce complexity.

In addition, it is preferable that the above-described filter is adaptively applied according to the size of a current block (block to be intra-predicted). That is, when the current block size is smaller than the first size, a filter having a narrow bandwidth may be applied or a filter may not be applied, and a filter may be applied to a current block having a first size to a second size It is desirable to increase the number of intra prediction modes. The current block in which the intra prediction is performed may be the size of the transform block.

In the case of the DC mode, since a prediction block is generated with an average value of reference pixels, there is no need to apply a filter. That is, when the filter is applied, only unnecessary calculation amount is increased. In addition, it is not necessary to apply the filter to the reference pixel in the vertical mode in which the image has vertical correlation. It is not necessary to apply the filter to the reference pixel even in the horizontal mode in which the image is related to the horizontal direction. Since the filtering is applied to the intra-prediction mode of the current block, the reference pixel can be adaptively filtered based on the intra-prediction mode of the current block and the size of the block to be intra-predicted. The reference pixel is not filtered if the size of the block on which intra prediction is to be performed is smaller than a predetermined size (for example, 4x4). Or may not filter the reference pixel even if it is greater than a predetermined size for complexity reduction. When the size of the block falls within a predetermined size range, any one of intra-prediction modes between a diagonal intra-prediction mode (a mode having a 45-degree angle with the horizontal or vertical mode) and a horizontal- When the reference pixels are filtered in one mode, the reference pixels are filtered in the directional modes between the mode and the diagonal intra prediction mode.

Another method for overcoming the above problem is to adaptively filter some pixels of a prediction block generated using the reference pixels to generate a new prediction block. The prediction pixels in contact with the reference pixels among the prediction pixels of the prediction block according to the intra prediction mode of the current block can be corrected using at least one reference pixel. This may be applied together at the time of generating the prediction block.

For example, in the DC mode, a prediction pixel in contact with reference pixels among prediction pixels is filtered using a reference pixel in contact with the prediction pixel. Therefore, the predictive pixel is filtered using one or two reference pixels according to the position of the predictive pixel. The filtering of the prediction pixel in the DC mode can be applied to the prediction block of all sizes.

In the vertical mode, the prediction pixels adjacent to the left reference pixel among the prediction pixels of the prediction block may be changed using reference pixels other than the upper pixel used to generate the prediction block. Likewise, in the horizontal mode, the prediction pixels adjacent to the upper reference pixel among the generated prediction pixels may be changed using reference pixels other than the left pixel used to generate the prediction block.

Meanwhile, the current block and the residual block of the prediction block generated by the intraprediction unit 120 are encoded through the transcoding / quantization unit 140 and the entropy encoding unit 150.

The residual block is transcoded first. For efficient energy compression, the size of a transform block for transform coding to be applied to the residual block is first determined, and transformed into a block unit of a determined size. Or the size of the transform transform may be predetermined. In this case, the size of the current block performing intra prediction may be the size of the transform block. Different transcoding schemes may be applied depending on the intra prediction mode value. For example, integer-based DCT (Discrete Cosine Transform) may be applied in the horizontal and vertical directions for the intra-predicted residual block in the DC mode, and integer-based DST (discrete sine transform) may be applied in the horizontal and vertical directions for the planar mode .

This can be applied to blocks smaller than or equal to a predetermined size. However, only integer-based DCTs may be applied to transform blocks larger than a predetermined size regardless of the intra-prediction mode. The horizontal and vertical DCT and DST schemes may be applied adaptively according to the prediction mode.

Next, the transform coded residual block is quantized. Different quantization matrices are applied depending on the size of the residual block. Also, different quantization matrices may be applied to residual blocks of the same size. That is, the most effective quantization matrix of at least two or more quantization matrices can be applied based on the distribution of the coefficients of the transform coded residual block. In this case, information indicating the quantization matrix is transmitted to the decoder. In addition, different quantization matrices may be applied to the transcoded residual block according to the intra prediction mode.

Next, one of the predetermined two-dimensional quantized coefficients is selected and a one-dimensional quantized coefficient sequence is changed, followed by entropy coding. The scan pattern may be determined according to the intra-prediction mode or the size of the intra-prediction mode and the transform block.

4 is a block diagram illustrating a moving picture decoding apparatus according to an embodiment of the present invention.

4, the moving picture decoding apparatus according to the present invention includes an intropy decoding unit 210, an inverse quantization / inverse transformation unit 220, an adder 270, a deblocking filter unit 250, a picture storage unit 260 An intra prediction unit 230, a motion compensation prediction unit 240, and an intra / inter changeover switch 280.

The intropy decoding unit 210 decodes the encoded bit stream transmitted from the moving picture encoding apparatus into an intra prediction mode index, motion information, and a quantization coefficient sequence. The intropy decoding unit 210 supplies the decoded motion information to the motion compensation prediction unit 240. [ The intropy decoding unit 210 supplies the intra prediction mode index to the intraprediction unit 230 and the inverse quantization / inverse transformation unit 220. Also, the intropy decoding unit 210 supplies the inverse quantization coefficient sequence to the inverse quantization / inverse transformation unit 220.

The inverse quantization / inverse transform unit 220 transforms the quantized coefficient sequence into an inverse quantization coefficient of the two-dimensional array. One of a plurality of scanning patterns is selected for the conversion. One of a plurality of scanning patterns is selected based on the prediction mode of the current block (i.e., any one of intra prediction and inter prediction), the intra prediction mode, and the size of the conversion block. The intraprediction mode is received from the intra prediction unit or intropy decoding unit 210.

The inverse quantization / inverse transform unit 220 restores the quantization coefficients using the selected quantization matrix among the plurality of quantization matrices to the inverse quantization coefficients of the two-dimensional array. The quantization matrix may be determined using information received from the encoder. Different quantization matrices may be applied depending on the size of the current block (transform block) to be restored, and a quantization matrix may be selected based on at least one of a prediction mode and an intra prediction mode of the current block with respect to blocks of the same size. Then, the reconstructed quantized coefficient is inversely transformed to reconstruct the residual block.

The adder 270 reconstructs the image block by adding the residual block reconstructed by the inverse quantization / inverse transforming unit 220 to the intra prediction unit 230 or the prediction block generated by the motion compensation prediction unit 240.

The deblocking filter unit 250 performs deblocking filter processing on the reconstructed image generated by the adder 270. [ Accordingly, the deblocking artifact due to the video loss due to the quantization process can be reduced.

The picture storage unit 260 is a frame memory for holding a local decoded picture subjected to deblocking filter processing by the deblocking filter unit 250. [

The intraprediction unit 230 restores the intra prediction mode of the current block based on the intra prediction mode index received from the Intropy decoding unit 210. A prediction block is generated according to the restored intra prediction mode.

The motion compensation prediction unit 240 generates a prediction block for the current block from the picture stored in the picture storage unit 260 based on the motion vector information. When motion compensation with a decimal precision is applied, a prediction block is generated by applying a selected interpolation filter.

The intra / inter selector switch 280 provides the adder 270 with a prediction block generated in either the intra prediction unit 230 or the motion compensation prediction unit 240 based on the coding mode.

Hereinafter, a process of restoring a current block through intraprediction will be described with reference to FIG. 5 is a flowchart for restoring an intra block according to an embodiment of the present invention.

First, the intra-prediction mode of the current block is decoded from the received bitstream (S310).

To this end, the intropy decoding unit 210 restores the first intra prediction mode index of the current block by referring to one of the plurality of intra prediction mode tables.

The plurality of intra prediction mode tables are tables shared by the encoder and the decoder, and may be any one selected according to the distribution of intra prediction modes of a plurality of blocks adjacent to the current block. For example, if the intra prediction mode of the left block of the current block and the intra prediction mode of the upper block of the current block are the same, the first intra prediction mode table of the current block is restored by applying the first intra prediction mode table, The first intra prediction mode index of the current block can be restored by applying the second intra prediction mode table. As another example, when the intra prediction modes of the upper block and the left block of the current block are all the directional intra prediction modes, the direction of the intra prediction mode of the upper block and the intra prediction mode of the left block If the direction is within a predetermined angle, the first intra-prediction mode table of the current block is restored by applying the first intra-prediction mode table. If the direction is outside the predetermined angle, the second intra- The mode index can also be restored.

The intropy decoding unit 210 transmits the first intraprediction mode index of the restored current block to the intra predictor 230.

The intraprediction unit 230 receiving the index of the first intraprediction mode determines the maximum possible mode of the current block as the intra prediction mode of the current block when the index has the minimum value (i.e., 0). However, if the index has a value other than 0, the index indicating the maximum possible mode of the current block is compared with the first intra-prediction mode index. If the first intra-prediction mode index is not smaller than the index indicated by the maximum possible mode of the current block, the intra-prediction mode corresponding to the second intra-prediction mode index obtained by adding 1 to the first intra- The intra prediction mode of the current block is determined as the intra prediction mode corresponding to the first intra prediction mode index.

The intra prediction mode acceptable for the current block may be composed of at least one non-directional mode and a plurality of directional modes. The one or more non-directional modes may be a DC mode and / or a planar mode. In addition, either the DC mode or the planar mode may be adaptively included in the allowable intra prediction mode set. To this end, information specifying the non-directional mode included in the allowable intra prediction mode set may be included in the picture header or slice header.

Next, in order to generate an intra prediction block, the intra predictor 230 rotates the reference pixels stored in the picture storage unit 260, and determines whether there is a non-available reference pixel (S320). The determination may be made according to the presence or absence of the reference pixels used to generate the intra prediction block by applying the decoded intra prediction mode of the current block.

Next, when it is necessary to generate a reference pixel, the intra-prediction unit 230 generates reference pixels at positions that are not available using the reconstructed available reference pixels (S325). The definition of a reference pixel that is not available and the method of generating a reference pixel are the same as those in the intra prediction unit 120 shown in FIG. However, it is also possible to selectively reconstruct a reference pixel used for generating an intra prediction block according to the decoded intra prediction mode of the current block.

Next, in order to generate the prediction block, the intra-prediction unit 230 determines whether to apply the filter to the reference pixels (S330). That is, the intra-prediction unit 230 determines whether to apply filtering on the reference pixels to generate an intra-prediction block of the current block based on the decoded intra-prediction mode and the size of the current prediction block. Since the problem of blocking artifacts increases as the size of the block increases, the larger the size of the block, the larger the number of prediction modes for filtering reference pixels. However, when the block is larger than a predetermined size, it can be regarded as a flat area, so that reference pixels may not be filtered to reduce the complexity.

If it is determined that the reference pixel needs to be applied to the reference pixel, the reference pixels are filtered using the filter (S335).

At least two or more filters may be adaptively applied according to the difference in level difference between the reference pixels. The filter coefficient of the filter is preferably symmetrical.

In addition, the above two or more filters may be adaptively applied according to the size of the current block. That is, when a filter is applied, a filter having a narrow bandwidth may be applied to a block having a small size, and a filter having a wide bandwidth may be applied to a block having a large size.

In the case of the DC mode, since a prediction block is generated with an average value of reference pixels, there is no need to apply a filter. That is, when the filter is applied, only unnecessary calculation amount is increased. In addition, it is not necessary to apply the filter to the reference pixel in the vertical mode in which the image has vertical correlation. It is not necessary to apply the filter to the reference pixel even in the horizontal mode in which the image is related to the horizontal direction. Since the filtering is applied to the intra-prediction mode of the current block, the reference pixel can be adaptively filtered based on the intra-prediction mode of the current block and the size of the prediction block.

Next, in step S340, a prediction block is generated using the reference pixel or the filtered reference pixels according to the reconstructed intra prediction mode. The generation of the prediction block is the same as the operation in the encoder of FIG. 2 and thus is omitted. The planner mode is also the same as the operation in the encoder of FIG.

Next, it is determined whether to filter the generated prediction block (S350). The determination as to whether to perform the filtering may use information included in the slice header or the encoding unit header. It may also be determined according to the intra prediction mode of the current block.

If it is determined to filter the generated prediction block, the generated prediction block is filtered (S335). Specifically, a new pixel is generated by filtering pixels at a specific position of a prediction block generated using available reference pixels adjacent to the current block. This may be applied together at the time of generating the prediction block. For example, in the DC mode, a prediction pixel in contact with reference pixels among prediction pixels is filtered using a reference pixel in contact with the prediction pixel. Therefore, the predictive pixel is filtered using one or two reference pixels according to the position of the predictive pixel. The filtering of the prediction pixel in the DC mode can be applied to the prediction block of all sizes. In the vertical mode, the prediction pixels adjacent to the left reference pixel among the prediction pixels of the prediction block may be changed using reference pixels other than the upper pixel used to generate the prediction block. Likewise, in the horizontal mode, the prediction pixels adjacent to the upper reference pixel among the generated prediction pixels may be changed using reference pixels other than the left pixel used to generate the prediction block.

The current block is reconstructed using the predicted block of the current block restored in this manner and the residual block of the decoded current block.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the present invention as defined by the following claims It can be understood that

110: coding mode determination unit 120: intra prediction unit
130: motion compensation unit 131: motion estimation unit
140: Transcoding / quantization unit 150: Entropy encoding unit
160: Inverse quantization / conversion decoding unit 170: De-blocking filtering unit
180: Picture storage unit 190:
200: adder 210: intropy decoder
220: Inverse quantization / inverse transform unit 230:
240: motion compensation prediction unit 250: deblocking filter unit
260: Picture storage unit 270:
280: Intra / Inter switch

Claims (10)

Restoring an intra prediction mode;
Generating a reference pixel using an available reference pixel if there is a reference pixel that is not available in the current block;
Determining whether to filter reference pixels of a current block based on the intra prediction mode and the size of the current block;
Selecting a filter using the size of the current block and the step information between the reference pixels and filtering the reference pixels of the current block using the filter if it is determined to filter the reference pixels of the current block;
And generating a prediction block according to the intra prediction mode. The video decoding method of claim 1, wherein the intra prediction mode is selected from a predetermined number of directional intra prediction modes and two non-directional intra prediction modes. The method of claim 1, wherein as the size of the current block increases, the number of intra prediction modes for filtering a reference pixel increases. The video decoding method according to claim 1, wherein a reference pixel is generated using an available reference pixel nearest to a predetermined direction from a position of the unavailable reference pixel. 5. The video decoding method according to claim 4, wherein if there is no reference pixel available in the predetermined direction, the reference pixel is generated by copying the available reference pixel in the nearest position in the opposite direction. 5. The image decoding method of claim 4, wherein reference pixels of a current block belonging to the inter-coded reconstructed block are set as unavailable. 2. The method of claim 1, wherein when the reference pixels are filtered in a first intraprediction mode between a diagonal intra-prediction mode and a horizontal intra-prediction mode, the directionality between the first intraprediction mode and the diagonal- Wherein the reference pixels are filtered even in the intra prediction mode. 3. The method of claim 2, wherein the two non-directional modes are a DC mode and a planar mode. The method of claim 1, wherein if the reconstructed intra prediction mode is a vertical mode, prediction pixels of the prediction block are changed using reference pixels other than reference pixels used for generating a prediction block. The method of claim 1, wherein, when the reconstructed intra prediction mode is a horizontal mode, prediction pixels of the prediction block are changed using reference pixels other than reference pixels used for generating a prediction block.

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