KR20210148046A - Method for fast transform coefficient coding and apparatus for the same - Google Patents

Abstract

The present invention relates to a fast-transform coefficient encoding method executed by a fast-transform coefficient encoding apparatus. According to the present invention, the fast-transform coefficient encoding method comprises: encoding a last significant coefficient which is a non-zero transform coefficient existing last in a forward scan order in a transform block; encoding a significant map as a syntax element for whether there is at least one non-zero transform coefficient in a sub-block among the transform blocks and a syntax element for whether the value of each transform coefficient in the sub-block is 0; and using a syntax element for whether the absolute value of the transform coefficient is greater than 1, a syntax element for whether the absolute value of the transform coefficient is greater than 1, a syntax element for sign information of the transform coefficient, and a syntax element for a residual value of the absolute value for the transform coefficient to encode the transform coefficients in the sub-block. Accordingly, complexity of encoding can be reduced even in a situation where there are many transform coefficients to be encoded.

Description

Method and apparatus for encoding fast transform coefficients

The present invention relates to a method and apparatus for encoding a fast transform coefficient.

Recently, as broadcasting services having a high definition (HD) resolution are expanding not only in Korea but also around the world, many users are getting used to high-resolution and high-definition images.

Accordingly, many organizations are spurring the development of next-generation imaging devices. In addition, as interest in Ultra High Definition (UHD) having a resolution four times higher than that of HDTV increases along with HDTV, a compression technology for higher resolution and high-definition images is required.

In addition, for image compression, inter prediction technology for predicting pixel values included in the current picture from temporally previous and/or subsequent pictures, pixel values included in the current picture using pixel information in the current picture Predictive intra prediction techniques may be used. Also, for image compression, an entropy encoding technique in which a short code is assigned to a symbol having a high frequency of occurrence and a long code is assigned to a symbol having a low frequency of occurrence may be used.

However, the existing technology has a problem in that the complexity of encoding is large in a situation where there are many transform coefficients to be encoded.

Accordingly, it is intended to propose a technique capable of reducing the complexity of encoding even in a situation in which many transform coefficients to be encoded exist.

An object of the present invention is to solve all of the above problems.

Another object of the present invention is to provide a method for reducing the complexity of encoding even in a situation where there are many transform coefficients to be encoded.

Another object of the present invention is to encode in a bypass mode with respect to a combination of at least one of syntax elements encoded in the regular mode in transform coefficient encoding in a rate-distortion optimization process.

In order to achieve the object of the present invention as described above and to realize the characteristic effects of the present invention to be described later, the characteristic configuration of the present invention is as follows.

In the fast transform coefficient encoding method performed by the fast transform coefficient encoding apparatus according to an embodiment, the fast transform coefficient encoding method includes a last significant coefficient that is a non-zero transform coefficient that exists last in a forward scan order within a transform block. encoding; An important map is encoded as a syntax element for whether there is at least one non-zero transform coefficient in a sub-block among the transform blocks and a syntax element for whether the value of each transform coefficient in the sub-block is 0 or not. to do; and a syntax element for whether the absolute value of the transform coefficient is greater than 1, a syntax element for whether the absolute value of the transform coefficient is greater than 1, a syntax element for sign information of the transform coefficient, and a residual value of the absolute value for the transform coefficient The method may include encoding the transform coefficients in the subblock using syntax elements.

In the fast transform coefficient encoding method performed by the fast transform coefficient encoding apparatus according to another embodiment, the fast transform coefficient encoding method includes one of a diagonal scan, a horizontal scan, and a vertical scan. The method may further include a scanning step of rearranging the transform coefficients in an array form using at least one.

In the fast transform coefficient encoding method performed by the fast transform coefficient encoding apparatus according to another embodiment, the encoding of the last significant coefficient uses two-dimensional coordinates x and y as syntax elements for the last significant coefficient. to express the transform block, and dividing x and y into a suffix part and a prefix part, respectively, may include binarization.

In the fast transform coefficient encoding method performed by the fast transform coefficient encoding apparatus according to another embodiment, the encoding of the last significant coefficient may include a rate of at least one of the prefix part of x and the prefix part of y. - Can include calculating by encoding in bypass mode during distortion optimization.

In the fast transform coefficient encoding method performed by the fast transform coefficient encoding apparatus according to another embodiment, the encoding of the significant map or the encoding of the transform coefficient includes rate-distortion optimization for at least one of syntax elements. It may include calculating by encoding in the city bypass mode.

According to an embodiment, in an apparatus for encoding a fast transform coefficient, the apparatus for encoding a fast transform coefficient includes: a last significant coefficient encoding unit for encoding a last significant coefficient that is a non-zero transform coefficient that exists last in a forward scan order within a transform block; An important map is encoded as a syntax element for whether there is at least one non-zero transform coefficient in a sub-block among the transform blocks and a syntax element for whether the value of each transform coefficient in the sub-block is 0 or not. an important map encoding unit; and a syntax element for whether the absolute value of the transform coefficient is greater than 1, a syntax element for whether the absolute value of the transform coefficient is greater than 1, a syntax element for sign information of the transform coefficient, and a residual value of the absolute value for the transform coefficient and a transform coefficient encoder for encoding transform coefficients in the subblock using syntax elements.

In the fast transform coefficient encoding apparatus according to another embodiment, the fast transform coefficient encoding apparatus uses at least one of a diagonal scan, a horizontal scan, and a vertical scan to perform the transform coefficient It may further include a scan unit that rearranges the in the form of an array.

In the fast transform coefficient encoding apparatus according to another embodiment, the last significant coefficient encoding unit expresses a transform block using two-dimensional coordinates x and y as syntax elements with respect to the last significant coefficient, wherein the x and the It may include binarizing y by dividing it into a suffix part and a prefix part, respectively.

In the fast transform coefficient encoding apparatus according to another embodiment, the last significant coefficient encoding unit is calculated by encoding at least one of the prefix part of x and the prefix part of y in a bypass mode during rate-distortion optimization. may include doing

In the fast transform coefficient encoding apparatus according to another embodiment, the significant map encoding unit or the transform coefficient encoding unit may include calculating by encoding at least one of syntax elements in a bypass mode during rate-distortion optimization. can

The present invention has the effect of reducing the complexity of the encoder even in a situation where there are many transform coefficients to be encoded.

The present invention may provide a bypass mode encoding for at least one combination of syntax elements encoded in the regular mode in transform coefficient encoding in a rate-distortion optimization process. Therefore, the present invention has an effect of reducing the complexity of the encoder even in a situation where there are many transform coefficients to be encoded, such as in a high bit rate application field.

1 is a flowchart illustrating a fast transform coefficient encoding method according to an embodiment.
2 is a block diagram illustrating an apparatus for encoding a fast transform coefficient according to an embodiment.
3 illustrates a detailed configuration of a fast transform coefficient encoding apparatus according to an embodiment.
4 is a diagram illustrating an image decoding apparatus to which a fast transform coefficient encoding method according to an embodiment is applied.
5 is a diagram schematically illustrating an image segmentation structure when an image is encoded and decoded using a fast transform coefficient encoding method according to an embodiment.
6 is a diagram illustrating a form of a prediction unit that may be included in an encoding unit to which a fast transform coefficient encoding method according to an embodiment is applied.
7 is a diagram illustrating a form of a transform unit that may be included in an encoding unit to which a fast transform coefficient encoding method according to an embodiment is applied.
8 is a diagram illustrating entropy encoding to which a fast transform coefficient encoding method according to an embodiment is applied.
9 is a diagram illustrating encoding after the last significant coefficient among backward scans to which the fast transform coefficient encoding method according to an embodiment is applied.
10 is a diagram illustrating encoding of a reverse scan order of sub-blocks to which a fast transform coefficient encoding method is applied according to an embodiment.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a flowchart illustrating a fast transform coefficient encoding method according to an embodiment.

The fast transform coefficient encoding method performed by the fast transform coefficient encoding apparatus is performed in the following steps.

In step S101, the high-speed transform coefficient encoding apparatus performs a scan in which transform coefficients are rearranged in an array form using at least one of a diagonal scan, a horizontal scan, and a vertical scan. can do.

In step S102 , the apparatus for encoding a fast transform coefficient may encode a last significant coefficient that is a non-zero transform coefficient that exists last in the case of a forward scanning order within a transform block.

In this case, the high-speed transform coefficient encoding apparatus may express the transform block by using two-dimensional coordinates x and y as syntax elements for the last significant coefficient, and divide the x and y into a suffix part and a prefix part, respectively, to be binarized.

Also, the fast transform coefficient encoding apparatus may calculate by encoding at least one of the prefix part of x and the prefix part of y in the bypass mode during rate-distortion optimization.

In step S103, the high-speed transform coefficient encoding apparatus includes a syntax element for determining whether at least one non-zero transform coefficient in a sub-block among transform blocks and whether each transform coefficient in the sub-block has a value of 0 or 0 As a syntax element for whether or not it is, it is possible to encode a significant map.

In step S104, the fast transform coefficient encoding apparatus provides a syntax element for whether the absolute value of the transform coefficient is greater than 1, a syntax element for whether the absolute value of the transform coefficient is greater than 1, and a syntax element for sign information of the transform coefficient , a transform coefficient in a subblock may be encoded by using a syntax element for a residual value of an absolute value of the transform coefficient.

In this case, in step S103 or S104, the fast transform coefficient encoding apparatus may calculate by encoding at least one of the syntax elements in the bypass mode during rate-distortion optimization.

2 is a block diagram illustrating an apparatus for encoding a fast transform coefficient according to an embodiment.

First, referring to FIG. 2 , the entire system of the high-speed transform coefficient encoding apparatus is to be composed of a scan unit 210 , a last significant coefficient encoding unit 220 , a significant map encoding unit 230 , and a transform coefficient encoding unit 240 . can Of course, in some cases, the fast transform coefficient encoding apparatus 200 may include the last significant coefficient encoding unit 220 , the significant map encoding unit 230 , and the transform coefficient encoding unit 240 . In this case, the scan unit 210 , the last significant coefficient encoding unit 220 , the significant map encoding unit 230 , and the transform coefficient encoding unit 240 may include an electronic circuit, an electric circuit, and an integrated circuit. In addition, the scan unit 210 , the last significant coefficient encoder 220 , the significant map encoder 230 , and the transform coefficient encoder 240 may include a processor, a memory, and a data transceiver, but are limited thereto. it doesn't happen

The scan unit 210 may rearrange the transform coefficients in an array form using at least one of a diagonal scan, a horizontal scan, and a vertical scan.

The last significant coefficient encoder 220 may encode a last significant coefficient that is a non-zero transform coefficient that exists last in a forward scan order within a transform block.

At this time, the last significant coefficient encoding unit 220 expresses the transform block using two-dimensional coordinates x and y as syntax elements for the last significant coefficient, and divides x and y into a suffix part and a prefix part, respectively, to be binarized. can

Also, the last significant coefficient encoder 220 may calculate by encoding at least one of the prefix part of x and the prefix part of y in the bypass mode during rate-distortion optimization.

The important map encoder 230 determines whether there is at least one non-zero transform coefficient in a sub-block among transform blocks, and determines whether the value of each transform coefficient in the sub-block is 0 or not. It is possible to encode a critical map as a syntax element.

The transform coefficient encoding unit 240 includes a syntax element for whether the absolute value of the transform coefficient is greater than 1, a syntax element for whether the absolute value of the transform coefficient is greater than 1, a syntax element for sign information of the transform coefficient, and a transform coefficient. A transform coefficient in a subblock may be coded using a syntax element for a residual value of an absolute value of .

In addition, the significant map encoder 230 or the transform coefficient encoder 240 may calculate by encoding at least one of the syntax elements in the bypass mode during rate-distortion optimization.

3 illustrates a detailed configuration of a fast transform coefficient encoding apparatus according to an embodiment.

Referring to FIG. 3 , it is a block diagram showing the configuration of an image encoding apparatus that is a high-speed transform coefficient encoding apparatus. The image encoding apparatus 300 , which is a high-speed transform coefficient encoding apparatus, may include a motion predictor 311 , a motion compensator 312 , an intra predictor 320 , and a switch 315 . In addition, the video encoding apparatus 300, which is a high-speed transform coefficient encoding apparatus, includes a subtractor 325, a transformation unit 330, a quantization unit 340, an entropy encoding unit 350, an inverse quantization unit 360, and an inverse transform unit ( 370 ), an adder 375 , a filter unit 380 , and a reference picture buffer 390 may be included.

The image encoding apparatus 300, which is a high-speed transform coefficient encoding apparatus, may perform encoding on an input image in an intra mode or an inter mode and output a bitstream. Also, in the case of the intra mode, the switch 315 may be switched to the intra mode, and in the case of the inter mode, the switch 315 may be switched to the inter mode. Also, the image encoding apparatus 300 , which is a fast transform coefficient encoding apparatus, may generate a prediction block for an input block of an input image, and then encode a residual between the input block and the prediction block.

In the intra mode, the intra prediction unit 320 may generate a prediction block by performing spatial prediction using pixel values of an already encoded block around the current block. Also, in the inter mode, the motion predictor 311 may find a region that best matches the input block in the reference image stored in the reference picture buffer 390 during the motion prediction process to obtain a motion vector. Also, the motion compensator 312 may generate a prediction block by performing motion compensation using a motion vector. In this case, the motion vector is a two-dimensional vector used for inter prediction, and may indicate an offset between the current encoding and decoding target image and the reference image.

The subtractor 325 may generate a residual block by the difference between the input block and the generated prediction block.

The transform unit 330 may perform transform on the residual block to output a transform coefficient. Here, the transform coefficient may mean a coefficient value generated by performing transform on the residual block or the residual signal. Of course, in some cases, a quantized transform coefficient level generated by applying quantization to a transform coefficient may also be referred to as a transform coefficient.

The quantization unit 340 may quantize the input transform coefficient according to the quantization parameter and output a quantized transform coefficient level. In this case, the quantization unit 340 may quantize the input transform coefficient using a quantization matrix. In this case, the quantized transform coefficient level may be a quantized level, or in some cases, may be a part of the transform coefficient.

The entropy encoding unit 350 may output a bit stream by performing entropy encoding based on the values calculated by the quantization unit 340 or the encoding parameter values calculated during the encoding process.

In this case, when entropy encoding is applied, a small number of bits are allocated to a symbol having a high occurrence probability and a large number of bits are allocated to a symbol having a low occurrence probability, so that the symbol can be expressed. Of course, the size of the bit stream for the encoding target symbols may be reduced. In addition, compression performance of image encoding may be improved through entropy encoding.

In addition, the entropy encoder 350 derives a binarization method of the target symbol and a probability model of the target symbol or bin, and then arithmetic encoding using the derived binarization method or probability model. can also be performed. Also, the entropy encoder 350 may use an encoding method such as exponential golomb, Context-Adaptive Variable Length Coding (CAVLC), or Context-Adaptive Binary Arithmetic Coding (CABAC) for entropy encoding.

Since the image encoding apparatus 300 , which is a fast transform coefficient encoding apparatus according to an embodiment, performs inter prediction encoding, that is, inter prediction encoding, the currently encoded image needs to be decoded and stored to be used as a reference image. In addition, the quantized level is inverse quantized by the inverse quantization unit 360 and inversely transformed by the inverse transformation unit 370 . In addition, the inverse-quantized and inverse-transformed coefficients are added to the prediction block through the adder 375 and a reconstructed block is generated.

The reconstructed block passes through the filter unit 380, and the filter unit 380 applies at least one of a deblocking filter, a sample adaptive offset (SAO), and an adaptive loop filter (ALF) to the reconstructed block or the reconstructed picture. can do. In this case, the filter unit 380 may be an adaptive in-loop filter. In addition, the deblocking filter may remove block distortion generated at the boundary between blocks. The SAO may add an appropriate offset value to a pixel value to compensate for a coding error. The ALF may perform filtering based on a value obtained by comparing the reconstructed image and the original image. The reconstructed block that has passed through the filter unit 380 may be stored in the reference picture buffer 390 .

4 is a diagram illustrating an image decoding apparatus to which a fast transform coefficient encoding method according to an embodiment is applied.

Referring to FIG. 4 , the image decoding apparatus 400 to which the fast transform coefficient encoding method is applied includes an entropy decoding unit 410 , an inverse quantization unit 420 , an inverse transform unit 430 , an intra prediction unit 440 , and motion compensation. It may include a unit 450 , an adder 455 , a filter unit 460 , and a reference picture buffer 470 .

The image decoding apparatus 400 to which the fast transform coefficient encoding method is applied receives the bitstream output by the encoder which is the fast transform coefficient encoding apparatus, performs decoding in intra mode or inter mode, and outputs a reconstructed image, that is, a reconstructed image. can do. Specifically, in the intra mode, the switch may be switched to intra, and in the inter mode, the switch may be switched to inter.

Also, the image decoding apparatus 400 to which the fast transform coefficient encoding method is applied may obtain a reconstructed residual block from the received bitstream and generate a prediction block. Next, the image decoding apparatus 400 to which the fast transform coefficient encoding method is applied may generate a reconstructed block that is a reconstructed block by adding the reconstructed residual block and the prediction block.

The entropy decoding unit 410 entropy-decodes the input bitstream according to a probability distribution to generate symbols including symbols in the form of quantized levels. Also, the entropy decoding method may be performed as a reverse process of the entropy encoding.

The quantized level is inverse quantized by the inverse quantization unit 420 and inversely transformed by the inverse transformation unit 430 . As a result of inverse quantization and inverse transformation of the quantized level, a reconstructed residual block may be generated. In this case, the inverse quantizer 420 may apply a quantization matrix to the quantized level.

In the intra mode, the intra prediction unit 440 may generate a prediction block by performing spatial prediction using pixel values of an already encoded block around the current block. In the inter mode, the motion compensator 450 may generate a prediction block by performing motion compensation using a motion vector and a reference image stored in the reference picture buffer 470 .

The reconstructed residual block and the prediction block are added by the adder 455 , and the added block may pass through the filter unit 460 . The filter unit 460 may apply at least one of a deblocking filter, SAO, and ALF to a reconstructed block or a reconstructed picture. The filter unit 460 may output a reconstructed image, that is, a reconstructed image. In some cases, the reconstructed image may be stored in the reference picture buffer 470 and used for inter prediction.

5 is a diagram schematically illustrating an image segmentation structure when an image is encoded and decoded using a fast transform coefficient encoding method according to an embodiment.

The fast transform coefficient encoding apparatus may perform encoding and decoding with a coding unit (CU) in order to efficiently segment an image. The unit may be configured by combining a syntax element and a block including image samples. Also, a unit may be divided, and in this case, a block corresponding to the unit may be divided depending on the case.

Referring to FIG. 5 , in HEVC, the high-speed transform coefficient encoding apparatus may sequentially partition an image 500 in units of Largest Coding Units (LCUs), and then determine a division structure in units of LCUs. In some cases, the partition structure may indicate a distribution of encoding units (CUs) for efficiently encoding an image in the LCU 510 .

In this case, the fast transform coefficient encoding apparatus may determine whether to split the distribution of a CU into four CUs reduced by half of a horizontal size and a vertical size of one CU. Of course, the divided CU may be recursively divided into four CUs whose horizontal size and vertical size are reduced by half with respect to the divided CU in the same manner.

In addition, the fast transform coefficient encoding apparatus may recursively divide the CU segmentation to a predefined depth. In this case, the depth information is information indicating the size of a CU, and may be stored for each CU.

For example, the depth of the LCU may be 0, and the depth of the Smallest Coding Unit (SCU) may be a predefined maximum depth. Of course, the LCU may be a coding unit having the largest coding unit size as described above, and the Smallest Coding Unit (SCU) may be a coding unit having the smallest coding unit size.

The depth of the CU increases by 1 whenever division is performed from the LCU 510 to half of the horizontal and vertical sizes. In addition, for each depth, a CU that does not perform division has a size of 2Nx2N, and a CU that performs division can be divided into four CUs having a size of NxN from a CU having a size of 2Nx2N. In this case, the size of N may be reduced by half whenever the depth increases by 1.

Also, for example, the size of an LCU having a minimum depth of 0 may be 64x64 pixels, and a size of an SCU having a maximum depth of 3 may be 8x8 pixels. In this case, a CU (LCU) of 64x64 pixels may be expressed as depth 0, a CU of 32x32 pixels as depth 1, a CU of 16x16 pixels as depth 2, and a CU (SCU) of 8x8 pixels as depth 3 may be expressed.

In addition, information on whether to split a specific CU may be expressed through 1-bit partition information for each CU. This partitioning information may be included in all CUs except for the SCU, and in some cases, when the fast transform coefficient encoding apparatus does not split a CU, 0 may be stored in the partition information, and the fast transform coefficient encoding apparatus divides the CU. In this case, 1 may be stored in the division information.

6 is a diagram illustrating a form of a prediction unit that may be included in an encoding unit to which a fast transform coefficient encoding method according to an embodiment is applied.

Referring to FIG. 6 , the shape of the prediction unit PU that the encoding unit CU may include may be known. The apparatus for encoding a fast transform coefficient may split a CU that is no longer split among CUs split from an LCU into one or more prediction units.

In this case, the prediction unit is a basic unit for performing prediction, and is encoded and decoded by the high-speed transform coefficient encoding apparatus as any one of a skip mode, an inter mode, and an intra mode. It may be partitioned in various forms. For example, in the skip mode, the fast transform coefficient encoding apparatus may support the 2Nx2N mode 410 having the same size as the CU without a partition in the CU.

In addition, in the inter mode, the fast transform coefficient encoding apparatus may support 8 types of partitioned types in a CU. For example, the fast transform coefficient encoding apparatus includes a 2Nx2N mode 410, 2NxN mode 415, Nx2N mode 420, NxN mode 425, 2NxnU mode 430, 2NxnD mode 435, nLx2N mode ( 440), nRx2N mode 445 may be supported. Also, in the case of the intra mode, the fast transform coefficient encoding apparatus may support the 2Nx2N mode 410 and the NxN mode 425 in the CU.

7 is a diagram illustrating a form of a transform unit that may be included in an encoding unit to which a fast transform coefficient encoding method according to an embodiment is applied.

Referring to FIG. 7 , a form of a transform unit (TU) that the encoding unit (CU) may include may be known. In this case, the transform unit may be a basic unit used for transform, quantization, inverse transform, and inverse quantization processes in the CU. Also, the TU may be in the form of a square or rectangular shape.

A CU that is no longer split among CUs split from an LCU by the fast transform coefficient encoding apparatus may be split into one or more TUs by the fast transform coefficient encoding apparatus. In this case, the partition structure of the TU may be a quad-tree structure. For example, in some cases, one CU 710 may be divided one or more times according to a quadtree structure to be configured with TUs of various sizes.

8 is a diagram illustrating entropy encoding to which a fast transform coefficient encoding method according to an embodiment is applied.

An image encoder, which is a high-speed transform coefficient encoding apparatus, may use a combination of a size of a coding unit, a prediction mode, a size of a prediction unit, motion information, and a size of a transform unit. In this case, the image encoder, which is a high-speed transform coefficient encoding apparatus, may use a rate-distortion optimization method in order to provide high encoding efficiency.

In the rate-distortion optimization method, a rate-distortion cost ( rate-distortion cost). In this case, the video encoder, which is a high-speed transform coefficient encoding apparatus, may calculate the rate-distortion cost using the first equation D+λ*R. Of course, in the rate-distortion optimization method, the combination with the minimum rate-distortion cost may be selected as the optimal combination by the video encoder serving as the high-speed transform coefficient encoding apparatus.

In this case, D representing the distortion of Equation 1 may be a mean square error of squares of difference values between original transform coefficients and reconstructed transform coefficients in the transform block. In addition, R representing the rate in the first equation may be a bit rate using related context information. Also, λ in the first equation may be a Lagrangian multiplier.

Of course, R may include not only encoding parameter information such as prediction mode, motion information, and a coded block flag, but also bits generated when a transform coefficient is encoded.

An image encoder, which is a high-speed transform coefficient encoding apparatus, may undergo inter- or intra-picture prediction, transformation, quantization, entropy encoding, inverse quantization, and inverse transformation in order to accurately calculate D and R.

The fast transform coefficient encoding apparatus may convert a non-binarized symbol into a bin by binarizing it as a CABAC (context adaptive binary arithmetic coding) entropy encoding method among entropy encoding methods. Also, the apparatus for encoding a fast transform coefficient may determine a context model using encoding information of neighboring or encoding object blocks or information on symbols or bins encoded in a previous step. Of course, the apparatus for encoding a fast transform coefficient may output a bitstream by predicting the occurrence probability of a bin according to the determined context model and performing arithmetic encoding of the bin. In this case, the fast transform coefficient encoding apparatus may update the context model by using the encoded symbol or bin information for the context model of the next symbol or bin after determining the context model as a CABAC entropy encoding method.

The fast transform coefficient encoding apparatus may perform arithmetic encoding in two ways. In this case, the two methods may be divided into a regular mode using a context model and a bypass mode not using a context model.

In the regular mode, the fast transform coefficient encoding apparatus may output a bin using the context model as described above and update the context model according to the output bin.

Also, in the bypass mode, the high-speed transform coefficient encoding apparatus is based on the same probability model and does not require derivation and update of the context model, so the complexity is relatively lower than that of the regular mode.

In addition, the high-speed transform coefficient encoding apparatus may use each mode in a low-complexity form as an entropy encoding method by performing a table-based rate calculation method for the regular mode and the bypass mode in the rate-distortion optimization process.

In addition, in the bypass mode, the fast transform coefficient encoding apparatus does not require derivation and update operations for the context model, so it is possible to calculate the rate with lower complexity than in the regular mode.

Of course, according to an embodiment, when the CABAC entropy encoding method is used in rate-distortion optimization, the fast transform coefficient encoding apparatus may not use the regular mode in the arithmetic encoding and may use only the bypass mode.

9 is a diagram illustrating encoding after the last significant coefficient among backward scans to which the fast transform coefficient encoding method according to an embodiment is applied.

Referring to FIG. 9 , it can be seen that the high-speed transform coefficient encoding apparatus rearranges transform coefficients in an array form using a scan method to encode transform coefficients for one transform block in the entropy coding method. The high-speed transform coefficient encoding apparatus may use at least one of a diagonal scan, a horizontal scan, and a vertical scan as a scan method.

Also, the apparatus for encoding a fast transform coefficient may encode a syntax element for a position of a last significant coefficient in a transform block. In this case, the last significant coefficient may be a non-zero transform coefficient that exists last in the forward scan order in the transform block. The high-speed transform coefficient encoding apparatus may express a two-dimensional transform block in the form of (X, Y) coordinates as a syntax element for the last significant coefficient. In this case, (X, Y) may be location information on the X and Y locations.

In addition, the syntax element for the last significant coefficient is binarized by being divided into two parts, a prefix and a suffix, by the fast transform coefficient encoding apparatus. At this time, the prefix for the X position is last_sig_coeff_x_prefix, the suffix for the X position is last_sig_coeff_x_suffix, the prefix for the Y position is last_sig_coeff_y_prefix, and the suffix for the Y position is last_sig_coeff_y_suffix.

In addition, the fast transform coefficient encoding apparatus may express the prefix part in a truncated unary form, and may encode it in a regular mode. In addition, the fast transform coefficient encoding apparatus may express the suffix part in a fixed length form, and may encode the suffix part in a bypass mode.

According to an embodiment, the fast transform coefficient encoding apparatus does not use a regular mode when calculating a rate in a rate-distortion optimization process with respect to at least one of last_sig_coeff_x_prefix and last_sig_coeff_y_prefix, which are prefix parts for X and Y positions of the last significant coefficient. It can be encoded in bypass mode.

Also, the apparatus for encoding a fast transform coefficient may encode a significance map after encoding a syntax element for a position of a last significant coefficient.

In this case, the important map can be expressed in two ways. The first is information on whether there is at least one non-zero transform coefficient in a sub-block of a 4x4 unit, and the second is information on whether there is at least one non-zero transform coefficient in the sub-block. Information about whether the value is 0 or not.

In addition, whether there is even one non-zero transform coefficient in a subblock is expressed by the syntax element coded_sub_block_flag, and is coded from the last significant coefficient in the reverse scan order. In addition, coded_sub_block_flag is coded in the regular mode, and the context model may be derived using information of neighboring subblocks.

For example, when coded_sub_block_flag is 1, whether or not the value of each transform coefficient in a subblock is 0 may be expressed by the syntax element sig_coeff_flag, and may be encoded in units of subblocks in the reverse scan order. In addition, sig_coeff_flag is encoded in the regular mode, and the context model may be derived using a position within a transform block or a sig_coeff_flag value of a neighboring transform coefficient.

According to an embodiment, the fast transform coefficient encoding apparatus may encode at least one of coded_sub_block_flag and sig_coeff_flag in the bypass mode instead of the regular mode when calculating a rate in a rate-distortion optimization process.

10 is a diagram illustrating encoding of a reverse scan order of sub-blocks to which a fast transform coefficient encoding method is applied according to an embodiment.

Referring to FIG. 10 , it can be seen that the high-speed transform coefficient encoding apparatus can encode the transform coefficients after encoding the syntax elements for the significant map.

The fast transform coefficient encoding apparatus may perform encoding on the transform coefficients using the syntax element coeff_abs_level_greater1_flag for whether the absolute value of the transform coefficient is greater than 1 and the syntax element coeff_abs_level_greater2_flag for whether the absolute value of the transform coefficient is greater than 2. have. In addition, the fast transform coefficient encoding apparatus may perform encoding on the transform coefficient by using the syntax element coeff_sign_flag for sign information of the transform coefficient and the syntax element coeff_abs_level_remaining for the residual value of the absolute value of the transform coefficient.

The fast transform coefficient encoding apparatus may encode only 8 coeff_abs_level_greater1_flags in the regular mode in one subblock, and if there are more than 8 coeff_abs_level_greater1_flags, they may be encoded in the bypass mode using coeff_abs_level_remaining.

Also, the fast transform coefficient encoding apparatus may derive a context model according to whether coeff_abs_level_greater1_flag has a value of 1 in a previous subblock and a DC coefficient is included in the current subblock.

Of course, the fast transform coefficient encoding apparatus may encode only one regular mode when coeff_abs_level_greater2_flag is greater than 1 in one subblock. Also, the fast transform coefficient encoding apparatus may encode coeff_sign_flag using a sign data hiding method or may encode it in a bypass mode.

Also, the fast transform coefficient encoding apparatus may binarize coeff_abs_level_remaining into a Golomb-Rice code and an Exponential Golomb code, and may encode it in a bypass mode.

According to an embodiment, the fast transform coefficient encoding apparatus may encode at least one of coeff_abs_level_greater1_flag or coeff_abs_level_greater2_flag and a combination of one or more in the bypass mode instead of the regular mode when calculating a rate in a rate-distortion optimization process.

Also, according to an embodiment, the apparatus for encoding a fast transform coefficient includes at least one of last_sig_coeff_x_prefix, last_sig_coeff_y_prefix, coded_sub_block_flag, sig_coeff_flag, coeff_abs_level_greater1_flag, and coeff_abs_level_greater2_flag when a combination of at least one rate in a regular rate calculation process other than a regular rate calculation process and coeff_abs_level_greater2_flag It can be encoded in bypass mode.

In this case, since the fast transform coefficient encoding apparatus encodes the syntax elements in a bypass mode that does not perform context model derivation and update, it is possible to reduce the complexity of encoding.

The device described above may be implemented as a hardware component, a software component, and/or a combination of the hardware component and the software component. For example, devices and components described in the embodiments may include, for example, a processor, a controller, an arithmetic logic unit (ALU), a digital signal processor, a microcomputer, a field programmable array (FPA), It may be implemented using one or more general purpose or special purpose computers, such as a programmable logic unit (PLU), microprocessor, or any other device capable of executing and responding to instructions. The processing device may execute an operating system (OS) and one or more software applications running on the operating system. A processing device may also access, store, manipulate, process, and generate data in response to execution of the software. For convenience of understanding, although one processing device is sometimes described as being used, one of ordinary skill in the art will recognize that the processing device includes a plurality of processing elements and/or a plurality of types of processing elements. It can be seen that can include For example, the processing device may include a plurality of processors or one processor and one controller. Other processing configurations are also possible, such as parallel processors.

Software may comprise a computer program, code, instructions, or a combination of one or more thereof, which configures a processing device to operate as desired or is independently or collectively processed You can command the device. The software and/or data may be any kind of machine, component, physical device, virtual equipment, computer storage medium or apparatus, to be interpreted by or to provide instructions or data to the processing device. , or may be permanently or temporarily embody in a transmitted signal wave. The software may be distributed over networked computer systems and stored or executed in a distributed manner. Software and data may be stored in one or more computer-readable recording media.

The method according to the embodiment may be implemented in the form of program instructions that can be executed through various computer means and recorded in a computer-readable medium. The computer-readable medium may include program instructions, data files, data structures, etc. alone or in combination. The program instructions recorded on the medium may be specially designed and configured for the embodiment, or may be known and available to those skilled in the art of computer software. Examples of the computer-readable recording medium include magnetic media such as hard disks, floppy disks and magnetic tapes, optical media such as CD-ROMs and DVDs, and magnetic media such as floppy disks. - includes magneto-optical media, and hardware devices specially configured to store and execute program instructions, such as ROM, RAM, flash memory, and the like. Examples of program instructions include not only machine language codes such as those generated by a compiler, but also high-level language codes that can be executed by a computer using an interpreter or the like. The hardware devices described above may be configured to operate as one or more software modules to perform the operations of the embodiments, and vice versa.

As described above, although the embodiments have been described with reference to the limited embodiments and drawings, various modifications and variations are possible from the above description by those skilled in the art. For example, the described techniques are performed in an order different from the described method, and/or the described components of the system, structure, apparatus, circuit, etc. are combined or combined in a different form than the described method, or other components Or substituted or substituted by equivalents may achieve an appropriate result. Therefore, other implementations, other embodiments, and equivalents to the claims are also within the scope of the following claims.

Claims (2)

In the video encoding method,
encoding a plurality of syntax elements indicating positions of non-zero transform coefficients that exist last in a scan order within a transform block;
encoding a plurality of syntax elements representing absolute values of each transform coefficient in the transform block; and
Including the step of encoding a syntax element for the sign information of the transform coefficient,
At least one of a plurality of syntax elements indicating a position of a non-zero transform coefficient that exists last in a scan order in the transform block is coded in an arithmetic coding mode based on the same probability model,
The arithmetic encoding mode based on the same probability model does not update the context model.
In the video decoding method,
decoding a plurality of syntax elements indicating positions of non-zero transform coefficients that exist last in a scan order in a transform block;
decoding a plurality of syntax elements representing absolute values of each transform coefficient in the transform block; and
Decoding a transform coefficient in the transform block by using a syntax element for sign information of the transform coefficient,
At least one of a plurality of syntax elements indicating a position of a non-zero transform coefficient that exists last in a scan order in the transform block is decoded in an arithmetic decoding mode based on the same probability model,
The arithmetic encoding mode based on the same probability model does not update the context model.

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