KR20190084919A - Method And Apparatus For Video Encoding And Decoding - Google Patents

Abstract

The present invention relates to a video encoding method, a video decoding method, and an apparatus using the same. According to an embodiment of the present invention, the video encoding method comprises the steps of: determining a bit depth value per pulse coding modulation (PCM) sample for a current block to which PCM is applied; and signaling information on a bit depth per PCM sample. The information on the bit depth per PCM sample may include a difference value for a reference value of the bit depth per PCM sample for the current block.

Description

TECHNICAL FIELD [0001] The present invention relates to a video encoding and decoding method,

The present invention relates to a video encoding / decoding method and apparatus, and more particularly, to a method and apparatus for encoding video information in a PCM (Pulse Coding Modulation) mode and a method and apparatus for decoding.

Recently, as a multimedia environment has been established, a variety of terminals and networks have been used, and user demands have been diversified accordingly.

For example, as the performance and computing ability of a terminal are diversified, the performance to be supported varies with each device. In addition, the network in which the information is transmitted is also diversified not only by the external structure such as a wired / wireless network, but also by the type of information to be transmitted, information amount and speed, and the like. The user selects the terminal and the network to be used according to the desired function, and the spectrum of the terminal and the network provided by the enterprise to the user is also diversified.

In recent years, as broadcasts having HD (High Definition) resolution are expanded not only in the domestic market but also in the world, many users are becoming accustomed to high resolution and high definition video. As a result, many video-related organizations are spurring the development of next-generation video equipment.

In addition, with the increasing interest in UHD (Ultra High Definition), which has a resolution more than four times that of HDTV in addition to HDTV, there is a growing demand for a technique for compressing and processing higher resolution and higher image quality.

An inter prediction technique for predicting a pixel value included in a current picture from a previous and / or a temporal picture in order to compress and process an image, an inter prediction technique for predicting a pixel value included in a current picture, An entropy encoding technique for assigning a short code to a symbol having a high appearance frequency and a long code to a symbol having a low appearance frequency can be used.

As the demand for high-resolution and high-definition video services increases, a method of appropriately controlling or minimizing the amount of information to be transmitted or the amount of information to be processed is needed.

It is an object of the present invention to provide a method and a system for directly encoding a differential value corresponding to a difference between a sample value or a sample value and a sampled predicted value, such as intra-coding in a PCM (Pulse Code Modulation) mode, It is possible to provide a method and an apparatus which can easily control the bit rate even if such a mode is used by overcoming the limitations of the prior art which can not control the bit amount.

It is another object of the present invention to overcome the limitations of the prior art by inserting bit depth information per sample for blocks to directly encode sample values or difference values, such as PCM mode, Value of the signaling overhead by minimizing the signaling overhead.

It is still another object of the present invention to introduce a mapping relationship between a quantization parameter (QP) and a bit depth per sample to derive a bit depth of a sample value or a difference value encoded by only QP allocation and signaling, It is possible to easily control the generated bit amount or to derive the QP value of the current block by signaling only the bit depth information per sample of the coded sample value or the difference value so that the QP information signaling of the current block can be omitted And to provide a method and an apparatus for performing the method.

(1) One embodiment of the present invention relates to a video encoding method, comprising: determining a bit depth value per PCM sample for a current block to which PCM (Pulse Coding Modulation) is applied; Wherein the information on the bit depth per PCM sample may include a difference value relative to a reference value of bit depth per PCM sample for the current block.

(2) In (1), the reference value may be a bit depth reference value per PCM sample transmitted through a high-level syntax.

(3) In (2), in the signaling step, the bit depth reference value per PCM sample may be transmitted through a sequence parameter set or a picture parameter set.

(4) In (2), in the signaling step, the difference value may be transmitted at a slice header level or a processing unit level.

(5) In (1), the reference value may be a bit depth per PCM sample of a block to which a PCM mode is applied among neighboring blocks of the current block.

(6) In (5), the reference value may be a bit depth per PCM sample of a slice or a first block of a picture to which the current block belongs among blocks to which the PCM mode is applied.

(7) In (5), the reference value may be the bit depth per PCM sample of the block closest to the current block in the scan order or encoding order among the blocks to which the PCM mode is applied.

(8) Another embodiment of the present invention is a video encoding method comprising the steps of: determining a bit depth value per PCM sample for a current block to which PCM (Pulse Coding Modulation) is applied; and signaling information on bit depth per PCM sample Wherein the information on the bit depth per PCM sample may include a quantization parameter (QP) mapped to a bit depth per PCM sample for the current block.

(9) According to still another embodiment of the present invention, there is provided a video decoding method comprising the steps of: receiving bit depth information per PCM sample for a current block to which PCM (Pulse Coding Modulation) is applied; And the bit depth information per PCM sample for the current block may include a difference value with respect to a reference value of bit depth per PCM sample for the current block.

(10) In (9), the reference value may be a bit depth reference value per PCM sample transmitted through a high-level syntax.

(11) In (10), the bit depth reference value per PCM sample may be transmitted through a sequence parameter set or a picture parameter set.

(12) In (10), the difference value may be transmitted at the slice header level or processing unit level.

(13) In (9), the reference value may be a bit depth per PCM sample of a block to which a PCM mode is applied, from neighboring blocks of the current block.

(14) In (13), the reference value may be a bit depth per PCM sample of a slice or a first block of a picture to which the current block belongs, among the blocks to which the PCM mode is applied.

(15) In (13), the reference value may be the bit depth per PCM sample of the block closest to the current block in the scan order or decoding order among the blocks to which the PCM mode is applied.

(16) According to still another embodiment of the present invention, there is provided a video decoding method comprising: receiving bit depth information per PCM sample for a current block to which PCM (Pulse Coding Modulation) is applied; And the bit depth information per PCM sample for the current block may include a quantization parameter (QP) mapped to a bit depth per PCM sample for the current block .

According to the present invention, it is possible to easily control the bit rate even if the PCM mode is used, by overcoming the limitations of the prior art that can not control the intra-coding angle picture in the PCM (Pulse Code Modulation) mode or the amount of bits generated in each block .

According to the present invention, the bit depth information per PCM sample is inserted into the blocks to be encoded in the PCM mode, and the signaling overhead can be minimized by using this information by predicting and using this information from a higher level value or surrounding value.

According to the present invention, by introducing the mapping relationship between the quantization parameter (QP) and the bit depth per PCM sample, it is possible to easily control the generated bit amount of a block to which intra coding of the PCM mode is applied only by QP allocation and signaling.

1 is a block diagram showing a basic configuration according to an embodiment of an encoding apparatus.
2 is a block diagram showing a basic configuration according to an embodiment of a decoding apparatus.
3 is a flowchart schematically illustrating an example of a bit rate control operation for a PCM sample performed in an encoding apparatus according to the present invention.
4 is a flowchart schematically illustrating another example of a bit rate control operation for a PCM sample performed in an encoding apparatus according to the present invention.
5 is a schematic diagram for explaining bit amount information for a PCM mode signaled according to the present invention.
6 is a diagram schematically illustrating a method of predicting a bit depth value per PCM sample of a current block using information of a block encoded / decoded in a PCM mode among neighboring blocks of a current block according to the present invention.
7 is a flowchart schematically illustrating a method of restoring a block to which a PCM mode is applied in a decoding apparatus according to the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In describing the embodiments of the present invention, if the detailed description of related known structures or functions is deemed to obscure the subject matter of the present specification, the description may be omitted.

When an element is referred to herein as being "connected" or "connected" to another element, it may mean directly connected or connected to the other element, Element may be present. In addition, the content of " including " a specific configuration in this specification does not exclude a configuration other than the configuration, and means that additional configurations can be included in the scope of the present invention or the scope of the present invention.

The terms first, second, etc. may be used to describe various configurations, but the configurations are not limited by the term. The terms are used for the purpose of distinguishing one configuration from another. For example, without departing from the scope of the present invention, the first configuration may be referred to as the second configuration, and similarly, the second configuration may be named as the first configuration.

In addition, the constituent elements shown in the embodiments of the present invention are shown independently to represent different characteristic functions, which do not mean that each constituent element is composed of separate hardware or a single software constituent unit. That is, each constituent unit is included in each constituent unit for convenience of explanation, and at least two constituent units of each constituent unit may form one constituent unit or one constituent unit may be divided into a plurality of constituent units to perform a function. The integrated embodiments and the separate embodiments of each component are also included in the scope of the present invention unless they depart from the essence of the present invention.

1 is a block diagram showing a basic configuration according to an embodiment of an encoding apparatus.

1, the encoding apparatus 100 includes an inter prediction unit 110, an intra prediction unit 120, a switch 125, a subtractor 130, a transform unit 135, a quantization unit 140, An inverse quantization unit 160, an inverse transform unit 170, an adder 175, a filter unit 180, and a picture buffer 190.

The encoding apparatus 100 may encode an input image in an intra mode or an inter mode and output a bitstream. In the intra mode, the switch 125 is switched to the intra mode, and in the inter mode, the switch 125 is switched to the inter mode. The encoding apparatus 100 may generate a prediction block for an input block of an input image and then encode a difference between the input block and the prediction block.

In the intra mode, the intraprediction unit 120 may generate a prediction block by performing spatial prediction using the pixel value of the already encoded block around the current block.

In the inter mode, the inter-prediction unit 110 can obtain a motion vector by searching an area corresponding to an input block in a reference image stored in the picture buffer 190 in a motion prediction process. The inter prediction unit 110 may generate a prediction block by performing motion compensation using a motion vector and a reference image stored in the picture buffer 190. [

The subtractor 130 may generate a residual block by a difference between the input block and the generated prediction block. The conversion unit 135 may perform a transform on the residual block to output a transform coefficient. The quantization unit 140 may quantize the input transform coefficient according to the quantization parameter to output a quantized coefficient. The entropy encoding unit 150 entropy-encodes the quantized coefficients according to the probability distribution, based on the values calculated in the quantization unit 140 or the encoding parameter values calculated in the encoding process, and outputs a bitstream .

The quantized coefficients can be inversely quantized in the inverse quantization unit 160 and inversely transformed in the inverse transformation unit 170. The inverse quantized and inverse transformed coefficients can be added to the prediction block through the adder 175 and a reconstruction block can be generated.

The restoration block passes through the filter unit 180 and the filter unit 180 applies at least one of a deblocking filter, a sample adaptive offset (SAO), and an adaptive loop filter (ALF) can do. The filter unit 180 may determine whether to apply the ALF when SAO is applied. The restoration block having passed through the filter unit 180 may be stored in the picture buffer 190.

2 is a block diagram showing a basic configuration according to an embodiment of a decoding apparatus.

2, the decoding apparatus 200 includes an entropy decoding unit 210, an inverse quantization unit 220, an inverse transform unit 230, an intra prediction unit 240, an inter prediction unit 250, a filter unit 260 And a picture buffer 270.

The decoding apparatus 200 receives the bitstream output from the encoding apparatus, decodes the bitstream into an intra mode or an inter mode, and outputs a reconstructed image, that is, a reconstructed image. In the intra mode, the switch is switched to the intra mode, and in the inter mode, the switch can be switched to the inter mode.

The decoding apparatus 200 may obtain a residual block reconstructed from the input bitstream, generate a prediction block, and add the reconstructed residual block and the prediction block to generate a reconstructed block, i.e., a reconstructed block .

The entropy decoding unit 210 entropy-decodes the input bitstream according to a probability distribution. By entropy decoding, a quantized (transform) coefficient can be generated.

The quantized coefficients are inversely quantized in the inverse quantization unit 220 and inversely transformed in the inverse transformation unit 230. As a result that the quantized coefficients are inversely quantized / inverse transformed, a reconstructed residual block can be generated.

In the intra mode, the intraprediction unit 240 may generate a prediction block by performing spatial prediction using the pixel value of the already encoded block around the current block. In the inter mode, the inter-prediction unit 250 may generate a prediction block by performing motion compensation using a motion vector and a reference image stored in the picture buffer 270. [

The restored residual block and the prediction block are added through the adder 255, and the added block is passed through the filter unit 260. The filter unit 260 may apply at least one of the deblocking filter, SAO, and ALF to the restoration block or the restored picture. The filter unit 260 may determine whether to apply ALF when SAO is applied. The filter unit 260 outputs a reconstructed image, that is, a reconstructed image. The restored image is stored in the picture buffer 270 and can be used for inter-view prediction.

On the other hand, when the prediction mode for the current block is the intra mode, the encoding apparatus and the decoding apparatus can use the PCM (Pulse Coding Modulation) mode in addition to the intraprediction mode described above for lossless coding.

The PCM mode is a safety device for preventing the compressed bit amount of the encoding target block from becoming larger than the original bit amount, and directly encodes the sample value without performing the prediction / conversion process.

When the PCM mode is applied to the current block, the encoding device can directly encode the sample value of the current block to which the PCM mode is applied, and transmit the encoded data to the decoding device without performing the prediction / conversion process.

The decoding apparatus may not perform prediction / conversion for the block to which the PCM mode is applied. For a block to which the PCM mode is applied, the decoding apparatus can parse the bit stream transmitted from the encoding apparatus and construct a reconstructed block based on the parsed pixel value.

In the case where the PCM mode is applied, the encoding device can transmit to the decoding device information indicating that the PCM mode is applied to the current block. The decoding apparatus can determine whether to apply the PCM mode to the current block based on the information received from the encoding apparatus. At this time, the block to which the PCM mode is applied may be a processing unit of any of CU, PU, or TU. In addition, information indicating whether the PCM mode is applied may be transmitted as a flag.

An in-loop filter may be applied to the block reconstructed in the PCM mode, for example, a deblocking filter, SAO and / or ALF may be applied to the reconstructed block in the PCM mode.

On the other hand, when image coding is performed in an environment in which CBR (Constant Bit-Rate) is applied as in a broadcasting environment, quantization intervals allocated to blocks constituting each screen or each screen are referred to as quantization parameters (QP) The bit rate is controlled so as to enable transmission of a constant bit rate.

However, in the PCM mode, since the sample value is directly coded without the quantization process, the quantization interval can not be controlled. Therefore, for a block or picture to which the PCM mode is applied, the bit rate can be controlled by a method other than the quantization interval control.

Specifically, when applying the PCM mode according to the present invention, the encoding apparatus can signal the sample bit depth to the decoding apparatus for the block to which the PCM mode is applied.

In the case of applying the PCM mode according to the present invention, a part or all of the information on the PCM mode applied to the current block, for example, the bit depth, may be predicted by the decoding device. It is possible to reduce the amount of bits required to transmit information on the bit depth of a sample (hereinafter, referred to as 'PCM sample') of a block to which a PCM mode is applied by predicting part or all of the bit depth information in the decoding apparatus have.

Since the general bit rate control controls the amount of bits generated at the time of information transmission through the QP value control, when the PCM mode is applied according to the present invention, by mapping the bit depths of the QP and the PCM samples, The bit rate control using the QP may be performed for the block. At this time, a mapping relationship in which the encoding apparatus transmits bit depth information per PCM sample so that the decoding apparatus derives the QP may be used, and a mapping relationship in which the encoding apparatus transmits the QP and the decoding apparatus derives the bit depth value per PCM sample It can also be used.

Hereinafter, the present invention will be described in detail with reference to the drawings and tables.

In order to adjust the bit amount of the block encoded in the PCM mode, the encoding device transmits a bit stream containing information on the bit depth per PCM sample to the decoding device. The decoding apparatus parses the received bit stream to obtain information on the bit depth per PCM sample. The decoding apparatus can recover the block to which the PCM mode is applied based on the bit depth per PCM sample.

Here, the bit depth per PCM sample indicates how many bits the sample value of the luma component and / or the chroma component will be represented when encoding / decoding in the PCM mode.

The encoding apparatus can set a reference value of the bit depth per PCM sample (hereinafter, referred to as a 'bit depth reference value per PCM sample') for indicating the bit depth per PCM sample. The encoding apparatus can transmit the difference between the reference value of the bit depth per PCM sample set and the bit depth per PCM sample for the current block when the PCM mode is applied to the current block. The decoding apparatus receives from the encoding device a bit depth reference value per PCM sample and a difference value between the reference value and the bit depth per PCM sample for the current block (hereinafter referred to as 'bit depth difference value per PCM sample' can do. The decoding apparatus can recover the block to which the PCM mode is applied based on the received bit depth reference value per the PCM sample and the difference value.

For convenience of explanation, the method and apparatus applied to the luma signal are described herein, but the same can be applied to the chroma signal through the same method and apparatus.

3 is a flowchart schematically illustrating an example of a bit rate control operation for a PCM sample performed in an encoding apparatus according to the present invention.

Referring to FIG. 3, the encoding apparatus determines a bit depth reference value per sample for the PCM mode (S310).

The encoding apparatus determines a bit depth value per PCM sample of a block to which the PCM mode is applied (S320).

The encoding device signals information on the bit depth value per PCM sample (S330). Information about the bit depth value per PCM sample includes the bit depth reference value per PCM sample and the bit depth difference value per PCM sample. Instead of directly signaling the bit information per PCM sample for each block to which the PCM mode is applied, the encoding device signals the bit depth reference value per PCM sample in a high-level header such as a slice, picture, or sequence to reduce the amount of signaled signal, You can signal the bit depth difference value per PCM sample at the lower level.

Here, for convenience of explanation, the encoding apparatus is described as controlling the bit amount, but the present invention is not limited to this. For example, S310 among the internal configurations of the encoding apparatus shown in FIG. 1 may be performed in the quantization unit, and step S320 may be performed in the entropy encoding unit.

Meanwhile, as described above, when the PCM mode is applied, the QP and the bit depth of the PCM sample are mapped to allow the bit rate control using the QP to be performed on the block to which the PCM mode is applied.

4 is a flowchart schematically illustrating another example of a bit rate control operation for a PCM sample performed in an encoding apparatus according to the present invention. In the case of FIG. 4, bit amount control is performed on a block to which the PCM mode is applied by mapping the bit depth of the QP and the PCM sample.

In the example of FIG. 4, QP and bit depth information per PCM sample are mapped first, unlike the case of FIG. 3 (S410). The encoding apparatus can map bit depth information and QP per PCM sample using a mapping table or a mapping calculation formula as described later. The encoding device may determine depth information per PCM sample that is mapped to a QP corresponding to the bit depth per sample to be applied to the current block.

Subsequently, the encoding apparatus determines a bit depth reference value per sample for the PCM mode, as in FIG. 3 (S420).

The encoding apparatus determines a bit depth value per PCM sample of a block to which the PCM mode is applied (S430).

The encoding device signals information regarding the bit depth value per PCM sample (S440).

Information about the bit depth value per PCM sample includes the bit depth reference value per PCM sample and the bit depth difference value per PCM sample. Instead of directly signaling the bit information per PCM sample for each block to which the PCM mode is applied, the encoding device signals the bit depth reference value per PCM sample in a high-level header such as a slice, picture, or sequence to reduce the amount of signaled signal, You can signal the bit depth difference value per PCM sample at the lower level.

4, bit depth information per PCM sample corresponding to the QP is transmitted to control the bit depth value per PCM sample of the current block. Conversely, the bit depth per PCM sample is determined, and the corresponding QP value is transmitted, It is also possible to control the bit depth value per sample. In this case, the transmitted QP value can be used for inverse quantization, filtering, etc. in addition to controlling the bit depth value per PCM sample.

In the example of FIG. 4, the encoding apparatus controls the bit amount for convenience of explanation, but the present invention is not limited to this. For example, among the internal configurations of the encoding apparatus shown in FIG. 1, steps S410 and S420 may be performed in the quantization unit, and step S430 may be performed in the entropy encoding unit.

As in the examples of FIGS. 3 and 4, in the present invention, the amount of bits for the PCM mode can be controlled by signaling the depth difference value per PCM sample.

5 is a schematic diagram for explaining bit amount information for a PCM mode signaled according to the present invention.

Referring to FIG. 5, a bit depth reference value 510 per PCM sample is transmitted in a higher level sequence parameter set (SPS) or a picture parameter set (PPS).

At the lower level, the actual bit depth per PCM sample can be determined and burned. For example, a bit depth value 520 per PCM sample may be determined in a slice header, or a bit depth value 530 per PCM sample may be determined at a processing unit level such as CU, PU, TU.

At this time, the bit depth value per PCM sample of the current block can be transmitted as a difference value from the bit depth reference value per PCM sample.

For example, when signaling the bit depth value 530 per PCM sample of the processing unit (CU, PU, TU, etc.), the difference value 530 from the per bit PCM sample per bit depth reference value 530, Signaling.

It may also send a bit depth value 530 per PCM sample of the processing unit level, mediating the bit depth value 520 per PCM sample of the slice header level. For example, the bit depth value 520 per PCM sample of the slice header level can be indicated by transmitting a difference value 540 to the bit depth reference value 510 per PCM sample. The PCM per sample bit depth value 530 at the processing unit level can be indicated by sending a difference value 550 to the bit depth value 520 per PCM sample of the slice header level. At this time, if the encoding apparatus and the decoding apparatus are set to transmit or receive only the bit depth value per PCM sample of the slice header level, the difference value 550 from the bit depth value 520 per PCM sample of the slice header level is transmitted It may not.

Table 1 is an example of the syntax for the bit depth per PCM sample transmitted at each level.

<Table 1>

Referring to Table 1, in the SPS or PPS, the bit depth reference value per PCM sample is transmitted. The bit depth reference value per PCM sample transmitted in the SPS or PPS is applied in common to the corresponding sequence or the corresponding picture.

In the present invention, a bit depth difference value per PCM sample can be transmitted in a slice header. The bit depth difference value per PCM sample can be combined with the bit depth reference value per PCM sample to indicate the bit depth value per actual PCM sample. The bit depth difference value per PCM sample transmitted in the slice header is commonly applied to the corresponding slice.

In the present invention, the bit depth difference value per PCM sample may be transmitted at the processing unit level such as CU, PU, TU, and the like. The bit depth difference value per PCM sample can be combined with the bit depth reference value per PCM sample to indicate the bit depth value per actual PCM sample. The bit depth difference value per PCM sample transmitted at the processing unit level is commonly applied to the corresponding processing unit level.

Although Table 1 describes only the luma component, as described above, the present invention can be similarly applied to the chroma component. Thus, the bit depth reference value per PCM sample transmitted at the SPS or PPS level for the chroma component may be pcm_bit_depth_chroma or pcm_bit_depth_cr / pcm_bit_depth_cb. The bit depth difference value per PCM sample transmitted at the slice header or processing unit level may be pcm_bit_depth_delta_chroma or pcm_bit_depth_delta_cr / pcm_bit_depth_delta_cb.

When signaling the bit depth reference value per PCM sample as shown in Table 1, it is also possible to reduce the number of signaling bits using already encoded bit depth information per sample.

For example, suppose that the bit depth per sample is transmitted as bit_depth_luma_minus8 through the SPS information. In this case, instead of directly signaling the bit depth reference value per PCM sample as shown in Table 1, it is also possible to signal a difference value from the already signaled bit depth per sample as shown in Table 2 below.

<Table 2>

Information about the bit depth per PCM sample can only be signaled when the PCM mode is applied to the target block. For example, the encoding apparatus can transmit the per-PCM bit-per-sample depth reference values (pcm_bit_depth_luma, pcm_bit_depth_cr, pcm_bit_depth_cbluma) when the prediction mode of the current block is the intra prediction mode and the PCM mode is applied.

<Table 3>

At this time, the bit depth value per PCM sample can be transmitted through the bit depth difference value (pcm_bit_depth_delta_luma, pcm_bit_depth_delta_cr, pcm_bit_depth_delta_cb) per PCM sample as shown in Table 4.

<Table 4>

On the other hand, instead of transmitting the difference value from the bit depth information per a high-level PCM sample, the bit depth value per PCM sample of the current block is predicted and encoded using the bit depth value per PCM sample of the neighboring block already encoded in the PCM mode You may.

6 is a diagram schematically illustrating a method of predicting a bit depth value per PCM sample of a current block using information of a block encoded / decoded in a PCM mode among neighboring blocks of a current block according to the present invention.

Assume that CU, PU, or TU are divided as shown in FIG. 6 and blocks P1, P2, and P3 are already encoded / decoded in PCM mode. When the PCM mode is applied to the current block X, that is, the prediction target block or the encoding / decoding target block, the bit depth per PCM sample of the current block X is set to one bit depth per one PCM sample Can be predicted using a value. Therefore, the encoding apparatus can signal only the difference value between the bit depth per PCM sample and the predicted value for the current block. The decoding apparatus can receive the difference value between the bit depth per PCM sample and the predicted value for the current block and add the difference value to the predicted value to derive the bit depth per PCM sample for the current block.

For example, in FIG. 6, the bit depth per PCM sample of the current block can be predicted using the block closest to the current block in the coding order among the blocks already coded in the PCM mode. Therefore, in the encoding apparatus, the bit depth per PCM sample of the current block can be predicted using a block that is already encoded in the PCM mode and is the closest to the current block in the encoding order. In the decoding apparatus, The bit depth per PCM sample of the current block can be predicted using the block closest to the current block.

In particular, if the encoding or decoding order is a raster scan order in LCU and depth-first scans within the LCU, then the bit depth value per PCM sample of current block X in FIG. 6 is based on the bit depth per PCM sample of P3 block Can be predicted.

That is, the bit depth value per PCM sample applied to the P2 block can be set as the bit depth predicted value per PCM sample with respect to the current block X. [ The encoding apparatus can signal the difference between the bit depth value per PCM sample applied to the P2 block and the bit depth value per PCM sample of the current block. The decoding device sets the depth value per PCM sample applied to the P2 block as the bit depth prediction value per PCM sample of the current block and adds the difference value of the bit depth per PCM sample received from the encoding device to determine the bit depth per PCM sample Value can be derived.

In the case where the current block in the current picture or the current slice is first encoded or decoded by the PCM mode (for example, P1 block in Fig. 6), since there is no peripheral block already encoded or decoded in the PCM mode, PCM related information (bit depth reference value per PCM sample, bit depth value per PCM sample of slice header, etc.) can be used as a kind of prediction value.

When the bit depth per PCM sample of the current block to which the PCM mode is applied is obtained, the sample value of the current block can be recovered using this bit depth.

PCM sample value restoration is a process of converting the PCM sample values expressed in bits per PCM sample to fit the number of bits per sample to be restored.

Table 5 shows an example of a method for restoring PCM sample values.

<Table 5>

ReconstructedLumaBlock [x] [y] represents the restored luma signal value at the current block position (x, y). Each signal value is represented by a bit number of BitDepthLuma.

PCMSampleLuma [i] represents the PCM luma sample value at the i-th position in the raster scan order of the current block. Each sample value is represented by a number of bits equal to PCMBitDepthLuma. The PCMBitDepthLuma value for the current block is the number of bits used to represent each PCM luma sample value in the current block.

The conversion process as shown in Table 5 can be performed in the encoding apparatus and the decoding apparatus in the same manner. However, in the encoding apparatus, a process of converting the sample value of the current block into the PCM sample value and encoding the same before the conversion process of Table 5 may be added.

Table 6 shows an example of a method of converting the sample values of the current block into PCM sample values and encoding them.

<Table 6>

Table 6 shows a method of converting the pixel value of a luma block into a PCM sample value by shifting the difference between the bit depth value per sample and the bit depth value per PCM sample.

Table 7 shows another example of a method of converting a sample value of a current block into a PCM sample value and encoding the same.

<Table 7>

In the example of Table 7, when shifting the pixel value of the luma block by the difference between the bit depth value per sample and the bit depth per PCM sample, the rounding value is taken into consideration and converted to the PCM sample value.

Meanwhile, as described above, the encoding apparatus and the decoding apparatus may use a method of controlling the bit amount of a sample by mapping QP and bit depth information per PCM sample.

According to a general bit rate control method, the amount of generated bits of a sample is controlled by controlling the QP value. Therefore, by introducing the mapping relationship between QP and PCM sample bit depth information, the amount of bits generated for the PCM mode block can also be controlled by allocating and signaling QP. It is also possible to determine the bit depth per PCM sample and assign a corresponding QP to control the bit depth per PCM sample through the QP.

The mapping relationship between QP and bit depth per PCM sample can be defined using a mapping table.

Table 8 is an example of a mapping table indicating a mapping relationship between QP and bit depth per PCM sample.

<Table 8>

As shown in Table 8, the mapping relationship between QP and bit depth may be one to one as well as many to one, one to many, many to many. For a given QP, if the corresponding bit depth per PCM sample is desired to be used, the encoding device may additionally signal which bit depth per PCM sample to use if there are many bit depths per corresponding PCM sample. Or if it is desired to use a QP corresponding to a bit depth per given PCM sample, if the corresponding QP is several, then the encoding device may further signal which QP it will use.

The mapping relationship between QP and bit depth per PCM sample can be defined using a calculation formula rather than a mapping table.

Equation 1 is an example of an equation expressing a mapping relationship between QP and bit depth per PCM sample.

&Lt; Formula 1 >

PCMSampleBitDepth = MAX (8-Max (QP-13,0) / 6, 3)

If the mapping relationship between the QP and the PCM sample bit depth value is preset, the encoding apparatus does not need to signal the bit depth value or QP value per PCM sample every time. The decoding device may derive the bit depth value per PCM sample based on the signaled QP value or derive the QP value based on the bit depth value per signaled PCM sample.

The mapping relationship between the QP and the bit depth value per PCM sample may be set in advance between the encoding apparatus and the decoding apparatus in advance.

Alternatively, the encoding apparatus may separately transmit information necessary for setting a mapping relationship between the QP and the PCM sample bit depth value, for example, a mapping table or a mapping type parameter through a sequence parameter set, a picture parameter set, a slice parameter set, have.

If a mapping relationship between QP and bit depth per PCM sample is set, the bit depth per PCM sample obtained using the QP value is set as a bit depth prediction value per PCM sample for the current block, and a sequence parameter set, At the picture parameter set, slice header, or processing unit level, only the difference value between the bit depth value and the predicted value per PCM sample of the current block to which the PCM mode is applied may be transmitted.

7 is a flowchart schematically illustrating a method of restoring a block to which a PCM mode is applied in a decoding apparatus according to the present invention.

Referring to FIG. 7, the decoding apparatus receives information on the bit depth value per PCM sample from the encoding apparatus (S710).

Information about the bit depth value per PCM sample received by the decoding device includes the bit depth reference value per PCM sample and the bit depth difference value per PCM sample. The bit depth reference value per PCM sample can be transmitted via SPS or PPS. The bit depth difference value per PCM sample can be transmitted at the processing unit level or at the slice header and processing unit level, respectively.

The information on the bit depth per PCM sample received by the decoding device may be a difference value between the bit depth per PCM sample of the current block and the bit depth per PCM sample of the current block. The bit depth prediction value per PCM sample of the current block is the bit depth value per PCM sample of the block decoded first in the PCM mode among the neighboring blocks of the current block. The decoding apparatus can derive the bit depth value per PCM sample of the current block by adding the received difference value to the bit depth predicted value per PCM sample. Whether to use a bit depth value per PCM sample of a block decoded in the surrounding PCM mode as a predicted value may be set in advance or may be signaled from the encoding apparatus. For example, the bit depth value per PCM sample of the current picture or the block decoded first in the PCM mode in the current slice can be used as the bit depth prediction value per PCM sample of the current block to which the PCM mode is applied. Alternatively, the bit depth per PCM sample of the block closest to the current block in the scanning order or decoding order among the blocks decoded to the PCM mode first in the current picture or the current slice is set to a value per PCM sample of the current block to which the PCM mode is applied It can also be used as a bit depth prediction value.

The bit depth value per PCM sample received by the decoding device may also include a QP value that is mapped to the bit depth per PCM sample for the current block.

The decoding apparatus can determine the bit depth value per PCM sample of the current block (S720). The decoding apparatus can determine the bit depth per PCM sample of the current block based on the received information as described above.

For example, in the case of receiving the bit depth reference value per PCM sample and the bit depth difference value per PCM sample, the decoding apparatus adds the bit depth reference value per PCM sample and the bit depth difference per PCM sample, The bit depth can be derived.

When receiving the difference value between the bit depth value per PCM sample of the current block and the bit depth per PCM sample of the current block, the decoding apparatus calculates the bit depth value per PCM sample of the current block and the bit depth per PCM sample of the current block The bit depth per PCM sample for the current block can be derived by adding the difference from the predicted value.

When a QP value mapped to the bit depth per PCM sample for the current block is received, the decoding device can derive the bit depth per PCM sample of the current block based on the received QP value.

The decoding apparatus can restore the current block based on the bit depth per PCM sample of the current block (S730). As a method of converting the PCM sample values into the sample values of the current block, an inverse transformation of the transformation used in the example of Table 6 or Table 7 can be used.

In the example of FIG. 7, for convenience of description, each step is described as being performed by the decoding apparatus, but the present invention is not limited thereto. Each step of Fig. 7 may be performed, for example, by the internal constituent units of the decoding apparatus shown in Fig. For example, if the PCM mode is applied, steps S710 and S720 may be performed in the entropy decoding unit, and step S730 may be performed in the inverse quantization unit.

Signaling certain information in this specification means that the encoding device inserts the information into the bitstream so that the decoding device can recognize the information, and the decoding device obtains information by parsing the bitstream.

Also, while in the exemplary system described above, methods are described based on a flowchart as a series of steps or blocks, the present invention is not limited to the order of steps, and some steps may be performed in a different order than the steps described above Can occur at the same time. In addition, the above-described embodiments include examples of various aspects. For example, combinations of the embodiments are also to be understood as one embodiment of the present invention.

Claims (13)

Obtaining bit depth information per PCM sample from a bit stream;
Deriving a bit depth per PCM sample based on the obtained bit depth information per PCM sample;
Determining whether a PCM mode is applied to a current block; And
Decoding the current block based on a bit depth per PCM sample when it is determined that a PCM mode is applied to the current block,
Wherein the decoding of the current block comprises:
Deriving a quantization parameter (QP) based on the bit depth per PCM sample; And
And dequantizing the current block based on the quantization parameter,
Wherein the prediction mode for the current block is an intra mode,
Wherein the bit depth per PCM sample is derived by summing a value indicated by the bit depth information per PCM sample and a predetermined value, The method according to claim 1,
Wherein the bit depth information per PCM sample is included in a sequence parameter set or a picture parameter set. The method according to claim 1,
Wherein the bit depth information per PCM sample comprises bit depth information per PCM sample for a luma signal and bit depth information per PCM sample for a chroma signal. The method according to claim 1,
Wherein the step of determining whether a PCM mode is applied to the current block is performed based on PCM mode adaptation information obtained from a bitstream. 5. The method of claim 4,
The current block is a CU (Coding Unit), a PU (Prediction Unit), or a TU (Transform Unit)
Wherein the PCM mode application information is included in a unit level of the current block. 5. The method of claim 4,
And the PCM mode application information is flag information. Determining a bit depth per PCM sample;
Encoding bit depth information per PCM sample based on the determined bit depth per PCM sample;
Determining whether a PCM mode is applied to a current block; And
And encoding the current block based on a bit depth per PCM sample when it is determined that a PCM mode is applied to the current block,
Wherein the encoding of the current block comprises:
Deriving a quantization parameter (QP) based on the bit depth per PCM sample; And
And quantizing the current block based on the quantization parameter,
Wherein the prediction mode for the current block is an intra mode,
Wherein the bit depth information per PCM sample is encoded with a difference value between a bit depth per PCM sample and a predetermined value, 8. The method of claim 7,
Wherein the bit depth information per PCM sample is included in a sequence parameter set or a picture parameter set. 8. The method of claim 7,
Wherein the bit depth information per PCM sample includes bit depth information per PCM sample for a luma signal and bit depth information per PCM sample for a chroma signal. 8. The method of claim 7,
And encoding the PCM mode adaptation information indicating whether the PCM mode is applied to the current block. 11. The method of claim 10,
The current block is a CU (Coding Unit), a PU (Prediction Unit), or a TU (Transform Unit)
Wherein the PCM mode adaptation information is included in a unit level of the current block. 11. The method of claim 10,
Wherein the PCM mode application information is flag information. A computer-readable non-transitory medium for storing image data received and decoded by an image decoding apparatus and used for reconstructing an image,
Wherein the image data includes bit depth information per PCM sample,
The bit depth information per PCM sample is used to derive the bit depth per PCM sample,
Wherein the bit depth per PCM sample is used to decode the current block if it is determined that a PCM mode is applied to the current block,
The decoding of the current block may include deriving a quantization parameter (QP) based on the bit depth per PCM sample, dequantizing the current block based on the quantization parameter,
Wherein the prediction mode for the current block is an intra mode,
Wherein the bit depth per PCM sample is derived by summing a value indicated by the bit depth information per PCM sample with a predetermined value and wherein the predetermined value is one.

Images