JP2011223316A - Image encoding apparatus, image decoding apparatus, and method for image encoding and decoding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image encoding apparatus having an improved encoding efficiency.SOLUTION: A prediction image conversion quantization section 202 outputs a first in-screen prediction data from a reduced image in an image reduction section 201 based on a reduction image quantization parameter. A prediction image inverse quantization inverse conversion section 203 outputs a local decoded prediction image from the first in-screen prediction data. A prediction image enlargement section 204 enlarges the local decoded prediction image and generates a first in-screen prediction image. A difference image generation section 102 outputs a difference image between a block image and the first in-screen prediction image. A difference conversion quantization section 103 performs frequency conversion and quantization of the difference image and outputs a conversion coefficient. An entropy encoding section 104 entropy-encodes the first in-screen prediction data and the conversion coefficient and outputs a bitstream.

Description

  The present invention relates to an image coding apparatus, an image coding method, an image decoding apparatus for decoding compressed data, and an image decoding method that perform intra prediction when an image is compressed and transmitted.

  For example, H.264 recommended by ITU-T (International Telecommunication Union Telecommunication Standardization Sector). In the H.264 moving image encoding method, intra-frame redundancy is removed by performing intra-screen prediction, and a prediction error signal is compression-encoded. Conventionally, there has been an apparatus as disclosed in Patent Document 1, for example, as such an encoding apparatus that performs compression encoding and a decoding apparatus that decodes the encoding apparatus.

  In such a conventional image encoding device, in order to generate an encoded bit stream from an input image, first, the input image is a macroblock that is an input image having a macroblock size that is a predetermined encoding unit by an image dividing unit. The image is divided into input images and processed in units of macroblocks. The macroblock input image is subtracted from the prediction image generated by the intra prediction unit by the subtraction unit, and a difference image signal obtained as a result is output. The difference image signal is input to the frequency conversion unit, converted to a conversion coefficient representing the amplitude for each frequency by performing frequency conversion, and output to the quantization unit. The transform coefficient is quantized in the quantization unit, and the quantized transform coefficient is output. The output quantized transform coefficient is entropy-encoded in the entropy encoding unit and output as an encoded bit stream. The quantized transform coefficient is also input to the inverse quantization unit. The inverse quantization unit inversely quantizes the quantized transform coefficient and outputs a decoded transform coefficient. The decoded transform coefficient is inversely frequency-converted by an inverse frequency converter, thereby obtaining a decoded difference image. The decoded difference image is added to the predicted image by the adding unit, and is stored in the frame memory as a locally decoded image. The local decoded image stored in the frame memory is used by the prediction unit to generate a predicted image.

H. performed in the prediction unit. In the H.264 intra-screen prediction method, a predicted image is generated by linearly expanding a locally decoded image of an encoded block adjacent to a block to be encoded. At this time, in the intra 4 × 4 prediction mode and the intra 8 × 8 prediction mode, the optimal prediction direction is selected from the eight types of directions and the DC prediction in which prediction is performed using the average value of surrounding pixels. select. In the intra 16 × 16 prediction mode, an optimal one is selected from a total of four types of horizontal direction, vertical direction, diagonal direction, and DC prediction.
The selected prediction mode and prediction direction are each entropy-encoded in the entropy encoder and multiplexed into the encoded bitstream.

International Publication No. 08/07500

  However, in the conventional image encoding device, as described above, H.264 is used. In the H.264 intra-frame prediction, a predicted image is generated by linearly expanding a local decoded image around a block to be encoded. Therefore, a predicted image in which a change in the peripheral local decoded image is formed as a straight edge as it is is generated. Generated. Therefore, when the edge of the straight edge-like predicted image does not match the edge of the actual input image, a straight edge is added to the prediction error signal, resulting in a decrease in coding efficiency. That is, the conventional intra-frame prediction has a problem that the prediction efficiency is good for a video having an edge in a specific direction, and the prediction efficiency is poor for a video having an edge in another direction.

  The present invention has been made to solve the above-described problems, and obtains an image coding apparatus capable of performing stable and efficient prediction regardless of the texture of the input image and improving the coding efficiency. For the purpose.

  An image encoding apparatus according to the present invention receives image data, divides the image into a plurality of blocks, outputs a block image, and inputs the block image to generate a first intra prediction image and A first intra prediction unit that outputs first intra prediction data, which is information for reconstructing one intra prediction image, and performing a difference calculation between the block image and the first intra prediction image A difference image generation unit that outputs an image, a difference conversion quantization unit that frequency-converts the difference image, quantizes the obtained difference image conversion coefficient based on a predetermined difference image quantization parameter, and outputs the conversion coefficient; An entropy encoding unit that entropy-encodes the first intra-screen prediction data and the transform coefficient and outputs a bitstream, and the first intra-screen prediction unit reduces the block image to reduce the reduced image A reduced image conversion unit, a reduced quantization parameter output unit that outputs information for determining the quantization step size of the reduced image as a reduced image quantization parameter, a frequency conversion of the reduced image, and a reduced image conversion coefficient obtained Predictive image transform quantization unit that quantizes based on reduced image quantization parameter and outputs first intra prediction data, and inverse quantization and inverse frequency transform of first intra prediction data, local decoded prediction image Is provided with a predicted image inverse quantization inverse transform unit and a predicted image enlargement unit that expands the local decoded predicted image and generates a first intra-screen predicted image.

  An image encoding apparatus according to the present invention includes an image reducing unit that reduces a block image and outputs a reduced image, and performs frequency conversion and quantization on the reduced image based on a reduced image quantization parameter from a reduced image quantization parameter output unit. A prediction image transform quantization unit that outputs one intra-screen prediction data, a prediction image inverse quantization transform unit that performs inverse quantization and inverse frequency conversion on the first intra-screen prediction data and outputs a locally decoded prediction image, and a local Because it has a prediction image enlargement unit that enlarges the decoded prediction image and generates the first in-screen prediction image, it can perform stable and efficient prediction regardless of the texture of the input image, and improve the encoding efficiency Can do.

It is a block diagram which shows the structure of the image coding apparatus which concerns on Embodiment 1 of this invention. It is a flowchart which shows operation | movement of the image coding apparatus which concerns on Embodiment 1 of this invention. It is a flowchart which shows operation | movement of the 1st intra estimation part of the image coding apparatus which concerns on Embodiment 1 of this invention. It is a block diagram which shows the modification of the image coding apparatus which concerns on Embodiment 1 of this invention. It is explanatory drawing which shows the structure of the bit stream of the image coding apparatus which concerns on Embodiment 1 of this invention. It is a block diagram which shows the structure of the image decoding apparatus which concerns on Embodiment 2 of this invention. It is a flowchart which shows operation | movement of the image decoding apparatus which concerns on Embodiment 2 of this invention. It is a flowchart which shows operation | movement of the 1st intra estimated image generation part of the image decoding apparatus which concerns on Embodiment 2 of this invention. It is a block diagram which shows the modification of the image decoding apparatus which concerns on Embodiment 2 of this invention.

Embodiment 1 FIG.
FIG. 1 is a block diagram showing an image coding apparatus according to Embodiment 1 of the present invention.
FIG. 1 is a block diagram showing a configuration of an image encoding device 100 according to Embodiment 1. The image encoding device 100 includes a block division unit 101, a first intra prediction unit (first intra prediction unit) 200, a difference image generation unit 102, a difference transform quantization unit 103, and an entropy encoding unit. 104, a difference inverse transform inverse quantization unit 105, an addition unit 106, a loop filter unit 107, a local decoded image storage unit 108, a motion compensation prediction unit 109, and a prediction method determination unit 110.

  The block dividing unit 101 inputs a moving image as an original image, divides the moving image into blocks, and generates an image of each divided block (hereinafter referred to as a block image) as a difference image generating unit 102, a first image To the intra prediction unit 200 and the motion compensation prediction unit 109. At this time, the block size may be a fixed size of 16 pixels × 16 pixels, for example, or may be a size adaptively selected from 64 pixels × 64 pixels, 32 pixels × 32 pixels, and 16 pixels × 16 pixels. Also good. The first intra prediction unit 200 performs intra-frame prediction to generate a block prediction image and outputs the block prediction image to the prediction method determination unit 110, and information about the prediction image to the entropy encoding unit 104 as a prediction image transform coefficient. Output. The motion compensation prediction unit 109 generates an inter prediction image by performing inter-frame prediction by performing motion compensation prediction using the local decoded image stored in the local decoded image storage unit 108 and the input block image. The prediction method determining unit 110 outputs the motion vector and information specifying the referenced local decoded image to the entropy encoding unit 104 as motion information.

  The prediction method determination unit 110 compares the prediction performance or the coding performance based on the intra-frame prediction performed by the first intra prediction unit 200 and the inter-frame prediction performed by the motion compensation prediction unit 109, and determines and determines the optimal prediction method. Is generated and output to the difference image generation unit 102 and the addition unit 106, and the selected prediction method is output to the entropy encoding unit as a block mode. The difference image generation unit 102 takes the difference between the block image from the block division unit 101 and the block prediction image from the prediction method determination unit 110 and outputs the difference to the difference transform quantization unit 103 as a difference block image. The difference transform quantization unit 103 performs orthogonal transform such as DCT on the difference block image from the difference image generation unit 102 in units of transform block size specified by the input transform block size information, and the generated orthogonality The transform coefficient is quantized according to the quantization step size determined by the input difference image quantization parameter, and the quantized coefficient is output to the entropy coding unit 104 and the difference inverse transform inverse quantization unit 105. The entropy encoding unit 104 entropy-encodes the predicted image transform coefficient, motion information, block mode, quantization coefficient, and difference image quantization parameter by variable length encoding, arithmetic encoding, and the like, and outputs the result as a bit stream to the outside.

  The difference inverse transform inverse quantization unit 105 inversely quantizes the quantization coefficient according to the quantization step size determined by the difference image quantization parameter to obtain an inverse quantization orthogonal transform coefficient, and the generated inverse quantization orthogonal The transform coefficient is subjected to inverse orthogonal transform, and the local decoded difference block image is output to the adding unit 106. The addition unit 106 outputs the local decoded block image to the loop filter unit 107 by adding the block prediction image and the local decoded difference block image. The loop filter unit 107 uses the local decoded block image and the local decoded image stored in the local decoded image storage unit 108, for example, H. A filtering process such as a deblocking filter process used in H.264 is performed, and the result is output to the local decoded image storage unit 108 as a local decoded image. The local decoded image storage unit 108 stores one or a plurality of local decoded images and uses them to generate a predicted image.

  As shown in FIG. 1, the first intra prediction unit 200 includes an image reduction unit 201, a predicted image transform quantization unit 202, a predicted image inverse quantization inverse transform unit 203, a predicted image enlargement unit 204, and a reduced block size selection unit 205. , A reduced image quantization parameter output unit 206 and a transform block size output unit 207. The image reducing unit 201 reduces the input block image at a reduction rate based on the reduced block size information output from the reduced block size selecting unit 205, and outputs the reduced image to the predicted image transform quantization unit 202. Image reduction methods include, for example, a method in which an average value of pixel values for every 2 × 2 pixels, 4 × 4 pixels, or 8 × 8 pixels is used as a pixel value of a reduced image, or a method of sub-sampling after applying a low-pass filter Any method may be used as long as the input image is reduced to generate a low-resolution image. The predictive image transform quantization unit 202 performs orthogonal transform such as DCT on the reduced image input from the image reduction unit 201 and outputs the generated orthogonal transform coefficient from the reduced image quantization parameter output unit 206. The image is quantized based on the reduced image quantization parameter, and is output to the entropy coding unit 104 and the predicted image inverse quantization inverse transform unit 203 as a predicted image transform coefficient. The predictive image inverse quantization inverse transform unit 203 performs inverse quantization and inverse orthogonal transform, which are inverse processes of the predictive image transform quantization unit 202, on the predictive image transform coefficient input from the predictive image transform quantizer 202. As a result, a locally decoded reduced image is generated and output to the predicted image enlargement unit 204. In the predicted image enlarging unit 204, a process for improving the resolution is performed on the locally decoded reduced image input from the predicted image inverse quantization inverse transform unit 203, and the first image is enlarged so as to have the same size as the block image. The prediction method determination unit 110 outputs the intra prediction image. Here, for example, the processing content may be enlarged by interpolation processing, or the processing content is not particularly limited as long as it is a processing that improves the resolution of an input image by any other method.

The reduced block size selection unit 205 determines a reduced block size that specifies the block size after reduction in the image reduction unit 201, and outputs the reduced block size to the image reduction unit 201. The reduced block size may be any size as long as it is smaller than the block image, such as 1/2, 1/4, or 1/8 of the size of the input block image. For example, it is possible to determine a reduced block size by evaluating a prediction error and encoding performance by trying a plurality of reduced block sizes. In this way, an optimal reduction size can be selected and encoding can be performed efficiently. In this case, the reduced block size is also output to the entropy encoding unit 104 and configured to perform entropy encoding.
Alternatively, when the reduced image quantization parameter is large, it is considered that high frequency components are easily reduced by quantization, and it is considered that a prediction error does not easily occur even if the reduced image quantization parameter is large. However, when the reduced image quantization parameter is small, it may be determined to reduce the block to a larger block. In this way, an appropriate reduction size can be selected, and the amount of code can be reduced because there is no need to transmit the reduction size. The same effect can be obtained for the same reason even if it is determined to reduce to a smaller block when the difference image quantization parameter is large and to reduce to a larger block when the difference image quantization parameter is small.

In addition, because high-frequency components other than noise are locally low in high-resolution video, it can be assumed that prediction errors are unlikely to occur even if the block is reduced to a smaller block. You may comprise so that it may reduce to a block. Even in this case, an appropriate reduction size can be selected, and the amount of codes can be reduced because it is not necessary to transmit the reduction size.
Alternatively, an optimum reduced block size may be determined in slice units, picture units, or sequence units, and entropy coding may be performed using the reduced block size as header information. In this case, since the optimum reduced block size can be determined with a small code amount, efficient coding can be realized.

The reduced image quantization parameter output unit 206 determines a reduced image quantization parameter to be used when performing the quantization in the predicted image transform quantization unit 202 and the inverse quantization in the predicted image inverse quantization inverse transform unit 203 to perform the predicted image conversion. The data is output to the quantization unit 202. Experiments show that the optimal reduced image quantization parameter in the first intra prediction unit 200 varies depending on the value of the difference image quantization parameter used when the difference block image is quantized by the difference transform quantization unit 103. It has been confirmed. When the difference image quantization parameter is a large value, the difference block image is coarsely quantized, so that the finally obtained decoded image is an image in which the low frequency component is dominant. Therefore, when the reduced image quantization parameter is BPP_QP and the differential image quantization parameter is QP, BPP_QP can be set in conjunction with QP to obtain optimum encoding performance. At this time, for example, a table describing the relationship between the reduced image quantization parameter BPP_QP and the difference image quantization parameter QP is provided in advance, and a value obtained from the difference image quantization parameter QP is referred to this table to obtain the reduced image quantization parameter QP. The quantization parameter BPP_QP may be used, or BPP_QP obtained by the following equation (1) may be used as the predicted quantization step size.

BPP_QP = 27 (QP ≦ 41)
QP-15 (QP> 41) (1)

  In the example given here, the numbers and formulas themselves are not limited to this, but by learning a combination of BPP_QP and QP that maximizes the encoding performance, and creating a table or formula based on it Similar effects can be obtained. Further, since the optimum BPP_QP for the QP differs for each block according to the characteristics of the input signal, as another means, the optimum BPP_QP is determined and output by entropy encoding the value of the BPP_QP in the same manner as the QP. It may be. For example, a difference value between BPP_QP values in a block to be encoded can be encoded from a BPP_QP value in an adjacent block.

  The transform block size output unit 207 determines a transform block size that is a unit of orthogonal transform / inverse transform in the difference transform quantizer 103 and the difference inverse transform inverse quantizer 105, and determines the difference transform quantizer 103 and the inverse difference transform inverse. The data is output to the quantization unit 105. When the image signal contains a lot of high frequency components, the difference block image is divided into, for example, 4 × 4 pixel units or 8 × 8 pixel units so that the image signal can be expressed more precisely. Since the signal can be appropriately expressed by performing orthogonal transformation, high-performance coding can be realized. Conversely, when there are few high-frequency components, the overhead in entropy coding of the transform block increases, so that high-performance coding can be realized by performing orthogonal transform in units of large blocks such as 16 × 16 pixels. Therefore, the transform block size output unit 207 can realize high-performance coding by determining and outputting the optimum transform block size by comparing the coding performance of each transform block size. .

  Alternatively, when the difference image quantization parameter is a large value, since coarse quantization is performed and high-frequency components are difficult to generate, the encoding is performed with a large transform block size, and the difference image quantization parameter is a small value. On the contrary, encoding may be performed with a small transform block size. In this case, the transform block size is encoded without entropy coding by using one or a plurality of thresholds so that the optimum transform block size can be selected according to the difference image quantization parameter. It is also possible to perform. In addition, when a small value is selected as the reduced block size, it is considered that the block image to be encoded has few high-frequency components. Therefore, when the reduced block size is a small value, If a large value is used and, conversely, if the reduced block size is a large value, a high-performance encoding can be realized even if a small value is used as the transform block size.

Next, the operation of the image coding apparatus 100 according to the first embodiment will be described. FIG. 2 is a flowchart showing the processing of the image coding apparatus 100, and the numerical value of each step number corresponds to the code of the block that performs the processing.
First, when a moving image is input to the image coding apparatus 100, the moving image is divided into blocks by the block dividing unit 101, and each divided block image is output (step ST101). Next, each block image is subjected to intra-frame prediction in the first intra prediction unit 200, the first intra predicted image is output, and information about the predicted image is output as a predicted image transform coefficient (step ST200). ). When a block image is input to the motion compensation prediction unit 109, an inter prediction image is generated and output by performing motion compensation prediction using the local decoded image input from the local decoded image storage unit 108. The information specifying the motion vector and the referenced local decoded image is output as motion information (step ST109).

  When the first intra prediction image and the inter prediction image obtained in this way are input to the prediction method determination unit 110, the prediction method determination unit 110 performs intra-frame prediction by the first intra prediction unit 200 and a motion compensation prediction unit. The optimal prediction method is determined by comparing the prediction performance or the encoding performance by inter-frame prediction according to 109, the prediction image by the determined method is output as a block prediction image, and the selected prediction method is set as the block mode. Output (step ST110). The output block prediction image is subjected to a difference calculation with the block image from the block dividing unit 101 in the difference image generation unit 102, and as a result, a difference block image is output (step ST102). The difference block image is subjected to orthogonal transform such as DCT in the transform block size unit specified by the transform block size information input from the transform block size output unit 207 in the difference transform quantization unit 103 and the generated orthogonal transform. The coefficient is quantized according to the quantization step size determined by the input difference image quantization parameter, and the quantization coefficient is output (step ST103).

  The entropy coding unit 104 performs entropy coding such as variable length coding or arithmetic coding on the predicted image transform coefficient, motion information, block mode, quantization coefficient, and difference image quantization parameter generated by the above processing. And output as a bit stream (step ST104).

  On the other hand, the quantization coefficient is input to the difference inverse transform inverse quantization unit 105, and is inversely quantized according to the quantization step size determined by the difference image quantization parameter to obtain an inverse quantization orthogonal transform coefficient. The generated inverse quantization orthogonal transform coefficient is subjected to inverse orthogonal transform, and a local decoded difference block image is output (step ST105). The locally decoded difference block image obtained in this way is added to the block prediction image in the adding unit 106, thereby generating and outputting a locally decoded block image (step ST106). When the generated local decoded block image is input to the loop filter unit 107, the local decoded block image and the local decoded image using the local decoded image stored in the local decoded image storage unit 108, for example, H.264. A filtering process such as the deblocking filter process used in H.264 is performed, and the result is output as a locally decoded image (step ST107). The local decoded image obtained in this way is stored in the local decoded image storage unit 108 and used for generating a predicted image (step ST108).

FIG. 3 is a flowchart showing details of the operation of the first intra prediction unit 200. Also in this figure, the numerical value of each step number corresponds to the code of the block that performs the process.
First, the reduced block size selection unit 205 determines and outputs a reduced block size that specifies a block size after reduction in the image reduction unit 201 (step ST205). Further, the reduced image quantization parameter output unit 206 determines and outputs the reduced image quantization parameter used when performing the quantization in the prediction image transform quantization unit 202 and the inverse quantization in the prediction image inverse quantization inverse transform unit 203. (Step ST206). Further, transform block size output section 207 determines and outputs a transform block size as a unit of orthogonal transform / inverse transform in difference transform quantizer 103 and difference inverse transform inverse quantizer 105 (step ST207).

  When the block image input to the first intra prediction unit 200 is input to the image reduction unit 201, the block image is reduced at a reduction rate based on the reduced block size information output from the reduced block size selection unit 205, and the reduced image is It is output (step ST201). Subsequently, when the reduced image is input to the predicted image transform quantization unit 202, the input reduced image is subjected to orthogonal transform such as DCT, and the generated orthogonal transform coefficient is reduced to the reduced image quantization parameter output unit 206. It is quantized based on the reduced image quantization parameter that is output more and is output as a predicted image transform coefficient (step ST202). The predicted image transform coefficient is generated and output in the predicted image inverse quantization inverse transform unit 203 by performing inverse quantization and inverse orthogonal transform, which are the inverse processes of the predicted image transform quantization unit 202, to generate a locally decoded reduced image. (Step ST203). The locally decoded reduced image is input to the predicted image enlargement unit 204, subjected to processing for improving the resolution, enlarged so as to have the same size as the block image, and output as the first intra predicted image (step ST204).

  In addition, when the block prediction image from the motion compensation prediction part 109 is selected in the prediction method determination part 110, you may comprise so that it may encode by using the value preset as conversion block size, The transform block size may be encoded by entropy encoding.

  In the above description, the reduced image quantization parameter, the reduced block size, and the transformed block size can be selected. However, even if the preset values are used for these, the reduced image is encoded and enlarged. By doing so, the rough structure of the block image can be appropriately predicted by obtaining the block prediction image, so that high-performance encoding processing can be performed. Of course, the same effect can be obtained even if one or more of the reduced image quantization parameter, reduced block size, and transformed block size are made variable. Moreover, even if this method is applied as an encoding process for a still image by configuring so as not to perform motion compensation prediction, the same effect can be obtained.

  For example, as shown in FIG. The image encoding device 100a is configured to include the second intra prediction unit 200a that performs intra prediction by the H.264 encoding method, and is configured to select an optimal prediction mode from the first intra prediction and the second intra prediction. If so, higher performance encoding can be realized. Here, in FIG. 4, the configuration other than the addition of the second intra prediction unit 200 a is the same as that in FIG. 1, and thus the description thereof is omitted.

Next, the bit stream encoded by the image encoding device 100 will be described.
The input image is encoded by the image encoding device 100 in FIG. 1 based on the above-described processing, and is output as a bit stream in a block in which a plurality of blocks are bundled and in a unit in which a plurality of blocks are bundled (hereinafter referred to as a slice). Is done. FIG. 5 shows the data arrangement of the bit stream. The bit stream is configured as a collection of encoded data for the number of blocks included in a frame, and the blocks are unitized in units of slices. A picture level header for referencing blocks belonging to the same frame as common parameters is prepared, and block size information is stored in the picture level header. If the block size is fixed in sequence units higher than the picture level, the block size information may be multiplexed in the sequence level header.

  Each slice starts from a slice header, and subsequently, encoded data of each block in the slice is arranged. In the example of FIG. 5, it is shown that K blocks are included in the second slice. The block data is composed of a block header and a quantization coefficient. The block header includes a block mode, motion information, a difference image quantization parameter, a predicted image transform coefficient, a reduced image quantization parameter, a reduced block size, and a transform block. The sizes are arranged. It should be noted that the effect of the present invention can be obtained even if the blocks are configured as hierarchically configured macroblocks.

  As described above, according to the image coding apparatus of the first embodiment, the image data is input, the block dividing unit that outputs the block image by dividing the image data, the block image is input, and the first screen is displayed. A first intra prediction unit that generates first intra prediction image and outputs first intra prediction data that is information for reconstructing the first intra prediction image, and a block image and the first screen A difference image generation unit that performs a difference calculation of a predicted image and outputs a difference image, and frequency-converts the difference image, and quantizes the obtained difference image conversion coefficient based on a predetermined difference image quantization parameter to obtain a conversion coefficient. A differential transform quantization unit for outputting, an entropy encoding unit for entropy encoding the first intra-screen prediction data and the transform coefficient, and outputting a bitstream, and the first intra-screen prediction unit includes a block image An image reduction unit that outputs a reduced image by reducing the image, a reduced quantization parameter output unit that outputs information for determining the quantization step size of the reduced image as a reduced image quantization parameter, and frequency conversion of the reduced image The reduced image transform coefficient is quantized based on the reduced image quantization parameter and the first image prediction data is output, and the first image prediction data is inversely quantized and inverse frequency transformed. And a prediction image inverse quantization inverse transform unit that outputs a local decoded prediction image and a prediction image enlargement unit that expands the local decoded prediction image and generates a first in-screen prediction image. A stable and efficient prediction can be performed regardless of the texture, and the encoding efficiency can be improved.

  In addition, according to the image coding apparatus of Embodiment 1, the entropy coding unit entropy codes the reduced image quantization parameter and outputs it as a bit stream, and therefore selects the optimum reduced image quantization parameter. Can be encoded efficiently.

  In addition, according to the image coding apparatus of the first embodiment, the reduced image quantization parameter output unit outputs a value determined based on the difference image quantization parameter. Can be determined uniquely.

  Further, according to the image coding apparatus of the first embodiment, the reduced image quantization parameter output unit sets a large value when the differential image quantization parameter is a large value, and sets a small value for the differential image quantization parameter. In some cases, a reduced image quantization parameter having a magnitude relation equivalent to the magnitude relation of the difference image quantization parameter is output so as to be a small value, so that an appropriate reduced image quantization parameter can be determined. In addition, since it is not necessary to transmit the reduced image quantization parameter, the code amount can be reduced.

  In addition, according to the image coding method of the first embodiment, the image data is input, the block dividing step for dividing the block into a plurality of blocks and outputting the block image, the block image is input, and the first intra prediction image A first intra prediction step for generating first intra prediction data, which is information for reconstructing the first intra prediction image, and a block image and a first intra prediction image A difference image generation step for performing a difference operation and outputting a difference image; and a difference for frequency-converting the difference image, quantizing the obtained difference image conversion coefficient based on a predetermined difference image quantization parameter, and outputting the conversion coefficient A transform quantization step; an entropy encoding step for entropy encoding the first intra prediction data and the transform coefficient and outputting a bitstream; The prediction step includes an image reduction step for reducing a block image and outputting a reduced image, a reduced quantization parameter output step for outputting information for determining a quantization step size of the reduced image as a reduced image quantization parameter, and a reduced image Frequency conversion, quantize the obtained reduced image conversion coefficient based on the reduced image quantization parameter, and output the first in-screen prediction data, and reverse the first in-screen prediction data A prediction image inverse quantization inverse transform step that performs quantization and inverse frequency transform and outputs a local decoded prediction image; and a prediction image enlargement step that expands the local decoded prediction image and generates a first intra prediction image Therefore, stable and efficient prediction can be performed regardless of the texture of the input image, and the encoding efficiency can be improved.

Embodiment 2. FIG.
FIG. 6 is a block diagram showing a configuration of image decoding apparatus 300 according to Embodiment 2. The image decoding apparatus 300 is an apparatus that suitably decodes the bitstream generated by the image encoding apparatus 100 according to Embodiment 1, and outputs a decoded image obtained as a result. The image decoding apparatus 300 and the first intra Prediction image generation unit (first in-screen prediction image generation unit) 400, difference inverse transform inverse quantization unit 305, addition unit 306, loop filter unit 307, local decoded image storage unit 308, motion compensation unit 309, a prediction method determination unit 310, and a prediction changeover switch 311. Here, the entropy decoding unit 304 to the prediction method determination unit 310 and the first intra prediction image generation unit 400 are respectively the entropy encoding unit 104 to the prediction method determination unit 110 and the first intra prediction image generation unit 400 in the image encoding device 100 illustrated in FIG. It is a block of a decoding apparatus corresponding to one intra prediction unit 200.

  The entropy decoding unit 304 performs entropy decoding on the input bit stream by variable length decoding, arithmetic decoding, or the like, and each of the first bit stream is used as a predicted image transform coefficient, motion information, block mode, quantization coefficient, and difference image quantization parameter. It outputs to the intra estimated image production | generation part 400, the motion compensation part 309, the prediction method determination part 310, and the difference inverse transformation inverse quantization part 305. The difference inverse transform inverse quantization unit 305 inversely quantizes the quantization coefficient according to the quantization step size determined by the difference image quantization parameter to obtain an inverse quantization orthogonal transform coefficient, and the generated inverse quantization orthogonal transform The coefficients are subjected to inverse orthogonal transform, and the locally decoded difference block image is output to the adding unit 306. The first intra predicted image generation unit 400 generates a first intra predicted image by performing intra prediction based on the predicted image conversion coefficient, and outputs the first intra predicted image to the adding unit 306. The motion compensation unit 309 generates an inter prediction image by performing motion compensation using the local decoded image stored in the local decoded image storage unit 308 and the input motion information, and outputs the inter predicted image to the addition unit 306. The prediction method determination unit 310 determines whether to output either the first intra prediction image by the first intra prediction image generation unit 400 or the inter prediction image by the motion compensation unit 309 according to the block mode, and performs prediction. The changeover switch 311 is switched.

  When the prediction method determination unit 310 determines that the block mode is a mode for performing the first intra prediction, the prediction changeover switch 311 outputs the output from the entropy decoding unit 304 to the first intra prediction image generation unit 400. And the prediction image generated by the first intra prediction image generation unit 400 is connected to be output to the addition unit 306 as a block prediction image, and conversely, the block mode is determined to be a mode for performing motion compensation. In such a case, the output from the entropy decoding unit 304 is connected to the motion compensation unit 309, and the prediction image generated by the motion compensation unit 309 is connected to be output to the addition unit 306 as a block prediction image. The addition unit 306 adds the block prediction image and the local decoded difference block image to output the local decoded block image to the loop filter unit. The loop filter unit 307 performs filtering processing on the local decoded block image and the local decoded image using the local decoded block image and the local decoded image stored in the local decoded image storage unit 308, and uses the result as the local decoded image. Output to the external and local decoded image storage unit 308. The local decoded image storage unit 308 stores one or more local decoded images and uses them to generate a predicted image.

  As shown in FIG. 6, the first intra predicted image generation unit 400 includes a predicted image inverse quantization inverse transform unit 403, a predicted image enlargement unit 404, a reduced block size selection unit 405, a reduced image quantization parameter output unit 406, a transform. The block size output unit 407 is configured. These predicted image inverse quantization inverse transform unit 403 to transform block size output unit 407 are decoding corresponding to the predicted image inverse quantization inverse transform unit 203 to transform block size output unit 207 in the image coding apparatus 100 shown in FIG. It is the structure of an apparatus.

  The predicted image inverse quantization inverse transform unit 403 performs inverse quantization and prediction on the basis of the reduced image quantization parameter input from the reduced image quantization parameter output unit 406 with respect to the predicted image transform coefficient input from the entropy decoding unit 304. By performing inverse orthogonal transformation, a locally decoded reduced image is generated and output to the predicted image enlargement unit 404. The predicted image enlargement unit 404 performs processing for improving the resolution so that the input local decoded reduced image has the same size as the block image from the reduced block size input from the reduced block size selection unit 405. Is output to the adding unit 306 as an intra predicted image. The reduced block size selection unit 405 outputs a reduced block size that specifies the block size before enlargement in the predicted image enlargement unit 404 to the predicted image enlargement unit 404.

  Here, the reduced block size operates so as to reproduce the value determined by the image coding apparatus 100 according to the first embodiment. For example, in the image coding apparatus 100 according to the first embodiment, when a reduced block size is determined by evaluating a prediction error and coding performance by trying a plurality of reduced block sizes, entropy coding is performed for each block. Since the value obtained by entropy decoding the reduced block size is directly output from the entropy decoding unit 304 to the predicted image enlargement unit 404, the reduced block size selection unit 405 is unnecessary. Alternatively, in a flat area, since the high-frequency component of the image is small, it is considered that a prediction error is unlikely to occur even if the image is reduced to a small block. When the image coding apparatus 100 is configured to determine to reduce to a larger block when the conversion parameter is small, a reduced block size obtained by the same processing is output. Alternatively, when the image coding apparatus 100 is configured to determine to reduce to a smaller block when the difference image quantization parameter is large and to reduce to a larger block when the difference image quantization parameter is small, the image encoding apparatus 100 is obtained by the same process. The reduced block size to be output is output.

  In addition, since it can be assumed that high-frequency components other than noise are locally small in a high-resolution video, the image coding apparatus 100 is configured to reduce to a small block and conversely to a large block in a low-resolution video. , The reduced block size obtained by the same processing is output. Alternatively, when the image encoding apparatus 100 is configured to determine an optimal reduced block size in slice units, picture units, or sequence units, and to perform entropy encoding using the reduced block size as header information, the header information is entropy decoded. Since the value obtained in this way is directly output from the entropy decoding unit 304 to the predicted image enlarging unit 404, the reduced block size selecting unit 405 is unnecessary.

  The reduced image quantization parameter output unit 406 outputs the reduced image quantization parameter used when the inverse quantization in the prediction image inverse quantization inverse transformation unit 403 is performed to the prediction image inverse quantization inverse transformation unit 403. Here, the reduced image quantization parameter operates so as to reproduce the value determined by the image coding apparatus 100 according to the first embodiment. In the image coding apparatus 100, when the reduced image quantization parameter is set to BPP_QP and the difference image quantization parameter is set to QP, when the BPP_QP is set in conjunction with QP by a table or a mathematical expression, the same table or By using the mathematical formula, BPP_QP is determined and output as a reduced image quantization parameter. Further, in the image encoding device 100, when the BPP_QP value is configured to be entropy encoded by the same method as QP, the value obtained by entropy decoding is predicted from the entropy decoding unit 304 by the predicted image inverse quantization inverse transform. Since the data is directly output to the unit 403, the reduced image quantization parameter output unit 406 is not necessary.

  The transform block size output unit 407 outputs a transform block size that is a unit of inverse orthogonal transform in the difference inverse transform inverse quantization unit 305 to the difference inverse transform inverse quantization unit 305. Here, the transform block size operates so as to reproduce the value determined by the image coding apparatus 100 according to the first embodiment. When the image coding apparatus 100 is configured to determine and output an optimum transform block size by comparing the coding performance of each transform block size, the value obtained by entropy decoding is the entropy decoding unit 304. Since the difference is directly output to the inverse inverse transform inverse quantization unit 305, the transform block size output unit 407 is unnecessary.

  In addition, when the difference image quantization parameter is a large value, it is difficult to generate a high frequency component because coarse quantization is performed. Therefore, the encoding is performed with a large transform block size, and the difference image quantization parameter is a small value. On the other hand, in order to encode with a small transform block size, it is possible to select an optimum one from a plurality of transform block sizes according to the difference image quantization parameter using one or a plurality of threshold values. When the image coding apparatus 100 is configured to perform coding without entropy coding of the transform block size, a transform block size obtained by similar processing is output.

  In addition, when a small value is selected as the reduced block size, it is considered that the block image to be encoded has few high-frequency components. Therefore, when the reduced block size is a small value, When the image coding apparatus 100 is configured to use a large value and, on the contrary, to use a small value as the transform block size when the reduced block size is a large value, the transform block size obtained by the same processing is output. Is done.

Next, the operation of the image decoding apparatus 300 according to Embodiment 2 will be described. FIG. 7 is a flowchart showing the processing of the image decoding apparatus 300, and the numerical value of each step number corresponds to the code of the functional unit that performs the processing.
First, when a bitstream is input to the image decoding apparatus 300, the entropy decoding unit 304 performs entropy decoding such as variable length decoding or arithmetic decoding, and the predicted image transform coefficient, motion information, block mode, quantization, and the like. Coefficients and difference image quantization parameters are output (step ST304). In the inverse difference transform inverse quantization unit 305, the quantization coefficient is inversely quantized according to the quantization step size determined by the difference image quantization parameter to obtain an inverse quantization orthogonal transform coefficient, and the generated inverse quantization orthogonal transform is generated. The coefficients are subjected to inverse orthogonal transform, and a locally decoded difference block image is output (step ST305).

  In addition, the prediction method determination unit 310 determines which of the first intra prediction image by the first intra prediction image generation unit 400 or the inter prediction image by the motion compensation unit 309 is output according to the block mode, and the prediction The changeover switch 311 is changed over (step ST310). When the block mode is the first intra predicted image, the first intra predicted image generation unit 400 generates and outputs the first intra predicted image by performing intra prediction based on the predicted image conversion coefficient. (Step ST400). On the other hand, when the block mode is an inter prediction image, the motion compensation unit 309 performs motion compensation using the local decoded image stored in the local decoded image storage unit 308 and the input motion information, thereby performing the inter prediction image. Is generated and output (step ST309).

  When the block prediction image obtained in this way is input to addition section 306, the local decoded block image is output by adding the local decoded difference block image (step ST306). In the loop filter unit 307, filtering processing is performed on the local decoded block image and the local decoded image using the local decoded block image and the local decoded image stored in the local decoded image storage unit 108, and the result is the local decoded image. (Step ST307). In the local decoded image storage unit 308, one or a plurality of local decoded images are stored and used for prediction image generation (step ST308).

FIG. 8 is a flowchart showing details of the operation of the first intra predicted image generation unit 400. Also in this figure, the numerical value of each step number corresponds to the code of the functional unit that performs the process.
The reduced block size selection unit 405 outputs a reduced block size that specifies the block size before enlargement in the predicted image enlargement unit 404 (step ST405). Further, reduced image quantization parameter output section 406 outputs reduced image quantization parameters used when performing inverse quantization in predicted image inverse quantization inverse transform section 403 (step ST406). Further, transform block size output section 407 outputs a transform block size that is a unit of inverse orthogonal transform in difference inverse transform inverse quantization section 305 (step ST407). The predicted image inverse quantization inverse transform unit 403 performs inverse quantization on the predicted image transform coefficient input from the entropy decoding unit 304 based on the reduced image quantization parameter input from the reduced image quantization parameter output unit 406. By performing inverse orthogonal transform, a locally decoded reduced image is generated and output (step ST403). The predicted image enlarging unit 404 performs a process of improving the resolution so that the input local decoded reduced image has the same size as the block image from the reduced block size input from the reduced block size selecting unit 405. Are output as intra prediction images (step ST404).

  As an image encoding apparatus, as shown in FIG. In the case where the second intra prediction unit 200a that performs intra prediction by the H.264 encoding method is provided, as shown in FIG. It is preferable that a second intra-predicted image generation unit 400a for generating an intra-predicted image corresponding to the H.264 encoding method is provided so that the prediction method determination unit 310 can also select the second intra prediction according to the block mode. Can be decrypted. In the image decoding apparatus 300a shown in FIG. 9, the configuration other than the addition of the second intra predicted image generation unit 400a is the same as that of the image decoding apparatus 300 shown in FIG. Description is omitted.

  As described above, according to the image decoding apparatus of the second embodiment, the entropy decoding unit that entropy-decodes the bitstream and outputs the transform coefficient and the first in-screen prediction data, and the transform coefficient are determined in advance. A difference inverse transform inverse quantization unit that performs inverse quantization and inverse frequency transform based on the difference image quantization parameter and outputs a difference decoded image; and a first intra prediction image based on the first intra prediction data The first intra-screen prediction image generating unit that outputs the decoded image and the differential decoded image addition unit that outputs the decoded image by adding the differential decoded image and the first intra-screen predicted image, The intra-prediction image generation unit includes a reduced image quantization parameter output unit that outputs a predetermined reduced image quantization parameter, and performs inverse quantization and first quantization on the first intra-screen prediction data based on the reduced image quantization parameter. Since the prediction image inverse quantization inverse transform unit that performs inverse frequency transform and outputs the decoded predicted image, and the predicted image enlargement unit that expands the decoded predicted image and generates the first in-screen predicted image, are provided. The encoded image bitstream generated by the image encoding device of aspect 1 can be suitably decoded.

  Further, according to the image decoding apparatus of the second embodiment, an entropy decoding unit that entropy-decodes a bitstream and outputs a transform coefficient, a reduced image quantization parameter, and first in-screen prediction data; A differential inverse transform inverse quantization unit that performs inverse quantization and inverse frequency transform based on the determined differential image quantization parameter and outputs a differential decoded image, and a first screen based on the first intra prediction data A first intra-screen prediction image generation unit that reconstructs and outputs an intra-prediction image, and a differential decoded image addition unit that adds the differential decoded image and the first intra-screen prediction image and outputs a decoded image. The one intra-screen prediction image generation unit dequantizes the first intra-screen prediction data based on the reduced image quantization parameter and performs inverse frequency conversion, and outputs a decoded prediction image. Since the conversion unit and the prediction image enlargement unit for enlarging the decoded prediction image and generating the first intra-screen prediction image are provided, the encoded image bitstream can be efficiently decoded and reduced as a decoding device It is not necessary to generate an image quantization parameter, and the configuration can be simplified.

  Also, according to the image decoding apparatus of the second embodiment, the reduced image quantization parameter output unit determines the value of the reduced image quantization parameter based on the difference image quantization parameter. Parameters can be uniquely determined.

  Further, according to the image decoding apparatus of the second embodiment, the reduced image quantization parameter output unit sets a large value when the difference image quantization parameter is a large value, and sets a small value for the difference image quantization parameter. In such a case, a reduced image quantization parameter having a magnitude relation equivalent to the magnitude relation of the difference image quantization parameter is output so as to be a small value, so that an appropriate reduced image quantization parameter can be determined. In addition, since it is not necessary to transmit the reduced image quantization parameter, the amount of codes can be reduced.

  In addition, according to the image decoding method of the second embodiment, the entropy decoding step of entropy decoding the bitstream and outputting the transform coefficient and the first in-screen prediction data, and the transform coefficient as a predetermined difference image quantum Inverse quantization and inverse frequency conversion based on the quantization parameter, and a differential inverse transform inverse quantization step for outputting a differential decoded image, and the first intra prediction image is reconstructed based on the first intra prediction data A first in-screen prediction image generation step, and a differential decoded image addition step in which the difference decoded image and the first in-screen prediction image are added to output a decoded image, and the first in-screen prediction image is output. The generation step includes a reduced image quantization parameter output step for outputting a predetermined reduced image quantization parameter and a first in-screen prediction data as a reduced image quantization parameter. A predictive image inverse quantization inverse transform step that performs inverse quantization and inverse frequency transform based on a meter and outputs a decoded predicted image, and a predicted image enlargement step that expands the decoded predicted image and generates a first in-screen predicted image Therefore, the encoded image bitstream generated by the image encoding apparatus according to Embodiment 1 can be suitably decoded.

  100, 100a Image coding apparatus, 101 Block division unit, 102 Difference image generation unit, 103 Difference transform quantization unit, 104 Entropy coding unit, 105 Difference inverse transform inverse quantization unit, 106 Addition unit, 107 Loop filter unit, 108 local decoded image storage unit 109 motion compensation prediction unit 110 prediction method determination unit 200 first intra prediction unit 200a second intra prediction unit 201 image reduction unit 202 prediction image transform quantization unit 203 prediction Image inverse quantization inverse transform unit, 204 Predictive image enlargement unit, 205 Reduced block size selection unit, 206 Reduced image quantization parameter output unit, 207 Transform block size output unit, 300, 300a Image decoding device, 304 Entropy decoding unit, 305 Difference inverse transform inverse quantization unit, 306 addition unit, 307 loop Filter unit, 308 Local decoded image storage unit, 309 Motion compensation unit, 310 Prediction method determination unit, 311 Prediction changeover switch, 400 First intra prediction image generation unit, 400a Second intra prediction image generation unit, 403 Reverse prediction image Quantization inverse transform unit, 404 predicted image enlargement unit, 405 reduced block size selection unit, 406 reduced image quantization parameter output unit, 407 transformed block size output unit.

Claims (10)

A block dividing unit for inputting image data, dividing the block into a plurality of blocks, and outputting a block image;
In the first screen that inputs the block image, generates a first intra-screen prediction image, and outputs first intra-screen prediction data that is information for reconstructing the first intra-screen prediction image A predictor;
A difference image generation unit that performs a difference calculation between the block image and the first intra prediction image and outputs a difference image;
A difference transform quantization unit for frequency-transforming the difference image, quantizing the obtained difference image transform coefficient based on a predetermined difference image quantization parameter, and outputting the transform coefficient;
An entropy encoding unit that entropy-encodes the first intra-screen prediction data and the transform coefficient and outputs a bitstream;
The first in-screen prediction unit
An image reduction unit that reduces the block image and outputs a reduced image;
A reduced quantization parameter output unit that outputs information for determining a quantization step size of the reduced image as a reduced image quantization parameter;
A frequency conversion of the reduced image, a reduced image conversion coefficient obtained is quantized based on the reduced image quantization parameter, and a prediction image conversion quantization unit that outputs the first in-screen prediction data;
A predictive image inverse quantization inverse transform unit that performs inverse quantization and inverse frequency transform on the first intra-screen prediction data and outputs a locally decoded prediction image;
An image encoding apparatus comprising: a predicted image enlarging unit that expands the local decoded predicted image and generates the first intra-screen predicted image.   The image encoding apparatus according to claim 1, wherein the entropy encoding unit entropy-encodes the reduced image quantization parameter and outputs it as a bit stream.   2. The image coding apparatus according to claim 1, wherein the reduced image quantization parameter output unit determines a value of the reduced image quantization parameter based on the difference image quantization parameter.   The reduced image quantization parameter output unit sets the difference image quantization parameter to a large value when the difference image quantization parameter is a large value and to a small value when the difference image quantization parameter is a small value. 2. The image coding apparatus according to claim 1, wherein a reduced image quantization parameter having a magnitude relationship equivalent to a size relationship of the quantization parameters is output. An entropy decoding unit that entropy-decodes the bitstream and outputs transform coefficients and first intra prediction data;
A differential inverse transform inverse quantization unit for inversely quantizing and transforming the transform coefficient based on a predetermined differential image quantization parameter and outputting a differential decoded image;
A first intra-screen prediction image generating unit that reconstructs and outputs a first intra-screen prediction image based on the first intra-screen prediction data;
A difference decoded image adding unit that adds the difference decoded image and the first intra prediction image and outputs a decoded image;
The first in-screen predicted image generation unit
A reduced image quantization parameter output unit for outputting a predetermined reduced image quantization parameter;
A predicted image inverse quantization inverse transform unit that performs inverse quantization and inverse frequency transform on the first intra prediction data based on the reduced image quantization parameter, and outputs a decoded predicted image;
An image decoding apparatus comprising: a predicted image enlarging unit that expands the decoded predicted image and generates the first intra-screen predicted image. An entropy decoding unit that entropy-decodes the bitstream and outputs a transform coefficient, a reduced image quantization parameter, and first intra prediction data;
A differential inverse transform inverse quantization unit for inversely quantizing and transforming the transform coefficient based on a predetermined differential image quantization parameter and outputting a differential decoded image;
A first intra-screen prediction image generating unit that reconstructs and outputs a first intra-screen prediction image based on the first intra-screen prediction data;
A difference decoded image adding unit that adds the difference decoded image and the first intra prediction image and outputs a decoded image;
The first in-screen predicted image generation unit
A prediction image inverse quantization inverse transform unit that performs inverse quantization and inverse frequency transform on the first intra prediction data based on the reduced image quantization parameter, and outputs a decoded prediction image;
An image decoding apparatus comprising: a predicted image enlarging unit that expands the decoded predicted image and generates the first intra-screen predicted image.   6. The image decoding apparatus according to claim 5, wherein the reduced image quantization parameter output unit determines a value of the reduced image quantization parameter based on the difference image quantization parameter.   The reduced image quantization parameter output unit sets the difference image quantization parameter to a large value when the difference image quantization parameter is a large value and to a small value when the difference image quantization parameter is a small value. 6. The image decoding apparatus according to claim 5, wherein a reduced image quantization parameter having a magnitude relation equivalent to the magnitude relation of the quantization parameters is output. A block division step for inputting image data, dividing the block into a plurality of blocks, and outputting a block image;
In the first screen that inputs the block image, generates a first intra-screen prediction image, and outputs first intra-screen prediction data that is information for reconstructing the first intra-screen prediction image A prediction step;
A difference image generation step of performing a difference calculation between the block image and the first intra prediction image and outputting a difference image;
A difference transform quantization step for frequency-transforming the difference image, quantizing the obtained difference image transform coefficient based on a predetermined difference image quantization parameter, and outputting the transform coefficient;
An entropy encoding step of entropy encoding the first intra prediction data and the transform coefficient and outputting a bitstream;
The first in-screen prediction step includes
An image reduction step of reducing the block image and outputting a reduced image;
A reduced quantization parameter output step for outputting information for determining a quantization step size of the reduced image as a reduced image quantization parameter;
Predictive image transform quantization step of frequency-converting the reduced image, quantizing the obtained reduced image transform coefficient based on the reduced image quantization parameter, and outputting the first in-screen prediction data;
A predictive image inverse quantization inverse transform step of inversely quantizing and inverse frequency transforming the first intra-screen prediction data and outputting a locally decoded predicted image;
An image encoding method comprising: a predicted image enlargement step of enlarging the locally decoded predicted image and generating the first intra-screen predicted image. An entropy decoding step of entropy decoding the bitstream and outputting transform coefficients and first intra prediction data;
A difference inverse transform inverse quantization step of inversely quantizing and transforming the transform coefficient based on a predetermined difference image quantization parameter and outputting a difference decoded image;
A first intra prediction image generation step for reconstructing and outputting a first intra prediction image based on the first intra prediction data;
A difference decoded image addition step of adding the difference decoded image and the first intra prediction image and outputting a decoded image;
The first intra prediction image generation step includes
A reduced image quantization parameter output step for outputting a predetermined reduced image quantization parameter;
A predictive image inverse quantization inverse transform step of inversely quantizing and inverse frequency transforming the first intra prediction data based on the reduced image quantization parameter, and outputting a decoded predicted image;
An image decoding method comprising: a predicted image enlargement step of enlarging the decoded predicted image to generate the first intra-screen predicted image.

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