JP2011182167A - Image encoding device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image encoding device performing highly efficient encoding. <P>SOLUTION: A prediction means 11 selects a reference signal for an encoding object block from among reconfigured pixel signals reconfigured from an encoded signal, and determines prediction information for predicting a pixel signal for the entire encoding object block. A compensation means 12 generates a prediction signal using the reconfigured pixel signals and the prediction signal. A subtractor 19 obtains a difference between an input moving image layer signal and the prediction signal to generate a prediction residual signal for the encoding object block. The prediction residual signal is subjected to orthogonal transformation, quantization and encoding to output code information. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an image coding device, and more particularly to an image coding device capable of performing coding for each unit block with high coding efficiency.

  Conventionally, a method for reducing spatial redundancy is known in order to improve coding efficiency in image coding. In intra-frame predictive coding in H.264, a coding target block is predicted using coded neighboring pixels. H.264 is disclosed in Non-Patent Document 1.

  In Patent Document 1, a similar location is searched from an encoded area using an encoded adjacent pixel as a template, and an adjacent area having the same positional relationship as the encoding target block is used as a prediction value of the encoding target block. A moving image encoding device has been proposed.

  In Patent Literature 2, an intra prediction code for a video that divides an encoding target block into a plurality of parts, encodes and decodes a part of the divided block, and uses some pixels of the decoded block for prediction of the remaining pixels. A device has been proposed.

  Patent Document 3 proposes a moving image encoding apparatus that uses a high correlation between adjacent pixels and uses not only adjacent pixels between blocks but also adjacent pixels in the encoding target block as predicted values.

JP 2007-036551 A JP 2007-074725 A JP 2009-049969 A

Kakuno et al., “H.264 / AVC Textbook Impress Standard Textbook Series”, Impress Net Business Company, 2004

  In the H.264 intra prediction, the prediction value of the encoding target block is determined based on the encoded neighboring pixel, so that the prediction is larger as the pixel of the encoding target block is farther from the prediction reference pixel. There is a problem that an error occurs.

  In the moving image encoding apparatus of Patent Document 1, it is not necessary to store location information representing a block used for prediction of a block to be encoded, but even if adjacent pixels serving as templates are similar, the blocks are similar. Not always. Therefore, there is a problem that the prediction accuracy may not be sufficient.

  In the video intra prediction encoding apparatus disclosed in Patent Document 2, when a divided encoding target block is predicted, a part of the first encoding block has the same problem as H.264.

  In the moving image encoding device of Patent Document 3, when there is a state where adjacent pixels are not encoded, a difference value from the adjacent pixels in the original image is encoded, and therefore, a quantization error may be propagated. There are challenges.

  An object of the present invention is to solve the above-described problems and provide an image encoding device capable of performing encoding with high encoding efficiency.

  In order to solve the above-described problems, the present invention provides an image encoding apparatus that encodes an input image for each unit block of encoding using prediction, and includes a signal reconstructed using an encoded signal. A prediction unit that selects a reference signal for each unit block and calculates prediction information for linearly predicting a signal of the entire unit block with respect to the signal of the encoding target block using the reference signal, and an encoded signal A compensation means for generating a prediction signal using the reconstructed signal and the prediction information calculated by the prediction means, and a difference between the signal for the encoding target block and the prediction signal generated by the compensation means It has a difference calculating means for generating a prediction residual signal, and the basic feature is that the prediction residual signal generated by the difference calculating means is orthogonally transformed, quantized and encoded. .

  In the present invention, when encoding an image signal of an encoding target block, a reference signal is selected in units of unit blocks from signals reconstructed using encoded signals, and linear prediction is performed. Spatial redundancy can be reduced, the amount of information of the image signal of the encoding target block can be reduced, and the encoding efficiency can be improved.

It is a functional block diagram which shows 1st Embodiment of the image coding apparatus which concerns on this invention. It is a functional block diagram which shows the image decoding apparatus which decodes the image encoded by the image encoding apparatus of FIG. It is a functional block diagram which shows 2nd Embodiment of the image coding apparatus which concerns on this invention. It is a figure which shows notionally the method for selecting the unit block of the prediction residual signal in a reconstruction screen used as a reference signal. It is a figure which shows notionally other methods for selecting the unit block of the prediction residual signal in a reconstruction screen used as a reference signal. It is a functional block diagram which shows the image decoding apparatus which decodes the image encoded by the image encoding apparatus of FIG.

  Hereinafter, the present invention will be described with reference to the drawings. First, a first embodiment of an image encoding device according to the present invention will be described. Note that. An image to be encoded by the present invention may be a moving image or a still image.

  FIG. 1 is a functional block diagram showing a first embodiment of an image coding apparatus according to the present invention. The prediction means 11, the compensation means 12, the orthogonal transform means 13, the quantization means 14, the coding means 15, and the inverse quantization Means 16, inverse orthogonal transform means 17, storage means 18, subtractor 19 and adder 20 are provided.

  The subtractor 19 calculates the difference between the input image signal and the prediction signal from the compensation means 12 for each unit block of encoding. That is, the subtracter 19 generates a prediction residual signal for the encoding target block, and reduces spatial redundancy. The prediction residual signal generated by the subtracter 19 is sent to the orthogonal transform means 13.

  The adder 20 is for compensating for the spatial redundancy, and adds the prediction residual signal from the inverse transform unit 17 and the prediction signal from the compensation unit 12 to generate a reconstructed pixel signal. The reconstructed pixel signal is a signal obtained by reconstructing a prediction residual signal that is a remainder of a prediction signal generated by prediction and an input image signal, and is reconstructed from an encoded signal. Includes quantization error. The reconstructed pixel signal generated by the adder 20 is sent to the storage means 18. Thereafter, it is sent to the prediction means 11 and the compensation means 12, respectively.

  The accumulating unit 18 accumulates the reconstructed pixel signal output from the adder 20. The storage means 18 may have a capacity for a unit block used for prediction and compensation in the prediction means 11 and the compensation means 12. The reconstructed pixel signal stored in the storage unit 18 is used for prediction in the prediction unit 11 and generation of a prediction signal in the compensation unit 12.

  The orthogonal transform means 13 performs orthogonal transform on the prediction residual signal from the subtracter 19 and transforms it into the frequency domain to generate transform coefficients. The transform coefficient generated by the orthogonal transform means 13 is sent to the quantization means 14. For the orthogonal transform in the orthogonal transform means 13, DCT, approximate transform of DCT, DWT, or the like can be used. Each picture (frame) of the input image signal is divided into unit blocks composed of a predetermined number of pixels (for example, 32x32 pixels, 16x16 pixels, 8x8 pixels, 4x4 pixels, or a combination thereof). Is orthogonally transformed.

  The quantizing unit 14 quantizes the transform coefficient from the orthogonal transform unit 13. The quantized values generated by the quantizing means 14 are sent to the encoding means 15 and the inverse quantization means 16, respectively. The quantization parameter used for quantization in the quantization means 14 may be set as a combination of constant values, or may be controlled according to the information amount of the transform coefficient. If the quantization parameter is controlled according to the information amount of the transform coefficient, the output bit rate can be kept constant.

  The encoding means 15 encodes the quantized value from the quantization means 14 and the prediction information from the prediction means 11, and outputs an encoded image signal (code information). For encoding by the encoding means 15, variable length encoding or arithmetic encoding that removes redundancy between codes can be used.

  The inverse quantization means 16 performs processing reverse to the quantization in the quantization means 14, and generates a transform coefficient by inverse quantization of the quantized value from the quantization means 14. This transform coefficient includes a quantization error. The transform coefficient generated by the inverse quantization means 16 is sent to the inverse transform means 17.

  The inverse transform unit 17 performs processing reverse to the orthogonal transform in the orthogonal transform unit 13, and performs inverse orthogonal transform on the transform coefficient from the inverse quantization unit 16 to generate a prediction residual signal. This prediction residual signal also includes a quantization error. The prediction residual signal generated by the inverse conversion means 17 is sent to the adder 20.

  The prediction unit 11 determines prediction information for reducing the spatial redundancy of the pixel signal in the unit block. For this purpose, the prediction unit 11 first selects a unit block of the reconstructed pixel signal that predicts the pixel signal of the encoding target block from among the reconstructed pixel signals stored in the storage unit 18, and the unit block The reconstructed pixel signal is used as a reference signal. Note that the reconstructed pixel signal for predicting the pixel signal of the encoding target block is not limited to being present in the same frame, but may be present in a temporally different frame.

  Hereinafter, a method of selecting a unit block of a reconstructed pixel signal that predicts a pixel signal of an encoding target block will be described.

  In the selection of the unit block of the reconstructed pixel signal that predicts the pixel signal of the encoding target block in the prediction unit 11, the pixel signal of the encoding target block in the input image signal and the unit block stored in the storage unit 18 The similarity of the reconstructed pixel signal is evaluated, and the unit block of the reconstructed pixel signal having the highest similarity to the pixel signal of the encoding target block is selected. Note that a unit block having a uniform value (for example, an intermediate value between the highest and lowest pixel values) is assumed in order to enable selection of a unit block even at the beginning of image input.

  To evaluate the similarity between the pixel signal of the encoding target block and the reconstructed pixel signal of each unit block stored in the storage means 18, correlation, SAD (Sum of Absolute Difference), SATD (Sum of Absolute Transformed Difference) SSD (Sum of Squared Difference), MAD (Mean of Absolute Difference), etc. can be used. Here, SAD means the sum of absolute differences of pixel signals, and SATD means the sum of absolute differences of coefficients generated by applying a Hadamard transform. Further, SSD means the sum of square differences of pixel signals, and MAD means the average of absolute differences of pixel signals. The target of similarity evaluation when selecting a unit block of a reconstructed pixel signal that predicts a pixel signal of an encoding target block is a pixel signal for each unit block of encoding.

  In addition, a unit block of a reconstructed pixel signal having high similarity to the pixel signal of the encoding target block may be selected so that the encoding cost is minimized.

  The encoding cost Cost can be calculated by the equation (1) using the generated code amount R, the encoding distortion D, and the Lagrange constant λ.

  The prediction means 11 outputs the location information of the unit block of the reconstructed pixel signal having the highest similarity to the pixel signal of the encoding target block as prediction information. Further, the prediction unit 11 calculates a prediction coefficient for performing linear prediction (approximation) on the pixel signal of the encoding target block using the reconstructed pixel signal of the selected unit block as a reference signal.

  A method for calculating a prediction coefficient for linearly predicting the pixel signal of the encoding target block will be described below.

For example, when the prediction unit 11 predicts the pixel signal of the block to be encoded by a linear expression, the pixel signal S _{i of the} block to be encoded includes the selected reconstructed pixel signal R _i and the prediction coefficients a and b (multipliers). It is given by equation (2) using a and correction value b). Here, n represents the number of pixels in the unit block.

  The prediction coefficients a and b may be determined so as to minimize the square of the error due to prediction. Specifically, the prediction coefficients a and b can be calculated by the following method. The square of the error due to prediction (square error) E is expressed by equation (3).

  At this time, the partial differentiation of the square error E by the prediction coefficients a and b is expressed by Expression (4).

  In order to minimize the square error E, the expression (3) needs to be zero. Therefore, the prediction coefficients a and b can be calculated by solving equation (5).

  When equation (5) is solved, prediction coefficients a and b that minimize the square error E are obtained by equation (6).

  Note that the prediction coefficient (correction value) b can be held as a DC component by the orthogonal transform means 13, and therefore does not need to be explicitly held again. The prediction means 11 only needs to obtain the prediction coefficient (multiplier) a.

  The unit block location information of the reconstructed pixel signal searched by the prediction unit 11 and the calculated prediction coefficient are sent to the compensation unit 12 and the encoding unit 15 as prediction information.

  The compensation means 12 predicts spatial redundancy and generates a prediction signal. Specifically, a reconstructed pixel signal at a position corresponding to the location information included in the prediction information is read from the reconstructed pixel signals accumulated in the accumulating unit 18, and a prediction function set in advance is calculated. A prediction signal is generated by applying the prediction coefficient.

For example, when the prediction unit 11 uses a linear function as a prediction function and the prediction information is composed of prediction coefficients a and b, the prediction signal S _i is generated by Expression (1). The prediction coefficient may be only the multiplier a (b = 0) or only the correction value b (a = 1). Therefore, the prediction means 11 only needs to calculate the multiplier a or the correction value b. The residual prediction signal S _{i in} this case is generated by the equation (7) or the equation (8).

  The prediction signal generated by the compensation unit 12 is sent to the subtracter 19 and the adder 20, respectively.

  As described above, in the image encoding device in FIG. 1, the prediction residual signal from the subtracter 19 is orthogonally transformed, quantized, and encoded. Since this prediction residual signal is generated using a prediction signal generated by linear prediction in units of blocks, spatial redundancy in the prediction residual is reduced. As a result, even when there are bright and dark portions on the screen, the prediction accuracy can be improved, and the information amount of the image signal of the block to be encoded can be reduced to improve the encoding efficiency.

  FIG. 2 is a functional block diagram illustrating an image decoding apparatus that decodes an image encoded by the image encoding apparatus of FIG. The image decoding apparatus includes decoding means 21, inverse quantization means 22, inverse orthogonal transform means 23, compensation means 24, storage means 25, and adder 26.

  The decoding unit 21, the inverse quantization unit 22, and the inverse orthogonal transform unit 23 perform processes opposite to those of the encoding unit 15, the quantization unit 14, and the orthogonal transform unit 13 of FIG. The accumulation means 25 accumulates the pixel signal output from the adder 26. The storage means 25 only needs to have a capacity for a unit block used for compensation in the compensation means 24. The reconstructed pixel signal stored in the storage unit 25 is used for generating a prediction signal in the compensation unit 24.

  The compensator 24 operates in the same manner as the compensator 12 of FIG. 1, reads out the pixel signal of the unit block at the location corresponding to the location information included in the prediction information from the decoder 21 from the accumulator 25, and uses the pixel signal as the pixel signal. A prediction signal is generated by applying a prediction coefficient.

  The adder 26 adds the prediction residual signal from the inverse orthogonal transform unit 23 and the prediction signal from the compensation unit 24 to generate a pixel signal.

  Next, a second embodiment of the image encoding device according to the present invention will be described. In the first embodiment, a pixel signal is to be encoded, but in the second embodiment, an intra prediction residual signal generated by intra prediction is to be encoded.

  FIG. 3 is a functional block diagram showing a second embodiment of the image coding apparatus according to the present invention, and the same or equivalent parts as in FIG.

  The image encoding apparatus according to the second embodiment of the present invention includes an intra-screen prediction unit 31, an intra-screen compensation unit 32, a prediction unit 11, a compensation unit 12, an orthogonal transform unit 13, a quantization unit 14, an encoding unit 15, and an inverse quantum. Comprising means 16, inverse orthogonal transform means 17, storage means 18 and 33, subtractors 19 and 34, and adders 20 and 35.

  The intra-screen prediction unit 31, the intra-screen compensation unit 32, the storage unit 33, the subtracter 34, and the adder 35 generate an intra-screen prediction residual signal by intra-screen prediction. That is, the subtractor 34 generates an intra-screen prediction residual signal by obtaining a difference between the input image signal and the intra-screen prediction signal from the intra-screen compensation means 32 for each encoding unit block. The intra-screen prediction means 31 determines intra-screen prediction information for predicting the input image signal using the reconstructed pixel signal stored in the storage means 33. The intra-screen compensation unit 32 generates an intra-screen prediction signal using the intra-screen prediction information and the reconstructed pixel signal stored in the storage unit 33. The adder 35 generates a reconstructed pixel signal by adding the intra-screen prediction signal and the reconstructed intra-screen prediction residual signal, and the storage unit 33 reconstructs unit blocks used for intra-screen prediction and compensation. Accumulate pixel signals.

  Since the reconstructed intra prediction prediction signal and the reconstructed pixel signal are reconstructed from the encoded signals, they contain quantization errors.

  In the conventional intra prediction encoding, the intra prediction prediction signal is orthogonally transformed, quantized and encoded. In the image encoding apparatus shown in FIG. 3, the present invention is applied to the intra prediction prediction signal. Thus, a residual prediction residual signal is generated, and the residual prediction residual signal is orthogonally transformed, quantized, and encoded to further reduce spatial redundancy.

  Hereinafter, functions of each unit of the image encoding device in FIG. 3 will be described in detail.

  The subtractor 34 calculates the difference between the input image signal and the intra-screen prediction signal from the intra-screen compensation means 32 for each encoding unit block. That is, the subtracter 34 reduces the spatial redundancy by generating an intra prediction residual signal for the encoding target block. The intra prediction residual signal generated by the subtracter 34 is sent to the prediction means 11 and the subtracter 19, respectively.

  The subtractor 19 calculates the difference between the intra prediction prediction signal from the subtractor 34 and the residual prediction signal from the compensation means 12. That is, the subtracter 19 generates a residual prediction residual signal for the encoding target block, and further reduces the spatial redundancy. The residual prediction residual signal generated by the subtracter 19 is sent to the orthogonal transform means 13.

  The adder 20 is for compensating for the spatial redundancy, and adds the residual prediction residual signal from the inverse transform means 17 and the residual prediction signal from the compensation means 12 to reconstruct the intra prediction residual Generate a signal. The reconstructed intra prediction residual signal is a signal obtained by reconstructing an intra prediction residual signal that is a difference between an intra prediction signal generated by intra prediction and an input image signal. Since this is reconstructed from the encoded signal, it contains a quantization error. The reconstructed intra prediction prediction signal generated by the adder 20 is sent to the storage means 18 and the adder 35, respectively.

  The adder 35 is for further compensating for the spatial redundancy, and adds the reconstructed intra-screen prediction residual signal from the adder 20 and the intra-screen prediction signal from the intra-screen compensation means 32 to reconstruct the pixel. Generate a signal. Since the reconstructed pixel signal is also a signal reconstructed from the encoded signal, it contains a quantization error. The reconstructed pixel signal generated by the adder 35 is sent to the storage means 33.

  The orthogonal transform means 13 generates a transform coefficient by transforming the residual prediction residual signal from the subtracter 19 into the frequency domain by orthogonal transform. The transform coefficient generated by the orthogonal transform means 13 is sent to the quantization means 14. For the orthogonal transform in the orthogonal transform means 13, DCT, approximate transform of DCT, DWT, or the like can be used. Each picture (frame) of the input image signal is divided into unit blocks composed of a predetermined number of pixels (for example, 32x32 pixels, 16x16 pixels, 8x8 pixels, 4x4 pixels, or a combination thereof). Is orthogonally transformed.

  The quantizing unit 14 quantizes the transform coefficient from the orthogonal transform unit 13. The quantized values generated by the quantizing means 14 are sent to the encoding means 15 and the inverse quantization means 16, respectively. The quantization parameter used for the quantization process in the quantization means 14 may be set as a combination of constant values, or may be controlled according to the information amount of the transform coefficient. If the quantization parameter is controlled according to the information amount of the transform coefficient, the output bit rate can be kept constant.

  The encoding unit 15 encodes the quantized value from the quantization unit 14, the intra prediction information from the intra prediction unit 31, and the residual prediction information from the prediction unit 11. For the encoding process in the encoding means 15, variable length encoding or arithmetic encoding that removes redundancy between codes can be used.

  The inverse quantization means 16 performs a process reverse to the quantization process in the quantization means 14, and inversely quantizes the quantized value from the quantization means 14 to generate a transform coefficient. This transform coefficient includes a quantization error. The transform coefficient generated by the inverse quantization means 16 is sent to the inverse transform means 17.

  The inverse transform unit 17 performs a process reverse to the orthogonal transform process in the orthogonal transform unit 13, and performs inverse orthogonal transform on the transform coefficient from the inverse quantization unit 17 to generate a residual prediction residual signal. This residual prediction residual signal also includes a quantization error. The residual prediction residual signal generated by the inverse conversion means 17 is sent to the adder 20.

  The intra-screen prediction means 31 determines intra-screen prediction information for reducing spatial redundancy by intra-screen prediction, and predicts an input image signal based on the reconstructed pixel signal stored in the storage means 33. In-screen prediction information is determined. The reconstructed pixel signal accumulated in the accumulation means 33 is reconstructed from the encoded signal and includes a quantization error. The intra-screen prediction information determined by the intra-screen prediction unit 31 is sent to the intra-screen compensation unit 32 and the encoding unit 15, respectively.

  Various methods are known for intra prediction. Various methods can be used for the intra prediction by the intra prediction means 11. For example, when using standardized H.264 Intra prediction, select the Intra prediction mode that individually encodes in each Intra prediction mode and minimizes the coding cost calculated from the code amount and distortion amount. In-screen prediction information. A method for minimizing the coding cost is described in Non-Patent Document 1, for example.

  The intra-screen compensation unit 32 generates an intra-screen prediction signal by predicting spatial redundancy, and is based on the intra-screen prediction information from the intra-screen prediction unit 31 and the reconstructed pixel signal stored in the storage unit 33. An intra-screen prediction signal of the encoding target block is generated. The intra-screen prediction signal generated by the intra-screen compensation means 32 is sent to the subtracter 34 and the adder 35, respectively.

  The prediction means 11 determines residual prediction information that reduces the spatial redundancy remaining in the intra prediction residual signal in the unit block. For this purpose, the prediction unit 11 first predicts the intra prediction residual signal of the encoding target block from the intra prediction prediction residual signal stored in the storage unit 18. A unit block of the signal is selected, and the reconstructed intra prediction prediction signal of the unit block is used as a reference signal. Note that the reconstructed intra prediction residual signal for predicting the intra prediction residual signal of the block to be encoded is not limited to being present in the same frame, but may be present in a temporally different frame. Further, in order to enable selection of a unit block even at the beginning of image input, a unit block having a uniform value (for example, an intermediate value between the highest and lowest values of an intra prediction residual signal) is assumed.

  Hereinafter, a method of selecting a unit block of the reconstructed intra prediction residual signal (reference signal) for predicting the intra prediction residual signal of the encoding target block will be described.

  In the selection of the unit block of the reconstructed intra prediction residual signal for predicting the intra prediction residual signal of the encoding target block, the reconstructed intra prediction residual signal and the encoding target block stored in the storage means 18 are selected. Reconstructed intra prediction residual signal with the highest similarity to the intra prediction residual signal of the current block from the reconstructed intra prediction residual signal. Select the unit block.

  To evaluate the similarity between the reconstructed intra prediction residual signal and the intra prediction residual signal of the encoding target block, correlation, SAD (Sum of Absolute Difference), SATD (Sum of Absolute Transformed Difference), SSD (Sum of Squared Difference), MAD (Mean of Absolute Difference), etc. can be used. Here, SAD means the sum of absolute values of the difference between the intra prediction residual signal and the reconstructed intra prediction residual signal, and SATD is the difference between the coefficients generated by applying the Hadamard transform. Means the sum of absolute values. SSD means the sum of squares of the difference between the intra prediction residual signal and the reconstructed intra prediction residual signal, and MAD is the difference between the intra prediction residual signal and the reconstructed intra prediction residual signal. Mean absolute value.

  The evaluation target when selecting a unit block of the reconstructed intra prediction residual signal for predicting the intra prediction residual signal of the encoding target block is the intra prediction prediction residual for each unit block. The means 31 evaluates the similarity in the same block unit as the unit block to which the intra prediction is applied.

  When selecting the unit block of the reconstructed intra prediction residual signal for predicting the intra prediction residual signal of the encoding target block, all units of the reconstructed intra prediction residual signal stored in the storage means 18 are selected. You may search for a block. However, by limiting the search range to a reasonable one, it is possible to select a unit block of the reconstructed intra prediction residual signal for predicting the intra prediction residual signal of the encoding target block at high speed.

  Hereinafter, a method for speeding up selection of a unit block of a reconstructed intra prediction residual signal for predicting an intra prediction residual signal of an encoding target block will be described.

  FIG. 4 is a diagram conceptually illustrating a method for speeding up selection of a unit block of a reconstructed intra prediction residual signal for predicting an intra prediction residual signal of a block to be encoded. The region before the encoding target unit block (A) has already been encoded, and the reconstructed intra prediction prediction signal and the intra prediction information (prediction mode) for each unit block have already been obtained. When attention is paid to the intra prediction residual signals for the two unit blocks, the prediction residuals for the respective pixels have the same tendency between the unit blocks having the same intra prediction information. That is, the prediction residual for each pixel in the unit block tends to increase as the distance from the reference pixel increases, so if the in-screen prediction information is the same, the prediction residual for each pixel in the unit block is the same. The prediction residual has the same trend.

  Therefore, the search target is limited to the unit block whose intra prediction information is the same as the encoding target block. For example, as shown in FIG. 4, when the intra prediction information of the encoding target block (A) is the prediction mode 0, only the unit blocks (B), (C),. A unit block having another prediction mode as a target is not a search target.

  As described above, in the encoding target block (A) and the unit blocks (B), (C),... With the same in-screen prediction information, the prediction residual for each pixel in the unit block has the same tendency. Therefore, by limiting the search target to only such unit blocks (B), (C),..., The search target is limited to an appropriate one in order to improve the encoding efficiency. The selection of the unit block of the reconstructed intra prediction residual signal for predicting the intra prediction residual signal of the block can be accelerated.

  If there is no unit block to be searched as a result of restricting the search target, for example, (1) the unit block with the closest in-screen prediction information is included in the search target and the reconfiguration screen of the selected unit block (2) Re-encode the unit block with the closest intra-screen prediction information with the same prediction information, include the re-encoded unit block in the search target, select and re-encode (3) The prediction by prediction means 11 and compensation means 12 is not applied. However, in this case, the prediction of whether to apply the prediction for each unit block is used. A method such as making it a part of information (residual prediction information) may be adopted.

  FIG. 5 is a diagram conceptually illustrating another method for speeding up the selection of the unit block of the reconstructed intra prediction residual signal for predicting the intra prediction residual signal of the encoding target block. In this method, the search target is limited to a unit block in which the intra-screen prediction information of the unit block including the pixel referred to by the encoding target block and the intra-screen prediction information of the unit block positioned relatively in the same place are the same.

  For example, as shown in FIG. 5, the intra prediction information of the encoding target block (A) is the prediction mode 0, and the intra prediction information of the unit block (A ′) including the prediction pixel is the prediction mode 0. In some cases, only the unit blocks (B), (C),... Whose in-screen prediction information of the unit blocks (B '), (C'),. Search target. Even with this method, the search target is limited to a reasonable one in order to improve the coding efficiency, and the unit block of the reconstructed intra prediction residual signal that predicts the intra prediction residual signal of the target block is encoded. You can speed up the selection. As a result of limiting the search target as described above, if there is no unit block to be searched, the search target is expanded by using the intra prediction information as described above, or the prediction unit 11 and the compensation unit 12 are used. What is necessary is just not to apply prediction by.

The prediction means 11 outputs the location information of the unit block of the reconstructed intra prediction prediction signal having the highest similarity to the intra prediction residual signal of the encoding target block as prediction information. Further, the prediction unit 11 calculates a prediction coefficient for performing linear prediction (approximation) on the intra-frame prediction residual signal of the encoding target block using the reconstructed intra-frame prediction residual signal of the selected unit block as a reference signal. Method of calculating the prediction coefficients, an intra prediction residual signal of the encoding target block and S _i, if reconstruction intra prediction residual signal R _i, which is selected, is the same as the first embodiment The description is omitted.

  The unit block location information of the reconstructed intra prediction prediction residual signal selected by the prediction means 11 and the calculated prediction coefficient are sent to the compensation means 12 and the encoding means 15 as residual prediction information.

  The compensation unit 12 predicts spatial redundancy and generates a residual prediction signal. Specifically, a reconstructed in-screen prediction residual signal at a position corresponding to the location information included in the prediction information is read out from the reconstructed in-screen predicted residual signal stored in the storage unit 18, and this is stored in advance. A residual prediction signal is generated by applying the set prediction function and the calculated prediction coefficient. The residual prediction signal generated by the compensation means 12 is sent to the subtracter 10 and the adder 20.

  As described above, in the image coding apparatus according to the second embodiment, the residual prediction residual signal from the subtracter 19 is orthogonally transformed, quantized, and encoded. The residual prediction residual signal is generated by performing intra prediction and residual prediction from the already-encoded reconstructed pixel signal and the reconstructed intra prediction residual signal. As described above, in the second embodiment, when encoding an image signal of an encoding target block, intra-frame prediction is performed using a pixel signal of an already encoded unit block, and an encoded prediction residual signal is encoded. Thus, the prediction residual prediction is performed, so that the spatial redundancy in the prediction residual can be reduced, the information amount of the image signal of the block to be encoded can be reduced, and the encoding efficiency can be improved.

  FIG. 6 is a functional block diagram showing an image decoding apparatus that decodes an image encoded by the image encoding apparatus of FIG. 3, and the same or equivalent parts as in FIG.

  The image decoding apparatus includes decoding means 21, inverse quantization means 22, inverse orthogonal transform means 23, compensation means 24, storage means 25, and adders 26 and 43.

  The decoding unit 21, the inverse quantization unit 22, and the inverse orthogonal transform unit 23 perform processes opposite to those of the encoding unit 13, the quantization unit 14, and the orthogonal transform unit 15 in FIG. The accumulating means 25 accumulates the intra prediction residual signal output from the adder 26. The storage means 25 only needs to have a capacity for a unit block used for compensation in the compensation means 24. The reconstructed intra-screen prediction residual signal stored in the storage unit 25 is used to generate a residual prediction signal in the compensation unit 24.

  The compensator 24 operates in the same manner as the compensator 12 of FIG. 3, reads out the intra prediction residual signal of the unit block at the location corresponding to the location information included in the prediction information from the decoder 21 from the accumulator 25, A prediction coefficient is applied to the intra prediction residual signal to generate a residual prediction signal.

  The adder 26 adds the residual prediction residual signal from the inverse orthogonal transform unit 23 and the residual prediction signal from the compensation unit 24 to generate an intra-screen prediction signal.

  The intra-screen compensation unit 41 operates in the same manner as the intra-screen compensation unit 32 in FIG. 3, reads out the pixel signal used for prediction from the storage unit 42 according to the prediction information from the decoding unit 21, and generates an intra-screen prediction signal. .

  The adder 43 adds the intra-screen prediction signal from the intra-screen compensation means 41 to the intra-screen prediction residual signal from the adder 26 to generate a pixel signal for the input image.

  As mentioned above, although embodiment was described, this invention is not limited to the said embodiment. For example, in the prediction unit 11, when the minimum value of the encoding cost calculated from the weighted sum of the generated code amount and the distortion amount is larger than a preset threshold value, high encoding efficiency is achieved even if the prediction here is applied. It is judged that it cannot be obtained. In such a case, the prediction by the prediction unit 11 and the compensation unit 12 may not be applied. However, in this case, it is necessary to determine whether or not prediction is applied for each unit block as part of the prediction information (residual prediction information).

  In addition, when the minimum value of the encoding cost calculated from the weighted sum of the generated code amount and the distortion amount is smaller than a preset threshold value in the intra prediction unit 31, sufficiently high encoding efficiency is obtained by intra prediction. Will be. Even in such a case, the prediction by the prediction unit 11 and the compensation unit 12 may not be applied. However, in this case, it is necessary to set whether or not prediction is applied for each unit block as a part of the residual prediction information.

  Furthermore, it is possible to combine with a conventional prediction scheme that reduces temporal redundancy, thereby further improving the coding efficiency.

11 ... Predicting means, 12 ... Compensating means, 13 ... Orthogonal transforming means, 14 ... Quantizing means, 15 ... Encoding means, 16, 22 ... Inverse quantizing means, 17, 23 ... Inverse orthogonal transform means, 18, 25, 33 ... Accumulation means, 19, 34 ... Subtractor, 20, 26, 35, 43 ... Adder, 21 ... Decoding means, 31 ... Intra-screen prediction means, 32,41 ... In-screen compensation means,

Claims (11)

In an image encoding apparatus that encodes an input image for each unit block of encoding using prediction,
Prediction for selecting a reference signal in units of unit blocks from signals reconstructed using encoded signals, and linearly predicting signals of the entire unit block with respect to the signals of the block to be encoded using the reference signals A prediction means for calculating information;
Compensation means for generating a prediction signal using the signal reconstructed using the encoded signal and the prediction information calculated by the prediction means;
Difference calculating means for generating a prediction residual signal that is a difference between the signal for the encoding target block and the prediction signal generated by the compensation means;
An image encoding apparatus, wherein the prediction residual signal generated by the difference calculation means is orthogonally transformed, quantized, and encoded.   The signal reconstructed using the encoded signal is a reconstructed pixel signal, and the prediction means uses a unit block unit as a reference from among reconstructed pixel signals reconstructed using the encoded signal. The image encoding apparatus according to claim 1, wherein a signal is selected, and prediction information for linearly predicting a pixel signal of a coding target block is calculated using the reference signal.   The signal reconstructed using the encoded signal is a reconstructed intra-screen prediction residual signal based on intra-screen prediction, and the predictor is configured to reconstruct the reconstructed screen using the encoded signal. A reference signal is selected for each unit block from prediction residual signals, and prediction information for linearly predicting an intra prediction residual signal of a coding target block is calculated using the reference signal. Item 2. The image encoding device according to Item 1.   The prediction means selects a reference signal so as to minimize the encoding cost calculated from the weighted sum of the generated code amount and the distortion amount, and uses the unit block location information of the reference signal as part of the prediction information. The image coding apparatus according to claim 1, wherein the image coding apparatus calculates the image coding apparatus.   The prediction unit determines not to apply the prediction unit and the prediction based on the unit prediction when the minimum value of the coding cost calculated from the sum of the weights of the generated code amount and the distortion amount is larger than a preset threshold value. The image encoding apparatus according to claim 1, wherein the presence / absence of application of prediction is generated as part of the prediction information for each unit block.   The prediction means does not apply the prediction by the prediction means and the means prediction when the minimum value of the coding cost calculated from the weighted sum of the generated code amount and the distortion amount in the intra prediction is smaller than a preset threshold value. The image encoding apparatus according to claim 3, wherein the image encoding device generates the presence / absence of application of prediction for each unit block as part of the prediction information.   The image encoding apparatus according to claim 3, wherein, when selecting the reference signal, the prediction unit limits the selection range to a unit block whose intra prediction information is the same as the encoding target block.   The prediction means, when selecting a reference signal, the pixel to be referred to by the encoding target block, the unit block including the pixel and the intra-screen prediction information of the unit block, the reference pixel, the unit block including the pixel, and the 4. The image encoding apparatus according to claim 3, wherein the selection range is limited to unit blocks having the same relationship between intra-screen prediction information of unit blocks.   The image encoding apparatus according to claim 1, wherein the prediction unit calculates a prediction coefficient as prediction information.   The image coding apparatus according to claim 9, wherein the prediction coefficient includes one or both of a multiplier of a linear expression and a correction value.   The image coding apparatus according to claim 9, wherein the prediction coefficient is calculated so that an error of a signal of an entire unit block with respect to a reference signal and a signal of an encoding target block is minimized.

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