JP2007300557A - Image encoding device and image encoding method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To set a code amount corresponding to human sight characteristics. <P>SOLUTION: An image encoding device comprises a target code amount determining means for determining a target code amount of an image to be encoded, a calculation means for calculating a block distortion degree using a decoded image signal outputted from a decoding means, and a target code amount control means for judging a magnitude of the block distortion degree calculated by the calculation means and controlling the target code amount in accordance with the magnitude of the block distortion degree. When it is judged that the block distortion degree is great, the target code amount of the image to be encoded is increased and when it is judged that the block distortion degree is small, on the other hand, the target code amount of the image to be encoded is decreased, so that the code amount is set while taking into account quantitative deterioration conditions of image quality or human sight characteristics. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image encoding apparatus and an image encoding method, and more particularly to an image encoding apparatus having a decoding unit that locally decodes encoded data encoded by an encoding unit. The present invention relates to a technique suitable for use in performing code amount control in consideration.

  Conventionally, various moving image compression encoding systems have been proposed with the development of multimedia. Typical examples are MPEG-1, 2, 4 and H.264. There is something like 26L. In these compression encoding processes, an original image (image) included in a moving image is divided into predetermined regions called blocks, and motion compensation prediction and DCT conversion processing are performed in units of the divided blocks. .

In addition, when performing motion compensation prediction, an image obtained by local decoding of already encoded image data is used as a reference image, so that a decoding process is required even when encoding is performed.
In addition, when compressing and encoding an image in accordance with the MPEG system, the amount of code often varies greatly depending on the spatial frequency characteristics, which are characteristics of the image itself, the scene, and the quantization scale value. An important technique for realizing a decoded image with good image quality in realizing an encoding apparatus having such encoding characteristics is code amount control.

  TM5 (Test Model 5) is generally used as one of the code amount control algorithms. The code amount control algorithm according to TM5 is composed of the following three steps, and the code amount is controlled in the following three steps so that the bit rate is constant for each GOP (Group Of Picture).

First step (STEP1)
The target code amount of the picture to be encoded from now is determined. Rgop, which is a code amount that can be used in the current GOP, is calculated by the following equation (1).
Rgop = (ni + np + nb) * (bits_rate / picture_rate) (1) where ni, np, nb are the number of remaining pictures in the current GOP of I, P, and B pictures, respectively, bits_rate Represents the target bit rate, and picture_rate represents the picture rate.

Further, the complexity of the picture is obtained from the encoding result for each of the I, P, and B pictures by the following equations (2-1) to (2-3).
Xi = Ri * Qi (2-1) Formula Xp = Rp * Qp (2-2) Formula Xb = Rb * Qb (2-3) Formula

   Here, Xi, Xp, and Xb are also called complexity, and Ri, Rp, and Rb are code amounts obtained as a result of encoding I, P, and B pictures, respectively. Qi, Qp and Qb are average values of the Q scale in all macroblocks in the I, P and B pictures, respectively. From the equations (1) and (2-1) to (2-3), the target code amounts Ti, Tp, and Tb for the I, P, and B pictures are expressed by the following (3-1) to (3-3). ).

Ti = max {(Rgop / (1 + ((Np * Xp) / (Xi * Kp)) + ((Nb * Xb) / (Xi * Kb)))), (bit_rate / (8 * picture_rate))} (3-1) Formula Tp = max {(Rgop / (Np + (Nb * Kp * Xb) / (Kb * Xp))), (bit_rate / (8 * picture_rate))} (3-2) Equation Tb = max {(Rgop / (Nb + (Np * Kb * Xp) / (Kp * Xb))), (bit_rate / (8 * picture_rate))} (3- 3) where Np and Nb are the remaining number of P and B pictures in the current GOP, respectively, and constants Kp = 1.0 and Kb = 1.4.

Second step (STEP2)
Three virtual buffers are used for each P and B picture, and the difference between the target code amount and the generated code amount obtained by the above equations (3-1) to (3-3) is managed. The data accumulation amount of the virtual buffer is fed back, and the reference value of the Q scale is set for the macroblock to be encoded next so that the actual generated code amount approaches the target code amount based on the data accumulation amount.

For example, when the current picture type is a P picture, the difference between the target code amount and the generated code amount can be obtained by arithmetic processing according to the following equation (4).
dp, j = dp, 0 + Bp, j−1 − ((Tp * (j−1)) / MB_cnt) (4)

  Here, the subscript j is the number of the macroblock in the picture, dp, 0 indicates the initial fullness of the virtual buffer, Bp, j is the total code amount up to the jth macroblock, and MB_cnt is the macroblock in the picture Indicates a number.

Next, when the reference value of the Q scale in the j-th macroblock is obtained using dp, j (hereinafter referred to as “dj”), equation (5) is obtained.
Qj = (dj * 31) / r (5) where r = 2 * bits_rate / picture_rate (6).

Third step (STEP3)
A process of finally determining the quantization scale is executed based on the spatial activity of the macroblock to be encoded so as to improve the visual characteristics, that is, the image quality of the decoded image.
ACTj = 1+ min (vblk1, vblk2, ..., vblk8) (7)

In the equation (7), vblk1 to vblk4 indicate spatial activities in 8 × 8 sub-blocks in the macroblock of the frame structure. vblk5 to vblk8 indicate 8x8 sub-block spatial activities in the field-structured macroblock. Here, the calculation of the space activity can be obtained by the following equations (8) and (9).
vblk = Σ (Pi−Pbar) ² (8)
Pbar = (1/64) * ΣPi (9)

  Here, Pi is a pixel value in the i-th macroblock, and Σ in equations (8) and (9) is an operation of i = 1 to 64. Next, ACTj obtained by the equation (7) is normalized by the following equation (10).

N_ACTj = (2 * ACTj + AVG_ACT) / (ACTj + AVG_ACT) (10) where AVG_ACT is the reference value of ACTj in the previously encoded picture, and finally the quantization scale (Q scale) Value) MQUANTj is obtained by the following equation (11).
MQUANTj = Qj * N_ACTj (11) formula

  According to the above TM5 algorithm, a large amount of code is allocated to the I picture by the processing of STEP1, and furthermore, the amount of code is in a flat part (low spatial activity) that is visually noticeable in the picture. Will be distributed more.

  As a coding method applying the TM5 method, Patent Document 1 introduces a method for determining a target code amount so that an SN ratio between an image signal and a locally decoded image becomes a certain value. This method has an effect of stabilizing the image quality for all the pictures by setting a target code amount that keeps the SN ratio constant.

  Further, Patent Document 2 introduces a method of setting the code amount of each picture of I picture, P picture, and B picture to an optimum value by a method improved from Patent Document 1. In this method, the code amount of each frame (I picture, P picture, B picture) is distributed and controlled so that the SN ratio of the I picture is larger than the SN ratio of the B picture. That is, the I picture that is the origin of the GOP by controlling the code amount of each frame (I picture, P picture, B picture) so that the coding error of the I picture becomes smaller than the coding error of the B picture. It has the effect of improving the image quality.

Japanese Patent Laid-Open No. 02-219388 Japanese Patent Laid-Open No. 08-070458

  However, the above-described TM5 algorithm has the following problems. That is, as determination information for obtaining the final MQUANTj, except for the difference between the target code amount and the code amount in equation (4), the Q scale reference value (Qj) of the previous picture encoding result in equation (5) and , Only the spatial activity (ACTj) in the processing of STEP3 is used.

  For this reason, the degree of quantitative deterioration of image quality and human visual characteristics are not sufficiently considered in the code amount control in TM5, and it is difficult to perform code amount control that matches human visual characteristics according to the coding situation. Met.

  In addition, the methods described in Patent Document 1 and Patent Document 2 have the following problems. That is, in Patent Document 1, it is possible to maintain a constant image quality by keeping the SN ratio constant for each picture. Further, in Patent Document 2, it is possible to maintain a constant image quality as in Patent Document 1 by considering the SN ratio and code distribution of each picture.

  However, since all of these methods use the SN ratio as the determination information for determining the target code amount, the degree of quantitative deterioration in image quality and human visual characteristics are not fully considered. That is, it is conceivable that the relationship between the SN ratio and the image quality is not necessarily a proportional relationship.

  For example, an image composed of small-amplitude signals such as lawn and sky is less likely to cause a significant decrease in the signal-to-noise ratio even when the image quality is degraded, but visually noticeable noise such as block noise is likely to occur.

  Conversely, an image composed of a large amplitude signal such as a tree or a texture pattern may have a large SN ratio even if the image quality is slightly deteriorated, but the block noise tends to be inconspicuous. Therefore, the conventional method in which the target code amount is determined based on the SN ratio has a problem that it is difficult to set a code amount that matches human visual characteristics.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to make it possible to set a code amount in accordance with human visual characteristics.

  An image encoding apparatus according to the present invention includes an encoding unit that encodes an encoding target image, and a decoding unit that locally decodes encoded data encoded by the encoding unit. A device for determining a target code amount for determining a target code amount of the encoding target image; a calculating unit for calculating a block distortion degree using a decoded image signal output from the decoding unit; And a target code amount control means for determining a block distortion degree calculated by the means and controlling a target code amount determined by the target code amount determination means according to the block distortion degree. Features.

  An image encoding method according to the present invention includes an encoding process for encoding an image to be encoded, and a decoding process for locally decoding the encoded data encoded in the encoding process. A method for determining a target code amount of the encoding target image; a calculation step for calculating a block distortion degree using a decoded image signal output from the decoding step; and the calculation A target code amount control step of determining a block distortion degree calculated in the process and controlling a target code amount determined by the target code amount determining means according to the block distortion degree. Features.

  The program according to the present invention is a computer that performs an image encoding method including an encoding step for encoding an image to be encoded and a decoding step for locally decoding the encoded data encoded in the encoding step. A target code amount determination step of determining a target code amount of the encoding target image, and a calculation step of calculating a block distortion degree using a decoded image signal output from the decoding step; A target code amount control step of determining a block distortion degree calculated by the calculation step and controlling a target code amount determined by the target code amount determining means according to the block distortion degree. A computer is caused to execute the image coding method.

  According to the present invention, since the target code amount is controlled according to the calculated degree of block distortion, it is possible to set the code amount according to human visual characteristics, and to obtain a decoded image with good image quality. Can be obtained.

(First embodiment)
A first embodiment of the present invention will be described below with reference to FIGS.
FIG. 1 is a block diagram showing a configuration of an encoding apparatus that realizes the first encoding method according to the present invention, and is configured to be able to execute the above-described TM5 algorithm.

  Specifically, it corresponds to the MPEG-1, MPEG-2 or MPEG-4 standards. FIG. 2 is a flowchart for explaining processing of the encoding apparatus of FIG. FIG. 3 clarifies macroblocks and block boundaries. FIG. 4 is a diagram showing the offset amount of the target code amount according to the block distortion degree, and FIG. 5 is a flowchart for explaining the target code amount setting process according to the block distortion degree.

Hereinafter, the flow of the setting method of the target code amount corresponding to the encoding process and the degree of block distortion will be specifically described with reference to FIGS.
In FIG. 1, 100 is an input signal sent from, for example, a CCD and a line input terminal provided in a digital video camera, 101 is an orthogonal transformation circuit, 102 is a quantization circuit, and 103 is variable length coding. Circuit. Reference numeral 104 denotes an inverse orthogonal transform circuit, 105 denotes an inverse quantization circuit, 106 denotes an inverse variable length decoding circuit, 107 denotes a reference frame 108 used in a motion compensation circuit (not shown), an inverse quantization circuit, and an inverse quantization circuit. This is a memory for storing a local decode frame 109 which is an image signal locally decoded by the orthogonal transform circuit 104.

  110 is a code amount control unit for determining the target bit rate of the GOP to be encoded according to the bit rate and the target code amount of the picture, and 111 is the target code amount of the picture determined by the code amount control unit 110 Is a quantization control unit that determines the quantization coefficient of the macroblock, and the quantization circuit 102 performs quantization using the quantization parameter (also referred to as a quantization scale) determined by the quantization control unit 111. .

  The quantized image signal is encoded by the variable length encoding circuit 103 and output as an output signal 112 to a recording medium (not shown) or an output terminal. At the same time, the inverse quantization circuit 105 and the inverse orthogonal transform circuit 104 are used. A reference frame 108 to be used for encoding the next picture is generated. A block distortion degree calculation circuit 113 calculates a block distortion degree from an input signal and a local decoded frame that is a locally decoded image.

Next, the processing procedure of the encoding device will be described with reference to the flowchart of FIG. 2. First, in order to use STEP1 of the above-described TM5 algorithm in step S201, equations (3-1) to (3-3) Accordingly, the initial values of the target code amounts Ti, Tp, and Tb for each of the picture types (I, P, and B pictures) are determined. At this time, since Xi, Xp, and Xb for determining the initial values do not exist, the initial values of the target code amounts Ti, Tp, and Tb are set using arbitrary values or values calculated from the image information before encoding. Set.

Next, the process proceeds to step S202, and encoding of the encoding target picture is started. If necessary, register setting in the encoding apparatus is performed in step S202.
Next, the process proceeds to step 203. When the picture type is I picture, the orthogonal transform circuit 101 performs orthogonal transform on the input signal divided into macro blocks by a block division unit (not shown). Also, the orthogonal transform output coefficient is quantized using the quantization scale determined by the quantization control unit 111.

  When the picture type is a P picture or a B picture, motion prediction and motion compensation (not shown) are performed using the input signal and the reference frame 108 (macroblock data) divided into macroblocks by the block division unit. Then, the orthogonal transformation circuit 101 performs orthogonal transformation on the difference value between the resulting output and the input signal, and the orthogonal transformation output coefficient is quantized using the quantization scale determined by the quantization control unit 111. The calculation of the quantization scale, which is a quantization parameter, is calculated by performing a process corresponding to step 2 of TM5, and thus the description thereof is omitted here.

  Here, the input macroblock before encoding is input to the block distortion degree calculation circuit 113 in order to be used for calculation of the block distortion degree described later. The processing in the block distortion degree calculation circuit 113 will be described in detail later.

  Next, in step S204, the encoded data generated by the process of step S203 is subjected to inverse transform processing by the inverse quantization circuit 105 and the inverse orthogonal transform circuit 104 to generate a local decode frame 109 which is decoded data.

  Next, in step S205, the block distortion degree calculation circuit 113 compares the macroblock before encoding with the macroblock at the same coordinates as the macroblock before encoding in the data of the local decode frame 109. Next, the degree of block distortion is calculated as a parameter for evaluating the distortion of the image generated by the MPEG processing. The following method is mentioned as a calculation method of a block distortion degree.

With respect to the two images before encoding and after decoding, each of them is an 8 × 8 block, and the difference sum calculation according to the equation (21) is executed for each pixel at the boundary of the 8 × 8 block.
FIG. 3 shows a macro block (FIG. 3A), an 8 × 8 pixel block before encoding (FIG. 3B) constituting the macro block, and an 8 × 8 pixel block after encoding (FIG. 3B). 3 (c)).

For each of the boundary pixels of the four 8 × 8 blocks constituting the macroblock, the luminance component of the input image (P0, P1, P2, P3...) And the luminance component of the local decode data (R0, R1, R2, R3). )), The difference absolute value sum (diff_sum) of the two can be obtained by the following equation (21).
diff_sum = Σabsolute (Pj−Rj) (21) The block distortion degree calculation circuit 113 can calculate the block distortion degree by the method described above.

The description returns to the flowchart of FIG.
If the block distortion degree is calculated in step S205, the process proceeds to step S206, and it is determined whether or not the processing from step S203 to step S205 has been performed for all macroblocks in the picture. At this time, the quantization parameter used in each macroblock is determined by the quantization control unit 111 using the code amount of the macroblock that is variable-length encoded by the variable-length encoding circuit 103. If the result of this determination is that it has not been performed for all macroblocks, the process returns to step S202 and the above-described processing is repeated. If all the processes are completed, the process proceeds to step S207.

  Next, in step S207, after encoding all macroblocks of the encoding target picture, the code amount control unit 110 uses the above-described equation (1) to express Xi, Xp, Xb. Is calculated. Xi, Xp, and Xb are obtained by multiplying the code amount obtained as a result of encoding each picture by the average value of the Q scale in all macroblocks in the picture.

Next, the process proceeds to step S208, and the code amount control unit 110 uses the target code amount of the next encoding target picture using Xi, Xp, and Xb and the block distortion degree calculated by the block distortion degree calculation circuit 113. Ti, Tp, and Tb are determined.
Thereafter, in step S209, it is determined whether or not it is the last picture. If it is the last picture, the process is terminated. If it is not the final picture, the process returns to step S202 and the above-described processing is repeatedly executed.

This target code amount calculation process will be described with reference to the flowcharts of FIGS.
FIG. 4 shows the offset amount of the target code amount according to the block distortion degree, and this offset amount is a function of the block distortion degree. α and β (α> 0, β <0) are arbitrary constants and can be freely set by the encoding device.

  First, in step S501, Tpictype_base is calculated using equation (1). Here, Tpictype_base is a tentative target code amount that is tentatively calculated using equation (1) for each of the I, P, and B pictures. Then, if the picture to be encoded in the next frame is an I picture, Ti_base is obtained (the target code amount of each picture is not calculated every time one picture is encoded). In the following, in order to avoid confusion in the description, the description will be made assuming that the next encoding target picture is an I picture.

Next, the process proceeds to step S502, and the block distortion degree calculated by the block distortion degree calculation circuit 113 is compared with the threshold value th1. If the degree of block distortion is small as a result of this comparison, the process proceeds to step S504 to set the target code amount Ti of the next encoding target picture.
Ti = Ti_base + β (β <0) (Processing represented by equation (22) is performed.)

On the other hand, if the block distortion degree is larger than the threshold th1 in the comparison result in step S502, the process proceeds to step S503.
In step S503, the block distortion degree is compared with the threshold value th2. As a result of this comparison, if the degree of block distortion is small, the process proceeds to step S505, and the target code amount Ti of the next coding target picture is set.
Ti = Ti_base ((α−β) * (diff_sum-th1) / (th2−th1)) + β (23) Processing is performed.

On the other hand, as a result of the comparison in step S503, if the block distortion degree is larger than the threshold th2, the process proceeds to step S506, and the target code amount Ti of the next encoding target picture is set.
Ti = Ti_base + α (α> 0) (24) The processing is performed.

  By performing the above processing, the processing corresponding to step 1 of the TM5 algorithm cannot set the target code amount in consideration of human visual characteristics. The image quality can be improved by performing the setting. Note that the block distortion degree calculation formula is not limited to the above method, and any block distortion degree can be calculated in any form.

  Similarly, the method for setting the target code amount is not limited to the above method, and any method may be used as long as the degree of block distortion affects the setting of the target code amount. Furthermore, when the target code amount is not controlled based on the degree of block distortion, it is also possible to determine the target code amount by performing only the process corresponding to step 1 of TM5.

(Second Embodiment)
Next, a second embodiment of the present invention will be described with reference to FIGS.
FIG. 6 is a block diagram of an encoding apparatus showing a configuration of an apparatus that implements the second encoding method according to the present invention, and is configured to be able to execute the above-described TM5 algorithm. Specifically, it corresponds to the MPEG-1, MPEG-2 or MPEG-4 standards. 7 to 9 are diagrams illustrating a deblocking filter to be described later.

  Further, since the basic process flow and the target code amount setting method according to the block distortion degree are the same as those in the first embodiment, the encoding process and the process shown in FIGS. A flow of a method for setting a target code amount according to the degree of block distortion will be specifically described.

  In FIG. 6, 600 is a video signal from a CCD and line input terminal provided in a digital video camera, for example, 601 is an orthogonal transformation circuit, 602 is a quantization circuit, and 603 is a variable length coding circuit. It is.

  Reference numeral 604 denotes an inverse orthogonal transform circuit, reference numeral 605 denotes an inverse quantization circuit, and reference numeral 606 denotes an inverse variable length decoding circuit. A memory 607 stores a reference frame 608 used in a motion compensation circuit (not shown) and a local decode frame 609 that is an image signal locally decoded by the inverse quantization circuit 605 and the inverse orthogonal transform circuit 604.

  A code amount control unit 610 determines the target bit rate of the GOP to be encoded from now on and the target code amount of the picture according to the bit rate. Reference numeral 611 denotes a quantization control unit that determines the quantization coefficient of the macroblock based on the target code amount of the picture determined by the code amount control unit 610. The quantization parameter (quantization parameter) determined by the quantization control unit 611 The quantization circuit 602 performs quantization using a scale).

  The quantized image signal is encoded by the variable-length encoding circuit 603 and output as an output signal 612 to a recording medium (not shown) or an output terminal. At the same time, a reference frame 608 used for encoding the next picture is generated via the inverse quantization circuit 605 and the inverse orthogonal transform circuit 604.

  Reference numeral 613 denotes a deblocking filter, which is a post filter for making the block boundary of the output signal inconspicuous at the time of decoding. The deblocking filter 613 removes 8 × 8 pixel block (DCT block) and block noise generated at the macroblock boundary when the bit rate of the video to be encoded is low or when complex video is encoded. It is. This is often mounted on an encoding / decoding circuit that involves orthogonal transform in units of blocks in order to provide high-quality video.

The deblocking filter is not particularly defined in the MPEG standard, but the following method is given as an example with reference to FIGS.
FIG. 7 is a diagram showing deblocking filter processing at the boundary between four 8 × 8 pixel blocks (FIG. 7A and 701 to 704) constituting the macroblock and the 8 × 8 pixel blocks 701 and 702 (FIG. 7). (B)).

As the luminance component (P0, P1, P2, P3...) Of 701 and the luminance component (R0, R1, R2, R3...) Of 702, the difference absolute value sum (diff_sum) of each luminance value is (31 ).
diff_sum = Σabsolute (Pj−Rj) (31)

  The macroblock is quantized with a quantization parameter (quantization scale) determined by the quantization control unit at the time of encoding. The quantization parameter is calculated for each macroblock by the inverse variable length decoding circuit 606 at the time of decoding.

Next, the process of the deblocking filter 613 is demonstrated using the flowchart of FIG. 8, and the filter characteristic of FIG.
First, in step S801, it is determined whether or not diff_sum calculated using equation (31) is greater than threshold th_val and quantization parameter Qj is greater than threshold th_q. If the result of this determination is large, it is determined that block noise has occurred, and the process advances to step S802 to perform filter processing on the block boundary.

  At this time, a filter that drops a band such as 902 to 904 among the filter characteristics shown in FIG. 9 is used. In addition, the selection of 902 to 904 varies depending on the diff_sum value and Qj. On the other hand, if the condition in step S801 is not satisfied, it is determined that no block noise has occurred, the process proceeds to step S803, and the filter process is not performed. The filter characteristics at this time are as indicated by 901 shown in FIG.

  Here, the diff_sum value calculated as a parameter for selecting whether or not to perform the filtering process in the deblocking filter 613 and the filter strength is equivalent to the block distortion degree in the first embodiment.

  Since the deblocking filter 613 plays the role of a post filter, it is generally operated during normal decoding but not during encoding. However, in the present embodiment, the deblocking filter 613 is operated even during encoding, and the block distortion degree calculated by the block distortion degree calculation circuit 113 in the first embodiment is calculated.

  The method of setting the target code amount using the block distortion degree can be performed by the same method (the flowchart of FIG. 2) as the method described in the first embodiment, and thus the description thereof is omitted here. To do. The block distortion degree calculation and filter characteristics in the blocking filter are not limited to the above method.

  As shown in FIG. 6, by inputting the input signal 600 and the local decode frame 609 to the deblocking filter, it is possible to perform exactly the same processing as in the first embodiment, and the block distortion degree can be calculated. It doesn't matter.

  Similarly, the method for setting the target code amount is not limited to the above method, and any method may be used as long as the degree of block distortion affects the setting of the target code amount. Further, when the target code amount is not controlled based on the degree of block distortion, it is possible to determine the target code amount by performing only the process corresponding to step 1 of TM5.

(Third embodiment)
Next, a third embodiment will be described with reference to FIG.
FIG. 10 is a block diagram of an encoding apparatus showing the configuration of an apparatus that implements the third encoding method according to the present invention, and is configured to be able to execute processing equivalent to the above-described TM5 algorithm. . Specifically, H.C. The H.264 standard corresponds to a standard including a loop filter (so-called deblocking filter) in the encoding process.

  Hereinafter, with reference to FIG. 10, the flow of a method for setting a target code amount in accordance with the encoding process and the degree of block distortion will be specifically described. In this encoding apparatus, H.264 is used. H.264 / MPEG4-AVC (hereinafter referred to as H.264) is taken as an example. And H. Blocks not related to the essence of the present invention such as intra prediction and loop filter specifications used in the H.264 coding system are not displayed, and description in the text is also omitted.

  In FIG. 10, 1000 is a video signal from a CCD and line input terminal provided in a digital video camera, for example, 1001 is an orthogonal transformation circuit, 1002 is a quantization circuit, and 1003 is an entropy coding circuit. is there. Reference numeral 1004 denotes an inverse quantization circuit, reference numeral 1005 denotes an entropy decoding circuit, and reference numeral 1006 denotes an inverse orthogonal transform circuit. Reference numeral 1007 denotes a memory for storing a reference frame 1008 used in a motion compensation circuit (not shown) and a local decode frame 1009 that is an image signal locally decoded by an inverse quantization circuit and an inverse orthogonal transform circuit 1004.

  A code amount control unit 1010 determines the target bit rate of the GOP to be encoded from now on and the target code amount of the picture according to the bit rate. Reference numeral 1011 denotes a quantization control unit that determines the quantization coefficient of the macroblock based on the target code amount of the picture determined by the code amount control unit 1010. The quantization circuit 1002 performs quantization using the quantization parameter (also referred to as a quantization scale) determined by the quantization control unit 1011.

  The quantized image signal is encoded by the entropy encoding circuit 1003 and output as an output signal 1012 to a recording medium or an output terminal (not shown). At the same time, a reference frame 1008 used for encoding the next picture is generated via the inverse quantization circuit 1005 and the inverse orthogonal transform circuit 1004.

  A loop filter 1013 performs the same function as the deblocking filter described in the second embodiment. H. H.264 improves coding efficiency and image quality by using a reference frame from which block noise has been removed by the loop filter when motion prediction is performed by incorporating the loop filter into the coding.

  The loop filter 1013 is configured to detect the degree of block distortion and change the filter processing coefficient in accordance with the degree of distortion. After the block distortion detection degree is calculated by the loop filter 1013, the target code amount can be set by the same processing as in the first embodiment and the second embodiment. Omitted. Furthermore, when the target code amount is not controlled based on the degree of block distortion, it is also possible to determine the target code amount by performing only the process corresponding to step 1 of TM5.

(Other embodiments according to the present invention)
Each means constituting the image coding apparatus and each step of the image coding method in the embodiment of the present invention described above can be realized by operating a program stored in a RAM or ROM of a computer. This program and a computer-readable recording medium recording the program are included in the present invention.

  In addition, the present invention can be implemented as, for example, a system, apparatus, method, program, storage medium, or the like. Specifically, the present invention may be applied to a system including a plurality of devices. The present invention may be applied to an apparatus composed of a single device.

  In the present invention, a software program (in the embodiment, a program corresponding to the flowcharts shown in FIGS. 2, 5, and 8) for realizing the functions of the above-described embodiments is directly or remotely supplied to the system or apparatus. In addition, this includes a case where the system or the computer of the apparatus is also achieved by reading and executing the supplied program code.

  Accordingly, since the functions of the present invention are implemented by computer, the program code installed in the computer also implements the present invention. In other words, the present invention includes a computer program itself for realizing the functional processing of the present invention.

  In that case, as long as it has the function of a program, it may be in the form of object code, a program executed by an interpreter, script data supplied to the OS, and the like.

  Examples of the recording medium for supplying the program include a floppy (registered trademark) disk, hard disk, optical disk, magneto-optical disk, MO, CD-ROM, CD-R, and CD-RW. In addition, there are magnetic tape, nonvolatile memory card, ROM, DVD (DVD-ROM, DVD-R), and the like.

  As another program supply method, a browser on a client computer is used to connect to an Internet home page. The computer program itself of the present invention or a compressed file including an automatic installation function can be downloaded from the homepage by downloading it to a recording medium such as a hard disk.

  It can also be realized by dividing the program code constituting the program of the present invention into a plurality of files and downloading each file from a different homepage. That is, a WWW server that allows a plurality of users to download a program file for realizing the functional processing of the present invention on a computer is also included in the present invention.

  In addition, the program of the present invention is encrypted, stored in a storage medium such as a CD-ROM, distributed to users, and key information for decryption is downloaded from a homepage via the Internet to users who have cleared predetermined conditions. Let It is also possible to execute the encrypted program by using the downloaded key information and install the program on a computer.

  Further, the functions of the above-described embodiments are realized by the computer executing the read program. In addition, based on the instructions of the program, an OS or the like running on the computer performs part or all of the actual processing, and the functions of the above-described embodiments can also be realized by the processing.

  Further, the program read from the recording medium is written in a memory provided in a function expansion board inserted into the computer or a function expansion unit connected to the computer. Thereafter, the CPU of the function expansion board or function expansion unit performs part or all of the actual processing based on the instructions of the program, and the functions of the above-described embodiments are realized by the processing.

1 is a block diagram illustrating a configuration example of an encoding device according to a first embodiment of this invention. FIG. It is a flowchart for demonstrating the 1st Embodiment of this invention and demonstrating an example of the procedure of an encoding process. 1 shows a first embodiment of the present invention, (a) is a macroblock, (b) is an 8 × 8 pixel block before encoding, and (c) is an 8 × 8 pixel block after encoding. It is. It is a figure which shows the 1st Embodiment of this invention and shows the offset amount of the target code amount according to the block distortion degree. 5 is a flowchart illustrating a target code amount setting process according to a block distortion degree according to the first embodiment of this invention. It is a block diagram which shows the 2nd Embodiment of this invention and shows the structural example of an encoding apparatus. FIG. 5A shows a second embodiment of the present invention, where FIG. 8A is a diagram showing four 8 × 8 pixel blocks constituting a macroblock, and FIG. FIG. It is a flowchart which shows the 2nd Embodiment of this invention and demonstrates an example of the process sequence of a deblocking filter. It is a figure which shows the 2nd Embodiment of this invention and demonstrates the filter strength of a deblocking filter. It is a block diagram which shows the 3rd Embodiment of this invention and shows the structural example of an encoding apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Input signal 101 Orthogonal transformation circuit 102 Quantization circuit 103 Variable length encoding circuit 104 Inverse orthogonal transformation circuit 105 Inverse quantization circuit 106 Inverse variable length decoding circuit 107 Memory 108 Reference frame 109 Local decoding frame 110 Code amount control part 111 Quantum Control unit 112 output signal 113 block distortion degree calculation circuit

Claims (8)

An image encoding apparatus comprising: encoding means for encoding an encoding target image; and decoding means for locally decoding encoded data encoded by the encoding means,
Target code amount determining means for determining a target code amount of the encoding target image;
Calculating means for calculating a degree of block distortion using a decoded image signal output from the decoding means;
Target code amount control means for determining the degree of block distortion calculated by the calculation means and controlling the target code amount determined by the target code amount determination means in accordance with the magnitude of the block distortion degree. An image encoding apparatus characterized by that.   The image coding apparatus according to claim 1, wherein the target code amount control unit increases the target code amount of the encoding target image when it is determined that the degree of block distortion is large.   The image coding apparatus according to claim 1, wherein the target code amount control unit decreases the target code amount of the encoding target image when it is determined that the degree of block distortion is small.   The target code amount control means has a deblocking filter that changes the filter strength in accordance with the block distortion degree, and controls the target code amount according to the block distortion degree calculation means in the deblocking filter. The image encoding device according to claim 1.   The encoding means and the decoding means may be MPEG or H.264. The image coding apparatus according to any one of claims 1 to 4, wherein the image coding apparatus conforms to a H.264 coding system.   The deblocking filter is H.264. The image coding apparatus according to claim 4, wherein the image coding apparatus is a loop filter in a H.264 coding system. An image encoding method comprising: an encoding step for encoding an encoding target image; and a decoding step for locally decoding the encoded data encoded in the encoding step,
A target code amount determining step for determining a target code amount of the encoding target image;
A calculation step of calculating a block distortion degree using the decoded image signal output from the decoding step;
A target code amount control step of determining the degree of block distortion calculated by the calculation step and controlling a target code amount determined by the target code amount determining means according to the block distortion degree. An image encoding method characterized by the above. A program for causing a computer to execute an image encoding method including an encoding process for encoding an image to be encoded and a decoding process for locally decoding the encoded data encoded in the encoding process. And
A target code amount determining step for determining a target code amount of the encoding target image;
A calculation step of calculating a block distortion degree using the decoded image signal output from the decoding step;
A target code amount control step of determining the degree of block distortion calculated by the calculation step and controlling a target code amount determined by the target code amount determining means according to the block distortion degree. A program for causing a computer to execute an image encoding method.

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