JP2012104940A - Moving image encoder, moving image encoding method and program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a moving image encoder capable of improving subjective image quality and improving encoding efficiency.SOLUTION: The moving image encoder includes: a first encoding part for encoding input video signals using a prescribed first quantization parameter and generating a bit stream; a decoding part for decoding the bit stream generated by the first encoding part and generating decoded video signals and encoding information for the time of first encoding; an evaluation part for calculating an image quality degradation evaluation index indicating the degree of distortion in the decoded video signals on the basis of a difference between the decoded video signals decoded by the decoding part and the input video signals; a quantization parameter calculation part for calculating a second quantization parameter on the basis of the image quality degradation evaluation index calculated by the evaluation part and the encoding information, outputted by the decoding part, including a slice type, a macro block type and a macro block generation code amount; and a second encoding part for encoding the input video signals using the second quantization parameter calculated by the quantization parameter calculation part.

Description

  The present invention relates to a moving image encoding apparatus, a moving image encoding method, and a program.

  Currently, when encoding a moving image, predictive encoding and block division transform encoding are performed. In predictive coding, a prediction error signal is generated by performing intraframe predictive coding and motion compensation interframe predictive coding (see, for example, Non-Patent Document 1). The prediction error signal is a signal representing a difference between a pixel value in a macroblock and a predicted value of the pixel value. A macroblock is an area in which a plurality of adjacent pixels (for example, 8 × 8 pixels) are collected, and is an object to be encoded. In intra-frame predictive coding, a high compression rate is realized by predicting pixel values in a macroblock from pixel values of adjacent coded macroblocks. On the other hand, in motion compensation interframe predictive coding, in addition to interframe predictive coding using a difference signal between adjacent frames, information indicating how much an object in a frame has moved from a coded frame (motion vector) ) Is used to predict the pixel value of the macroblock. Thereby, a high compression rate is realized. In block division transform coding, a prediction error signal is coded by intraframe prediction coding and motion compensation interframe prediction coding. That is, a high compression rate is realized by performing discrete cosine transform (DCT) on the prediction error signal in units of macroblocks.

  FIG. 4 is a block diagram showing a functional configuration of the moving picture coding apparatus 20 that performs coding combining prediction coding and block division transform coding. The moving picture coding apparatus 20 includes a predictive coding unit 21, a block division transform coding unit 22, and a quantization unit 23. The predictive encoding unit 21 receives a video signal to be encoded (hereinafter referred to as an input video signal), and performs intraframe prediction encoding and motion compensation interframe prediction encoding on a macroblock in the input video signal. I do. Then, the predictive encoding unit 21 outputs the generated prediction error signal to the block division transform encoding unit 22. The block division transform encoding unit 22 performs discrete cosine transform on the input prediction error signal, thereby transforming the frequency component into a frequency component and using the transformed frequency component as an orthogonal transform coefficient. This removes spatial redundancy. The quantization unit 23 rounds the result obtained by dividing the orthogonal transform coefficient transformed by the block division transform coding unit 22 by a specified value (hereinafter referred to as a quantization step) to an integer value, and quantizes the result rounded to an integer value. It is a digitized value. That is, the quantization unit 23 associates the input orthogonal transform coefficient with one of the predetermined quantization representative values. As a result, the code amount is significantly reduced while allowing distortion due to quantization.

  Here, when performing encoding, the quantization unit 23 first determines a quantization parameter (an integer value from 0 to 51) for each macroblock, and performs a quantization step based on the determined quantization parameter. Is derived. The quantization parameter is a parameter that determines the quantization step. For example, H.M. In H.264 / AVC, the logarithm of the quantization parameter and the quantization step is proportional. Specifically, when the quantization parameter is increased by 6, the quantization step is doubled. Then, the quantization unit 23 calculates a quantization value by rounding the result obtained by dividing the orthogonal transform coefficient by the quantization step to an integer value.

  Non-Patent Document 2 describes SSIM (Structural SIMilarity), which is a method for objectively evaluating the similarity of images. Non-Patent Document 3 proposes an algorithm that can improve the encoding efficiency in units of macroblocks and realize high compression.

ITU-T Rec. H.264-ISO / IEC 14496-10, "Advanced video coding for generic audiovisual service", Mar. 2010. http://www.itu.int/rec/T-REC-H.264 2009, 2009. Zhou Wang, Alan Conrad Bovik, Hamid Rahim Sheikh, Eero P. Simoncelli, "Image Quality Assessment: From Error Visibility to Structural Similarity," IEEE Transactions on Image Pro-cessing, vol. 13, no. 4, pp. 600-612, Apr. 2004. "Study of high-efficiency two-pass coding algorithm focusing on rate / distortion characteristics of macroblock", Kazuya Yokobari, Satoshi Tomita, Kazuo Uekura, Information Processing Society of Japan "68th Audio-Visual Complex Information Processing" .2010-AVM-68 No.2, February 25, 2010

  In the prior art, the amount of code is reduced by performing quantization in the quantizing unit 23. However, since distortion due to quantization is allowed at this time, distortion may occur. However, it is impossible to know in advance how much the generated distortion is and how much it is distorted. Therefore, it is difficult to optimize in advance the quantization parameter used for quantization, and as a result, there is a problem that distortion due to quantization may adversely affect image quality.

  The present invention has been made in view of such circumstances, and by setting appropriate quantization parameters used for encoding and suppressing distortion due to quantization, the subjective image quality is improved and the encoding efficiency is improved. An object of the present invention is to provide a moving picture coding apparatus, a moving picture coding method, and a program capable of improving the above.

  The present invention includes a first encoding unit that encodes an input video signal using a predetermined first quantization parameter to generate a bitstream, and decodes the bitstream generated by the first encoding unit. A decoding unit that generates a decoded video signal and encoding information at the time of first encoding, and a degree of distortion in the decoded video signal based on a difference between the decoded video signal decoded by the decoding unit and the input video signal Based on coding information including an evaluation unit that calculates an image quality deterioration evaluation index indicating the image quality deterioration evaluation index calculated by the evaluation unit, and a slice type, a macroblock type, and a macroblock generation code amount output by the decoding unit A quantization parameter calculation unit for calculating a second quantization parameter and a second quantization parameter calculated by the quantization parameter calculation unit for the input video signal. Characterized in that it is provided with a second encoding unit for encoding.

  The present invention is characterized in that the evaluation unit calculates the image quality degradation evaluation index using SSIM (Structural SIMularity).

マクロブロック番号をｉとし、前記画質劣化評価指標を前記レート歪み曲線ｆ（ｘ_ｉ）とし、前記マクロブロック発生符号量を正規化した値をｘ_ｉとして式（１）におけるａ_ｉ を式（２）により算出し、

発生符号量に対する前記画質劣化評価指標を表す目標符号化効率をＥ_ｐｉｃとして、マクロブロック発生符号量の目標値である目標マクロブロック発生符号量ＴＭｂＢｉｔ_ｉを式（３）により算出し、

前記マクロブロック発生符号量をｇ（ｙ_ｉ）とし、α_ｉ、β_ｉを前記スライスタイプ及びマクロブロックタイプより所定の値から選択し、前記第一量子化パラメータをｙ_ｉとして、定数γ_ｉを式（４）により算出し、

前記目標マクロブロック発生符号量をＴＭｂＢｉｔ_ｉとし、α_ｉ、β_ｉ、γ_ｉの値として、第二量子化パラメータｙ_ｉを式（５）により算出し、

前記第二量子化パラメータを算出することを特徴とする。 In the present invention, the quantization parameter calculation unit relates to a rate distortion curve f (x _i ) defined by Equation (1),

The macro block number is i, the image quality degradation evaluation index is the rate distortion curve f (x _i ), the value obtained by normalizing the macro block generation code amount is x _i , and a _i in the equation (1) is expressed by the equation (2) )

A target coding efficiency TMbBit _i , which is a target value of the macroblock generation code amount, is calculated by Equation (3), where E _pic is the target coding efficiency representing the image quality degradation evaluation index for the generated code amount,

The macroblock generation code amount is g (y _i ), α _i and β _i are selected from predetermined values from the slice type and macro block type, the first quantization parameter is y _i , and the constant γ _i is Calculated by equation (4),

The target macroblock generation code amount is set to TMbBit _i, and the second quantization parameter y _i is calculated by Equation (5) as the values of α _i , β _i , and γ _i .

The second quantization parameter is calculated.

  The present invention is a moving picture coding method in a moving picture coding apparatus including a first coding unit, a decoding unit, an evaluation unit, a quantization parameter calculation unit, and a second coding unit, A first encoding step in which an encoding unit encodes an input video signal using a predetermined first quantization parameter to generate a bitstream; and the decoding unit performs the first encoding step. A decoding step of decoding the generated bit stream to generate a decoded video signal and encoded information at the time of first encoding, and a difference between the decoded video signal decoded by the decoding unit and the input video signal by the decoding step Based on the evaluation step of calculating an image quality deterioration evaluation index indicating the degree of distortion in the decoded video signal, and the image quality deterioration calculated by the quantization parameter calculation unit in the evaluation step A quantization parameter calculating step for calculating a second quantization parameter based on encoding information including a valence index and a slice type, a macroblock type, and a macroblock generation code amount generated by the decoding step; and the second encoding And a second encoding step of encoding the input video signal using the second quantization parameter calculated in the quantization parameter calculating step.

  The present invention is characterized in that the evaluation step calculates the image quality degradation evaluation index by using SSIM (Structural SIMularity).

マクロブロック番号をｉとし、前記画質劣化評価指標を前記レート歪み曲線ｆ（ｘ_ｉ）とし、前記マクロブロック発生符号量を正規化した値をｘ_ｉとして式（６）におけるａ_ｉ を式（２）により算出し、

発生符号量に対する前記画質劣化評価指標を表す目標符号化効率をＥ_ｐｉｃとして、マクロブロック発生符号量の目標値である目標マクロブロック発生符号量ＴＭｂＢｉｔ_ｉを式（８）により算出し、

前記マクロブロック発生符号量をｇ（ｙ_ｉ）とし、α_ｉ、β_ｉを前記スライスタイプ及びマクロブロックタイプより所定の値から選択し、前記第一量子化パラメータをｙ_ｉとして、定数γ_ｉを式（９）により算出し、

前記目標マクロブロック発生符号量をＴＭｂＢｉｔ_ｉとし、α_ｉ、β_ｉ、γ_ｉの値として、第二量子化パラメータｙ_ｉを式（１０）により算出し、

前記第二量子化パラメータを算出することを特徴とする。 In the present invention, the quantization parameter calculation step relates to a rate distortion curve f (x _i ) defined by Equation (6),

The macro block number is i, the image quality degradation evaluation index is the rate distortion curve f (x _i ), the value obtained by normalizing the macro block generation code amount is x _i , and a _i in the equation (6) is expressed by the equation (2). )

A target coding efficiency TMbBit _i , which is a target value of the macroblock generated code quantity, is calculated by Expression (8), where E _pic is the target coding efficiency representing the image quality degradation evaluation index with respect to the generated code quantity,

The macroblock generation code amount is g (y _i ), α _i and β _i are selected from predetermined values from the slice type and macro block type, the first quantization parameter is y _i , and the constant γ _i is Calculated by equation (9),

The target macroblock generation code amount is set as TMbBit _i , α _i , β _i , and γ _i are calculated as values of the second quantization parameter y _{i according} to Equation (10),

The second quantization parameter is calculated.

  A computer on a moving image encoding apparatus is caused to execute the moving image encoding method according to any one of claims 4 to 6.

  According to the present invention, the quantization parameter used when the video input signal is encoded again is calculated using the image quality degradation evaluation index for the result of encoding the video input signal once. For this reason, an appropriate quantization parameter can be set, subjective image quality can be improved, and coding efficiency can be improved.

It is a block diagram which shows the function structure of the moving image encoder by this embodiment. It is a flowchart which shows the procedure of the encoding process by this embodiment. It is a graph which shows the result of having experimented with the moving image encoder in this embodiment. It is a block diagram which shows the function structure of the moving image encoder in a prior art.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram showing a functional configuration of a moving picture encoding apparatus 10 according to the present embodiment. The moving image encoding apparatus 10 includes a first encoding unit 11, a decoding unit 12, an evaluation unit 13, a quantization parameter calculation unit 14, and a second encoding unit 15. The first encoding unit 11 receives a video signal to be encoded (hereinafter referred to as an input video signal), encodes the input video signal, and sets the encoded result as a bit stream. Then, the first encoding unit 11 outputs the bit stream to the decoding unit 12. Specifically, the first encoding unit 11 first performs predictive encoding and block division transform encoding on each macroblock in the input video signal. Next, the first encoding unit 11 divides an orthogonal transform coefficient, which is a result of performing block division transform coding, by a quantization step. Then, the first encoding unit 11 rounds the division result to an integer value and calculates a quantized value. At this time, the first encoding unit 11 calculates a quantization step from the quantization parameter set in advance for each macroblock. In the present embodiment, the logarithm of the quantization parameter and the quantization step is proportional. For this reason, the first encoding unit 11 calculates the quantization step QS using the following equation (11). Here, QP is a quantization parameter. Hereinafter, the encoding performed by the first encoding unit 11 is referred to as first encoding.

  The decoding unit 12 decodes the input bit stream and uses the decoded result as a decoded video signal. Then, the decoding unit 12 outputs the decoded video signal to the evaluation unit 13, and outputs the encoded information of the bitstream acquired at the time of decoding to the quantization parameter calculation unit 14 and the second encoding unit 15. The encoding information is information when the input video signal is first encoded, and includes a macroblock type and a macroblock generation code amount. The macro block type is a result of predictive coding and block division transform coding of a macro block. The macroblock generated code amount (generated code amount) is a code amount generated when a macroblock is encoded.

The evaluation unit 13 receives the input video signal and the decoded video signal, and based on the difference between the input video signal and the decoded video signal in each macroblock (hereinafter referred to as a differential signal), the image quality degradation evaluation index by the first encoding Is calculated. The image quality degradation evaluation index is an index indicating the degree of distortion. The image quality degradation evaluation index in the present embodiment is an SSIM obtained from the luminance value difference, variance, and covariance indices in each macroblock. SSIM indicates that the larger the value, the smaller the image distortion, and the smaller the value, the larger the distortion. The image quality degradation evaluation index may be a sum of absolute differences or a sum of squares of the difference signals. Then, the evaluation unit 13 outputs the image quality degradation evaluation index to the quantization parameter calculation unit 14. Here, the evaluation unit 13 calculates the SSIM by the following equation (12). x represents an image in the input video signal, and y represents an image in the decoded video signal. Α ₁ , β ₁ , and γ ₁ are constants.

  Elements constituting the expression (12) are defined by the following expressions (13), (14), and (15), respectively.

Here, l (x, y) is a luminance value comparison function, c (x, y) is a contrast value comparison function, and s (x, y) is a structure comparison function. Further, μ _x used here is defined by the following equation (16). Here, lx _i is the luminance value of the i-th macroblock in the input video signal. N is a positive integer and is the number of macroblocks.

Μ _y is defined by the following equation (17). Here, ly _i is the luminance value of the i-th macroblock in the decoded video signal.

Σ _x is defined by the following equation (18).

Σ _y is defined by the following equation (19).

Σ _xy is defined by the following equation (20).

  The quantization parameter calculation unit 14 is a quantization used when the second encoding unit 15 performs encoding based on the encoding information output from the decoding unit 12 and the image quality degradation evaluation index output from the evaluation unit 13. Parameters are calculated for each macroblock. Here, the quantization parameter calculation unit 14 uses a macroblock generation code amount as the encoding information. Details of the quantization parameter determination method will be described later. Then, the quantization parameter calculation unit 14 outputs a quantization parameter set that is a combination of quantization parameters in each macroblock to the second encoding unit 15.

  The second encoding unit 15 performs encoding using the input video signal, the quantization parameter set output by the quantization parameter calculation unit 14, and the encoding information output by the decoding unit 12. That is, the second encoding unit 15 performs encoding while applying the value specified by the quantization parameter set to the macroblock type included in the encoding information, and outputs the encoded result as an encoded stream. To do. Specifically, the second encoding unit 15 first calculates a quantization step from the quantization parameter specified in the quantization parameter set. Then, the second encoding unit 15 divides the macroblock type by the quantization step, rounds the result of the division to an integer value, and calculates a quantization value. Hereinafter, the encoding in the second encoding unit 15 is referred to as second encoding.

  Next, the encoding process by the moving image encoding device 10 will be described with reference to FIG. FIG. 2 is a flowchart showing the procedure of the encoding process according to this embodiment. First, in step S101, the first encoding unit 11 performs first encoding on the input video signal. Next, in step S102, the decoding unit 12 decodes the bitstream that is the result of the first encoding. In step S103, the evaluation unit 13 calculates an image degradation evaluation index SSIM from the difference between the input video signal and the decoded video signal.

Next, in step S104, the quantization parameter calculation unit 14 calculates the target encoding efficiency (E _pic ). Here, the target coding efficiency E _pic = (∂D / ∂R) is a value representing distortion with respect to the generated code amount. D represents distortion and is a value of an image quality degradation evaluation index obtained by the evaluation unit 13. That is, the value of SSIM is entered in D. Also, R is a macroblock generation code amount included in the encoding information. For example, when using the average value of the macroblock generation code amount (average macroblock generation code amount) and the SSIM average value (average SSIM) in the first encoding result, E _pic = (∂D / ∂R) = Average SSIM / average macroblock generation code amount.

Next, in step S105, the quantization parameter calculation unit 14 obtains a rate distortion curve f (x _i ) in each macroblock. Here, i, which is a subscript of x, is a positive integer and means the i-th macroblock. The rate distortion curve f (x _i ) is defined by the following equation (21).

Here, x _i is a value obtained by normalizing the macroblock generation code amount at the time of the first encoding obtained from the decoding unit 12. Further, f (x _i ) is an image quality degradation evaluation index at the time of the first encoding obtained by the evaluation unit 13. a _i is a variable that uniquely defines f (x _i ). That is, the quantization parameter calculation unit 14 calculates a _i by the following equation (22) in order to obtain the equation (21).

Here, the macroblock generation code amount is defined as 0 to 3200 bits, but in equation (22), the macroblock generation code amount is divided by 3200 and the value range from 0 to 1 enters x _i .

Next, in step S106, the quantization parameter calculation unit 14 obtains a target generated code amount TMbBit _i that satisfies the target encoding efficiency E _pic on the rate distortion curve f (x _i ). The target generated code amount TMbBit _i is a target value of the macroblock generated code amount in the second encoding. It is clear from the definition that the target encoding efficiency E _pic = (∂D / ∂R) means a slope on f (x _i ). That is, it can be said that f _{(x i)} was differentiated for _{x i} f _{'(x i)} and as _{E pic} equals _{x i} is the target generated code amount TMbBit _i. Therefore, the quantization parameter calculation unit 14 obtains TMbBit _i using the following equation (23).

Here, since x _i = TMbBit _i , the quantization parameter calculation unit 14 calculates the target generated code amount TMbBit _i by the following equation (24).

Next, in step S107 and step S108, the quantization parameter calculation unit 14 determines the quantization parameter to macroblock so as to obtain a quantization parameter for which the macroblock generation code amount after the second encoding is the TMbBit _i obtained previously. A curve (QP-GenBit curve: g (y _i )) representing the relationship between the generated code amounts is calculated. The quantization parameter and the macroblock generation code amount have a monotonically decreasing relationship in which the macroblock generation code amount decreases as the quantization parameter increases. In addition, since there is a feature that the decrease width in the monotonous decrease gradually decreases, the QP-GenBit curve ((g (y _i )) is defined by a quadratic expression like Expression (25).

Here, y _i is a quantization parameter at the time of second encoding, α _i and β _i are constants determined by the slice type and macroblock type used at the time of the first encoding obtained from the decoding unit 12, and γ _i is g _{(y i)} uniquely define constant, g _{(y i)} is the macroblock generated code amount. I represents the i-th macroblock.

In the QP-GenBit curve, the macroblock generation code amount at the same quantization parameter differs greatly depending on the slice type and the macroblock type. Therefore, when the slice type and macroblock type are not taken into consideration, the correlation coefficient between the QP-GenBit curve and the quantization parameter versus the macroblock generation code amount may be small. Therefore, in step S107, α _i and β _i are set from the slice type and macroblock type at the time of the first encoding obtained from the decoding unit 12 in determining the shape of the QP-GenBit curve with a larger correlation coefficient. To do.

  The slice type is a value representing the type of slice. In the case of H.264 / AVC, values from 0 to 9 are defined as shown in Table 1.

  The macroblock type is a value representing the type of macroblock and is determined according to the slice type. Table 1 is defined for I slices, Table 3 for SI slices, Table 4 for P slices and SP slices, and Table 5 for B slices.

  Here, for P_Skip in Table 4 and B_Skip in Table 5, there is no information about the macroblock, so the macroblock type does not exist and is blank.

The values of α _i and β _i that determine the shape of the QP-GenBit curve and the position in the X-axis direction are determined in advance for each slice type and macroblock type. In determining α _i and β _i , a plurality of macroblocks are previously encoded for quantization parameters 0 to 51 by experiment to obtain macroblock generation code amount and SSIM data. Then, from the encoding result, classification is performed for each slice type and macroblock type, and the average macroblock generation code amount and average SSIM are taken for each quantization parameter, and the least square method is applied to those points (52 points). An approximate curve is obtained by using this.

The coefficients of y _i ² and y _i of the quadratic curve obtained here are defined as α (SliceType; MBType) and β (SliceType; MBType), respectively, and the slice used at the time of the first encoding obtained from the decoding unit 12 Α _i and β _i are determined according to the types (26) and (27) according to the type and the macroblock type.

  Here, it is not always necessary to use all 10 types of values from 0 to 9 for the classification of slice types. For example, when the slice types are 0 and 5, since both are P slices, they can be treated as being the same. At this time, α (SliceType; MBType) and β (SliceType; MBType) may be calculated after combining the data of slice types 0 and 5.

  Similarly, regarding macroblock classification, several macroblock types may be aggregated as necessary. For example, in the case of an I slice, since the prediction modes are the same for macroblock types 1 to 24, the tendency of the QP-GenBit curve may be similar. At this time, it can be considered that a total of three macro block types of 0, 1 to 24, and 25 exist in the I slice. Here, α (SliceType; MBType) and β (SliceType; MBType) are determined as shown in Table 6.

  In Table 6, values are determined for macro blocks of I slices and P slices, and values in other columns are used for all other slice types and macro block types. Further, the classification method of the slice type and the macroblock type is not limited to Table 6.

Next, in step S108, when obtaining the quantization parameter at the time of the second encoding, the quantization parameter calculation unit 14 firstly calculates the quantization at the time of the first encoding obtained from the decoding unit 12 to Expression (28). By substituting the parameters, the macro block generation code amount and α _i and β _i set in step S107, γ _i is obtained, and the QP-GenBit curve (g (y _i )) of each macro block is uniquely determined.

Next, in step S109, the quantization parameter calculation unit 14 determines the variable γ _i that uniquely determines the QPGenBit curve (g (y _i )) obtained by Expression (25) and the target generated code obtained by Expression (23). Substituting the quantity TMbBit _i into equation (29), the quantization parameter yi at the time of the second encoding is obtained.

Here, in order to uniquely find a solution of y _i , a constraint of 0 <y _i <51 is provided. In step S110, the quantization parameter calculation unit 14 determines whether or not the quantization parameter y _i has been output for all macroblocks. If the quantization parameter y _i has been calculated for all macroblocks, the process proceeds to step S111. On the other hand, if the quantization parameter y _i has not been calculated for all macroblocks, the process returns to step S105. Then, after obtaining y _i for all macroblocks, in step S111, the second encoding unit 15 performs second encoding using the quantization parameter y _i .

As described above, since the constants α _i and β _i are determined by the slice type and the macro block type, the quantization parameter can be obtained from the macro block generation code amount, and as a result, the coding efficiency is improved. Can be realized.

  FIG. 3 is a graph showing a result of an experiment performed by the moving image encoding apparatus 10 according to the present embodiment. In this figure, the horizontal axis represents the macroblock generated code amount (unit: kbit / s), and the vertical axis represents the image quality degradation evaluation index SSIM. A solid line 101 indicates the result of the second encoding, and a solid line 102 indicates the result of the first encoding. The experiment in this figure was conducted for the standard definition television (SDTV) size (720 × 480), interlace, and the number of frames of 450 frames, which are one of standard images in ITE (Video Information Media Society). SSIM indicates that the larger the value, the smaller the image distortion, and the smaller the value, the larger the distortion. For this reason, as shown in the figure, it can be confirmed that the result of the second encoding is improved in encoding efficiency as compared with the result of the first encoding.

  As described above, according to the present embodiment, the moving image encoding apparatus 10 calculates the quantization parameter from the image degradation evaluation index, and performs the second encoding using the calculated quantization parameter. For this reason, it becomes possible to set an optimal quantization parameter, subjective image quality can be improved, and coding efficiency can be improved.

  2 is recorded on a computer-readable recording medium, and the program recorded on the recording medium is read into a computer system and executed, thereby executing an encoding process. You may go. Here, the “computer system” may include an OS and hardware such as peripheral devices. Further, the “computer system” includes a homepage providing environment (or display environment) if a WWW system is used. The “computer-readable recording medium” means a flexible disk, a magneto-optical disk, a ROM, a writable nonvolatile memory such as a flash memory, a portable medium such as a CD-ROM, a hard disk built in a computer system, etc. This is a storage device.

  Further, the “computer-readable recording medium” means a volatile memory (for example, DRAM (Dynamic DRAM) in a computer system that becomes a server or a client when a program is transmitted through a network such as the Internet or a communication line such as a telephone line. Random Access Memory)), etc., which hold programs for a certain period of time. The program may be transmitted from a computer system storing the program in a storage device or the like to another computer system via a transmission medium or by a transmission wave in the transmission medium. Here, the “transmission medium” for transmitting the program refers to a medium having a function of transmitting information, such as a network (communication network) such as the Internet or a communication line (communication line) such as a telephone line. The program may be for realizing a part of the functions described above. Furthermore, what can implement | achieve the function mentioned above in combination with the program already recorded on the computer system, and what is called a difference file (difference program) may be sufficient.

  As described above, the embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to the above, and various design changes and the like can be made without departing from the scope of the present invention. It is possible to

  The present invention can also be applied to an application in which it is indispensable to calculate a quantization parameter used when encoding a video input signal again using an image quality degradation evaluation index for a result of encoding the video input signal once.

  DESCRIPTION OF SYMBOLS 10 ... Moving image encoding device, 11 ... 1st encoding part, 12 ... Decoding part, 13 ... Evaluation part, 14 ... Quantization parameter calculation part, 15 ... 2nd encoding part

Claims (7)

A first encoding unit that encodes an input video signal using a predetermined first quantization parameter to generate a bitstream;
A decoding unit that decodes the bitstream generated by the first encoding unit to generate a decoded video signal and encoding information at the time of the first encoding;
An evaluation unit that calculates an image quality degradation evaluation index indicating a degree of distortion in the decoded video signal based on a difference between the decoded video signal decoded by the decoding unit and the input video signal;
A quantization parameter calculation unit that calculates the second quantization parameter based on the image quality degradation evaluation index calculated by the evaluation unit and the encoding information including the slice type, macroblock type, and macroblock generation code amount output by the decoding unit When,
A video encoding device comprising: a second encoding unit that encodes the input video signal using the second quantization parameter calculated by the quantization parameter calculation unit.   The moving image encoding apparatus according to claim 1, wherein the evaluation unit calculates the image quality degradation evaluation index using SSIM (Structural SIMularity). The quantization parameter calculation unit relates to the rate distortion curve f (x _i ) defined by Equation (1).

The macro block number is i, the image quality degradation evaluation index is the rate distortion curve f (x _i ), the value obtained by normalizing the macro block generation code amount is x _i , and a _i in the equation (1) is expressed by the equation (2) )

A target coding efficiency TMbBit _i , which is a target value of the macroblock generation code amount, is calculated by Equation (3), where E _pic is the target coding efficiency representing the image quality degradation evaluation index for the generated code amount,

The macroblock generation code amount is g (y _i ), α _i and β _i are selected from predetermined values from the slice type and macro block type, the first quantization parameter is y _i , and the constant γ _i is Calculated by equation (4),

The target macroblock generation code amount is set to TMbBit _i, and the second quantization parameter y _i is calculated by Equation (5) as the values of α _i , β _i , and γ _i .

The moving image encoding apparatus according to claim 1, wherein the second quantization parameter is calculated. A moving image encoding method in a moving image encoding device including a first encoding unit, a decoding unit, an evaluation unit, a quantization parameter calculation unit, and a second encoding unit,
The first encoding unit encodes the input video signal using a predetermined first quantization parameter to generate a bitstream; and
A decoding step in which the decoding unit decodes the bitstream generated in the first encoding step to generate a decoded video signal and encoding information at the time of the first encoding;
An evaluation step in which the evaluation unit calculates an image quality degradation evaluation index indicating a degree of distortion in the decoded video signal based on a difference between the decoded video signal decoded in the decoding step and the input video signal;
The quantization parameter calculation unit is configured to perform second quantization based on encoding information including an image quality degradation evaluation index calculated in the evaluation step and a slice type, a macroblock type, and a macroblock generation code amount generated in the decoding step. A quantization parameter calculating step for calculating a parameter;
The second encoding unit has a second encoding step for encoding the input video signal using the second quantization parameter calculated in the quantization parameter calculating step. Encoding method.   5. The moving picture encoding method according to claim 4, wherein the evaluation step calculates the image quality degradation evaluation index using SSIM (Structural SIMularity). The quantization parameter calculation step relates to the rate distortion curve f (x _i ) defined by Equation (6),

The macro block number is i, the image quality degradation evaluation index is the rate distortion curve f (x _i ), the value obtained by normalizing the macro block generation code amount is x _i , and a _i in the equation (7) is expressed by the equation (2). )

A target coding efficiency TMbBit _i , which is a target value of the macroblock generated code quantity, is calculated by Expression (8), where E _pic is the target coding efficiency representing the image quality degradation evaluation index with respect to the generated code quantity,

The macroblock generation code amount is g (y _i ), α _i and β _i are selected from predetermined values from the slice type and macro block type, the first quantization parameter is y _i , and the constant γ _i is Calculated by equation (9),

The target macroblock generation code amount is set as TMbBit _i , α _i , β _i , and γ _i are calculated as values of the second quantization parameter y _{i according} to Equation (10),

6. The moving picture coding method according to claim 4, wherein the second quantization parameter is calculated.   A computer program for causing a computer on a moving image encoding apparatus to execute the moving image encoding method according to any one of claims 4 to 6.

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