JP2006157084A - Image coding apparatus, image coding method, and computer program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an image with high quality by efficiently coding a moving image. <P>SOLUTION: The image coding apparatus is provided with two kinds of filters 4, 5 as the filter just before encoding, the ε filter 4 protects the occurrence of edges in the image and smoothes the image as its filter processing, the k filter 5 suppresses coding distortion and avoids a buffer from its failure as its filter processing, the ε filter 4 eliminates noise in a flat part of a region of the input image and the k filter 5 places band limit on the image in the other region, so that the image encoder can prevent the visual image quality from being degraded over the entire image regions. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image encoding device, an image encoding method, and a computer program, and is particularly suitable for use in encoding a moving image.

  Conventionally, as an image encoding method, an intra-frame encoding method such as Motion JPEG or Digital Video, or H.264 using inter-frame predictive encoding is used. 261, H.H. Coding schemes such as H.263, MPEG-1 and MPEG-2 are known. These encoding methods are internationally standardized by ISO (International Organization for Standardization) and ITU (International Telecommunication Union). The intra-frame coding method performs coding independently for each frame, and is easy to manage the frames, so that it is most suitable for an apparatus that requires editing of moving images and special reproduction. In addition, the inter-frame predictive coding method has a feature that coding efficiency is high because inter-frame prediction based on a difference in image data between frames is used.

  FIG. 12 shows an example of the configuration of a conventional moving picture encoding apparatus that performs encoding using MPEG-2, and FIG. 13 shows an example of the structure of a coded picture encoded by the moving picture encoding apparatus. The encoded picture structure encoded by MPEG is configured by a combination of three types of pictures having different prediction methods as shown in FIG. These three types of pictures are called an I picture (intraframe coding), a P picture (forward prediction coding), and a B picture (bidirectional prediction coding), respectively.

  A combination of a plurality of these pictures is called a group of picture (hereinafter referred to as GOP). Since this GOP includes only one I picture, it is often an editing unit. These prediction modes are switched by switches 101 and 108 according to a control signal from the mode determiner 105 as shown in FIG. In the I picture, DCT (Discrete Cosine Transform) is performed by the DCT unit 102 on the encoded image itself. On the other hand, in the P picture and the B picture, the DCT is performed by the DCT unit 102 on the error signal of the motion compensation prediction by the motion compensator 109.

After the quantization of the DCT coefficient obtained by the DCT unit 102 is performed by the quantizer 103 according to the control based on the output from the rate controller 100, the variable length coding is variable together with other additional information such as a motion vector. This is performed by the long encoder 104, and the code string is output as a “bit stream”. At this time, the quantization scale is controlled by the rate controller 100 according to the code amount from the variable length encoder 104. On the other hand, the output coefficient of the quantizer 103 is supplied to an inverse quantizer 106 and an inverse DCT unit 107, and is locally decoded and stored in a frame memory (FM) 110 for each block.
In the GOP structure, the interval between the I picture and the P picture is represented by M, and the number of frames in the GOP is represented by N. In the example shown in FIG. 13, M = 3 and N = 15.

  Since MPEG-2 performs variable length coding, the amount of generated code per unit time is not constant. Therefore, it is possible to control to a desired bit rate by appropriately changing the quantization scale at the time of quantization in the quantizer 103 in units of macroblocks. Step 3 of MPEG-2 Test Model 5 (see Non-Patent Document 1) describes a method of changing the quantization scale based on the variance value of each macroblock.

  Here, the compression rate can be increased by increasing the quantization scale at the time of quantization. However, when the quantization scale is increased, the quantization error of the high frequency component increases, coding distortion called block distortion or mosquito distortion occurs, and the image quality significantly decreases. Further, since the interframe coding method uses interframe prediction, the coding is performed depending on both the high frequency component in the spatial direction and the amount of motion in the temporal direction. Therefore, even if a simple image having no high-frequency component moves rapidly, a large amount of high-frequency component is included in the prediction error, so that much coding distortion occurs.

In addition to this basic structure of video coding, the input image is preliminarily subjected to a band limiting filter to remove visually inconspicuous high frequency components and reduce the amount of code, thereby reducing the subjective image quality of the decoded image. It is generally performed to improve. At this time, the characteristics of the band limiting filter are set according to the compression rate, and are set to a narrow band when the compression rate is high, and to a wide band when the compression rate is low. Furthermore, a method is known in which the band limiting filter is controlled according to the amount of generated code that is an encoded output.
Other detailed contents such as MPEG will be entrusted to international standard documents by ISO / IEC.

MPEG-2 Test Model, Document ISO / IEC JTC1 SC29 WG11 / 93-400, Test Model Editing Committee, April 1993.

  However, in the conventional technique, when the generated code amount is large, the band is remarkably limited by the filter, and not only high-frequency components but also low-frequency component image information may be deleted. Since the low-frequency component has a great influence on the visual sense, if it is deleted, the visual image quality is significantly deteriorated. Such band limiting processing should be performed according to the local nature of the image.

  In addition, when a moving image having a sequence with a large amount of motion is encoded even if the high-frequency component of the moving image is small, the generated code amount increases, and the band limiting filter acts in a direction to remove the high-frequency component. For this reason, not only the high-frequency component in the moving part but also the stationary part with a small amount of motion is removed, and the resolution of the still part where the human visual resolution is high is deteriorated. Therefore, the overall image quality evaluation of the reproduced image is greatly reduced. At the same time, if the cut-off frequency of the band limiting filter fluctuates, the resolution of the still portion fluctuates, so that when the entire image is viewed, the result is an unnatural image.

As described above, the conventional technique cannot achieve high image quality while efficiently suppressing the code amount.
The present invention has been made in view of the above-described problems, and an object thereof is to efficiently encode a moving image so as to obtain a high-quality image.

  The image encoding apparatus according to the present invention performs a band limitation on the input moving image data according to the feature amount of the input moving image data and the code amount of the moving image data encoded in the past. 1 preprocessing means and a second preprocessing for protecting edges of the input moving image data and smoothing the input moving image data based on a feature amount of the input moving image data Means for selecting one of the first pre-processing means and the second pre-processing means in accordance with the code amount and the feature quantity of the input moving image data, and the selection means And encoding means for encoding the moving image data output from the preprocessing means selected by the above.

  The image encoding method according to the present invention performs a band limitation on the input moving image data according to the feature amount of the input moving image data and the code amount of the moving image data encoded in the past. And a second preprocessing for protecting an edge of the input moving image data and smoothing the input moving image data in accordance with a feature amount of the input moving image data. A selection step of selecting one of the first preprocessing means and the second preprocessing means based on the code amount and the feature amount of the input moving image data; and the selection step And an encoding step for encoding the moving image data that has been preprocessed by the preprocessing step selected in step (b).

  A computer program according to the present invention causes a computer to execute the steps described above.

  According to the present invention, the first preprocessing for performing band limitation on the input moving image based on the feature amount of the input moving image and the code amount of the moving image encoded in the past, Based on a feature amount of the input moving image, pre-processing of any one of the second pre-processing for protecting edges of the input moving image and smoothing the input moving image After that, by encoding the moving image, the preprocessing and the code amount control are operated in an interlocked manner, so that the generated code amount is suitably controlled while visually preventing the image quality from deteriorating. To be able to do it easily.

(First embodiment)
Next, a first embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a block diagram illustrating an example of a configuration of an image encoding device according to the present embodiment. In the image coding apparatus according to the present embodiment, the minimum unit of control is a macro block.
In FIG. 1, reference numeral 1 denotes a feature amount measuring device that measures a feature amount for each macro block as a feature amount of an input image. In the present embodiment, the maximum value of the variance and inter-pixel difference for each macroblock is measured. Reference numeral 2 denotes a feature amount memory that accumulates feature amounts from the feature amount measuring device 1. In the present embodiment, feature amounts for M frames are accumulated.

  A filter coefficient calculator 3 calculates a filter coefficient from the accumulated feature amount. Reference numeral 4 denotes an ε filter that protects and smoothes edges. The ε filter 4 used in the present embodiment performs the filter processing represented by the following (formula 1) and (formula 2).

  In the filter processing shown in (Equation 1) and (Equation 2), the difference value between the central pixel f (x, y) and the neighboring pixel f (x + i, y + j) is calculated, and the absolute value thereof is calculated. If the value is larger than ε, the value of the neighboring pixel is replaced with the value of the central pixel, and smoothing processing is performed (x, y = −M,..., 0, 1,... M). As a result, in the output g (x, y) of the ε filter 4, the edge component can be protected and noise that is a harmonic having a small amplitude can be smoothed and suppressed. Details of the ε filter are described in “Harashima Hiroshi et al.,“ Ε-Separation Nonlinear Digital Filter and Its Application ”, IEICE 57-146 [A-36] April 1982”.

  Reference numeral 5 denotes a horizontal and vertical two-dimensional band limiting filter. The two-dimensional band limiting filter 5 used in the present embodiment is represented by the following (Equation 3).

  As shown in (Formula 3), in the present embodiment, the two-dimensional band limiting filter 5 is a three-pixel × three-line two-dimensional filter, and is a low-pass filter that sets a band based on a variable k. When the minimum value of the variable k is 2, and the value increases, the strength of the filter decreases and the band to be limited becomes narrow. Hereinafter, the two-dimensional band limiting filter is referred to as a k filter.

Reference numeral 6 denotes a selector that selects and outputs one of the image signals from the ε filter 4 and the k filter 5. A frame memory 7 stores the image signal selected by the selector 6. In the present embodiment, similarly to the feature amount memory 2, image signals for M frames are stored. Reference numeral 8 denotes an encoder that encodes an image signal stored in the frame memory 7.
Reference numeral 9 denotes an encoder output buffer for accumulating the stream output from the encoder 8. The buffer 9 outputs a generated code amount for each frame based on the stream output from the encoder 8 and a decoder buffer pointer assuming a decoder buffer. The decoder buffer pointer is a value obtained by subtracting the encoder buffer pointer from the buffer size.

  Reference numeral 10 denotes a code amount controller for controlling the encoder 8 based on the generated code amount output from the buffer 9. Reference numeral 11 denotes a filter coefficient calculator that calculates the coefficients of the ε filter 4 and the k filter 5 from the control parameter output from the encoder 8 and the buffer pointer output from the buffer 9. In this embodiment, the control parameter is a quantization scale.

  A coefficient memory 12 stores the coefficients output from the filter coefficient calculator 11. In the present embodiment, as in the feature amount memory 2, coefficients for M frames are accumulated. Reference numeral 13 denotes a k filter controller that outputs a control value to the k filter 5 to control the filter. The k filter controller 13 controls the ε filter controller 14 and the selector 6 simultaneously with the control of the k filter 5. Reference numeral 14 denotes an ε filter controller that outputs a control value to the ε filter 4 to control the filter.

Next, the operation of the image coding apparatus of the present embodiment having the above configuration will be described.
Processing in this embodiment is roughly classified into two. The process from the top to the M frame (hereinafter abbreviated as the top M frame) and the other frames. The process for the first M frame is executed until an image that has been subjected to filter processing for M frames is prepared before encoding. On the other hand, the other normal processing includes a process of encoding the frame subjected to the filter and a process of applying a filter to a frame to be encoded next. Here, the M frame is an MPEG ordering unit and is equal to the memory area essential for an encoder that handles B pictures.

Next, an example of the operation of the image coding apparatus when performing the filtering process for the first M frames (first frame filtering process) will be described with reference to the flowchart of FIG.
First, the video signal is input to the feature amount measuring device 1, and the feature amount measuring device 1 calculates the maximum value md of the difference between adjacent pixels in the macro block for each macro block (step S10). Here, the maximum value md of the difference between adjacent pixels in the macroblock is a value obtained for the luminance signal (= 16 pixels × 16 lines) in the macroblock. The formula for calculating the maximum value md of the inter-pixel difference is shown in the following (Formula 4).

md = MAX_i0_15_j0_14 (abs (p (i + 1, j) -p (i, j))) (Expression 4)
Here, i is the horizontal pixel position in the macroblock. j is the vertical line position in the macroblock. p (i, j) is a pixel in the macroblock (coordinates (i, j)). abs indicates an absolute value. MAX_i0_15_j0_14 indicates that the maximum value in i = 0 to 14, j = 0 to 15 is selected.

Next, the calculated maximum value md of the inter-pixel difference is stored in the feature amount memory 2 for M frames (step S11).
Next, the ε filter controller 14 calculates the average value mdm in the macroblock at the same position in the M frame from the maximum value md of the inter-pixel difference, and further calculates the filter control value ε from the average value mdm (step). S12). In the present embodiment, the filter control value ε is calculated by the following conversion formula (5).
ε = mdm / 2 (Expression 5)

  The ε filter 4 performs filter processing on the input video signal (input image) using the filter control value ε. The output image obtained by executing this filter processing is stored in the frame memory 7 via the selector 6 (step S13). In the first M frame, the filter process by the k filter 5 is not executed, and the selector 6 selects and outputs only the output from the ε filter 4.

Next, an example of the operation of the image encoding device when performing encoding processing in a steady state will be described with reference to the flowchart of FIG. In encoding a moving image, this processing is repeated for each M frame processing unit.
First, the code amount controller 10 calculates the quantization scale QP from the generated code amount from the buffer 9 and controls the encoder 8 (step S20).
Next, the encoder 8 encodes the image signal (frame) stored in the frame memory 7 (step S21).
Next, the coefficient calculator 11 calculates a filter coefficient ke from the buffer pointer from the buffer 9 and the quantization scale QP from the code amount controller 10 (step S22).
Next, the filter coefficient ke is stored in the coefficient memory 12 (step S23).

An example of the operation of the image encoding device (operation of step S22) when obtaining the filter coefficient ke will be described with reference to the flowchart of FIG.
First, the filter coefficient kq is calculated from the quantization scale QP (step S40). FIG. 5 is a graph showing an example of the relationship between the quantization scale QP and the filter coefficient kq. In FIG. 5, QPA in the graph is the value of the quantization scale QP when the filter strength is the lowest, and is a value that the curve is asymptotic.
In the present embodiment, the filter coefficient kq decreases when the value of the quantization scale QP is equal to or greater than this QPA.

Next, the filter coefficient kb is calculated from the decoder buffer pointer DBP (step S41). FIG. 6 is a graph showing an example of the relationship between the buffer pointer DBP and the filter coefficient kb. In FIG. 6, DB in the graph is the buffer size, and the value that the curve is asymptotic is DB / 2.
In order to prevent underflow of the decoder buffer, the filter coefficient kb decreases when the decoder buffer pointer DBP becomes ½ or less of the buffer size.

  Next, the coefficient calculator 11 compares the filter coefficients kq and kb, and selects the larger value as the filter coefficient ke (steps S42, S43 and S44). The filter coefficient ke is stored in the coefficient memory 12.

Next, an example of the operation of the image coding apparatus when performing the filtering process (stationary frame filtering process) at the normal time will be described with reference to the flowchart of FIG. In encoding a moving image, this processing is repeated for each M frame processing unit.
First, the video signal is input to the feature amount measuring device 1, and the feature amount measuring device 1 calculates the maximum value md of the variance for each macroblock and the inter-pixel difference (step S30). Since the processing regarding the maximum value md of the inter-pixel difference is as described above, a detailed description thereof will be omitted, and here, an operation until obtaining a variance value which is another feature amount will be described.

  In the present embodiment, the feature value measuring device 1 calculates a variance value for each macroblock. The calculated variance value for each macroblock is referred to as act. The variance value act is a value obtained by adding 1 to the minimum value of the variance values of four blocks in the luminance signal in the macroblock. The formula for calculating the dispersion value act is shown in the following (formula 6).

  Here, Pj is a luminance pixel value in the block. P_avg is an average value of the luminance pixel values in the block. MIN_block0to3 indicates that the minimum value is selected from the dispersion values of four blocks.

Next, the calculated variance act is stored in the feature amount memory 2 for M frames simultaneously with the maximum value md of the inter-pixel difference (step S31).
Next, in the same manner as in steps S12 and S13 described above, after the filter control value ε is calculated, filter processing is executed on the input video signal (input image) using this filter control value ε, and the frame Accumulate in the memory 7 (steps S32 and S33).

Next, the k filter controller 13 uses the variance act for each macroblock accumulated in the feature amount memory 2 to obtain the filter coefficient Ka obtained by the coefficient calculator 3 and the accumulated coefficient memory 12 in the coefficient memory 12. A filter control value k is calculated from the filter coefficient ke (step S33).
Next, the calculated filter control value k is compared with a predetermined value KE, and if the filter control value k is smaller than the predetermined value KE, the processes of steps S32 and S33 are executed, Otherwise, the filter processing by the k filter 5 is executed with the calculated filter control value k and stored in the frame memory 7 (step S34).

Here, an example of processing in the ε filter controller 14 will be described with reference to the flowchart of FIG. 8.
First, the filter control value k from the k filter controller 13 is input (step S50). Next, the input filter control value k is compared with a predetermined value KE (step S51). If the input filter coefficient ke is smaller than the predetermined value KE, the ε filter 4 is turned off ( OFF) (step S51). On the other hand, if the input filter control value k is equal to or greater than a predetermined value KE, the filter control value ε is calculated (step S53) and the ε filter 4 is turned on (ON), as in steps S12 and S32. (Step S54).

Next, an example of processing in the k filter controller 13 will be described with reference to the flowchart of FIG.
First, an average value actm (hereinafter abbreviated as M frame average variance) of the variance values in the macroblocks at the same position in the M frame is calculated from the variance values act for each macroblock stored in the feature amount memory 2. A filter coefficient ka is calculated (step S60).
FIG. 10 is a graph showing an example of the relationship between the M frame average variance actm and the filter coefficient ka. In FIG. 10, “actA” in the graph is the minimum value of the actm of the variance, and is a value that the curve is asymptotic.
When the M frame average variance actm is greater than or equal to actA, the filter coefficient ka decreases.

Next, the filter coefficient ke accumulated from the coefficient memory 12 is input (step S61). At this time, an average value kem of macroblocks at the same position in the M frame (hereinafter, abbreviated as M frame average filter coefficient) is calculated from the filter coefficient ke.
Next, using the calculated M frame average filter coefficient kem and the filter coefficient ka obtained from the coefficient calculator 3, a filter control value k is calculated by the following (Expression 7) (step S62).
k = (XA × ka + XE × Kem) / (XA + XE) (7 formulas)
Here, XA is a weighting constant for the filter coefficient Ka, and XE is a weighting constant for the filter coefficient Ke.

Next, the filter control value k is compared with a predetermined value KE (step S63). If the filter control value k is equal to or greater than the predetermined value KE, the k filter 5 is turned off. (Step S64). On the other hand, if the filter control value k is smaller than the predetermined value KE, the filter control value k is output and the k filter 5 is turned on (step S65).
Based on the control signal from the k filter controller 13, the selector 6 selects the signal from the ε filter 4 or the k filter 5 and outputs it to the frame memory 7.

As described above, in the present embodiment, as the feature amount of the moving image, the variance and the difference between adjacent pixels are measured, the filter coefficient Ke is calculated from the buffer pointer and the quantization scale, and the filter coefficient ke and the variance value are calculated. Since the filter control value k is calculated from the above and the band limitation is performed by the k filter 5 immediately before encoding using the calculated filter control value k, the generated code is prevented while preventing the deterioration of the visual image quality. The amount can be easily and suitably controlled.
Also, as a filter immediately before encoding, an ε filter 4 that performs filter processing for protecting and smoothing the edge of an image, and filter processing for suppressing encoding distortion and avoiding a buffer failure k Two types of filters 5 are provided, the input image is divided into two areas, the noise of the flat portion is removed by the ε filter 4 for a certain area, and the band is limited by the k filter 5 for another area. As a result, it is possible to control the amount of generated codes suitably with a small load while preventing a decrease in visual image quality in the entire image.
In addition, since a plurality of frames stored in the memory are subjected to the same strength filtering process, there is no sudden change in the band limitation of the image, and the deterioration of the visual image quality can be further prevented. it can.
Further, since the filtering process and the encoding process can be performed separately by the arbitration of the memory, the two processes can be operated in parallel.

In this embodiment, the variance value act is obtained using (Equation 6) as the image feature amount based on the variance value in the block. However, the image feature amount is obtained by a formula other than this. It doesn't matter.
In addition, a two-dimensional k filter as shown in (Expression 3) is used as the band limiting filter, but another type of filter may be used. At this time, if there are a plurality of coefficients for controlling the band of the filter, a table in which a combination of a plurality of coefficients is defined for k in this embodiment may be prepared and used.

Further, when the filter coefficient is obtained from the buffer pointer, the effect of the filter is set to ½ or less of the buffer size, but other values may be used.
Further, the relational expression for calculating the filter coefficient may be an expression other than the expression described in the present embodiment. A simple proportional expression may be used for easier implementation.
Furthermore, for simplification of processing, either one of the two types of filters may be fixedly handled. For example, the threshold value of the ε filter 4 may be a fixed value. In that case, only the variance is measured as the feature quantity.
Further, although the cycle for switching the filters is set to the macro block unit, other units may be used.

(Second Embodiment)
The image coding apparatus in the first embodiment described above can be realized using a computer as shown in FIG.
In FIG. 11, reference numeral 1000 denotes a central processing unit (CPU) that controls the entire computer and performs various processes. Reference numeral 1001 denotes an operating system (OS), software, data, and storage area required for control of the computer. Is a memory that provides The memory 1001 is also used as a work area when the CPU 1000 performs various processes.

A bus 1002 connects various devices and exchanges data and control signals. Reference numeral 1003 denotes a storage device (recording medium) that stores various types of software. Reference numeral 1004 denotes a storage device (recording medium) that accumulates moving image data. Reference numeral 1005 denotes a monitor that displays images and system messages from the computer.
A communication interface 1007 transmits encoded data to the communication circuit 1008, and is connected to a LAN, a public line, a wireless line, a broadcast wave, and the like outside the apparatus. Reference numeral 1006 denotes a terminal for starting up the computer and setting various conditions such as a bit rate.

  The memory 1001 stores an OS for controlling the entire computer and operating various software and software to be operated, an area for reading image data for encoding, and temporarily stores code data. There is a working area for storing a code area to be used, parameters for various operations, and the like.

  In the computer having such a configuration, prior to processing, based on the operation of the terminal 1006 by the user, the moving image data to be encoded is selected from the moving image data stored in the storage device 1004 and the computer is instructed to start. The Then, the software stored in the storage device 1003 is expanded in the memory 1001 via the bus 1002, and the software is activated.

Then, in the encoding operation of the moving image data stored in the storage device 1004 by the CPU 1000, the program code (the above-described software) according to the flowcharts shown in FIGS. 2 to 4 and FIGS. 7 to 9 is executed. become.
As described above, the computer according to the present embodiment functions as a device that implements the image coding device according to the first embodiment.

(Other embodiments of the present invention)
Software program code for realizing the functions of the above-described embodiment for a computer in an apparatus or a system connected to the various devices so as to operate the various devices to realize the functions of the above-described embodiments. Are implemented by operating the various devices in accordance with a program stored in a computer (CPU or MPU) of the system or apparatus.

  In this case, the program code of the software itself realizes the functions of the above-described embodiments, and the program code itself and means for supplying the program code to the computer, for example, the program code The stored recording medium constitutes the present invention. As a recording medium for storing the program code, for example, a flexible disk, a hard disk, an optical disk, a magneto-optical disk, a CD-ROM, a magnetic tape, a nonvolatile memory card, a ROM, or the like can be used.

  Further, by executing the program code supplied by the computer, not only the functions of the above-described embodiments are realized, but also the OS (operating system) or other application software in which the program code is running on the computer, etc. It goes without saying that the program code is also included in the embodiment of the present invention even when the functions of the above-described embodiment are realized in cooperation with the embodiment.

  Further, after the supplied program code is stored in the memory provided in the function expansion board of the computer or the function expansion unit connected to the computer, the CPU provided in the function expansion board or function expansion unit based on the instruction of the program code Needless to say, the present invention also includes a case where the functions of the above-described embodiment are realized by performing part or all of the actual processing.

1 is a block diagram illustrating an example of a configuration of an image encoding device according to a first embodiment of this invention. FIG. 5 is a flowchart illustrating an example of an operation of the image encoding device when performing the first frame filtering process according to the first embodiment of this invention. It is a flowchart which shows the 1st Embodiment of this invention and demonstrates an example of operation | movement of the image coding apparatus at the time of performing the encoding process at the time of steady state. It is a flowchart which shows the 1st Embodiment of this invention and demonstrates an example of operation | movement of the image coding apparatus at the time of calculating | requiring the filter coefficient ke. It is the figure which showed the 1st Embodiment of this invention and graphed and showed an example of the relationship between the quantization scale QP and the filter coefficient kq. It is the figure which showed the 1st Embodiment of this invention and graphed and showed an example of the relationship between buffer pointer DBP and filter coefficient kb. 5 is a flowchart illustrating an example of the operation of the image encoding device when performing steady frame filter processing according to the first embodiment of this invention. It is a flowchart which shows the 1st Embodiment of this invention and demonstrates an example in the epsilon filter controller. It is a flowchart which shows the 1st Embodiment of this invention and demonstrates an example in the k filter controller. FIG. 5 is a diagram illustrating an example of a relationship between an M frame average variance actm and a filter coefficient ka according to the first embodiment of this invention. It is the block diagram which showed the 2nd Embodiment of this invention and showed an example of the structure of the computer system which implement | achieves an image coding apparatus. It is the block diagram which showed the prior art and showed an example of the structure of the conventional moving image encoder. It is the figure which showed the prior art and showed an example of the encoding picture structure.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Feature amount measuring device 2 Feature amount memory 3, 11 Coefficient calculator 4 ε filter 5 k filter 6 Selector 7 Frame memory 8 Encoder 9 Buffer 10 Code amount controller 12 Coefficient memory 13 k filter controller 14 ε filter controller 1000 CPU
1001 Memory 1002 Bus 1003, 1004 Storage device (recording medium)
1005 Monitor 1006 Terminal 1007 Communication I / F

Claims (7)

First preprocessing means for performing band limitation of the input moving image data according to the feature amount of the input moving image data and the code amount of the moving image data encoded in the past;
Second pre-processing means for protecting edges of the inputted moving image data and smoothing the inputted moving image data based on the feature amount of the inputted moving image data;
A selection unit that selects one of the first preprocessing unit and the second preprocessing unit according to the code amount and the feature amount of the input moving image data;
An image encoding apparatus comprising: encoding means for encoding moving image data output from the preprocessing means selected by the selection means. Feature quantity measuring means for measuring the feature quantity of the input moving image data for each region;
First filter coefficient calculation means for calculating a first filter coefficient using the feature quantity measured by the feature quantity measurement means;
Second filter coefficient calculation means for calculating a second filter coefficient using the control parameter used when the moving image data is encoded by the encoding means and the code amount;
Using the first filter coefficient calculated by the first filter coefficient calculating means and the second filter coefficient, a first control value for controlling the first preprocessing means is calculated. First control value calculating means;
A second control value for controlling the second pre-processing means is calculated using the first control value calculated by the first control value calculating means and the feature amount. Control value calculation means,
The first pre-processing unit performs band limitation on the input moving image data using the first control value calculated by the first control value calculation unit,
The second pre-processing means protects an edge of the inputted moving image data using the second control value calculated by the second control value calculating means, and the inputted moving image data. Smoothes
The selection unit selects one of the first preprocessing unit and the second preprocessing unit by using the first control value calculated by the first control value calculation unit. The image encoding device according to claim 1. The feature amount measuring unit divides the input moving image data in an area equivalent to a unit encoded by the encoding unit, and distributes the input moving image data for each of the divided regions. A dispersion value measuring means for measuring a value;
The image coding apparatus according to claim 2, further comprising a difference value measuring unit that measures a difference value between adjacent pixels of the input moving image data for each of the divided regions. The first preprocessing means band-limits the spatial frequency of the input moving image data in a two-dimensional space,
The image coding apparatus according to claim 2 or 3, wherein the second preprocessing means smoothes only a flat portion of the input moving image data.   The second filter coefficient calculation unit includes a filter coefficient calculated using a quantization scale used when the moving image data is encoded by the encoding unit, and a filter coefficient calculated using the code amount. The image encoding apparatus according to claim 2, wherein the second filter coefficient is obtained based on the comparison result. A first preprocessing step for performing band limitation of the input moving image data in accordance with a feature amount of the input moving image data and a code amount of the moving image data encoded in the past;
A second pre-processing step for protecting an edge of the input moving image data and smoothing the input moving image data according to a feature amount of the input moving image data;
A selection step of selecting one of the first preprocessing unit and the second preprocessing unit based on the code amount and the feature amount of the input moving image data;
An image encoding method comprising: an encoding step for encoding moving image data preprocessed by the preprocessing step selected in the selection step.   A computer program for causing a computer to execute the steps according to claim 6.

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