JP3901154B2 - Program, information storage medium, data compression system, and computer control method - Google Patents

Description

  The present invention relates to a program, an information storage medium, a data compression system, and a computer control method.

  Conventionally, data compression is performed by key frame interpolation in which data to be key frames (key data) is selected from sampling data and stored, and during reproduction, the key frames are interpolated with a spline function. In this way, the amount of stored data can be reduced as compared with the case where all the sampling data is solid data.

  Here, in order to increase the accuracy in reproducing the sampling data from the key frame data, it is important to select which point of the sampling data as the data to be the key frame.

  However, there is no fixed method for selecting the key frame data for improving the approximation accuracy, and it has been done manually by trial and error, which takes time and increases the cost.

Therefore, the present inventor has developed a method for automatically selecting key data with high approximation accuracy.
JP 2000-106529 A

  The above patent document discloses a method of selecting key frame data by a difference quotient, and according to the above method, key frame selection can be automated.

  However, when the data contains noise or has discontinuity, the differentiation and difference quotient have the property of amplifying the noise and discontinuity. For example, since the data acquired by motion capture or the like actually includes noise, when such data is used as sampling data, there is a problem that the key frame is lost in the above method.

  The present invention has been made in view of the problems as described above. The object of the present invention is to control a program, an information storage medium, a data compression system, and a computer that can automate the selection of key data and are noise-resistant. Is to provide a method.

(1) The present invention is a program for selecting key data from a plurality of sampling data y _i .
Interpolation function computing means for obtaining information of an interpolation function S _i (x) for interpolating between sampling data y _i and y _{i + 1} .
Difference parameter calculation means for obtaining a difference parameter k _i corresponding to the sampling data y _i based on the interpolation function S _i (x);
Based on the difference parameter k _i corresponding to y _i, and the key data selection means for selecting key data to determine whether to select the y _i as the key data,
And making the computer function.

  The present invention also relates to a data compression system including the above means. The present invention also relates to a computer-readable information storage medium that stores (records) a program that causes a computer to function as each of the above-described means.

Here, the sampling data y _i (i = 0, 1, 2,...) Is discrete data. For example, y _i may be sampling data at time t _i , or may be sampling data related to other factors such as position.

  Key data is data that does not spread when thinned data compression is performed. When restoring compressed data, the data thinned using interpolation curve information, etc. is restored based on the key data. To do.

  For example, the sampling data may be data acquired by a motion capture system. In this case, the key data is key frame data.

According to the present invention, an interpolation function S _i (x) between y _i and y _{i + 1} is obtained by considering an interpolation function between solid sampling data (a section without data originally), and S _i (x ) To obtain a difference parameter k _i corresponding to y _i . Then, based on the difference parameter k _i corresponding to y _i , it is possible to select key data by determining whether or not y _i is selected as key data, so that the operation of selecting key data from sampling data is automated. Can do.

(2) The difference parameter calculation means of the present invention comprises:
The difference parameter k _i is obtained based on the value of the coefficient of the interpolation function S _i (x).

For example, when the interpolation function is given as an n-order spline function, the interpolation function is given by S _i (x) = a _ni (x−x _i ) ⁿ +... + A _1i (x−x _i ) + a _0i. The difference parameter k _i may be obtained based on the next coefficient a _ni .

(3) The difference parameter calculation means of the present invention comprises:
y first from _i-1 for interpolating between y _i 1 of the interpolation function S _i-1 and (x), y _i and y _{i + 1} second for interpolating between interpolation function S _i ( The difference parameter k _i corresponding to the sampling data y _i is obtained based on x).

According to the present invention, an interpolation function is considered between solid sampling data (originally no data section), and the first interpolation function S _i (x) before and after y _i and the second S _{i + 1.} Based on (x), a difference parameter k _i corresponding to y _i is obtained. Then, based on the difference parameter k _i corresponding to y _i , it is possible to select key data by determining whether or not y _i is selected as key data, so that the operation of selecting key data from sampling data is automated. Can do.

(4) The difference parameter calculation means of the present invention comprises:
A difference function F _i (x) is set based on the first interpolation function S _i −1 (x) and the second interpolation function S _i (x), and the difference parameter k _i is set based on the difference function F _i (x). It is characterized by seeking.

In this case, the difference function F _i (x) may be set based on the difference between the first interpolation function S _i −1 (x) and the second interpolation function S _i (x). It may be set as a function.

(5) The difference parameter calculation means of the present invention comprises:
The difference function F _i (x) is set as a function given as a difference between the first interpolation function S _i −1 (x) and the second interpolation function S _i (x), and the difference function F _i (x ) To obtain the difference parameter k _i based on the value of the coefficient.

For example, in the case of an nth-order spline function, the difference function is given by F _i (x) = l _i (x−x _i ) ⁿ , so the difference parameter k _i may be obtained based on l _i .

(6) The difference parameter calculation means of the present invention comprises:
The difference function F _i (x) is set as a function given as a difference between the first interpolation function S _i −1 (x) and the second interpolation function S _i (x), and the difference function F _i (x ), And a difference parameter k _i is obtained based on the obtained integral value.

For example, the difference parameter k _i may be obtained based on the area of the region determined by the function S _i (x) and the function S _{i + 1} (x) in a small section determined by x _i and x _{i + 1} .

In this case, the difference function F _i (x) may be set based on the difference between the first interpolation function S _i −1 (x) and the second interpolation function S _i (x). It may be set as a function.

(7) The key data selection means of the present invention comprises:
Based on the difference parameter, determine the threshold,
The difference parameter k _i is compared with the threshold value, and sampling data serving as key data is selected based on the comparison result.

(8) The key data selection means of the present invention comprises:
It is compared with a predetermined threshold value and the difference parameter k _i, and selects the sampling data to be the key data based on the comparison result.

(9) The present invention is characterized in that each interpolation function S _i (x) is set by a spline function.

  In practice, it is often a cubic spline function.

  (10) The present invention is a computer-readable information storage medium characterized by storing any of the above programs.

(11) The present invention is a data compression system for selecting key data from a plurality of sampling data y _i (i = 0, 1, 2,...)
An interpolation function computing means for obtaining information on an interpolation function S _i (x) for interpolating between the sampling data y _i ;
difference parameter calculation means for obtaining a difference parameter k _i corresponding to the sampling data y _i based on an interpolation function S _i (x) for interpolating between y _i and y _{i + 1} ;
Based on the difference parameter k _i corresponding to y _i, and the key data selection means for selecting key data to determine whether to select the y _i as the key data,
It is characterized by including.

(12) The data compression system of the present invention
The difference parameter calculation means is
y first from _i-1 for interpolating between y _i 1 of the interpolation function S _i-1 and (x), y _i and y _{i + 1} second for interpolating between interpolation function S _i ( The difference parameter k _i corresponding to the sampling data y _i is obtained based on x).

(13) The present invention is a computer control method for causing a computer to execute processing for selecting key data from among a plurality of sampling data y _i (i = 0, 1, 2,...)
An interpolation function calculation step for obtaining information of an interpolation function S _i (x) for interpolating between each data of the sampling data y _i ;
a difference parameter calculation step for obtaining a difference parameter k _i corresponding to the sampling data y _i based on an interpolation function S _i (x) for interpolating between y _i and y _{i + 1} ;
Based on the difference parameter k _i corresponding to y _i, and the key data selection step of selecting key data to determine whether to select the y _i as the key data,
It is characterized by including.

(14) A computer control method according to the present invention includes:
The difference parameter step comprises:
y first from _i-1 for interpolating between y _i 1 of the interpolation function S _i-1 and (x), y _i and y _{i + 1} second for interpolating between interpolation function S _i ( The difference parameter k _i corresponding to the sampling data y _i is obtained based on x).

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

  In addition, this embodiment demonstrated below does not limit the content of this invention described in the claim at all. Further, not all of the configurations described in the present embodiment are essential as a solution means of the present invention.

  FIG. 1 shows discrete data (sampling data) sampled at a predetermined interval.

  Here, the case where the sampling data is data such as the rotation angle of the joint sampled every 1/60 seconds by motion capture or the like as motion data will be described as an example.

y ₀ , y ₁ , y ₂ ,... are sampling data (motion data) acquired at time t (t = x ₀ , x ₂ , x ₃ ,...).

Here, since all the data y ₀ , y ₁ , y ₂ ,... Are stored as solid motion data, the amount of data becomes enormous, so only key frame data and interpolation function information is stored as compressed data. Let Based on the key frame data and the interpolation function, the motion can be reproduced by restoring the data between the key frames.

  In the present embodiment, such key frame data can be automatically selected by the method described below.

First, information on interpolation functions S ₀ (x), S ₁ (x), S ₂ (x),... For interpolating between each data of solid data y ₀ , y ₁ , y ₂ ,. Ask for.

S _i (x) is an interpolation function in a small section from the frame x _i to the next frame x _{i + 1} .

Based on the interpolation function S _i (x), a difference parameter k _i corresponding to the sampling data y _i is obtained.

  For example, when the interpolation function is a cubic spline function, the interpolation function is given by the following expression.

S _i (t) = a _i (x−x _i ) ³ + b _i (x−x _i ) ² + c _i (x−x _i ) + d _i
Then determine the interpolation function in small sections all, as its a _i value difference parameter k _i corresponding to y _i, based on the difference parameter k _i, also determine whether to select the y _i as the key data Good.

  2A and 2B are diagrams for explaining the difference function of the present embodiment.

As shown in FIG. 2A, the section [x _i−1 , x _i ) is T _i −1 and the section [x _i , x _{i + 1} ) is T _i . And in the interval T _i over _1, y _i-1, a function for interpolating the _{y i S i-1 (x} ), in the interval T _i, y _i, a function for interpolating the y i _{+ 1} S Let _i (x).

FIG. 2B is a diagram for explaining the relationship between the interpolation function S _i-1 (x) and the interpolation function S _i (x) in the section T _i .

In this embodiment, consider the trajectory 10 in the interval T _i of the interpolation function S _i-1 (x) in the interval T _i-1. Consider the locus 30 in the section T _i of the interpolation function S _i (x) in the section T _i . Here, the locus 30 (interpolation function S _i in the interval T _i (x)) is added a predetermined difference function F _i (locus 20) in the locus 10 (interpolated in the interval T _i function S _i-1 (x)) If it is obtained, the following formula is established.

S _i (x) −S _i−1 (x) = F _i (x)
In the present embodiment, the difference parameter k _i can also be determined based on the difference function F _i (x). Then, based on the difference parameter k _i , it may be determined whether to select y _i as key frame data.

For example, the difference parameter may be obtained based on the value of the coefficient of the difference function F _i (x) that is the difference between the first interpolation function S _i −1 (x) and the second interpolation function s _i (x). .

  A case where an m-order spline function is used as an interpolation function between sampling data will be described as an example.

Here, the m-th order spline function is an m-order polynomial defined separately on the small interval [x _j , x _{j + 1} ), j = 0,. It is a “piecewise” analytic function (polynomial) that is connected together so that the values of the differential coefficients match.

FIG. 3 shows cubic spline functions S _i and S _{i + 1} having only one node (x _j , y _j ).

Cubic spline function S is on both sides of the equinox x _j, expressed in each separate cubic polynomial s _j-1, s _j, the node (x _j, y _j) on points, twice continuously differentiable is a (second derivative is also referred to as an idiom .C ² class in the sense of continuity).

  Here, the following formula is established from the definition of the spline function.

  From this, the following equation holds.

Here, c _j is an appropriate constant.

In the present embodiment, the corresponding c _i is calculated for each section Ti (section [x _i−1 , x _i ), i = 0, 1, 2,...), And this is used as a difference parameter to obtain sampling data. It is determined whether or not y _i is selected as key frame data.

  4A and 4B are diagrams for explaining an example of key frame data extraction based on the difference parameter in the present embodiment.

4A is a table of a _i corresponding to the sampling data y _{i at} each point i, and FIG. 4B is a graph of a _i corresponding to the sampling data y _{i at} each point i.

a _i (i = 2, 3, 4,...) is S _i (t) = a _i (x−x _i ) in the section T _i (i = 2, 3, 4,...). ³ + b _i (x−x _i ) ² + c _i (x−x _i ) + d _i is the coefficient of the interpolation function (x−x _i ) ³ given by

In this embodiment, it is considered that the greater the value | a _i |, the greater the contribution (the value to be selected as a key frame is greater), and whether or not y _i corresponding to | a _i | To do.

A threshold value ε may be determined based on the difference parameter a _i , the difference parameter a _i may be compared with the threshold value ε, and sampling data serving as a key frame may be selected based on the comparison result.

For example, the threshold value ε may be determined by averaging a _i and multiplying by a predetermined coefficient.

Here, if the set threshold value _{ε = ε 1 (ε 1 =} 0.1) and is, for example, _{| a i | ≧ | ε 1} | and extracts a _i made, corresponding yi key frame data You may make it. In this case, a ₁ , a ₇ , a ₈ , a ₉ , a ₁₀ , a ₁₁ , a ₁₂ , a ₁₄ , a ₁₅ , a ₁₆ are extracted, and the corresponding sampling data y ₁ , y ₇ , y ₈ are extracted. , Y ₉ , y ₁₀ , y ₁₁ , y ₁₂ , y ₁₄ , y ₁₅ , y ₁₆ are selected as key frame data.

Also in case of setting the threshold _{ε = ε 2 (ε 2 =} 0.2) and is, for example, _{| a i | ≧ | ε 2} | and formed by extracting a _i, the corresponding y _i key frame data You may make it. In this case, a ₇ , a ₈ , a ₉ , a ₁₀ , a ₁₁ , a ₁₅ , a ₁₆ are extracted, and the corresponding sampling data y ₇ , y ₈ , y ₉ , y ₁₀ , y ₁₁ , y ₁₅ are extracted. , y ₁₆ is selected as a key frame data.

Instead of determining the threshold value using the value of a _i , a predetermined value prepared in advance may be used.

  FIG. 5 is a diagram for explaining another example of the difference parameter according to the present embodiment.

From time x _i and time x _{i + 1} interval T function at _i s _i (x) function s _i-1 may be obtained difference parameter based on the area M _i of area determined in (x). Here, the area M _i is the area of the region surrounded by the function s _i (x), the function s _i-1 (x), and the function x = x _{i + 1} (if the times are unequal intervals, some normalization is performed). ).

Thus, for each sampling data y _i , the area M _i surrounded by the function s _i (x), the function s _i-1 (x), and x = x _{i + 1} is calculated, and the area M _i is used as a difference parameter to calculate the area. The corresponding y _i when M _i satisfies a predetermined condition may be selected as key frame data.

  The present invention is realized as a sampling data compression device or the like by a program on a computer system.

  The present invention will be described in detail when motion caption data is used as an example of sampling data.

  FIG. 6 is a configuration example of a system that collects motion caption data and compresses the data.

  6, the system includes a processing unit 110, a storage unit 120, an information storage medium 130, a display unit 140, an input unit 150, a communication unit 160, a motion data acquisition unit 170, and the like.

  The storage unit 120 serves as a work area such as the processing unit 110 and the communication unit 160, and its function can be realized by hardware such as a RAM.

  The information storage medium 130 (computer-readable medium) stores programs, data, and the like, and functions as an optical disk (CD, DVD), a magneto-optical disk (MO), a magnetic disk, a hard disk, and a magnetic tape. Alternatively, it can be realized by hardware such as a memory (ROM).

  The processing unit 100 performs various processes of the present embodiment based on a program (data) stored in the information storage medium 130. That is, the information storage medium 130 stores a program for causing a computer to function as each unit of the present embodiment (a program for causing a computer to execute processing of each unit).

  The display unit 140 outputs an image generated according to the present embodiment, and its function can be realized by hardware such as a CRT, LCD, touch panel display, or HMD (head mounted display).

  The communication unit 160 performs various controls for communicating with the outside (for example, a host device or other game system), and functions thereof include hardware such as various processors or communication ASICs, It can be realized by a program.

  A program (data) for causing a computer to function as each unit of the present embodiment is distributed from the information storage medium of the host device (server) to the information storage medium 130 (storage unit 120) via the network and communication unit 160. You may do it. Use of the information storage medium of such a host device (server) can also be included in the scope of the present invention.

  The processing unit 100 (processor) performs various processes based on input data from the input unit 150, a program, and the like. The processing unit 100 performs various processes using the storage unit 120 as a work area. The function of the processing unit 100 can be realized by hardware such as various processors (CPU, DSP, etc.), ASIC (gate array, etc.), and a program (game program).

In the processing unit 100, a program for selecting key data from the plurality of sampling data y _i is executed, and an interpolation function S _i (x for interpolating between the sampling data y _i and y _{i + 1} data). Interpolation function calculating means for obtaining information on)
Difference parameter calculation means for obtaining a difference parameter k _i corresponding to the sampling data y _i based on the interpolation function S _i (x);
Based on the difference parameter k _i corresponding to y _i , it functions as key data selection means for determining whether to select y _i as key data and selecting key data.

Here, the difference parameter k _i may be obtained based on the coefficient value of the interpolation function S _i (x).

The basis of y _i-1 interpolation function to interpolate between y _i S _i-1 and (x), the y _i and y _{i + 1} interpolation function to interpolate between the S _i (x), A difference parameter k _i corresponding to the sampling data y _i may be obtained.

Further, the difference parameter k _i is obtained based on the value of the coefficient of the difference function F _i (x), which is the difference between the first interpolation function S _i −1 (x) and the second interpolation function S _i (x). Also good.

Further, a threshold value may be determined based on the difference parameter, the difference parameter k _i may be compared with the threshold value, and sampling data serving as key data may be selected based on the comparison result.

Also by comparing the predetermined threshold with the difference parameter k _i, may be selected sampling data as the key data based on the comparison result.

Further, the difference parameter k _i may be obtained based on the area of the region determined by the function s _i (x) and the function s _{i + 1} (x) in a small section determined by x _i and x _{i + 1} .

  The motion data acquisition unit 170 uses, for example, a motion capture system that is a system for collecting data representing human motion.

  FIG. 7 is a flowchart for explaining the flow of processing of the present embodiment.

  First, the system 100 collects motion data from the motion data acquisition unit 170 and stores it in the storage unit 120 or the like (step S10). The motion data acquired by the motion data acquisition unit 170 via a motion capture system or the like is, for example, the actual movement of each part of the human face, shoulder, collarbone, chest, arm, hand, waist, thigh, knee, and foot. Are collected as a three-axis rotational movement with respect to the joint by a sensor or the like attached to a human, and the whole movement is collected as the center x, y, z coordinates. When the movement of each part is determined by the rotational movement of the joint based on the center coordinates and the connection relation of each joint, the entire movement can be reproduced. These motion data are sampled as motion data every 1/30 seconds or 1/60 seconds, for example, and become sampling data of this embodiment. If data of a large number of parts is collected for a long time in this way, the total amount of data is large.

Next, an interpolation function S _i for interpolating between the collected motion data y _i (sampling data) is obtained (step S20). Here, the interpolation function S _i may be given as a cubic spline function.

Next, a difference parameter k _i corresponding to each motion data y _i is obtained based on the coefficient of the interpolation function S _i (step S30). When the interpolation function S _i is given as a cubic spline function, S _i (t) = a _i (x−x _i ) ³ + b _i (x−x _i ) ² + c _i (x−x _i ) + d _i Therefore, a _i which is a coefficient of (x−x _i ) ³ may be used as the difference parameter k _i .

Next, a threshold value ε is set based on the difference parameter k _i (step S40).

  Next, the first difference parameter is set (step S50). The difference parameter is compared with the threshold value ε (step S70), and the motion data corresponding to the difference parameter that is larger than the threshold value ε is set as key frame data (step S80). This is sequentially performed until there is no difference parameter (step S90). The key frame data determination process is performed independently for each part and each coordinate.

  According to the present embodiment, the key frame data can be automatically selected from the sampling data in this way, so that it is possible to save manual labor and trial and error associated with the key frame selection.

  In addition, in order to restore the original motion data from the compressed and stored data in this way, a spline function that passes through the key data of the stored motion data is obtained, and the original sampling is performed from this spline function. The recorded data.

  The present invention is not limited to that described in the above embodiment, and various modifications can be made.

For example, in the present embodiment, the coefficient _{a i {a i} i =} 0, ··, calculated threshold from the value of n, taking the case of selecting the frame having the threshold value or more a _i Examples Although explained, it is not limited to this.

For example, {a _i } i = 0,..., N subsets {a _i } i = 0,..., M are determined, an error from the original data is obtained, and repeated until the error is minimized (minimum). Update the subset. Here, the error is updated in the direction of decreasing the predetermined error function by repeatedly updating the subset {a _i } i = 0,..., M of the coefficients {a _i } i = 0,. It is configured to settle in an equilibrium state expressing the solution. At this time, well-known techniques such as a neural network, a simulated annealing method in a Boltzmann machine, or a genetic algorithm can be used.

  For example, the following error function can be used.

It shows discrete data (sampling data) sampled at a predetermined interval. 2A and 2B are diagrams for explaining the difference function of the present embodiment. FIG. 3 shows cubic spline functions S _i and S _{i + 1} having only one node (x _j , y _j ). 4A and 4B are diagrams for explaining an example of key frame data extraction based on the difference parameter in the present embodiment. It is a figure for demonstrating the other example of the difference parameter of this Embodiment. It is a configuration example of a system that collects motion caption data and compresses the data. It is a flowchart figure for demonstrating the flow of a process of this Embodiment.

Explanation of symbols

110 processing unit 120 storage unit 130 information storage medium 140 display unit 150 input unit 160 communication unit 170 motion data acquisition unit

Claims (9)

A program for selecting key data from a plurality of sampling data y _i ,
Information for the first interpolation function S _i-1 (x) for interpolating between the sampling data y _i-1 and y _i data and for interpolating between the sampling data y _i and y _{i + 1} data Interpolation function calculating means for obtaining information of the second interpolation function S _i (x);
A difference function F _i (x) is set based on the first interpolation function S _i-1 (x) and the second interpolation function S _i (x), and sampling data y is determined based on the difference function F _i (x). difference parameter calculation means for obtaining a difference parameter k _i corresponding to _i ;
Based on the difference parameter k _i corresponding to y _i, and the key data selection means for selecting key data to determine whether to select the y _i as the key data,
A program that causes a computer to function. In claim 1,
The difference parameter calculation means includes
The difference function F _i (x) is set as a function given as a difference between the first interpolation function S _i-1 (x) and the second interpolation function S _i (x), and the difference function F _{i is set.} A program characterized in that a difference parameter k _i is obtained based on a coefficient value of (x). In claim 1,
The difference parameter calculation means includes
The difference function F _i (x) is set as a function given as a difference between the first interpolation function S _i-1 (x) and the second interpolation function S _i (x), and the difference function F _{i is set.} obtains the integrated value of (x), the program and obtains the difference parameter k _i based on the integration values obtained. In any one of Claims 1 thru | or 3,
The key data selection means includes
Based on the difference parameter, determine the threshold,
A program characterized by comparing the difference parameter k _i with the threshold value and selecting sampling data as key data based on the comparison result. In any one of Claims 1 thru | or 3,
The key data selection means includes
A program that compares a predetermined threshold value with the difference parameter k _i and selects sampling data as key data based on the comparison result. In any one of Claims 1 thru | or 5,
A program characterized in that the first interpolation function S _i-1 (x) and the second interpolation function S _i (x) are set by a spline function.   A computer-readable information storage medium, wherein the program according to any one of claims 1 to 6 is stored. A data compression system for selecting key data from a plurality of sampling data y _i ,
Information for the first interpolation function S _i-1 (x) for interpolating between the sampling data y _i-1 and y _i data and for interpolating between the sampling data y _i and y _{i + 1} data Interpolation function calculating means for obtaining information of the second interpolation function S _i (x);
A difference function F _i (x) is set based on the first interpolation function S _i-1 (x) and the second interpolation function S _i (x), and sampling data is set based on the difference function F _i (x). difference parameter calculation means for obtaining a difference parameter k _i corresponding to y _i ;
Based on the difference parameter k _i corresponding to y _i, and the key data selection means for selecting key data to determine whether to select the y _i as the key data,
A data compression system comprising: A computer control method for causing a computer having an interpolation function calculation means, a difference parameter calculation means, and a key data selection means to execute a process of selecting key data from a plurality of sampling data y _i ,
The interpolation function calculation means includes information on the _first interpolation function S _i-1 (x) for interpolating between the sampling data y _i-1 and y _i , and the sampling data y _i and y _{i + 1} . An interpolation function calculating step for obtaining information of the second interpolation function S _i (x) for interpolating between the data;
The difference parameter calculation means sets a difference function F _i (x) based on the first interpolation function S _i-1 (x) and the second interpolation function S _i (x), and the difference function F _i A difference parameter calculation step for obtaining a difference parameter k _i corresponding to the sampling data y _i based on (x);
A key data selection step in which the key data selection means determines whether to select y _i as key data based on the difference parameter k _i corresponding to y _i , and selects key data;
A computer control method comprising:

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