KR100781271B1 - Apparatus and method for focusing image - Google Patents

Abstract

Disclosed are an apparatus and method for focusing an image. The apparatus for focusing an image using a focus lens is an image focusing apparatus for focusing an image using a focus lens, comprising: a focus lens shifter for moving a focus lens at predetermined intervals, and focus of the focus lens; A focus value reader for reading a value, a start position determiner for determining and outputting a position of a focus lens having the largest focus value among the focus values as a start position, and focus values and positions of the positions before and after the start position A progress position determiner for determining and outputting the progress position by using differences between large focus values, and a control signal generator for generating the control signal according to the amount of change of the read focus values, wherein the focus lens shifter Output from the progress position determiner at the start position output from the start position determiner. Characterized in that for moving the focus lens by a predetermined interval corresponding to the control signal in the forward direction position. Therefore, the problem of encountering the local maxima is prevented in advance, and the number of focus operations is reduced compared to the prior art, thereby focusing the image at high speed while focusing the image quickly without erroneous operation due to noise.

Description

Apparatus and method for focusing image

1 is a block diagram of an embodiment of an image focusing apparatus according to the present invention.

2 is a flowchart for explaining an embodiment of an image focusing method according to the present invention.

FIG. 3 is a flowchart for explaining an embodiment of the present invention with respect to the thirtieth step shown in FIG. 2.

FIG. 4 is a graph to help understand the focusing method of the image illustrated in FIG. 2.

FIG. 5 is a flowchart for explaining an exemplary embodiment of the present invention for the thirty-second step shown in FIG. 2.

FIG. 6 is a flowchart for explaining an exemplary embodiment of the present invention for the thirty-fourth step shown in FIG. 2.

FIG. 7 is a flowchart for explaining another embodiment of the present invention with respect to the thirty-fourth step shown in FIG. 2.

FIG. 8 is a flowchart for describing an exemplary embodiment of the present invention with respect to step 110 illustrated in FIG. 7.

FIG. 9 is a graph to help understand an image focusing method according to the present invention shown in FIG. 8.

10 (a) to (d) are diagrams showing a change amount of a focus value.

FIG. 11 is a flowchart for describing an exemplary embodiment of the present invention with respect to step 112 illustrated in FIG. 7.

FIG. 12 is a graph to help understand an image focusing method according to the present invention shown in FIG. 11.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to imaging devices, such as digital cameras, camera phones, or camcorders, and more particularly, to a focusing apparatus and method for focusing an image when capturing an image having two or more focus points.

In recent years, consumer demand for digital camera expansion and double performance has been increasing. As a representative example of high performance, a camera module having the high resolution and autofocus function of the camera module may be mentioned.

In general, the camera module uses a hill-climbing algorithm of 'Bisection', 'Smart scan' or 'Full scan' when performing the auto focus operation. For example, if the focus of an image having two or more focal lengths is found using such methods, there is a problem in that a local maxima cannot be found and a desired optimal focal length cannot be found. Here, the local maxima means the second largest focus, not the global maxima, which is the largest of the two focal lengths.

It is an object of the present invention to provide an apparatus and method for focusing an image capable of quickly and accurately finding a focal point of an image having at least two focal lengths.

In order to achieve the above object, the image focusing apparatus according to the present invention for focusing an image using a focus lens, in the image focusing apparatus for focusing an image using a focus lens, moves the focus lens at predetermined intervals. A focus lens shifting unit, a focus value reading unit for reading a focus value of the focus lens, a start position determining unit for determining and outputting a position of a focus lens having the largest focus value among the focus values as a start position, and the start Generation of a control signal for generating the control signal according to the change amount of the read position and the moving position determiner for determining and outputting the traveling position using the difference between the focus values of the positions before and after the position and the largest focus value And the focus lens shifter outputs from the start position determiner again. At the beginning it is characterized in that for moving the focus lens by a predetermined interval corresponding to the control signal in the forward direction to the location output from the traveling position determining unit.

In order to achieve the above object, the image focusing method according to the present invention for focusing an image using a focus lens, the position of the focus lens showing the largest focus value among the focus values measured while moving the focus lens at equal intervals Determining as a starting position, determining a traveling position using differences between the focus values among the positions before and after the starting position and the largest focus value, and the focus in the direction of the traveling position from the starting position. And determining the optimum position of the focus lens having the highest focus value while moving the lens, and preferably reducing the amount of movement of the focus lens whenever the amount of change in the focus value before and after the focus lens shift is reduced.

Hereinafter, the configuration and operation of an embodiment of an apparatus for focusing an image according to the present invention and an embodiment of the method for focusing the image will be described below with reference to the accompanying drawings.

1 is a block diagram of an embodiment of an image focusing apparatus according to the present invention, which includes a focus lens shifter 10, a focus value reader 12, a start position determiner 14, a progress position determiner 16, and It consists of a control signal generator 18.

The focusing apparatus for an image according to the present invention illustrated in FIG. 1 focuses an image as follows using a focus lens.

The focus lens shifter 10 shown in FIG. 1 moves the focus lens at equal intervals when determining the start position. Further, the width of the focus lens to be moved is determined in accordance with the control signal input from the control signal generator 18, and the focus lens is moved from the start position to the travel position direction by dividing the focus lens twice in the determined width. That is, the focus lens shifter 10 determines the movement width indicating how much the focus lens is to be moved. To this end, the focus lens shifter 10 may include a motor / actuator for moving the focus lens.

The focus value reader 12 reads the focus value of the focus lens moved by the focus lens shifter 10, and outputs the read focus value to the start position determiner 14 and the control signal generator 18. .

The start position determiner 14 determines the position of the focus lens showing the largest focus value among the focus values input from the focus value reader 12 as a start position, and determines the determined start position as the focus lens shifter 10 and Output to the advance position determination part 16, respectively.

The advancing position determiner 16 determines the advancing position using the difference between the focus values of the position before the start position and the positions after the start position and the largest focus value inputted from the start position determiner 14, and the determined advancing. The position is output to the focus lens shifter 10.

The control signal generator 18 generates a control signal according to the change amount of the focus values read by the focus value reader 12, and outputs the generated control signal to the focus lens shifter 10. To this end, the control signal generator 18 may be implemented by the change amount calculator 20 and the change amount determiner 22. Here, the change amount calculating unit 20 calculates the change amount of the focus value from the focus value read out from the focus value reading unit 12, and outputs the calculated change amount to the change amount determining unit 22. The change amount discriminating unit 22 determines the decrease and increase of the change amount input from the change amount calculating unit 20, and outputs the determined result to the focus lens shift unit 10 as a control signal. In this case, the finally focused focus may be output through the output terminal OUT from the focus lens shifter 10.

2 is a flowchart for explaining an embodiment of an image focusing method according to an embodiment of the present invention, comprising: determining a starting position (step 30), determining a moving position (step 32), and determining an optimal position; It consists of a step (step 34).

The image focusing method according to the present invention illustrated in FIG. 2 may be performed by the apparatus for focusing an image illustrated in FIG. 1.

In the focusing method of an image according to the present invention, first, a position of a focus lens having the largest focus value among the measured focus values while moving the focus lens at the same interval is determined as a start position (step 30).

FIG. 3 is a flowchart for explaining an embodiment of the present invention with respect to the thirtieth step shown in FIG. 2, which includes obtaining focus values (step 50) and selecting a largest focus value (step 52). And determining the starting position (step 54).

4 is a graph to help understand the focusing method of the image illustrated in FIG. 2, where the horizontal axis represents the position of the focus lens, and the vertical axis represents the focus value, respectively.

Although the present invention is described with reference to FIG. 4, the present invention is not limited thereto.

The focus lens shifter 10 moves the focus lens at the same interval S1, and the focus value reader 12 moves the points x1 through which the focus lens is moved when the focus lens is moved at the same interval S1. The focus values f1 to f10 at x10 are obtained (step 50).

After the 50th step, the start position determiner 14 selects the largest focus value among the focus values obtained by the focus value readout 12 (step 52). In the case of FIG. 4, the focus value f8 is selected as the largest focus value fm among the focus values f1 to f10.

After the 52nd step, the start position determiner 14 determines the position of the focus lens showing the largest focus value as the start position, and determines the determined start position to the advance position determiner 16 and the focus lens shifter 10. Output each (step 54). In the case of Fig. 4, the position x8 of the focus lens showing the largest focus value f8 is determined as the starting position.

After the thirtieth step, the advancing position is determined using the difference between the focus value of the previous position and the largest focus value and the difference between the focus value of the rear position and the largest focus value (step 32). Here, the previous position corresponds to x7 in the case of FIG. 4 as a position ahead of the start position by the interval S1, and the rear position corresponds to x9 in the case of FIG.

FIG. 5 is a flowchart for explaining an embodiment of the present invention with respect to the thirty-second step shown in FIG. 2, wherein obtaining differences between the focus values of the before and after positions and the largest focus value (step 80). And determining the advancing position according to the magnitude of the differences (82-90 th to 90 th). Here, the 80 th through 90 th steps shown in FIG. 5 are performed in the advancing position determiner 16 shown in FIG. 1.

After the thirtieth step, the progress position determiner 16 differs between the focus value at the previous position and the largest focal value ahead of the start position input from the start position determiner 14 by the interval S1 and the distance from the start position The difference between the focus value and the largest focus value at the position after inferior by (S1) is obtained (step 80). In the case of FIG. 4, the progress position determiner 16 has a focal value f _m-1 = f7 and a largest focal value f _m = of the previous position x7 that is advanced by the interval S1 before the start position x8. The difference Δ1 is obtained from f8) as shown in the following equation.

Further, the difference as shown in the following equation 2 between the focal value f _{m + 1} = f9 and the largest focal value f _m = f8 at the position x9 after falling behind the starting position x8 by the interval S1. (Δ2) is obtained.

After step 80, it is determined whether the differences Δ1 and Δ2 are the same (step 82). If it is determined that the differences Δ1 and Δ2 are not the same, the smallest value among the differences Δ1 and Δ2 is determined. Select a value (step 84). That is, it is determined whether the difference Δ1 obtained by the focus value f7 at the front position x7 is smaller than the difference Δ2 obtained by the focus value f9 at the rear position x9 (step 84). ).

The advancing position determination unit 16 determines the position showing the focus value used when obtaining the selected small value as the advancing position (steps 86 and 88). That is, if it is determined that the difference obtained by the focus value at the previous position is smaller than the difference obtained by the focus value at the later position, the traveling position determining unit 16 determines the previous position as the traveling position (step 86). However, if it is determined that the difference obtained by the focus value at the previous position is larger than the difference obtained by the focus value at the later position, the progress position determining unit 16 determines the rear position as the progress position (step 88). In the case of FIG. 4, since the difference Δ2 is smaller than the difference Δ1, the traveling positioning unit 16 determines the rear position x9 as the traveling position.

In this way, since the location where the difference is small is a high probability that there is an optimal focus range, the progress position is determined where the difference is small.

However, when the difference obtained by the focus value at the front position is the same as the difference obtained by the focus value at the rear position, the direction in which the focus value increases with respect to the largest focus value among the front position and the rear position is increased. The position is determined as the progress position (step 90). For example, unlike in FIG. 4, if the differences Δ1 and Δ2 are equal, the front position x7 lies in the direction of decreasing focus value and the rear position x9 lies in the direction of increasing focus value. Since it lies, the rear position x9 is determined as the advancing direction. That is, which position (xi) lies in the direction of increasing focus value relative to the largest focus value or lies in the direction of decreasing focus value, is the subsequent rear position (xi +) of that position (xi)? dx) and the focal values fi + df and fi-df at the front position xi-dx preceding the position xi and the focal value fi at that position. Where dx is the increment of the position and df is the increment of the focus value. That is, in the case of the position xi in the direction of increasing the focus value with respect to the largest focus value, the focus value fi + df of the rear position xi + dx is the focus value fi of the position xi. Will be less. Also, for the position xi in the direction of decreasing focal value, the focal value fi-df of the front position xi-dx will be less than the focal value fi of the position xi.

On the other hand, after step 32, the optimum position of the focus lens that gives the highest focus value while moving the focus lens from the start position toward the travel position direction is determined (step 34). That is, in the case of FIG. 4, the optimum position is determined while moving the focus lens from the start position x8 to the travel position x9 direction. In a thirty-fourth step, whenever the amount of change in the focus value of the moving focus lens decreases, the amount of movement of the focus lens is reduced.

FIG. 6 is a flowchart for explaining an exemplary embodiment of the present invention with respect to the thirty-fourth step shown in FIG. 2, and includes a step (step 100) of determining an optimal position while moving by the same amount of movement once.

After the thirty-second step, the optimal position of the focus lens is determined while moving the focus lens once by the same amount of movement until the amount of change in the focus value decreases (step 100). If it is determined in step 32 shown in FIG. 2 that the difference obtained by the focus value at the previous position is the same as the difference obtained by the focus value at the later position, step 100 is performed after step 32. That is, when the progress position is determined by the 90th step shown in FIG. 5, the 34th step shown in FIG. 2 may be performed as shown in FIG. 6.

FIG. 7 is a flowchart for explaining another embodiment of the present invention with respect to the thirty-fourth step shown in FIG. 2, wherein the focus narrow band is determined (step 110) and the optimal position is moved once by the same amount of movement. Determining (step 112).

If the travel position is determined by the 86th or 88th steps shown in FIG. 5, the 34th step shown in FIG. 2 may be performed as shown in FIG. 7.

In the case of FIG. 7, after the thirty-second step, the focal narrow band is determined by dividing and moving the focus lens at least twice until the amount of change in the focus value decreases (step 110). Here, the focus narrow band means a narrow area near the optimum focus.

FIG. 8 is a flowchart for describing an exemplary embodiment of the present invention with respect to step 110 of FIG. 7, wherein the focus lens is moved by a first moving section and the focus value of the moved focus lens is read (130). And step 132), moving the focus lens by the second moving section and reading a focus value of the moved focus lens (steps 134 and 136), and determining whether to decrease by obtaining a change amount of the focus value ( Steps 138 and 140) and returning the position of the focus lens (step 142).

FIG. 9 is a graph to help understand the focusing method of an image according to the present invention shown in FIG. 8, where the horizontal axis represents the position of the focus lens, and the vertical axis represents the focus value, respectively.

The method shown in Fig. 8 is performed in the direction from the start position x8 to the progress position x9. This direction is shown enlarged as shown in FIG. 9 to facilitate understanding of the present invention.

The focus lens shifter 10 moves the focus lens by the first movement section S2 at the start position x8 (step 130).

After operation 130, the focus value reader 12 reads the focus value fa of the focus lens moved by the first movement section S2 (operation 132). After operation 132, the focus lens shifter 10 moves the focus lens by the second movement section S3 (operation 134). After operation 134, the focus value reader 12 reads the focus value fb at the position x11 of the focus lens moved by the second movement section S3 (operation 136).

The change amount calculating unit 20 subtracts the focus value f8 immediately before the focus lens is moved in step 130 from the focus value fb read in step 136 and uses the subtracted result as a change amount to determine the change amount 22. In step 138, the output is performed.

After the step 138, the change amount determiner 22 determines whether the change amount of the focus value decreases, and outputs the determined result to the focus lens shifter 10 as a control signal (step 140).

At this time, since it is determined that the change amount of the focus value does not decrease through the control signal, the focus lens shifter 10 performs step 130 again. In this way, the focus lens shifter 10, the focus value reader 12, the change calculator 20, and the change detector 22 repeatedly perform the above-described steps 130 to 140.

That is, since it is determined that the amount of change in the focus value does not decrease through the control signal, the focus lens shifter 10 moves the focus lens again from the position x11 by the first movement section S2 (step 130). After operation 130, the focus value reader 12 reads the focus value fc of the focus lens moved by the first movement section S2 (step 132). After operation 132, the focus lens shifter 10 moves the focus lens by the second movement section S3 (operation 134). After operation 134, the focus value reader 12 reads the focus value fd of the focus lens moved by the second movement section S3 (operation 136).

After step 136, the change amount calculator 20 subtracts the focus value fb just before the focus lens is moved in step 130 from the focus value fd read by the focus value reader 12 in step 136. In operation 138, the subtracted result is output to the change amount discriminating unit 22 as the change amount Δ3 of the focus value.

The change amount discriminating unit 22 determines whether the change amount Δ3 of the focus value calculated by the change amount calculating unit 20 decreases, and outputs the determined result to the focus lens shifting unit 10 as a control signal (140). step). Here, the negative value of the focal point value Δ3 from Equation 3 means that the amount of change in the focal value decreases. Therefore, if it is determined that the change amount of the focus value is reduced through the control signal, the focus lens shifter 10 moves the focus lens back to the position x12 before the operation 134 is performed (operation 142).

Accordingly, the second moving section S3 144, which is a section in which the focus lens is returned and moved again in step 142, is determined as the focus narrow band. It is preferable to set the above-described first moving section S2 to be shorter than the second moving section S3. For example, S3 may be four times S2. That is, S2 may be '2' and S3 may be '8'.

Meanwhile, as shown in the graph shown in FIG. 9, when finding the narrow focus band 144, the focus lens shifter 10 moves the focus lens twice.

10 (a) to (d) are diagrams showing a change amount of a focus value.

Referring to FIGS. 10A and 10B, in the graph shown in FIG. 9, regardless of whether the initial increase in the first moving section S2 is increased by the increment d1 or decreased by the increment d3, If it later increases by the increment d2 or d4 in the second moving section S3, this is considered to increase the amount of change in the focus value. Also, referring to FIGS. 10 (c) and 10 (d), in the graph shown in FIG. 9, regardless of whether the first decrease in the first moving section S2 is increased by the increment d5 or increased by the increment d7. Preferably, if the amount later decreases by the increment d6 or d8 in the second moving section S3, the amount of change in the focus value is considered to decrease.

Meanwhile, after operation 110, an optimal position of the focus lens having the highest focus value is determined while moving the focus lens once at the same interval within the focus narrow band until the amount of change in the focus value decreases (operation 112). While step 112 is performed in the focal narrow band, step 100 is only different from the start position toward the travel position, and step 100 shown in FIG. 6 is the same as step 112 shown in FIG. 7. . Hereinafter, in order to help the understanding of the present invention, it will be described based on the step 112, but the description can be equally applied to the step 100.

FIG. 11 is a flowchart for describing an exemplary embodiment of the present disclosure with respect to step 112 of FIG. 7, wherein the focus lens is moved by a third moving section and the focus value of the moved focus lens is read (160). And step 162), determining the amount of change in the focus value and determining whether it decreases by a predetermined number of times (steps 164 to 168) and moving the focus lens to an optimal position (step 170).

FIG. 12 is a graph to help understand the focusing method of an image according to the present invention shown in FIG. 11, where the horizontal axis represents the position of the focus lens, and the vertical axis represents the focus value, respectively.

The method shown in FIG. 11 is performed within the focal narrow band. In the case of the focal narrow band section, x12 to x13, this section is shown enlarged as shown in FIG. 12 for better understanding.

When it is recognized that the change amount Δ3 of the focus value decreases through the control signal input from the change amount determining unit 22, the focus lens shifter 10 moves the focus lens, which has been moved to the position x13, to the position x12 again. After returning, that is, after step 110, the focus lens shifting unit 10 moves the focus lens by the third moving section S4 at the position x12 (step 160).

After operation 160, the focus value reader 12 reads the focus value fe of the focus lens moved by the third movement section S4 (operation 162).

After operation 162, the change calculator 22 subtracts the focus value fc just before the focus lens is moved in operation 160 from the focus value fe read in operation 162, and subtracts the subtracted result from the focus value fe. The change amount is output to the change amount discriminating unit 22 (step 164).

After step 164, the change amount determiner 22 determines whether the change amount of the focus value decreases, and outputs the determined result to the focus lens shifter 10 as a control signal (step 166).

In this case, since it is determined that the change amount of the focus value does not decrease through the control signal, the focus lens shifter 10 performs step 160 again. As described above, the focus lens shifter 10, the focus value reader 12, the change calculator 20, and the change detector 22 repeatedly perform steps 160 through 166.

That is, since it is determined that the amount of change in the focus value does not decrease through the control signal, the focus lens shifter 10 moves the focus lens again from the position x14 by the third movement section S4 (step 160). After operation 160, the focus value readout unit 12 reads the focus value ff of the focus lens moved by the third movement section S4 (step 162). After step 162, the change amount calculator 20 subtracts the focus value fe just before the focus lens is moved in step 160 from the focus value ff read by the focus value reader 12 in step 162. The subtracted result is output to the change amount discriminating unit 22 as the change amount Δ4 of the focus value (step 164). After step 164, the change amount determiner 22 determines whether the change amount Δ4 of the focus value decreases, and outputs the determined result to the focus lens shifter 10 as a control signal (step 166).

Since it is determined that the change amount of the focus value does not decrease through the control signal, the focus lens shifter 10 moves the focus lens again from the position x15 by the third moving section S4 (step 160). After operation 160, the focus value readout unit 12 reads the focus value fg of the focus lens moved by the third movement section S4 (step 162). After step 162, the change amount calculator 20 subtracts the focus value ff immediately before the focus lens is moved in step 160 from the focus value fg read by the focus value reader 12 in step 162. Next, the subtracted result is output to the change amount discrimination unit 22 as the change amount Δ5 of the focus value (step 164).

The change amount discriminating unit 22 determines whether the change amount Δ5 of the focus value calculated by the change amount calculating unit 20 decreases (step 166). Here, the negative change amount Δ5 from the equation 4 means that the change amount of the focus value decreases.

Since the change amount of the focus value has decreased, the change amount discriminating unit 22 determines whether the change amount of the focus value has decreased by a predetermined number of times (step 168). For example, when the predetermined number is '2', it is determined whether the amount of change in the focus value is decreased twice. However, since the amount of change in the focus value is decreased only once, the flow proceeds to step 160.

Since it is determined through the control signal that the amount of change in the focus value does not reach the predetermined number of times, the focus lens shifting unit 10 moves the focus lens again from the position x16 by the third moving section S4 (second). 160 steps). After operation 160, the focus value reader 12 reads the focus value fh of the focus lens moved by the third movement section S4 (operation 162). After operation 162, the change amount calculator 20 subtracts the focus value fg immediately before the focus lens is moved in operation 160 from the focus value fh read by the focus value reader 12 in operation 162. Then, the subtracted result as shown in Equation 5 is outputted to the change amount discriminating unit 22 as the change amount Δ6 of the focus value (step 164).

The change amount discriminating unit 22 determines whether the change amount Δ6 of the focus value calculated by the change amount calculating unit 20 decreases (step 166). Here, since the change amount Δ6 of the focus value is negative from Equation 5, that is, the change amount of the focus value has decreased, it is determined whether the change amount of the focus value has decreased by a predetermined number of times, for example, '2' (step 168). ). Here, since the amount of change in the focus value has decreased by a predetermined number of times, the focus lens is moved to a position x15 before the focus lens is moved a predetermined number of times in step 160 (operation 170). In this case, the position of the focus lens in operation 170 corresponds to an optimal position.

As described above, the reason for determining the optimum position only when the focus value is decreased by a predetermined number of times is not determined when the amount of change in the focus value decreases only once, and to determine the optimum position accurately.

According to another embodiment of the present invention, the image focusing method shown in FIG. 11 may not provide step 168. In this case, when it is determined that the change amount of the focus value decreases, the change amount determining unit 22 outputs a control signal to the focus lens shifting unit 10.

If it is determined that the amount of change in the focus value is reduced through the control signal, the focus lens shifter 10 moves the focus lens to the position x15 before the focus lens moves in step 160 (operation 170). At this time, the position of the focus lens moved in step 170 becomes an optimal position that produces the best focus value 66, and the optimum position is output from the focus lens shifter 10 through the output terminal OUT.

The interval S2 at which the focus lens moves when determining the focus narrow band is preferably larger than the interval S4 at which the focus lens moves when determining the optimal position. That is, the third moving section S4 is preferably set shorter than the first moving section S2. For example, S4 may be set to '1'.

As described above, the apparatus and method for focusing an image according to the present invention seeks the position of the focus lens having the highest focus value from the beginning at equal intervals, thereby optimizing the wrong position 60 in the image having two or more focal lengths. Unlike the conventional method of finding by the position of, at first, the entire moving area of the focus lens is scanned at regular intervals (S1) rather than finely, and thus the starting position and the advancing position are determined. The focus lens is moved largely from the start position to the traveling position direction until the focus narrow band is found, and within the found focus narrow band, the focus lens is moved small to find the optimal position, that is, defocusing (de Move the focus lens greatly in the -focusing area, and focus the focus lens in the focusing area such as the narrow focus band. Find the optimal position without moving rapidly because, by reducing the number of focus behavior strongly malfunction while focusing on the image at a higher speed than the conventional noise has the effect that an image can be focused.

Claims (13)

In an image focusing apparatus for focusing an image using a focus lens, A focus lens shifter which moves the focus lens at a predetermined interval; A focus value reading unit configured to read a focus value of the focus lens; A start position determiner which determines and outputs a position of a focus lens having the largest focus value among the focus values as a start position; A progress position determiner configured to determine and output the progress position by using differences between the focus values of the positions before and after the start position and the largest focus value; And And a control signal generator for generating the control signal according to the change amount of the read focus values, And the focus lens shifter moves the focus lens at a predetermined interval corresponding to the control signal from a start position output from the start position determiner to a travel position direction output from the advance position determiner. . The method of claim 1, wherein the control signal generator A change amount calculator for calculating a change amount of the focus value from the read focus value; And A change amount discriminating unit for discriminating the decrease and increase of the change amount and outputting the determined result as the control signal, And the focus lens shifter determines a width to be moved in response to the control signal, and moves the focus lens in the direction from the start position to the travel position by dividing twice by the determined width. In the image focusing method of focusing an image using a focus lens, (a) determining the position of the focus lens showing the largest focus value among the measured focus values while moving the focus lens at equal intervals as a start position; (b) determining a traveling position using the differences between the focus values among the positions before and after the starting position and the largest focus value; And (c) determining an optimal position of the focus lens that produces the highest focus value while moving the focus lens from the start position toward the travel position; In the step (c), whenever the amount of change in the focus value before and after the movement of the focus lens decreases, the amount of movement of the focus lens is reduced. The method of claim 3, wherein step (a) Obtaining focus values at points where the focus lens is moved, while moving the focus lens at the same intervals; Selecting the largest focus value among the obtained focus values; And And determining the position of the focus lens showing the largest focus value as the starting position. The method of claim 3, wherein step (b) Obtaining a difference between a focus value at the previous position and the largest focus value preceding the start position by the interval and a difference between the focus value and the largest focus value at the rear position that is later than the start position by the interval; step; Selecting a smaller value of the differences; And And determining the position showing the focus value used when obtaining the selected small value as the progress position. The method of claim 5, wherein step (b) And when the differences are the same, determining, as the traveling position, a position in the direction in which the focus value increases based on the largest focus value among the front position and the back position. How to focus video. The method of claim 6, wherein step (c) And determining the optimum position of the focus lens while moving the focus lens once by the same amount of movement until the amount of change in the focus value decreases. The method of claim 3, wherein step (c) Determining a focus narrow band while moving the focus lens in at least two divisions until the amount of change in the focus value decreases; And Determining the optimum position of the focus lens while moving the focus lens once by the same amount of movement within the focus narrow band until the amount of change in the focus value decreases, And an interval at which the focus lens moves when determining the focal narrow band is greater than an interval at which the focus lens moves when determining the optimal position. 9. The method of claim 8, wherein determining the focus narrow band (c11) moving the focus lens by a first moving section; (c12) reading a focus value of the focus lens moved by the first moving section; (c13) moving the focus lens by a second movement section; (c14) reading a focus value of the focus lens moved by the second moving section; (c15) obtaining the change amount by subtracting the focus value just before the focus lens is moved in the step (c11) from the focus value read in the step (c14); (c16) determining whether the change amount decreases, and if it is determined that the change amount increases, proceeding to step (c11); And (c17) if it is determined that the amount of change decreases, moving the focus lens back to a position before the step (c13) is performed, and proceeding to determining the optimal position, And when it is determined that the change amount decreases, the second moving section moved in the step (c14) corresponds to the focal narrow band. 10. The method of claim 9, wherein the first moving section is shorter than the second moving section. 10. The method of any of claims 7 to 9, wherein determining the optimal position (c21) moving the focus lens by a third moving section; (c22) reading a focus value of the focus lens moved by the third moving section; (c23) subtracting a focus value just before the focus lens is moved in step (c21) from the focus value read in step (c22) to obtain the change amount; (c24) determining whether the change amount decreases, and if it is determined that the change amount increases, proceeding to step (c21); And (c25) if it is determined that the amount of change is reduced, moving the focus lens to the optimal position which is a position before the focus lens moves in the step (c21). The image focusing method of claim 11, wherein the third moving section is shorter than the first moving section. 12. The method of claim 11, wherein determining the optimal position If it is determined that the change amount decreases, determining whether the change amount has been decreased by a predetermined number of times; and if it is determined that the change amount has not been decreased by the predetermined number of times, further proceeding to step (c21). If it is determined that the amount of change decreases by the predetermined number of times, the focusing lens is moved to the optimum position which is a position before the focus lens moves by the predetermined number of times in step (c21). .

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