KR102154203B1 - Camera module and auto-focus method thereof - Google Patents

Abstract

A camera module according to an embodiment of the present invention includes a lens; An actuator sequentially moving the lens in a plurality of successive steps; A memory unit for storing a focus evaluation value calculated for each step in which the lens is moved; And comparing the focus evaluation values of the plurality of steps to determine a peak focus evaluation value, and determining a lens position according to a comparison of the peak focus evaluation value and the peak focus evaluation value and each of two focus evaluation values of adjacent steps. A control unit; It may include.

Description

Camera module and its auto focus method {CAMERA MODULE AND AUTO-FOCUS METHOD THEREOF}

The present invention relates to a camera module and an autofocus method thereof.

Recently, digital camera functions have been incorporated in portable small electronic devices such as mobile phones and PDAs having display means. As technologies related to lenses, image sensors, and image processing processors used in camera modules included in these portable small electronic devices have rapidly developed, advanced shooting technologies included in general digital still cameras are being applied to small camera modules. to be.

One of these functions is an auto focus function that automatically focuses on a subject to be photographed. The auto focus function calculates a focus evaluation value for an image photographing a subject at the moved position while moving the lens position in a preset step, detects a peak from the focus evaluation value, and moves the lens to the position of the detected peak. It can be done in a way.

However, in order to perform autofocus, a method of detecting an approximate peak through a first scan and a precise peak through a second scan has been used. In this case, it takes time to perform the second scan. There is a problem.

An object of the present invention is to provide a camera module capable of detecting focus in a single scan and an autofocus method thereof.

A camera module according to an embodiment of the present invention includes a lens; An actuator sequentially moving the lens in a plurality of successive steps; A memory unit for storing a focus evaluation value calculated for each step in which the lens is moved; And comparing the focus evaluation values of the plurality of steps to determine a peak focus evaluation value, and determining a lens position according to a comparison of the peak focus evaluation value and the peak focus evaluation value and each of two focus evaluation values of adjacent steps. A control unit; It may include.

The camera module and its autofocus method according to an embodiment of the present invention can quickly detect focus with a single scan.

1 is a schematic configuration diagram of a camera module according to an embodiment of the present invention.
2 is a flow chart showing an auto focus method according to the present invention.
3 and 4 are graphs showing an example of a focus evaluation value.

DETAILED DESCRIPTION OF THE INVENTION The detailed description of the present invention to be described later refers to the accompanying drawings, which illustrate specific embodiments in which the present invention may be practiced. These embodiments are described in detail sufficient to enable a person skilled in the art to practice the present invention. It is to be understood that the various embodiments of the present invention are different from each other, but need not be mutually exclusive. For example, specific shapes, structures, and characteristics described herein may be implemented in other embodiments without departing from the spirit and scope of the present invention in relation to one embodiment. In addition, it should be understood that the location or arrangement of individual components within each disclosed embodiment may be changed without departing from the spirit and scope of the present invention. Accordingly, the detailed description to be described below is not intended to be taken in a limiting sense, and the scope of the present invention, if properly described, is limited only by the appended claims, along with all scopes equivalent to those claimed by the claims. Like reference numerals in the drawings refer to the same or similar functions over several aspects.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings in order to enable those of ordinary skill in the art to easily implement the present invention.

1 is a schematic configuration diagram of a camera module according to an embodiment of the present invention.

Referring to FIG. 1, a camera module according to an embodiment of the present invention may include a lens unit 10, a signal processing unit 20, a control unit 30, and an actuator driving unit 40, and additionally, a memory unit 50 ) May be further included.

The lens unit 10 may include a lens 11, an actuator 12, an image sensor 13, a barrel 14, and a sensor substrate.

The lens 11 may form an image of a subject with the image sensor 13, and may be provided in a plurality of sheets.

The actuator 12 may provide a physical force to the lens 11 so that the lens 11 can move along the barrel 14. The actuator 12 may include one of a stepping motor, a voltage controlled actuator (VCA), and a piezo actuator. When performing autofocus, the lens 11 can move the reference distance in one step by the physical force provided from the actuator 12.

The image sensor 13 may detect light incident through the lens. The image sensor 13 may include one of a Complementary Metal Oxide Semiconductor (CMOS) sensor and a Charge Coupled Device (CCD) sensor, and may convert an image formed by the lens 11 into an electrical image signal.

The barrel 14 may provide a passage through which the lens 11 can move. The circuit board 15 may mount the image sensor 13 and transmit the image detected by the image sensor 13 to the signal processing unit 20.

The signal processor 20 may process the image detected by the image sensor 13 and calculate an auto focus evaluation value for auto focus.

The signal processing unit may include an image signal processing unit 21 and an auto focus detection processing unit 22.

The image signal processing unit 21 may perform image processing such as color processing and sharpness processing of the electrical image signal output from the image sensor 13.

The auto focus detection processing unit 22 may calculate a focus evaluation value for auto focus from the image signal transmitted from the image signal processing unit 21. The auto focus detection processing unit 22 may use a filtering value calculated by applying a high-pass filter to at least a portion of the image signal as a focus evaluation value.

The controller 30 may generate a command for moving the lens according to a control signal by the user and an auto focus evaluation value. The controller 30 may control the operation of the image sensor 13, the signal processing unit 20, and the actuator driving unit 40 according to a control signal (user input) input from the outside.

The actuator driving unit 40 may provide a physical force for moving the position of the lens 11 according to the lens movement command of the controller 30, and the memory unit 50 includes read only memory (ROM) and random access (RAM). memory), a variety of information necessary to drive the camera can be stored.

2 is a flow chart showing an auto focus method according to the present invention. Hereinafter, an autofocus method according to an embodiment of the present invention will be described in detail with reference to FIGS. 1 and 2.

The auto focus method according to an embodiment of the present invention includes the steps of sequentially moving a lens in a plurality of consecutive steps (S21); Storing a focus evaluation value calculated for each step in which the lens is moved (S22); Comparing the focus evaluation values of the plurality of steps and determining a peak focus evaluation value (S23, S24, S25); And determining a lens position according to a comparison between the peak focus evaluation value and the peak focus evaluation value and two focus evaluation values of adjacent steps (S26). It may include.

When the autofocus is started, the lens 11 moves to a preset step within the barrel 14 to obtain an image at a position corresponding to each step (S21). The lens 11 can move the reference distance in one step.

The lens 11 moves to a step set in advance by the actuator 11 while autofocus is in progress. When the autofocus is started, the lens 11 is the most moving area to be moved for autofocus. By moving to the distal end, it is possible to move from the distal end to a predetermined step. That is, the lens 11 may start step movement for auto focus from a position closest or farthest from the image sensor 13 among the moving ranges.

For each step in which the lens 11 is moved, the image sensor 13 acquires an image, and the image sensor 13 calculates a focus evaluation value using all or at least a portion of the acquired image, and stores the calculated focus evaluation value. Can be (S22).

When the lens 11 moves to a predetermined step, the image sensor 13 detects an image that passes through the lens 11 and forms an image, and the image signal processing unit 21 may image-process the detected image signal. The image output from the image signal processing unit 21 is transmitted to the autofocus detection processing unit 22, and the autofocus detection processing unit 22 calculates a focus evaluation value using all or at least a portion of the transmitted image.

The auto focus detection processor 22 may apply a filtering value obtained by applying a highpass filter to at least a portion of an image as a focus evaluation value. When a high pass filter is applied to an image signal, only edge components present in the image remain. When the focus is accurately achieved in the same image, since the contour component is further increased, a filtering value obtained by applying a high pass filter can be used as a focus evaluation value.

The focus evaluation value output by the auto focus detection processing unit 22 may be stored in real time in the memory unit 50 by the control unit 30.

The control unit 30 determines an increase or decrease in the continuous focus evaluation value stored in the memory unit 50 (S23). The control unit 30 compares the focus evaluation value stored in the current step with the focus evaluation value stored in the previous step to determine whether to increase or decrease.

In other words, when the focus evaluation value obtained at the current lens 11 position is calculated and stored by the autofocus detection processing unit 22, the control unit 30 is calculated and stored at the position of the lens 11 immediately before the current lens 11 position. It is determined whether the focus evaluation value is increased or decreased by comparing the focus evaluation value and the currently stored focus evaluation value. Subsequently, the control unit 30 determines whether a change in the increase or decrease in the focus evaluation value has occurred (S24). Specifically, the control unit 30 determines whether the focus evaluation value is changed from an increasing state to a decreasing state or from a decreasing state to an increasing state. When the increase/decrease state of the focus evaluation value is maintained, the control unit 30 continues to move the lens to a predetermined step in step S21.

Unlike the above, when the increase/decrease state of the focus evaluation value is changed, the control unit 30 determines whether the increase/decrease level of the focus evaluation value is changed by more than the critical focus evaluation value (S25). For example, when the focus evaluation value changes from an increasing state to a decreasing state, it is determined whether the reduction level of the focus evaluation value is equal to or greater than the critical focus evaluation value, and when the focus evaluation value changes from a decreasing state to an increasing state, the increase level of the focus evaluation value It is judged whether it is more than this threshold focus evaluation value.

When the increase/decrease level of the focus evaluation value is less than the critical focus evaluation value, the control unit 30 continues to move the lens to a preset step according to step S21, and when the increase/decrease level of the focus evaluation value is equal to or greater than the critical focus evaluation value, the increase/decrease state is The inverted focus evaluation value may be determined as a peak focus evaluation value.

After the peak focus evaluation value is determined, the controller 30 may determine the lens position according to the peak focus evaluation value and the comparison between the peak focus evaluation value and each of the two focus evaluation values of the adjacent step (S26).

Hereinafter, for convenience of explanation, the peak focus evaluation value and the focus evaluation value having a large level difference between the peak focus evaluation value and the two focus evaluation values adjacent to each other are referred to as a minimum focus evaluation value, and the peak focus evaluation value and the focus having a small level difference The evaluation value will be described by referring to the maximum focus evaluation value.

The controller 30 may determine a moving direction and a moving distance of the lens by comparing the level difference between the peak focus evaluation value and the maximum focus evaluation value and the level difference between the peak focus evaluation value and the minimum focus evaluation value.

In more detail, the control unit 30 moves the lens in the step direction of the maximum focus evaluation value with a small increase/decrease ratio with the peak focus evaluation value among two focus evaluation values of adjacent steps based on the step of the peak focus evaluation value. Can be determined.

In addition, the control unit 30 applies a coefficient calculated according to the relationship between the level difference between the peak focus evaluation value and the minimum focus evaluation value and the level difference between the peak focus evaluation value and the maximum focus evaluation value to the reference distance per step, The lens movement distance can be determined based on the step of the evaluation value.

For example, the coefficient may be determined according to Equation 1 below, and the moving distance may be determined according to Equation 2 below. Here, C is a coefficient, Vaf _peak is a peak focus evaluation value, Vaf _Rmax is a maximum focus evaluation value, Vaf _Rmin is a minimum focus evaluation value, D is a lens movement distance, and D _step is a reference distance per step.

3 and 4 are graphs showing an example of a focus evaluation value.

Hereinafter, a method of determining a lens movement position in an autofocus method according to an exemplary embodiment of the present invention will be described in detail with reference to FIGS. 3 and 4.

Referring to FIGS. 3 and 4, the position of the lens is moved by 14 for each step, and focus evaluation values may be obtained in the first to third steps. In FIGS. 3 and 4, in the focus evaluation value of the second step, since the increase or decrease of the focus evaluation value is changed from an increasing state to a decreasing state, the focus evaluation value of the second step may be referred to as a peak focus evaluation value.

Referring to FIG. 3, of the two focus evaluation values of the first and third steps adjacent to the peak focus evaluation value, the focus evaluation value of the first step having a large difference in level from the peak focus evaluation value may be referred to as a minimum focus evaluation value. The peak focus evaluation value and the focus evaluation value of the third step having a small level difference may be referred to as a maximum focus evaluation value.

Based on the second step of the peak focus evaluation value, the controller may determine the lens movement direction in the third step direction of the maximum focus evaluation value having a small increase/decrease ratio with the peak focus evaluation value among two focus evaluation values of adjacent steps.

The control unit applies a coefficient calculated according to the relationship between the level difference between the peak focus evaluation value and the minimum focus evaluation value and the level difference between the peak focus evaluation value and the maximum focus evaluation value to the reference distance per step, The lens movement distance is determined based on a step. According to Equation 3 below, the aforementioned coefficient C may be about 0.62371, and the coefficient C is reflected in the reference distance 14 per step according to Equation 4 below. , The moving distance may be about 8.7.

That is, 441 moved in the positive direction by 8.7 from the position 432 of the second step may be the moving position of the lens.

Referring to FIG. 4, of the two focus evaluation values of the first and third steps adjacent to the peak focus evaluation value, the focus evaluation value of the first step having a large difference in level from the peak focus evaluation value may be referred to as a maximum focus evaluation value. The peak focus evaluation value and the focus evaluation value of the third step having a small level difference may be referred to as a minimum focus evaluation value.

Based on the second step of the peak focus evaluation value, the control unit may determine the lens movement direction in the first step direction of the maximum focus evaluation value having a small increase/decrease ratio with the peak focus evaluation value among two focus evaluation values of adjacent steps.

The control unit applies a coefficient calculated according to the relationship between the level difference between the peak focus evaluation value and the minimum focus evaluation value and the level difference between the peak focus evaluation value and the maximum focus evaluation value to the reference distance per step, The lens movement distance is determined based on a step. According to Equation 5 below, the aforementioned coefficient C may be about 0.53839, and the coefficient C is reflected in the reference distance 14 per step according to Equation 6 below. , The moving distance may be about 7.53.

That is, 439 moving in the negative direction by 7.53 from the position 446 of the second step may be the moving position of the lens.

Referring to FIGS. 3 and 4, it can be seen that the calculated moving positions of the lenses 441 and 439 substantially coincide with the peak positions of the outline of the subject. That is, the camera module and the autofocus method thereof according to an embodiment of the present invention can detect focus quickly and accurately.

In the above, the present invention has been described by specific matters such as specific elements and limited embodiments and drawings, but this is provided only to help a more general understanding of the present invention, and the present invention is not limited to the above embodiments. , Anyone with ordinary knowledge in the technical field to which the present invention pertains can make various modifications and variations from these descriptions.

Accordingly, the spirit of the present invention is limited to the above-described embodiments and should not be defined, and all modifications that are equally or equivalent to the claims as well as the claims to be described later fall within the scope of the spirit of the present invention. I would say.

10: lens unit
11: lens
12: actuator
13: image sensor
14: barrel
15: sensor board
20: signal processing unit
21: image signal processing unit
22: auto focus detection processing unit
30: control unit
40: actuator drive unit
50: memory unit

Claims (12)

lens;
An actuator sequentially moving the lens in a plurality of successive steps;
A memory unit for storing a focus evaluation value calculated for each step in which the lens is moved; And
Comparing the focus evaluation values of the plurality of steps, determining a peak focus evaluation value, and determining a lens position according to a comparison of the peak focus evaluation value and the peak focus evaluation value and each of two focus evaluation values of adjacent steps Control unit; Including,
The two focus evaluation values of the adjacent steps include a maximum focus evaluation value and a minimum focus evaluation value,
The control unit applies a coefficient calculated according to a relationship between a level difference between the peak focus evaluation value and the minimum focus evaluation value and a level difference between the peak focus evaluation value and the maximum focus evaluation value to the reference distance per step, and the peak Determine the lens moving distance based on the step of the focus evaluation value,
The coefficient is determined according to the following equation.
[Equation]

(C: coefficient, Vafpeak: peak focus evaluation value, VafRmax: maximum focus evaluation value, VafRmin: minimum focus evaluation value)

The method of claim 1, wherein the control unit,
A camera module that determines the lens movement direction in a step direction of a focus evaluation value having a small increase/decrease ratio with the peak focus evaluation value among the two focus evaluation values based on the step of the peak focus evaluation value.
delete The method of claim 1,
The minimum focus evaluation value corresponds to a focus evaluation value having a large level difference from the peak focus evaluation value among two focus evaluation values of the adjacent steps,
The maximum focus evaluation value corresponds to a focus evaluation value having a small level difference from the peak focus evaluation value among two focus evaluation values of the adjacent steps.
delete The method of claim 1,
The lens movement distance is determined according to the following equation.
[Equation]

(D: lens movement distance, D _step : reference distance per step)
Sequentially moving the lens in a plurality of successive steps;
Storing a focus evaluation value calculated for each step in which the lens is moved;
Determining a peak focus evaluation value by comparing focus evaluation values of the plurality of steps; And
Determining a lens position according to a comparison between the peak focus evaluation value and the peak focus evaluation value and two focus evaluation values of adjacent steps; Including,
The two focus evaluation values of the adjacent steps include a maximum focus evaluation value and a minimum focus evaluation value,
The step of determining the lens position,
Step of the peak focus evaluation value by applying a coefficient calculated according to the relationship between the level difference between the peak focus evaluation value and the minimum focus evaluation value and the level difference between the peak focus evaluation value and the maximum focus evaluation value to the reference distance per step Determine the lens moving distance based on,
The autofocus method is determined according to the following equation.
[Equation]

(C: coefficient, Vafpeak: peak focus evaluation value, VafRmax: maximum focus evaluation value, VafRmin: minimum focus evaluation value)
The method of claim 7, wherein determining the lens position,
An autofocus method of determining the lens movement direction in a step direction of a focus evaluation value having a small increase/decrease ratio with the peak focus evaluation value among the two focus evaluation values based on the step of the peak focus evaluation value.
delete The method of claim 7,
The minimum focus evaluation value corresponds to a focus evaluation value having a large level difference from the peak focus evaluation value among two focus evaluation values of the adjacent steps,
The maximum focus evaluation value corresponds to a focus evaluation value having a small level difference from the peak focus evaluation value among two focus evaluation values of the adjacent steps.
delete The method of claim 7,
The autofocus method is determined according to the following equation.
[Equation]

(D: lens movement distance, D _step : reference distance per step)

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