KR100991551B1 - Focal point adjusting method in imaging apparatus - Google Patents

Abstract

The first and second test charts CH1 and CH2 each having an imaging shape formed by dividing the target object P between the subjects into white and black before and after are set, and the focus lens 3 Is focused in the optical axis X direction, and the focus of the imaging shape formed in the imaging device 5 is made in correspondence with the movement amount of the focus lens 3 for each of the first and second test charts CH1 and CH2. The evaluation value is obtained and the position of the focus lens 3 is set so that the focus evaluation value in the first test chart CH1 and the focus evaluation value in the second test chart CH2 coincide with each other.

Description

Focus adjustment method in imaging device {FOCAL POINT ADJUSTING METHOD IN IMAGING APPARATUS}

The present invention relates to a focus adjustment method in which an imaging lens is set at a focusing position by using an image signal obtained through an imaging device such as a CCD, for example.

Conventionally, as shown in Fig. 1 (a), in an imaging device 201 such as a camera, climbing which detects the contrast of the image projection light to be imaged and performs focus adjustment by moving the imaging optical system so that the contrast is maximum. A focus adjustment method using the method is known.

The imaging device 201 is configured to lead an image 203 of the subject 203 through an imaging lens 202 to an imaging device 204 such as a CCD to convert it into an electrical signal, and detect the contrast in the focus detection unit 205. .

As shown in FIG. 1B, when the imaging optical system such as the imaging lens 202 and the imaging device 204 is at the focusing point position with respect to the subject 203, the climbing target focusing method includes a subject 203. When the image becomes the maximum contrast and defocusing occurs, the contrast decreases. Thus, the position of the imaging lens 202 is adjusted so as to aim at the peak of the contrast characteristic.

In addition, when adjusting the focus, a method of adjusting the focus by measuring an MTF (Modulaion Transfer Function) on a photographed subject is known. In detail, there is a focus adjustment method that measures the change in the MTF accompanying the movement of the imaging lens and sets the position of the imaging lens so that the MTF of a predetermined spatial frequency is maximum (for example, Patent Documents 1 and 2). Reference).

[Patent Document 1: Japanese Patent Laid-Open No. 62-284314]

[Patent Document 2: Japanese Patent Application Laid-Open No. 2005-258360]

However, according to the focus adjustment method for finding the maximum value of the contrast and the maximum value of the MTF by the climbing method as in the prior art, generally, the image pickup lens is reciprocated on both sides with the focusing position in the optical axis direction interposed therebetween to obtain the best contrast position. Since it is necessary to detect, there is a possibility that the workability for focus adjustment may be impaired (that is, the workability may be impaired as compared with the method of moving and adjusting the imaging lens in one direction). In addition, when the contrast characteristic and the MTF characteristic with respect to the defocus amount are close to the flatness near the peak point, and the peak point does not appear clearly, it may be difficult to precisely adjust the focusing position of the imaging lens.

Therefore, in the imaging device, when adjusting the focusing position by moving the imaging lens in the optical axis direction, the focusing position can be precisely adjusted even if the peak point of the focus evaluation value in the captured contrast characteristic or MTF characteristic is not clear. Moreover, it aims at providing the focus adjustment method which can make the adjustment easy.

The invention according to claim 1 made to attain such an object is characterized in that the imaging lens for leading a subject image to an imaging element and the image for photoelectric conversion of the subject image drawn through the imaging lens and outputting an image signal An image pickup device using an image pickup device, comprising: first and second images having an imaging shape formed by partitioning white and black before and after a target position of the subject along an optical axis connecting the subject and the image pickup device; A test chart of which the image pickup lens was formed in the image pickup device in accordance with the movement amount of the image pickup lens for each of the first and second test charts. The focus evaluation value is obtained, and the focus evaluation value in the first test chart and the focus evaluation in the second test chart are shown. A focus adjustment method for setting the position of the imaging lens so that the values coincide, wherein the first test chart and the second test chart are arranged symmetrically through an orthogonal line perpendicular to the optical axis, and each of them is superimposed. In addition to disposing at a position not supported, the white and black edge portions of the imaging shape of the first test chart and the white and black edge portions of the imaging shape of the second test chart are arranged symmetrically, and When the edge of an imaging pattern is formed with the inclination angle with respect to the arrangement direction of the pixel of the said imaging element, when one direction of the said pixel arrangement is made into the main scanning direction, and the direction orthogonal to the main scanning direction is made into the sub scanning direction, the said Based on the inclination angle, the number of sampling that is the basis of scanning in the main scanning direction of the pixel arrangement of the imaging device is different from that of the inclined edge. The number of samplings in the main scanning direction so as to be the number of displacements of the pixels in the main scanning direction required to displace by about 1 pixel in the direction of the direction, and then scan one line for the main scanning direction with the sampling number Scan the image picked up by the imaging element for each pixel, and when the scanning of one line is completed, the scanning positions are shifted by one pixel in the sub-scanning direction, the scanning in the main scanning direction is repeated, and the pixel values at each scanning position are repeated. Obtains the step response of the edge, and then obtains an impulse response by differentiating the step response, obtains a Modulation Transfer Function (MTF) by Fourier transforming the impulse response, and calculates the MTF as an index of the focus evaluation value. Characterized in that.

According to the focus adjustment method in the imaging device according to claim 1, an image having an imaging shape which is formed by dividing white and black before and after the target position of a subject on the optical axis. 1, 2nd test chart is set, an imaging lens is moved to an optical axis direction, and focus evaluation of the imaging image formed in the imaging element was made for each of the 1st, 2nd test charts corresponding to the movement amount of an imaging lens. The position of the imaging lens is set so that the focus evaluation value in the first test chart coincides with the focus evaluation value in the second test chart, so that the peak point of the focus evaluation value on the subject imaged through the imaging lens is not clear. Even if the focusing position can be adjusted with high accuracy, the adjustment can be facilitated.

That is, it is only necessary to set the position of the imaging lens when the imaging lens is moved along the optical axis and the focus evaluation value of the first test chart and the focus evaluation value of the second test chart are the focusing positions. Compared with this, the focusing position can be obtained with high accuracy, and the adjustment time can be shortened.

Moreover, the focus adjustment method in the imaging device of Claim 1 has the said imaging form in the said 1st test chart and a 2nd test chart like the invention of Claim 2. By providing them side by side, the first test chart and the second test chart spaced apart along the optical axis can be simultaneously imaged, focusing can be easily adjusted, and the focusing position of the imaging lens can be detected with high accuracy. .

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According to the focus adjustment method in the imaging device of the present invention, on the optical axis, first and second images having an imaging shape formed by dividing white and black in front and rear with the target position of the subject interposed therebetween. A test chart is set, the imaging lens is moved in the optical axis direction, and each of the first and second test charts corresponds to the movement amount of the imaging lens to obtain a focus evaluation value of the imaging shape formed in the imaging device, and the first Since the position of the imaging lens is set so that the focus evaluation value in the test chart and the focus evaluation value in the second test chart coincide with each other, the accuracy is good even if the vicinity of the peak point of the focus evaluation value on the subject captured by the imaging lens is unclear. In addition to adjusting the focusing position, the adjustment can be facilitated.

Moreover, according to the focus adjustment method in the imaging device of this invention, the 1st test chart and the 2nd test chart spaced apart along the optical axis can be imaged simultaneously, and workability for focus adjustment is favorable, In addition, the focusing position of the imaging lens can be detected with high accuracy.

1 is an explanatory diagram of a conventional focus adjustment method.

FIG. 2 is a schematic view showing a focus adjustment method in an imaging device according to one embodiment of the present invention, (a) shows an example of installation of the first and second test charts, and (b) in FIG. The MTF characteristic to be detected is shown.

3 is a block diagram showing the configuration of the imaging device in the embodiment.

4 is a diagram illustrating a method of measuring MTF in the example.

5 is a flowchart showing a procedure of a focus adjustment method in the embodiment.

FIG. 6 is a modification of the test chart shown in FIG. 2A.

Next, an embodiment of a focus adjustment method in the imaging device of the present invention will be described with reference to the drawings.

Fig. 2 is a schematic diagram showing a focus adjustment method in the imaging device of this embodiment, in which (a) shows an example of installation of the first and second test charts, and (b) shows the MTF characteristics detected at that time. Indicates. 3 is a block diagram showing the configuration of the imaging device in the embodiment, FIG. 4 shows the MTF measurement method in the embodiment, and FIG. 5 shows the focus adjustment method in the embodiment. The flowchart which showed the procedure, and FIG. 6 are the figures which showed the modification of the test chart in FIG.

As shown in Fig. 2A, the focus adjustment method in the imaging device of this embodiment is a focus lens (so-called in the present invention) configured to be movable in the optical axis X direction in the imaging device 1. 3) and an image pickup device 5 for photoelectrically converting a subject image drawn through the focus lens 3 and outputting an image signal. The object P and the image pickup device 5 are provided. A first test chart CH1 and a second test having an imaging pattern formed by dividing the target position of the subject P into white and black before and after along the connecting optical axis X. The chart CH2 is set, the focus lens 3 is moved along the optical axis X, and through the focus adjusting device 21, the focus on the subject P forming an image on the imaging device 5 is in focus. The position of the focus lens 3 is adjusted.

In FIG. 2A, M is the distance from the focus lens 3 to the subject P, N is the distance from the focus lens 3 to the first test chart CH1, and F is the focus lens 3. ) And the second test chart CH2, and the first test chart CH1 and the second test chart CH2 are separated by approximately the same distance with respect to the target position of the subject P. It is arranged. In addition, about the position of the 1st test chart CH1 and the 2nd test chart CH2, MTF is computed beforehand from optical information, such as focal length and F value, of the focus lens 3, respectively, and is computed. The MTF may be obtained to be the same, or may be obtained experimentally using a tuned lens.

In detail, as shown in FIG.2 (b), the focus lens 3 is moved to the optical axis X direction, and it focuses for each of the 1st test chart CH1 and the 2nd test chart CH2. In accordance with the movement amount of the lens 3, the focus evaluation value of the imaging shape formed on the imaging device 5 is obtained, and in the focus evaluation value in the first test chart CH1 and the second test chart CH2, The position of the focus lens 3 is set so that the focus evaluation values of?

Next, as shown in FIG. 3, the imaging device 1 includes a filter for removing the front lens 2, the focus lens 3, harmful infrared rays, harmful reflected light, and the like (infrared ray removing filter or optical filter). (4), an imaging element (CCD: Charge Coupled Devices) 5, an analog front end (AFE) 6 for converting an analog image signal output from the imaging element 5 into a digital image signal C and outputting the same; Through the TG (Timing Generator) 13 which controls the imaging device 5 and the AFE 6 at predetermined cycles, the focus driver 12 and the sensor 11 which perform slide driving of the focus lens 3 in the optical axis direction. A focus detector 10 or the like for detecting the sliding amount of the focus lens 3 is provided.

The imaging element 5 is constituted by a plurality of photoelectric conversion elements arranged side by side, and configured to output an analog image signal by photoelectric conversion of the imaging signal S for each photoelectric conversion element.

The AFE 6 is correlated double sampling with a correlated double sampling circuit (CDS) 7 and a correlated double sampling circuit 7 which remove noise from an analog image signal output through the imaging element 5. A / D for converting an analog image signal from the image pickup device 5 input through a variable gain amplifier (AGC: Automatic Gain Control) 8 to amplify the image signal, and the variable gain amplifier 8 into a digital image signal. It is comprised by the converter 9, etc., and converts the image signal output from the imaging element 5 into a digital image signal at a predetermined sampling frequency, and outputs it to the focusing apparatus 15. FIG.

The focus adjusting device 15 processes the digital image signal C outputted from the imaging device 1 to calculate the MTF of the imaging shape in the first chart CH1 and the second chart CH2. MTF calculating section 16, MTF comparing section 25 for comparing whether the MTF value of the first chart CH1 and the MTF of the second chart CH2 match or ROM (Read Only Memory) 23 ), A CPU (Central Processing Unit) 24, a buffer 26 for temporarily storing image data output from the AFE 6, and the like, and the CPU 24 stores the control program stored in the ROM 23. Therefore, each process of the focus adjustment device 15 is controlled.

In addition, the function of the focus evaluation value in this invention is expressed by MTF.

In addition, the MTF calculating unit 16 includes the first calculating unit 17 for calculating the MTF of the first test chart CH1 and the second calculating unit 18 for calculating the MTF of the second test chart CH2. It is composed by.

Next, the measuring method of MTF in a present Example is demonstrated based on FIG. First, when obtaining the MTF, the first test chart CH1 and the second test chart CH2 are imaged on the imaging device 5 through the focus lens 3, and image data (digital) is obtained from the AFE 6. Signal C).

And as shown in FIG.4 (a), the imaging form of the 1st test chart CH1 and the 2nd test chart CH2 which were taken in the 1st calculating part 17 and the 2nd calculating part 18 was taken. The number of samplings is calculated based on the inclination angle of the edges of the edges. Next, the step response of the edges is obtained by scanning the image data and acquiring pixel values using the calculated number of samplings, and then the edges are differentiated by differentiating the step responses. The impulse response is obtained, and then the impulse response is Fourier transformed to obtain an MTF.

In detail, first, as shown to Fig.4 (a) (b), in the sampling number calculation part 17a, 18a, in the 1st test chart CH1 and the 2nd test chart CH2. The inclination angle α of the edge is calculated and the sampling number P serving as the basic unit of scanning in one direction of the image is calculated.

Next, as shown in Fig. 4C, one direction of the image is the main scanning direction and the other direction is the sub scanning direction (in this embodiment, the vertical direction is the main scanning direction and the horizontal direction is the sub scanning direction). The image picked up by the imaging device 5 is scanned. At this time, in the main scanning direction, the sampling number P is set to scan for one line, and the images are sequentially scanned. Then, as shown in Fig. 4D, the step response of the edge is obtained by acquiring the pixel value of each scan position.

As shown in Fig. 4B, when the edges of the imaging shapes of the test charts CH1 and CH2 are slightly inclined with respect to the vertical direction, the main scanning direction is vertical, and the edge lines are vertically divided by one pixel. Set the sampling number P to displace. Fig. 4B shows image data obtained by imaging, one by one of the rectangular edges represents the pixel, and Δ, □, ●, ○ and the like in the pixel represent the pixel values.

In the first chart CH1, the brightness of the left side is dark and the brightness of the right side is brightly expressed through the edge of the image data, and in the second chart CH2, the first chart CH1 appears symmetrically with the first chart, and the edge Through the brightness of the right side is dark, the brightness of the left side is expressed brightly.

In addition, when obtaining the inclination angle (alpha), as shown to Fig.4 (e), it is the y direction (vertical direction) with respect to the edge of the 1st test chart CH1 and the 2nd test chart CH2. S windows w are arranged. At this time, one window has a plurality of unit elements in the x direction (horizontal direction), and the height of each unit element is equal to one pixel, and the width is smaller than one pixel.

Next, using (Equation 1), the second derivative is performed in each window w.

L ^w (x) = 2 * P ^w (x) -P ^w (x-1) -P ^w (x + 1). (Equation 1)

In Formula (1), P ^w (x) is the pixel value at the point (x, Ey ^w ) in the window w, and L ^w (x) is the second derivative at that point. In addition, the point (x, Ey ^w ) is a position in the case where one unit element is set to one scale of x coordinate and y coordinate, and Ey ^w is 1, 2, 3, ... in FIG. ... which is equivalent to S.

Next, in each window w, the maximum value Lmax ^w and the minimum value Lmin ^{w of the} second derivative L ^w (x) are obtained, and the x coordinates Xmax ^w and Xmin ^w of those points are obtained. It calculates | requires and calculates x coordinate Ex ^w of the edge point in the window w using Formula (2).

Ex ^w = (Xmin ^w * | Lmax ^w | + Xmax ^w * | Lmin ^w |) / (| Lmax ^w | + | Lmin ^w |). (Equation 2)

Next, the angle of inclination α of the edge line is obtained from the group of edge points obtained from Expression (2), and the integer value obtained by rounding off cotα at this time is set as the sampling number P.

Next, transfer to the step response calculation units 17b and 18b, and as shown in Fig. 4C, first, the pixels of the first column are scanned by the number of samplings P along the vertical direction, and the first column When the scanning of the is finished, the scan position is shifted in the horizontal direction, and the scan position is again scanned by the sampling number P along the vertical direction, and the image data is sequentially scanned by the sampling number along the vertical direction.

Next, as shown in Fig. 4 (d), the pixel values of the respective scan positions are arranged in a circle to obtain the step response of the edge. In FIG.4 (d), the brightness value is shown on the vertical axis | shaft, and the position at the time of unfolding each scan position unitarily is shown on the horizontal axis | shaft. In other words, the step response calculation units 17b and 18b scan the pixel values near the edge by the sampling number P in the vertical direction, and arrange the pixel values in the scanning order to obtain the edge step response.

Next, it transfers to the impulse response calculation parts 17c and 18c, and converts into the impulse response by differentiating the step response obtained by the step response calculation parts 17b and 18b. The differentiation performed here can be performed, for example, by taking the difference between adjacent pixels in the step response.

Next, the MTF is determined by Fourier transforming the impulse response obtained by the impulse response calculating units 17c and 18c to the MTF calculating units 17d and 18d. At this time, by Fourier transform, a real part and an imaginary part are obtained for each frequency, and the MTF is obtained by adding the real part and the imaginary part. In addition, the calculation method of MTF is not limited to this, For example, you may use the resolution measuring method of ISO12233.

Next, the procedure at the time of obtaining the focusing position of the focus lens 3 using the 1st test chart CH1 and the 2nd test chart CH2 is demonstrated based on FIG. This procedure is executed by the CPU 24 giving a command signal to each functional unit based on the program stored in the ROM 23. In addition, S in FIG. 5 has shown the step.

First, this procedure starts when the start signal is input to the focus adjusting device 15 by the operator.

Next, in S101, the focus lens 3 is moved to a predetermined initial position and then moved to S102.

Next, in S102, photographing of the first chart CH1 and the second test chart CH2 is started, and in S103, the focus detection device 15 checks the image data output through the AFE 6. Output to.

Next, in S104, the MTF of the imaging shape in the 1st test chart CH1 is calculated and calculated | required in the 1st calculating part 17, and the 2nd test in the 2nd calculating part 18 is calculated | required. The MTF of the imaging pattern in the chart CH2 is calculated and calculated, and then transferred to S105.

Next, in S105, the difference between the MTF at the predetermined frequency calculated by the first calculation unit 17 and the MTF at the predetermined frequency calculated by the second calculation unit 18 is calculated, and then the procedure is moved to S106. . At this time, since the MTF can be calculated for each frequency component, the MTF corresponding to the predetermined high frequency component may be compared.

Next, in S106, it is determined whether or not the difference between the MTF calculated by the first calculation unit 17 and the MTF calculated by the second calculation unit 18 is zero (so-called first test chart CH1). The MTF obtained by photographing the second test chart CH2 is determined whether or not the MTF obtained is identical), and in S106, when the difference between them is zero (Yes), the focus lens 3 is positioned at the focusing position. If this is the case, the process ends (END), and if the difference is not zero (No), the process moves to S107.

Next, in S107, the focus lens 3 is moved along the optical axis X by a predetermined amount, thereafter, S103 to S106 are repeated, and when the difference between them reaches zero in S106, the present process is performed. Quit.

As described above, according to the focus adjusting method and the focus adjusting device in the imaging device 1 according to the embodiment, the white and black sections are formed in front and rear on the optical axis X through the target position of the subject P. The first test chart CH1 and the second test chart CH2 having the captured image shape are set, the focus lens 3 is moved in the optical axis X direction, and the first test chart CH1 is set. ) And each of the second test charts CH2 to obtain the MTF of the imaging pattern formed in the imaging device 5 in correspondence with the movement amount of the focus lens 3, and in the first test chart CH1. Since the position of the focus lens 3 is set so that the MTF of the MTF and the MTF in the second test chart CH2 coincide with each other, the focusing position can be adjusted with high accuracy even if the peak point of the focus evaluation value is not clear. It can be done easily.

Moreover, according to the focus adjustment method and the focus adjustment apparatus in the imaging device 1 described in the embodiment of the present invention, the first test chart CH1 and the second test chart spaced apart along the optical axis X image. (CH2) can be imaged simultaneously, the operation for focus adjustment is easy, and the focusing position of the focus lens 3 can be detected with high precision.

As mentioned above, although one Example of this invention was described, this invention is not limited to the said Example, A various form can be taken.

For example, as shown in FIG. 6, in the 1st test chart CH1 and the 2nd test chart CH2, you may have a some imaging form which has inclination edge, respectively. For this reason, the influence of noise can be reduced rather than single image pick-up, and a focus evaluation value can be obtained with high precision. In addition, by arranging a plurality of picked-up images at a plurality of positions, the focus position in the image can be set according to the use, and the added value can be improved.

In this embodiment, the position where the difference between the MTF value of the first test chart CH1 and the MTF value of the second test chart CH2 is zero is set as a focusing position. When it reaches, you may make it into a focusing position.

In addition, in this embodiment, although the chart which has the imaging image of white and black was used, the chart which has other colors (for example, red, green, blue) is used, and the focusing adjustment with respect to a specific color component is performed. You may also

In addition, in the present embodiment, the so-called autofocus function, which has a drive unit 12 (electric) of the focus lens 3, has been described. However, the present invention is directed to an image pickup device having an autofocus function. It is not limited, but it can also apply to the imaging device which adjusts the position of the focus lens 3 manually. In that case, for example, the focus lens 3 may be screwed along the optical axis X to be screwed at the focusing position.

In addition, when applying this invention to the imaging device which has autofocus, you may obtain the focusing point of the focus lens 3 using this invention, and may store them in ROM23, and may use as a parameter of autofocus.

The present invention is useful for setting an imaging lens to a focusing position by using an image signal obtained through an imaging device such as a CCD included in the imaging device.

Claims (7)

An imaging device using an imaging lens for leading a subject image to an imaging element and the imaging element for photoelectric conversion of the subject image led through the imaging lens and outputting an image signal, comprising: connecting the subject and the imaging element A first and a second test chart having an imaging shape formed by dividing the target position of the subject along the optical axis with the target position of the subject interposed into white and black are set, and the imaging lens is moved in the optical axis direction. For each of the first and second test charts, a focal evaluation value of the image capturing image formed on the image pickup device is obtained in correspondence with the amount of movement of the image pickup lens, and the focal evaluation value in the first test chart is used. As a focus adjustment method of setting the position of the imaging lens so that the focus evaluation values in the second test chart coincide, The first test chart and the second test chart are symmetrically arranged through orthogonal lines perpendicular to the optical axis, and each of the first test chart and the second test chart are arranged at positions not overlapped with each other. The white and black edge portions of the second test chart and the white and black edge portions of the imaging shape of the second test chart are arranged symmetrically, When the edge of the imaging shape is formed with an inclination angle with respect to the arrangement direction of the pixels of the imaging device, one direction of the pixel arrangement is the main scanning direction, and the direction orthogonal to the main scanning direction is the sub scanning direction. , Based on the inclination angle, the number of sampling that is the basis of scanning in the main scanning direction of the pixel arrangement of the imaging device is the pixel in the main scanning direction required for the inclined edge to be displaced by about 1 pixel in the sub scanning direction. The sampling number in the main scanning direction is calculated so that the displacement number of Subsequently, the main scanning direction is scanned for one line with the sampling number, so that the image captured by the imaging device is scanned for each pixel, and once scanning for one line is completed, one pixel in the sub-scan direction. By repeating scanning in the main scanning direction by shifting the scanning positions, obtaining a pixel value of each scanning position to obtain the step response of the edge, Next, the impulse response is obtained by differentiating the step response, and the MTF (Modulation Transfer Function) is obtained by Fourier transforming the impulse response. The said MTF is made into the index of the said focus evaluation value, The focus adjustment method in the imaging device characterized by the above-mentioned. The method according to claim 1, The said 1st test chart and the 2nd test chart are provided with the said imaging image in plurality in parallel, The focus adjustment method in the imaging device characterized by the above-mentioned. delete delete delete delete delete

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