KR20060043025A - Method and apparatus for automatic focus control - Google Patents

Abstract

In the case of focus control using focus points of a plurality of focus areas, the focus area with a subject is incorrectly recognized due to an eccentricity of the optical system or a change in focus point caused by aori of the image pickup device, thereby focusing on the peripheral part. Method and apparatus to prevent fit.

Secondly, the focusing points of the adjacent focus areas are differentially added, the second differential focusing points are added to the absolute value, and a value indicating the linearity of the change of the focusing points between adjacent focus areas is calculated. When the linearity is weak, it is determined that a certain subject has a main subject, the focus region where the main subject is located is focused, and the focusing point of the specified focus region is focused. If the linearity is strong, it is determined that there is no main subject in any focus area, and the focusing point of the focus area near the center is focused.

Auto focus control, digital camera

Description

Auto focus control method and automatic focus control device {Method and apparatus for automatic focus control}

1 is a block diagram showing the overall configuration of a digital video camera to which the present invention is applied;

2 is an explanatory diagram of a focus area in a digital video camera to which the present invention is applied;

3 is a block diagram illustrating an example of an AF detection circuit in a digital video camera to which the present invention is applied;

4 is a graph illustrating the relationship between the position of the focus lens and the number of pulses;

5 is a graph used for explaining the AF evaluation value;

6 is a flowchart used for describing an auto focus control to which the present invention is applied.

7 is a flowchart used for describing an auto focus control to which the present invention is applied.

8 is a flowchart used for describing an auto focus control to which the present invention is applied.

9 is an explanatory diagram of auto focus control in each shooting screen;

10 is a graph used to explain evaluation values in each shooting screen;

11 is an explanatory diagram of arithmetic processing for obtaining a value indicating linearity of a focusing point of an adjacent focus area.

<Explanation of symbols for the main parts of the drawings>

3 Focus lens 4 Image pickup device

7 Focus Motor 8 Timing Generator

12 memory 15 control (circuit)

19 AF detection (circuit) 24 Image signal processing circuit

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an autofocus control method and an autofocus control device which obtains an evaluation value for extracting a high frequency component of an image to evaluate a degree of focusing and obtains a focusing point. The present invention relates to dividing into a plurality so that the main subject can be focused.

In a digital camera, at a focusing point, the high frequency component level of the image signal is maximized to extract the high frequency component level of the image signal to obtain an AF (Automatic Focus) evaluation value, and the focus at which the AF evaluation value is maximum. The position of the lens is searched as the focus point, and the focus is placed on the position of the focus point.

In such an automatic focusing mechanism, a focus area is divided into a plurality of subjects so as to focus on a main subject, and a focus area in which the main subject is located is selected from among the focus areas, and the focusing point of the focus area in which the main subject is located is focused. It is proposed to try to match. In this case, conventionally, the focus area is specified by an algorithm that the main subject is located in the focus area that is the closest distance among the focus points of the plurality of focus areas.

For example, Japanese Patent Application Laid-open No. Hei 10-142490 calculates the degree of the main subject using a calculation formula of a characteristic proportional to the size of the image and the distance from the center of the screen and inversely proportional to the object distance, and based on the result A method of focusing is described.

By the way, some digital cameras have an eccentricity of an optical system or inclination in an imaging device (Aori of an imaging device) according to a manufacturing difference. As described above, in the case of using a camera having an eccentricity of the optical system or aori of the imaging device, the focusing point is different at the periphery of the screen and the center of the screen. For this reason, in the photographing scene with only the scenery without the subject, the focusing point of the focus area of the periphery can represent a distance closer to the center. As described above, when the focus area that is the closest distance among the focus points of the plurality of focus areas is specified as the focus area where the main subject is located and focused, the focus area of the periphery exhibits a closer distance than the center part. In this case, a so-called partial blurring phenomenon occurs, in which a main subject is erroneously recognized in the periphery and the focusing area is focused on the periphery.

Further, as shown in Japanese Patent Laid-Open No. 10-142490, due to the property inversely proportional to the object distance, it is poor with respect to the inclination (some blurring phenomenon) of the upper surface, and depending on the inclination, the part is obscured. There is a risk of causing the blurring of parts to promote blur.

SUMMARY OF THE INVENTION In view of the above-described conventional problems, the present invention prevents erroneous recognition of a focus area caused by an eccentricity of an optical system or aori of an imaging device when focus control is performed using focus points of a plurality of focus areas. It is an object of the present invention to provide an autofocus control method and an autofocus control device in which the focus is not focused in the focus area of the peripheral part even when there is an eccentricity of an optical system or an aberration of an imaging device.

The autofocus control method according to claim 1 is an autofocus control method which obtains an evaluation value for extracting a high frequency component of an image signal to evaluate a degree of focusing and obtains a focusing point. An evaluation value is obtained by moving the focus lens for each focus area, and a focus point is obtained for each focus area from the evaluation value acquired for each focus area, and a focus point of an adjacent focus area is obtained from the focus points obtained for each focus area. The linearity of the change is calculated by calculation, and when the linearity of the change of the focusing points of the adjacent focus areas is weak, it is determined that there is a main subject in a certain focus area, and the change of the focusing points of the adjacent focus areas is determined. If the linearity is strong, it is judged that there is no main subject in any focus area. It is characterized by that.

In the invention of claim 2, in the autofocus control method of claim 1, the operation for calculating the linearity of the change of the focusing points of the continuous focusing areas is the second derivative of the focusing points of the respective focusing areas, and the second differentiation is performed. It is characterized in that the absolute value is added to the focus point.

In the invention of claim 3, in the autofocus control method of claim 1, when it is determined that a certain subject has a main subject, a focus region including the main subject is specified, and the focus point of the specified focus region is focused. It is characterized by one.

In the invention of claim 4, the autofocus control method of claim 1 is characterized in that the focusing point of the focus area near the center is focused when it is determined that there is no main subject in any focus area.

An autofocus control apparatus according to the invention of claim 5 is an autofocus control apparatus configured to obtain an evaluation value for extracting a high frequency component of an image signal from an image pickup device to evaluate a degree of focusing, and to obtain a focusing point. Lens drive means for moving the lens; evaluation value detection means for obtaining an evaluation value for extracting a high frequency component of an image signal to evaluate focusing degree; focus area setting means for setting a plurality of focus areas; and for each focus area. Means for obtaining an evaluation value while moving the focus lens, means for obtaining a focus point for each focus area from evaluation values obtained for each focus area, and focus points for adjacent focus areas from focus points obtained for each focus area. Means for calculating the linearity of the change of In the case where the linearity of the change of the point alignment point is weak, it is determined that a certain subject has a main subject, and the focus region where the main subject is located is specified, the focusing point of the specified focus region is focused, and the adjacent focus is determined. When the linearity of the change of the focusing point of the area is strong, it is determined that there is no main subject in any focusing area, and means for focusing on the focusing point of the focusing area near the center is provided.

In the sixth aspect of the present invention, in the autofocus control apparatus of the fifth aspect, the operation for calculating the linearity of the change in the focusing point of each focus area is second derivative of the focusing points of the adjacent focus areas, and the second derivative. It is characterized by adding an absolute value to one focus point.

EMBODIMENT OF THE INVENTION Hereinafter, embodiment of this invention is described, referring drawings. 1 is a block diagram showing the overall configuration of a digital camera to which the present invention can be applied. In FIG. 1, 1 is a zoom lens, 2 is an iris, and 3 is a focus lens.

The position of the zoom lens 1 is movable by the zoom motor 5. The opening degree of the iris 2 is controllable by the iris motor 6. The position of the focus lens 3 can be controlled by the focus motor 7. The subject image light through the zoom lens 1, the iris 2, and the focus lens 3 is imaged on the light receiving surface of the image pickup device 4.

The imaging device 4 photoelectrically converts the subject image light formed on the light receiving surface. As the imaging device 4, a CCD (Charge Coupled Device) imaging device or a CMOS (Complementary MOS) imaging device is used. The color filter is arranged in front of the imaging element. As the arrangement of the color filters, a primary color filter of R (red), G (green), and B (blue) is used, and a complementary color filter of Cy (cyan), Mg (magenta), and Ye (yellow). You may use The imaging device 4 is driven by the timing signal from the timing generator 8.

The output signal of the image pickup device 4 is supplied to the analog to digital (A / D) converter 10 via a corelated double sampling (CDS) and automatic gain control (AGC) circuit 9. In the A / D converter 10, the image signal is digitized. The output signal of the A / D converter 10 is received through the image input controller 11.

The control circuit 15 controls the entire digital camera. The control circuit 15 receives an input signal from the shutter switch 16, the zoom switch 17, the recording / reproducing switch 18, and the like. Further, from the control circuit 15, a zoom drive signal for moving the zoom lens 1, a focus drive signal for moving the focus lens 3, an iris drive signal for opening and closing the iris 2, CDS and AGC circuits A gain control signal for controlling the gain of is output.

The AF (Automatic Focus) detection circuit 19 detects the high frequency component level of the image signal in order to perform the focus control. That is, at the focusing point, the high frequency component level of the image signal increases. Therefore, the focusing state can be determined by detecting the high frequency component level of the image signal. The AF detection circuit 19 detects the high frequency component level of the image signal, integrates the high frequency component level of the image signal between predetermined focus regions, and obtains an AF evaluation value. The obtained AF evaluation value is supplied to the control circuit 15. The control circuit 15 gives a focus drive signal to the focus motor 7 via the motor driver 21 in accordance with this AF evaluation value, and controls the focus lens 3 to the position of the focus point. In addition, focus control is mentioned later.

The AE (Automatic Exposure) and AWB (Automatic White Balance) detection circuit 20 detects an image signal level in order to perform exposure and white balance. The image signal level is detected by the AE and AWB detection circuits 20, and an exposure control signal and a white balance control signal are formed. This exposure control signal and white balance control signal are supplied to the control circuit 15. According to this exposure control signal, the iris drive signal is output from the control circuit 15 and a gain setting signal is output at the same time. The iris drive signal from the control circuit 15 is supplied to the iris motor 6 via the motor driver 22, and the opening degree of the iris 2 is controlled so as to reach a predetermined signal level. In addition, gain control from the control circuit 15 is supplied to the CDS and AGC circuit 9, and the gain of the CDS and AGC circuit 9 is controlled so as to be at a predetermined signal level. The gain of the three primary color signals is controlled by the image signal processing circuit 24 in accordance with the white balance control signal from the AE and AWB detection circuits 20.

By operating the zoom switch 17, the zoom lens 1 can be moved. That is, when the zoom switch 17 is operated, the zoom drive signal is output from the control circuit 15 accordingly. This zoom drive signal is supplied to the zoom motor 5 through the motor driver 23 to move the zoom lens 1.

By operating the recording / playback switch 18, the recording mode and the playback mode can be set. When the recording mode is set, the output signal of the imaging device 4 is digitized by the A / D converter 10 via the CDS and AGC circuit 9 and then supplied to the image signal processing circuit 24. The image signal processing circuit 24 performs image processing such as gamma correction, edge emphasis, and white balance. This picture signal is supplied to the video encoder 25. In the video encoder 25 a component color video signal is formed, and this color video signal is developed in a VRAM (Video RAM) 30. This color video signal is supplied to an image display device 29 such as an LCD (Liquid Crystal Display), and the monitor image being shot on the image display device 29 is illuminated.

In the case of taking an image, the shutter switch 16 is pressed. When the shutter switch 16 is pressed, the shutter signal is sent to the timing generator 8, and the image at that time is received by the image pickup device 4. The image signal for one screen at this time is accumulated in the memory 12.

The image signal for one screen received in the memory 12 is supplied to the image compression / expansion circuit 26 after image processing is performed in the image signal processing circuit 24. The image data is compressed and encoded by the image compression / extension circuit 26. As a compression method of image data, JPEG (Joint Photographic Experts Group) is used, for example. JPEG is a standard for compressing images using DCT (Discrete Cosine Transform). In addition, the compression method of image data is not limited to JPEG.

The compression-encoded image signal is supplied to the recording medium 32 via the media controller 31 and recorded on the recording medium 32. As the recording medium 32, a card-type removable memory using a flash memory is used. In this example, the memory card is used as the recording medium 32, but the present invention is not limited thereto. The image signal can also be recorded in the built-in nonvolatile memory, or recorded on a magnetic tape, a magnetic disk, an optical disk, or the like.

At the time of reproduction, the recording / reproduction switch 18 is operated to the reproduction side. When the record / playback switch 18 is operated to the playback side, it is set to the playback mode. In the reproduction mode, the image file of the recording medium 32 is opened, and the image data is read out. The image data read out from the recording medium 32 is supplied to the image compression / expansion circuit 26. The image compression / expansion circuit 26 performs the decompression processing of the image signal. The output of the picture compression / extension circuit 26 is supplied to the video encoder 25. The output signal of the video encoder 25 is supplied to the image display device 29 and the reproduced image is illuminated on the image display device 29.

Next, focus control in the digital camera to which the present invention is applied will be described. As described above, in the digital camera to which the present invention is applied, the AF detection circuit 19 is provided to perform auto focus control. The high frequency component level of the image signal is detected by the AF detection circuit 19, the high frequency component level of the image signal is integrated between the predetermined focus areas, and the AF evaluation value is obtained.

The focus area is divided into a plurality of focus areas A0 to A6 in the horizontal direction as shown in FIG. 2. When focus control is performed using the plurality of divided focus areas A0 to A6 as described above, the closest distance among the focus points of the plurality of focus areas A0 to A6 is usually adjusted so that the main subject is focused. The focus area to be focused is specified as the focus area where the main subject is located.

By the way, when there is an eccentricity of the optical system or aori of the imaging device, in a photographing scene such as a landscape where there is no main subject, for example, the focusing point of the focus area of the peripheral part may indicate a closer distance than the center. As described above, if the focus area that is the closest distance among the focus points of the plurality of focus areas A0 to A6 is specified as the focus area where the main subject is located and focused, the focus area of the peripheral part is located at the center. In the case of showing a relatively close distance, the peripheral object is mistakenly recognized as having a main subject in the periphery, and the focus is focused on the periphery.

Therefore, in the embodiment of the present invention, a value indicating the linearity of the change of the focus point of the adjacent focus area is calculated by calculation. In other words, when there is an eccentricity of the optical system or an aberration of the image pickup device, the focusing point obtained from the adjacent focusing region changes linearly. On the other hand, in the case of the main subject, only the focusing point obtained from the focus area in which the subject is located is greatly different. Therefore, when a value indicating a change linearity of focus points of adjacent focus areas is obtained, it is determined whether the change of focus points obtained from each focus area is caused by an eccentricity of an optical system or an aori of an imaging device or a main subject. Can be.

The value indicating the change linearity of the focus points of the adjacent focus areas is obtained by quadratic differentiating the focus points of the adjacent focus areas, and adding the absolute differential points. That is, when the adjacent focusing points change linearly, when the focusing points of the adjacent focusing areas are differentiated (takes the difference between the focusing points of the adjacent focusing areas), the value becomes almost the same. Therefore, when the focusing points of the adjacent focus areas are second-differentiated (the difference between the focus points of the adjacent focus areas is taken and the difference value is taken), the value becomes a small value.

On the other hand, when the change of the focus point of the adjacent focus area is not linear, even if the focus point of the adjacent focus area is not decomposed, the value is not nearly the same, but the focus point of the adjacent focus area is not. The second degree of microdegradation does not become small.

From this, the value of the second derivative of the focus points of the adjacent focus areas and the absolute value of the second differentiated focus points is a value representing the linearity of the change of the focus points between the adjacent focus areas. do. If the value of the second derivative of the focus points of the adjacent focus areas and the absolute value of the second derivatives of the focus points is small, the linearity of the change of the focus points between the adjacent focus areas is strong. If large, the linearity of the change of the focusing point between adjacent focus areas is weak.

If it is judged that the linearity of the change of the focus point of the adjacent focus area is strong from this calculated value, it is determined that the main subject is not in any focus area, and focusing is performed using the center focus area. If it is determined that the linearity of the adjacent focus area is weak from the value, it is determined that the main subject is in a certain focus area, and the focus area in which the subject is located is specified, and the focusing point of the specified focus area is focused. have.

3 shows a configuration of an AF detection circuit 19 in a digital camera to which the present invention is applied.

As shown in FIG. 3, the AF detection circuit 19 includes a high pass filter 51, a level detection circuit 52, and an area integration circuit 53. The image signal obtained from the imaging output of the imaging device 4 is supplied to the input terminal 50. This image signal is supplied to the high pass filter 51, and the high pass filter 51 extracts the high frequency component of the image signal. The output signal of the high pass filter 51 is supplied to the level detection circuit 52, and the high frequency component level of the image signal is detected by the level detection circuit 52. The output signal of the level detection circuit 52 is also supplied to the area integration circuit 53. The area integration circuit 53 is supplied with the focus area setting signal from the terminal 54. The region integrating circuit 53 integrates the high frequency component level of the image signal between predetermined focus regions. A signal obtained by integrating the high frequency component level of this image signal between predetermined focus regions is output from the output terminal 55 as an AF evaluation value.

The terminal 54 is supplied with a focus region setting signal for setting the seven focus regions A0 to A6 as shown in FIG. Thereby, AF evaluation value is obtained for each focus area | region A0-A6. Since the high frequency component level of the image signal is maximized at the focusing point, each focus area A0 to A6 is searched by searching for the position of the focus lens 3 having the maximum AF evaluation value for each focus area A0 to A6. You can find the focus point for each).

A step motor is used as the focus motor 7 for positioning the focus lens 3. When the step motor is used as the focus motor 7, the focus lens 3 moves in steps every time the pulse is applied to the focus motor 7, so that the position of the focus lens 3 is shifted to the focus motor 7. It can manage according to the number of pulses to give.

4 shows an example of the relationship between the position of the focus lens 3 and the number of pulses applied to the focus motor 7. In FIG. 4, the horizontal axis represents the position of the focus lens 3, and the vertical axis represents the number of pulses. When the focus lens 3 is located at the far position Far at infinity which is the initial position, the number of pulses becomes, for example, "0". When the focus lens 3 is moved to the nearest distance position (minimum object distance (MOD)), the number of pulses becomes, for example, "120". As shown in FIG. 4, the position of the focus lens 3 has a relationship corresponding to the number of pulses applied to the focus motor 7, and when the number of pulses applied to the focus motor 7 is known, the focus lens at that time is known. The position of (3) is uniquely determined.

The focusing points of the respective focus areas A0 to A6 are moved in stages by the focus motor 7 to the position MOD of the distance closest to the far distance Far from the infinity. Can be acquired by taking the AF evaluation value and searching for the lens position at which the AF evaluation value is maximum.

For example, when the focus lens 3 is moved stepwise to the position MOD of the nearest distance from the far position Far by infinity with the focus motor 7, the AF evaluation value is accepted in the meantime. Assume that the AF evaluation value as shown in Fig. 5 was obtained. In FIG. 5, the horizontal axis represents the position of the focus lens 3 (the number of pulses applied to the focus motor 7), and the vertical axis represents the AF evaluation value. In this case, the AF evaluation value becomes maximum at the position where the number of pulses is 30. Therefore, the position where the number of pulses is 30 becomes the focus point.

Here, if the position of the focus lens 3 as the focus point is x _a , the distance to the subject is x _b , and the focal length of the lens is f, (x _a × x _b ) is approximately equal to f ^2. The position of the focus lens 3, which is a focusing point, is inversely related to the distance of the subject.

Fig. 6 is a flowchart showing the entire auto focus control process to which the present invention is applied. As shown in FIG. 6, the focus lens 3 is first moved to a far position Far at infinity which is an initial position (step S1). Then, an AF search is performed for each focus area A0 to A6 (step S2).

In the AF search, as shown in FIG. 7, the focus lens 3 is moved in step by step to the position MOD of the nearest distance from the far position Far indefinitely (step S21). . In the meantime, the AF evaluation value at each position is accepted (step S22). It is determined whether the acceptance of the AF evaluation value has ended to the position MOD of the nearest distance from the far position Far to infinity (step S23), and returns to step S11 if the acceptance has not been completed. In step S23, when it is determined that the acceptance of the AF evaluation value is completed to the position MOD of the nearest distance from the far position Far to infinity, the position of the focus lens 3 with the largest AF evaluation value (focus motor 7 ), The number of pulses) is taken as a focusing point in the focus area (step S24).

In Fig. 6, when the AF search is performed in step S2 and the focusing points in the respective areas A0 to A6 are searched, the focusing points in the respective areas A0 to A6 are called (step S3). Then, a value AFsadd indicating the linearity of the change of the focusing points of the adjacent focusing areas using the focusing points in the respective areas A0 to A6 is obtained by calculation (step S4). As described above, the value AFsadd indicating the linearity of the change of the focusing points of the adjacent focusing areas is second-order differentiated from the focusing points of the respective focusing areas A0 to A6, and the second-differential focusing is performed. This is done by adding the absolute value of the point.

That is, as shown in FIG. 8, the derivative value is calculated | required by the difference of the focusing point of the adjacent focus area | regions among the focus areas A0-A6 (step S31). Further, the second derivative value is obtained by the difference in the derivative values of the focus points of the adjacent focus areas (step S32). The obtained second derivative is added to the absolute value, and a value AFsadd indicating the linearity of the change of the focus point of the adjacent focus area is obtained (step S33).

In FIG. 6, when a value AFsadd indicating the linearity of the change of the focus points of the adjacent focus areas is obtained in step S4, the value AFsadd indicating the linearity of the change of the focus points of the adjacent focus areas is obtained. Is determined to be smaller than the predetermined value P (step S5).

If the value AFsadd indicating the linearity of the change of the focus point of the adjacent focus area is smaller than the predetermined value P, the linearity is strong, and in this case, the main subject is applied to any of the focus areas A0 to A6. It is determined that there is no (step S6). In this case, the focusing point of the center focusing area A3 or the focusing area of the center part is prevented so that a partly blurring phenomenon does not occur due to the change of the focusing point caused by the eccentricity of the optical system or the duck of the imaging device. The focus is focused on the average positions of the focus points A2, A3, and A4) (step S7).

If the value AFsadd indicating the linearity of the change of the focus point of the adjacent focus area is larger than the predetermined value P, the linearity is weak, and it is determined that certain focus areas A0 to A6 have main subjects. (Step S8). In this case, the focus area where the subject is located among the focus areas A0 to A6 is specified (step S9). The focus area in which the subject is located can be identified by an algorithm in which the subject is located at the closest focus point among the focus points between the respective focus areas A0 to A6. Then, the focusing point of the specified focus area is focused (step S10).

As described above, in the embodiment of the present invention, the focus points of the adjacent focus areas A0 to A6 are second-differentially differentiated, the absolute value is added to the second differentiated focus points, and the focus of the adjacent focus areas is added. A value AFsadd indicating the linearity of the change of the fit point is calculated, and depending on whether or not the value AFsadd indicating the linearity of the change of the focus fit point of this adjacent focus area is smaller than the predetermined value P. It determines whether there is a main subject. When the value AFsadd indicating the linearity of the change of the focus point of the adjacent focus area is smaller than the predetermined value P (when the linearity is strong), the main subject is not included in any of the focus areas A0 to A6. The focusing point of the center focusing area is focused so that some blurring does not occur due to the change of the focusing point caused by the eccentricity of the optical system or the duck of the imaging device. When the value AFsadd indicating the linearity of the change of the focus point between adjacent focus areas A0 to A6 is larger than the predetermined value P (when the linearity is weak), it is determined that there is a main subject. A focus area with a subject is specified to focus on the main subject, and the focus point of the focus area in the center of the specified focus area is focused. For this reason, even when there is an eccentricity of an optical system, or an audibility of an imaging device, a focus is hit by a peripheral part, and a partly cloudy phenomenon does not generate | occur | produce.

This will be described with reference to FIGS. 9 to 11. 9A is a screen shot of a main subject 101. FIG. 9B is a photograph of a landscape-free main subject without a eccentricity of an optical system or an aori of an imaging device. FIG. 9C is a photograph of a landscape-only screen without a main subject with a digital camera having an eccentricity of an optical system or aori of an imaging device.

FIG. 10A is a case where a screen with a main subject 101 as shown in FIG. 9A is photographed, and shows a focus point for each focus area. FIG. 10B is a case where a screen without a main subject as shown in FIG. 9B is photographed by a camera without an eccentricity of an optical system or aori of an imaging device, and shows a focus point for each focus area. FIG. 10C shows a focusing point for each focus area in the case where a screen without a main subject as shown in FIG. 9C is photographed with a camera having an eccentricity of an optical system or aori of an imaging device.

As shown in FIG. 10A, when the screen including the main subject 101 is photographed, the focusing points of the respective focus regions A0 to A6 are determined by the focus regions A4, A5, and A6 having the subject 101. It greatly changes from the vicinity.

As shown in Fig. 10B, in the case of photographing a screen without a main subject, the focal points of the respective focus regions A0 to A6 become almost the same unless there is an eccentricity of the optical system or audibility of the image pickup device.

As shown in Fig. 10C, when photographing a screen without a main subject, the focusing points of the respective focus areas A0 to A6 change linearly when there is an eccentricity of the optical system or an audibility of the imaging device.

FIG. 11A illustrates a calculation process for obtaining a value indicating the linearity of the focusing points of adjacent focus areas when the screen on which the main subject 101 is located is photographed. As shown in Fig. 11A, the focusing point in the focus area A0 is 78 pulses, the focusing point in the focus area A1 is 80 pulses, the focusing point in the focus area A2 is 76 pulses, The focus point in the focus area A3 is 82 pulses, the focus point in the focus area A4 is 106 pulses, the focus point in the focus area A5 is 116 pulses, and the focus point in the focus area A6 is focused. The fit point is 112 pulses.

By differentiating the focusing points of adjacent focus areas A0 to A6, (80-78 = 2), (76-80 = -4), (82-76 = 6), (106-82 = 24), (116-106 = 10), (112-116 = -4).

Differential again, (-4-2 = -6), (6-(-4) = 10), (24-6 = 18), (10-24 = -14), (-4-10 = -14 )

Taking the absolute value of this second differential focusing point and adding it cumulatively, it becomes (6 + 10 + 18 + 14 + 14 = 62). In the case where the scene with the main subject is photographed in this manner, the second derivative of the focusing points of the adjacent focus areas is second-degree, and the absolute value of this second differential focusing point is added to a large value of "62".

When the second derivative of the focusing points of the adjacent focus areas and the absolute value of the second differential focusing point are added (when the linearity is weak) are judged that there is a main subject, the main subject is determined. Which focus area is specified. In the specification of the main focus area, an algorithm in which the main subject is located in the focus area that becomes the closest distance among the focus points of the plurality of focus areas is used. From this algorithm, in this case, the focus area A5 is specified as the focus area where the subject is located, and focusing control is performed using the focus point of the focus area A5.

In contrast, conventionally, a main subject has a focus area that is the closest distance among the focus points of a plurality of focus areas without performing arithmetic processing to obtain a value indicating the linearity of the focus points of adjacent focus areas. The focus area in which the subject is located is specified from the algorithm. In the case where there is a main subject 101 as shown in FIG. 9A, since the focus area A5 is closest to the distance (see FIG. 10A), the focus area A5 is identified as the focus area where the subject is located in the conventional method. The focusing point of the focus area A5 is used.

Fig. 11B shows a calculation process for obtaining a value indicating the linearity of the focusing point of each focus area when a screen without a main subject is photographed with a camera without an eccentricity of an optical system or aori of an imaging device. As shown in FIG. 11B, the focusing point in the focus area A0 is 80 pulses, the focusing point in the focus area A1 is 78 pulses, the focusing point in the focus area A2 is 84 pulses, The focusing point in the focus area A3 is 82 pulses, the focusing point in the focus area A4 is 80 pulses, the focusing point in the focus area A5 is 82 pulses, and the focusing point in the focus area A6 is focused. The fit point is 80 pulses.

Differentiating the focusing points of successive focus areas A0 to A6, (78-80 = -2), (84-78 = 6), (82-84 = -2), (80-82 = -2 ), (82-80 = 2), and (80-82 = -2).

Differential again, (6-(-2) = 8), (-2-6 = -8), (-2-(-2) = 0), (2-(-2) = 4), (- 2-2 = -4).

If the absolute value of this second derivative point of focus is taken and cumulatively added, it becomes (8 + 8 + 0 + 4 + 4 = 24). When there are no main subjects as described above, the value obtained by adding the absolute value to the focus points of the plurality of focus areas A0 to A6 is second-differentially differentiated to "24". The value is small.

When the focusing points of adjacent focus areas A0 to A6 are second-differentiated, and the absolute value of the second derivatives is added (when the linearity is weak), it is determined that there is no main subject. The focusing control is performed using the average of the focusing points of the center focusing area A3 or the focusing points of the focusing areas A2, A3 and A4 near the center.

In contrast, conventionally, a main subject has a focus area that is the closest distance among the focus points of a plurality of focus areas without performing arithmetic processing to obtain a value indicating the linearity of the focus points of adjacent focus areas. The focus area in which the subject is located is specified from the algorithm. In the case as shown in FIG. 9B, since the focus area A2 is the closest distance (see FIG. 10B), in the conventional method, the focus area A2 is specified as the focus area where the subject is located, and the focus area A2 is determined. ) Will be used. In the present invention, focus control is performed using an average of the focus points of the focus area A3 or the focus points of the focus areas A2, A3, and A4 near the center. However, the values of all focus points are almost the same. Therefore, as shown in Fig. 9B, when photographing with a camera without an eccentricity of an optical system or an audible image pickup device, the focusing point is almost the same in both the method according to the present invention and the conventional method.

Fig. 11C shows an arithmetic process for obtaining a value indicating the linearity of the focusing points of adjacent focus areas when a screen without a main subject is photographed with a camera having an eccentricity of an optical system or aori of an imaging device. As shown in FIG. 11C, the focus point in the focus area A0 is 80 pulses, the focus point in the focus area A1 is 84 pulses, the focus point in the focus area A2 is 96 pulses, The focus point in the focus area A3 is 100 pulses, the focus point in the focus area A4 is 104 pulses, the focus point in the focus area A5 is 112 pulses, and the focus point is in the focus area A6. The fit point is 116 pulses.

Differentiating the focusing points of adjacent focus areas A0 to A6, (84-80 = 4), (96-84 = 12), (100-96 = 4), (104-100 = 4), ( 112-104 = 8) and (116-112 = 4).

Differentiation again gives (12-4 = 8), (4-12 = -8), (4-4 = 0), (8-4 = 4) and (4-8 = -4).

If the absolute value of the second differential focusing point is taken and cumulatively added, it becomes (8 + 8 + 0 + 4 + 4 = 24). In the case where there is no main subject in this way, even if there is an eccentricity of the optical system or an aberration of the image pickup device, the value of the second derivative of the focusing points of the adjacent focusing areas and the absolute value of the second differentiating focusing points are added. The value is small as "24".

If the second derivative of the focus points of the adjacent focus areas and the absolute value of the second differentiated focus points are small, it is determined that there is no main subject, and the focus points of the center focus area A3 are determined. Or focus control is performed using the average of the focus points of the focus areas A2, A3 and A4 near the center.

In contrast, conventionally, a main subject has a focus area that is the closest distance among the focus points of a plurality of focus areas without performing arithmetic processing to obtain a value indicating the linearity of the focus points of adjacent focus areas. The focus area is specified from an algorithm to perform. In the case of the screen as shown in FIG. 9C, since the focus area A6 is the closest distance (see FIG. 10C), in the conventional method, the focus area A6 is specified as the focus area in which the subject is located and the focus area A6. ) Will be used. For this reason, the focus is on the periphery of the screen, and the central part is in a so-called partially blurred state, such as the focus is out. In the present invention, focus control is performed using an average of the focus points of the focus areas A3 or the focus points of the focus areas A2, A3, and A4 near the center. For this reason, the focus is on the center of the screen.

According to the present invention, an evaluation value for extracting a high frequency component of an image signal is obtained to evaluate a degree of focusing, and a plurality of focus areas are set to obtain evaluation values while moving a focus lens for each focus area, and each focus area is obtained. The focus point for each focus area is obtained from the evaluation values obtained for each time. And the linearity of the change of the focusing point of the adjacent focus area | region is calculated by calculation from the focusing point calculated | required for each focus area | region.

That is, a second derivative of the focusing points of the adjacent focus areas is added, and the absolute value is added to this second differential focusing point to calculate a value indicating the linearity of the change of the focusing points of the adjacent focus areas.

When the linearity of the change of the focus points of the adjacent focus areas is weak, it is determined that the main subject exists in any one of the focus areas, and the focus area in which the main subjects are located is specified. If the linearity of the change in the focus point of the adjacent focus area is strong, it is determined that there is no main subject in any focus area, and the focus point of the focus area near the center is focused.

Accordingly, even if there is an eccentricity of the optical system or aberration of the image pickup device, it is possible to erroneously recognize the focus area where the subject is located and to prevent focusing on the focus area of the peripheral part.

The present invention is suitable for use in focus control of a digital camera or a digital video camera.

This invention is not limited to embodiment mentioned above, A various deformation | transformation and an application are possible within the range which does not deviate from the summary of this invention.

Claims (6)

An autofocus control method for extracting a high frequency component of an image signal to obtain an evaluation value for evaluating a focusing point and obtaining a focusing point. Setting a plurality of focus areas, acquiring evaluation values while moving the focus lens for each focus area, From the evaluation value acquired for each focus area, a focusing point for each focus area is obtained, From the focus points obtained for each focus area, the linearity of the change of the focus points of the adjacent focus areas is calculated by calculation, If the linearity of the change of the focus point of the adjacent focus area is weak, it is determined that the main subject exists in a certain focus area, When the linearity of the change of the focus point of the adjacent focus area is strong, it is judged that there is no main subject in any focus area. The method of claim 1, wherein the operation for calculating the linearity of the change of the focusing points of the continuous focusing areas is performed by second-order differentiating the focusing points of the respective focusing areas, and adding the second differential focusing points to an absolute value. Auto focus control method characterized in that. The method of claim 1, wherein when it is determined that the main subject exists in a certain focus area, the focus area including the main subject is specified, and the focusing point of the specified focus area is focused. . The autofocus control method according to claim 1, wherein when it is determined that there is no main subject in any of the focus areas, the focusing point of the focus area near the center is focused. An automatic focus control device for extracting a high frequency component of an image signal from an image pickup device and acquiring an evaluation value for evaluating the degree of focusing to obtain a focusing point. Lens driving means for moving the focus lens; Evaluation value detection means for extracting a high frequency component of the image signal to obtain an evaluation value for evaluating focusing degree; Focus area setting means for setting a plurality of focus areas; Means for acquiring an evaluation value while moving the focus lens for each focus region; Means for obtaining a focusing point for each focus area from evaluation values obtained for each focus area, Means for calculating, by calculation, the linearity of the change of the focus points of the adjacent focus areas from the focus points obtained for each focus area by calculation; If the linearity of the change in the focus point of the adjacent focus area is weak, it is determined that the main subject is in a certain focus area, and the focus area where the main subject is located is specified, and the focus point of the specified focus area is focused. If the linearity of the change of the focus point of the adjacent focus area is strong, it is determined that there is no main subject in any focus area, and means for focusing on the focus point of the focus area near the center is provided. Auto focus control device characterized in that. The calculation for calculating the linearity of the change of the focus points of the respective focus areas is performed by second derivative of the focus points of the adjacent focus areas, and the absolute value is added to the second derivative. Auto focus control device characterized in that.

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