JP2011118058A - Characteristic adjustment method and characteristic adjustment device for imaging element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform highly accurate focusing by eliminating a focus error caused by a difference in characteristics of respective imaging elements, when a plurality of imaging surfaces for AF are configured by using individual imaging elements, in an autofocus system adopting an optical path length difference system. <P>SOLUTION: A characteristic adjustment method for an imaging element includes a gain adjustment process for adjusting the gain of at least one of a plurality of imaging elements, so that light quantity with which image signals obtained from the respective imaging elements become in a saturation state is matched when a white chart is used as an object, and a correction processing process for correct-processing a focus evaluation value obtained from at least one imaging element, so that the focus evaluation values obtained from the imaging elements respectively are coincident with each other, after the gain adjustment process is performed. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an image sensor characteristic adjustment method and an apparatus for adjusting characteristics, and in particular, a so-called optical path that performs automatic focus adjustment based on a focus evaluation value that indicates the contrast level of an image captured by a plurality of image sensors having optical path length differences. The present invention relates to an image sensor characteristic adjustment method and characteristic adjustment apparatus in an autofocus system that employs a long-difference autofocus.

  2. Description of the Related Art Conventionally, an AF method called an optical path length difference method is known as an autofocus (AF) adopted in a television camera for broadcasting or business use.

  In an autofocus system employing this optical path length difference type AF, for example, a light splitting optical system such as a half mirror is arranged in the photographing lens, and a part of the subject light incident on the photographing lens is passed from the main light path to the AF optical path. Fork. In the main optical path, an image pickup device of a camera body for acquiring a video signal for recording or reproduction (referred to as a video image pickup device in this specification) is arranged, and a video signal for recording or reproduction is transmitted by the video image pickup device. To be acquired.

  On the other hand, a plurality of imaging surfaces of an AF imaging element (referred to as an AF imaging element in this specification) are arranged with an optical path length difference in the AF optical path. The subject light branched into the AF optical path is split by a light splitting optical system arranged in the AF optical path and is incident on each imaging surface of the AF image sensor. As a result, a subject image is captured for each imaging surface, and a video signal for each imaging surface is obtained from the AF imaging element. The contrast of the subject image captured on each imaging surface is obtained as the focus evaluation value based on the video signal for each imaging surface thus obtained. Then, by comparing the focus evaluation values, the focus state (focus, front pin, rear pin) of the photographic lens with respect to the image pickup surface of the image pickup device for video is detected, and shooting is performed so that the focus state is in focus. The focus of the lens is controlled.

  Patent Document 1 describes an optical path length difference type autofocus system in which a plurality of imaging surfaces having optical path length differences are configured by individual imaging elements.

JP 2004-212458 A

  By the way, in the autofocus system that employs the optical path length difference method as represented by the autofocus system described in Patent Document 1, when a plurality of imaging surfaces for AF are configured by a plurality of imaging elements, Even when an image sensor is used, the characteristics do not completely match, and the focus state may not be detected accurately depending on conditions.

  For this reason, when a plurality of AF image sensors are used, adjustments are required to align these characteristics. As this adjustment method, for example, when photographing is performed while gradually changing the light amount by an iris operation using a white chart as a subject, each AF image sensor so that the focus evaluation values according to the light amount coincide between the image sensors. There is a method to adjust the gain.

  However, in such an adjustment method, even when the respective focus evaluation values are the same, the peak size of the focus evaluation value may differ when shooting an ordinary subject, or a white chart is shot. However, there are cases where the characteristics are not uniform and there is a case where the compromise is roughly made, and as a result, the focusing accuracy is lowered.

  The present invention has been made in view of such circumstances, and in an autofocus system employing an optical path length difference method, each imaging element is configured when a plurality of AF imaging surfaces are configured using individual imaging elements. It is an object of the present invention to provide a characteristic adjustment method and characteristic adjustment apparatus for an image pickup device that can perform high-precision focusing by eliminating a focus error caused by a difference in characteristics of the image pickup device.

  In order to achieve the above object, the characteristic adjustment method for an image pickup device according to claim 1, the subject image is picked up by a plurality of autofocus image pickup devices arranged at different positions of the optical path length, and the image is picked up. In a characteristic adjustment method of an image sensor in an autofocus system that performs automatic focus adjustment by controlling the focus of the photographing lens based on a focus evaluation value indicating a contrast height of an obtained subject image, a white chart is used as a subject. In some cases, the gain adjustment step for adjusting the gain of at least one of the plurality of image sensors and the gain adjustment step are performed so that the light amounts at which the video signals obtained from the respective image sensors are in a saturated state match. After that, the focus evaluation values obtained from at least one of the image sensors so that the focus evaluation values obtained from the respective image sensors coincide with each other. Characterized in that it comprises a correction processing step of performing a correction process for.

  The image sensor characteristic adjustment method according to claim 2 is the image sensor characteristic adjustment method according to claim 1, wherein the correction processing step determines a difference between focus evaluation values respectively obtained from the image sensors. The correction processing is performed using

  According to a third aspect of the present invention, there is provided a device for adjusting the characteristics of an image pickup device, wherein a subject image is picked up by a plurality of autofocus image pickup devices arranged at different optical path lengths, and the contrast of the subject image obtained by the image pickup is adjusted. Obtained from each image sensor when a white chart is used as a subject in an image sensor characteristic adjustment apparatus in an autofocus system that performs automatic focus adjustment by controlling the focus of the photographing lens based on a focus evaluation value indicating height A gain adjustment unit that adjusts the gain of at least one of the plurality of image sensors so that the amount of light at which the video signal is saturated is matched, and each gain after the gain adjustment is performed by the gain adjustment unit With respect to the focus evaluation value obtained from at least one of the image sensors so that the focus evaluation values obtained from the respective elements coincide with each other And correcting means for performing correction process, characterized by comprising a.

  The image sensor characteristic adjusting apparatus according to claim 4 is the image sensor characteristic adjusting apparatus according to claim 3, wherein the correction processing means determines a difference in focus evaluation value obtained from each image sensor. The correction processing is performed using

  According to the present invention, it is possible to completely align the characteristics of the AF image sensors, and it is possible to stably and accurately perform focus detection by the optical path length difference method.

The block diagram which showed the structure of the lens system to which this invention is applied Diagram showing the configuration of the photographic lens The image of the camera body image sensor and a pair of AF image sensors on the same optical axis Diagram for explaining the principle of focus state detection by the optical path length difference method The figure for explaining the problem when the peak of the focus evaluation value differs between image sensors The graph which showed an example of the characteristic of each image pick-up element for AF after adjustment was performed so that the focus evaluation value according to light quantity might correspond FIG. 6 is a diagram illustrating an example of a video signal obtained from each AF imaging element when a normal subject is photographed in the state where the adjustment of FIG. 6 has been performed. The graph which showed an example of the characteristic of each image sensor for AF after adjustment was performed so that the saturation light quantity of each image sensor for AF might correspond The figure which showed an example of the video signal obtained from each image pick-up element for AF, when a normal subject is image | photographed in the state where adjustment of FIG. 8 was performed Figure excerpted from the graph shown in Figure 8 The figure which showed simply the process by which a focus evaluation value is corrected in a correction processing step Flow chart showing processing procedure of CPU

  Hereinafter, an embodiment for carrying out an autofocus system according to the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a block diagram showing the configuration of a lens system to which the autofocus system of the present invention is applied. The lens system shown in FIG. 1 includes, for example, a shooting lens (shooting optical system) mounted on a camera body (camera head) of a broadcast television camera by a mount, and a control system that controls the shooting lens. It should be noted that the photographic lens and the control system except for a part are configured as an integrated lens device, or the photographic lens and the control system are configured as separate devices. Any type of apparatus may be used.

  The photographic lens is a photographic optical system that connects an object image to the imaging surface of the camera body. In addition to various fixed lens groups, the photographic lens is a focus lens shown in the figure as a lens group movable in the optical axis direction. A (group) FL and a zoom lens (group) ZL are arranged. When the focus lens FL moves, the focus position (subject distance) changes, and when the zoom lens ZL moves, the image magnification (focal distance) changes. Further, the photographing lens is provided with a diaphragm I shown in the figure which is driven to open and close in order to change the diaphragm value.

  The control system of the lens system includes a CPU 10, amplifiers FA, ZA, IA, motors FM, ZM, IM, focus demand 18, zoom demand 20, AF circuit 30 and the like. The CPU 10 performs overall control of the entire system. When drive signals are output from the CPU 10 to the amplifiers FA, ZA, and IA via the D / A converter 12, the motors FM, ZM, and IM receive the drive signals. It is driven at a rotation speed corresponding to the value (voltage). The motors FM, ZM, and IM are connected to the focus lens FL, zoom lens ZL, and diaphragm I of the photographing lens. The motors FM, ZM, and IM are driven together with the focus lens FL, zoom lens ZL, and diaphragm I. Is driven. Potentiometers FP, ZP, and IP that output voltage signals corresponding to their rotational positions are connected to the output shafts of the motors FM, ZM, and IM. The voltage signals from the potentiometers FP, ZP, and IP are A signal indicating the position of the lens FL, the position of the zoom lens ZL, and the position of the stop I is given to the CPU 10 via the A / D converter 14. Accordingly, the positions or operating speeds of the focus lens FL, zoom lens ZL, and diaphragm I of the photographing lens are controlled to a desired state by drive signals given from the CPU 10 to the amplifiers FA, ZA, and IA.

  The focus demand 18 and the zoom demand 20 are controllers provided with a manual operation member that manually designates a target position and moving speed of the focus (focus lens FL) and zoom (zoom lens ZL) of the photographing lens. The focus demand 18 and the zoom demand 20 are each connected to the CPU 10 via the A / D converter 14.

  In this lens system, the focus control can be performed by either manual focus (MF) or autofocus (AF). During the MF control, the focus is controlled according to the operation of the manual operation member at the focus demand 18. Control is performed. When the manual operation member of the focus demand 18 is operated during the MF control, for example, a focus command signal for designating a focus target position corresponding to the position of the operation member is given to the CPU 10. The CPU 10 controls the position of the focus lens FL by controlling the motor FM with a drive signal output to the amplifier FA so that the focus position becomes the target position specified by the focus command signal. In general, in the MF control, the position of the focus lens FL is controlled according to the target position given from the focus demand 18, but the target moving speed is given from the focus demand 18, and the speed control of the focus lens FL is performed accordingly. Is also possible.

  When a manual operation member of the zoom demand 20 is operated, for example, a zoom command signal that designates a zoom target movement speed corresponding to the position of the operation member is given to the CPU 10. The CPU 10 controls the moving speed of the zoom lens ZL by controlling the motor ZM with a drive signal output to the amplifier ZA so that the moving speed of the zoom becomes the target moving speed specified by the zoom command signal. In general, in zoom control, the speed control of the zoom lens ZL is performed according to the target moving speed given from the zoom demand 20, but the target position is given from the zoom demand 20 and the position control of the zoom lens ZL can be performed accordingly. Is possible.

  A camera body (not shown) is configured to provide the CPU 10 with an iris command signal that designates the target position of the iris I. The CPU 10 determines the position (opening / closing degree) of the iris I as a target position designated by the iris command signal. The motor IM is controlled by the drive signal output to the amplifier IA so that the position of the diaphragm I is controlled.

  As will be described in detail later, the AF circuit 30 is a circuit that detects a focus evaluation value indicating the level of contrast of the subject image, and information on the focus evaluation value is supplied from the AF circuit 30 to the CPU 10. During the AF control, the CPU 10 controls the motor FM with a drive signal output to the amplifier FA so that the focus state of the photographing lens is in focus based on the focus evaluation value information obtained from the AF circuit 30, and the focus lens Control FL.

  The AF circuit 30 includes a pair of AF image sensors 32A and 32B, an A / D converter 34, a gate circuit 36, a high-pass filter (HPF) 38, adder circuits 40A and 40B, and the like.

  A pair of AF imaging elements 32A and 32B (for example, a CCD sensor or a CMOS sensor) are provided separately from an imaging element (for example, a CCD sensor or a CMOS sensor) mounted on the camera body. The image pickup device of the camera body is an image pickup device for capturing an original image for recording or reproduction (hereinafter referred to as a video image pickup device), whereas the AF image pickup devices 32A and 32B are provided exclusively for AF. For example, the imaging element is disposed in an optical system of a photographic lens configured as shown in FIG.

  Here, the arrangement of the AF image pickup devices 32A and 32B will be described with reference to FIG. On the optical axis O of the photographic lens 60, the focus lens (group) FL, the zoom lens (group) ZL, the diaphragm I, the relay lens (relay optical system) including the front relay lens RA and the rear relay lens RB, etc. Are arranged in order. Subject light incident on the taking lens 60 passes through these lens groups and enters the camera body 50. The camera main body 50 includes a color separation optical system 68 that separates subject light incident from the photographing lens 60 into three wavelengths of red (R), green (G), and blue (B), and color separation of each color. An image pickup device for video for each of R, G, and B for picking up an image of subject light is arranged. Note that the image pickup devices for R, G, and B arranged at the position of the optically equivalent optical path length are represented by one image pickup device 70 as shown in FIG. The subject light incident on the imaging surface of the image pickup device 70 is photoelectrically converted by the image pickup device 70 and a video signal for recording or reproduction is generated by a predetermined signal processing circuit in the camera body 50.

  On the other hand, a half mirror 62 is disposed between the front relay lens RA and the rear relay lens RB of the relay optical system of the photographing lens 60. The half mirror 62 divides the optical path of the taking lens 60 into two. Of the subject light incident on the photographic lens 60, the subject light transmitted through the half mirror 62 is guided to the camera body 50 along the optical path of the optical axis O as described above. The subject light reflected by the half mirror 62 is guided to the optical path (AF optical path) of the optical axis O ′ substantially perpendicular to the optical axis O. Note that subject light having a light amount of, for example, about 50% of the subject light incident on the half mirror 62 passes through the half mirror 62. However, as the half mirror 62, a mirror having arbitrary transmittance and reflectance characteristics can be used.

  In the AF optical path, a relay lens RB ′ equivalent to the rear relay lens RB, a light splitting optical system 64 composed of two prisms 64A and 64B, and the AF imaging elements 32A and 32B are arranged. Yes. The subject light reflected by the half mirror 62 and guided to the AF optical path passes through the relay lens RB ′ and then enters the light splitting optical system 64. The subject light incident on the light splitting optical system is split into two subject lights with equivalent light quantities on the half mirror surface M where the first prism 64A and the second prism 64B are joined. The subject light reflected by the half mirror surface M is incident on the imaging surface of one AF imaging element 32A, and the subject light transmitted through the half mirror surface M is incident on the imaging surface of the other AF imaging element 32B.

  FIG. 3 is a diagram showing the image pickup element 70 for video and the AF image pickup elements 32A and 32B of the camera body 50 on the same optical axis. As shown in the figure, the optical path length of the subject light incident on one AF image sensor 32A is set shorter than the optical path length of the subject light incident on the other AF image sensor 32B. The optical path length of subject light incident on the imaging surface is set to be an intermediate length. That is, the pair of AF imaging elements 32 </ b> A and 32 </ b> B (imaging surfaces thereof) are disposed so as to be positioned at an equal distance d in the front-rear direction with respect to the imaging surface of the imaging element 70 for video.

  In this way, the pair of AF imaging elements 32A and 32B arranged on the imaging lens 60 captures the subject light incident on the imaging lens 60 at positions equidistant from the imaging surface of the video imaging element 70, respectively. A video signal equivalent to the case where the plane is arranged is acquired. Note that the AF imaging elements 32A and 32B do not need to capture color images, and in the present embodiment, monochrome image signals (luminance signals) are acquired from the AF imaging elements 32A and 32B. .

  In the AF circuit 30 of FIG. 1, video signals obtained by the AF imaging elements 32A and 32B are converted into digital signals by the A / D converter 34 and then input to the gate circuit 36. The gate circuit 36 extracts a video signal within a range corresponding to a predetermined AF area (for example, a rectangular area at the center of the screen) set within the shooting range (screen). The video signal in the AF area thus extracted is subsequently input to a high pass filter (HPF) 38, and only the high frequency component signal is extracted by the HPF 38.

  The signal of the high frequency component extracted by the HPF 38 is integrated by the addition circuit 40A for the signal obtained from the AF image sensor 32A, and the signal obtained from the AF image sensor 32B is integrated by one field by the adder circuit 40B. The integrated value is output from the AF circuit 30 for each field.

  The integrated values obtained from the adding circuits 40A and 40B in this way indicate values for evaluating the contrast height of the subject images captured by the AF imaging elements 32A and 32B, respectively. In this specification, this integrated value is referred to as a focus evaluation value. The focus evaluation value obtained from the image signal of the AF image sensor 32A is referred to as the chA focus evaluation value, and the focus evaluation value obtained from the image signal of the AF image sensor 32B is referred to as the chB focus evaluation value.

  The CPU 10 detects the focus state of the photographing lens 60 with respect to the image pickup device 70 based on the chA and chB focus evaluation values obtained in this way. The focus state is detected based on the following principle. FIG. 4 is a diagram illustrating the relationship between the focus position and the focus evaluation value when a certain subject is photographed, with the horizontal axis indicating the position (focus position) of the focus lens FL of the photographing lens 60 and the vertical axis indicating the focus evaluation value. It is. Curves A and B indicated by solid lines in the figure indicate the focus evaluation values of chA and chB obtained from the AF imaging elements 32A and 32B, respectively, with respect to the focus position. On the other hand, a curved line C indicated by a dotted line in the drawing indicates the focus evaluation value with respect to the focus position when it is assumed that the focus evaluation value is obtained from the video signal obtained from the video image sensor 70.

In the figure, the focus state is in focus when the focus is set at the focus position F0 when the focus evaluation value of the image pickup device for video 70 indicated by the curve C is maximum (maximum). If the focus of the photographic lens 60 is set to the focus position F1 closer to the focus position F0, the focus evaluation value of chA is the value V _{A1 of the} curve A corresponding to the focus position F1. , ChB focus evaluation value is the value V _{B1 of the} curve B corresponding to the focus position F1. In this case, as can be seen from the figure, the chA focus evaluation value V _A1 is larger than the chB focus evaluation value V _B1 . From this, when the focus evaluation value V _A1 of chA is larger than the focus evaluation value V _{B1 of} chB, the focus is set closer to the in-focus position F0, that is, the front pin It can be seen that

On the other hand, when the focus of the photographing lens 60 is set to the focus position F2 on the infinity side of the focus position F0, the focus evaluation value of chA is the value V _{A2 of the} curve A corresponding to the focus position F2. , ChB focus evaluation value is the value V _{B2 of the} curve B corresponding to the focus position F2. In this case, the chA focus evaluation value V _A2 is smaller than the chB focus evaluation value V _B2 . From this, when the focus evaluation value V _A2 of chA is smaller than the focus evaluation value V _{B2 of} chB, the focus is set to the infinity side from the in-focus position F0, that is, the rear It can be seen that the pin is in a state.

On the other hand, when the focus of the photographic lens 60 is set to the focus position F0, that is, the focus position, the focus evaluation value of chA becomes the value V _{A0 of the} curve A corresponding to the focus position F0. The focus evaluation value of chB is the value V _{B0 of the} curve B corresponding to the focus position F0. In this case, the chA focus evaluation value V _A0 is equal to the chB focus evaluation value V _B0 . From this, it can be seen that when the chA focus evaluation value V _A0 is equal to the chB focus evaluation value V _B0 , the focus is in the in-focus position F 0, that is, the in-focus state.

  In this way, it is possible to detect whether the current focus state of the photographic lens is a front pin, a rear pin, or an in-focus state with respect to the image pickup device 70 for video by using the focus evaluation values of chA and chB.

  In FIG. 1, the CPU 10 sequentially detects the focus state of the photographing lens 60 with respect to the image pickup device 70 based on the focus evaluation values of chA and chB as described above, so that the focus lens FL is brought into a focused state. To control. For example, when the focus state is the front pin, the focus lens FL is moved in the infinity direction, and when the focus state is the rear pin, the focus lens FL is moved in the closest direction. When the focus state is in focus, the focus lens FL is stopped. As a result, the focus lens FL moves to a position where the focus state of the photographing lens is in focus and stops. An AF method that performs automatic focus adjustment using a plurality of AF imaging elements having optical path length differences is referred to as an optical path length difference method.

  Note that the CPU 10 not only detects the focus state but also detects the degree of focus deviation from the difference or ratio of the focus evaluation values of chA and chB, and reflects them in the speed at which the CPU 10 moves the focus lens FL. It is also possible.

  By the way, when the chA imaging surface and the chB imaging surface are configured by two imaging elements (AF imaging elements 32A and 32B) as in the present embodiment, there is a difference in characteristics (for example, gain error). , ChA and chB focus evaluation values are as shown by curves A and B in FIG. In such a case, even when the amount of the subject light incident on the chA imaging surface and the chB imaging surface is the same, the overall sizes of the curves A and B are different. For this reason, if the focus position where the focus evaluation values of chA and chB match is determined as the focus position, the focus position F0 ′ is determined as the focus position in the example of the figure, and the focus error with respect to the true focus position F0 is determined. This causes a problem that the focusing accuracy is lowered.

  For this reason, when a plurality of AF imaging elements 32A and 32B are used, adjustments are required to make the characteristics uniform. Here, as an example of an adjustment method for aligning the characteristics of the AF image pickup devices 32A and 32B, each of the image pickup devices has a focus evaluation value corresponding to the amount of light when the white chart is taken as a subject. A method for adjusting the gain of the AF image sensors 32A and 32B will be described.

FIG. 6 shows an example of the characteristics (light quantity-focus evaluation value characteristics; white chart characteristics) of the AF image sensors 32A and 32B after adjustment is performed so that the focus evaluation values corresponding to the light quantities match. It is a graph. In the figure, the solid line is a graph showing the white chart characteristics of the AF image sensor 32A, and the broken line is the white chart characteristic of the AF image sensor 32B. Each graph corresponds to a portion where the focus evaluation value increases in proportion to the amount of light. It consists of an inclination straight line (straight line with respect to the horizontal axis) and a vertical straight line (straight line perpendicular to the horizontal axis) corresponding to a portion where the focus evaluation value suddenly drops from the maximum value to 0 when the light intensity is a predetermined amount It is a triangular mountain graph. In this graph, the amount of light (L _A , L _B ) where the vertical straight line is located indicates the amount of light when the video signal (luminance signal) obtained from the image sensor becomes saturated and the focus evaluation value cannot be calculated. In this specification, the light quantity at that time is referred to as a saturated light quantity. Although the characteristics of the AF image sensors 32A and 32B before the gain adjustment are not shown, the focus evaluation values at the same light amount differ between the image sensors (that is, the slope straight line of the graph is In this example, it is assumed that the focus evaluation value of the AF image sensor 32B is smaller than that of the AF image sensor 32A. This adjustment is performed in a state where the AF image sensors 32A and 32B are set to the same focal length (focus position).

  According to this adjustment method, the adjustment can be performed so that the noise levels included in the video signals obtained from the imaging elements 32A and 32B are equal. FIG. 7 is a diagram showing an example of a video signal obtained from each of the AF imaging elements 32A and 32B when a normal subject is photographed. A left pulse 80A is a video signal obtained from the AF imaging element 32A and a right pulse. Reference numeral 80B denotes a video signal obtained from the AF image sensor 32B, and reference numerals 82A and 82B denote noise components included in the respective video signals. As shown in the figure, when this adjustment is performed, the amounts (amplitudes) of the noise components 82A and 82B included in the video signals 80A and 80B are equal.

However, as described above, when the gain adjustment is performed so that the focus evaluation values obtained from the image sensors 32A and 32B coincide between the image sensors, the saturated light amounts L _A and L _{B of the} image sensors 32A and 32B are obtained. Cannot be matched, and it is difficult to completely align the characteristics of the AF image sensors 32A and 32B.

In the example shown in FIG. 6, the saturation amount _{L A} of the AF imaging devices 32A is smaller than the saturation amount _{L B} of the AF imaging device 32B _{(L A <L} B), towards the AF imaging devices 32A comes first It shows that it becomes saturated. As described above, when there is a difference in the saturation light amount between the AF image pickup devices 32A and 32B, the amount of incident light varies between the image pickup devices even when shooting is performed with the same light amount, and the image signals 80A and 80B shown in FIG. In addition, there is a difference in the level of the video signal obtained from each of the AF image sensors 32A and 32B. As a result, the focus evaluation values obtained from the AF image sensors 32A and 32B are different in magnitude as shown by the curves A and B shown in FIG. 5, which causes a reduction in focusing accuracy. .

Next, as another adjustment method for aligning the characteristics of the AF image sensors 32A and 32B, the saturation light amounts L _A and L _{B of the} AF image sensors 32A and 32B are captured when a white chart is photographed as a subject. A method for adjusting the gain of each of the AF imaging elements 32A and 32B so as to match the elements will be described.

FIG. 8 shows characteristics (light quantity-focus evaluation value characteristics) of the AF image sensors 32A and 32B after the adjustment is performed so that the saturation light quantities L _A and L _{B of the} AF image sensors 32A and 32B coincide with each other. It is the graph which showed an example of (white chart characteristic). As shown in the figure, in this adjustment method, the adjustment is performed so that the vertical straight lines (straight lines perpendicular to the horizontal axis) of the graphs indicating the white chart characteristics of the AF image pickup devices 32A and 32B coincide.

According to this adjustment method, as shown in FIG. 8, it is possible to avoid problems caused by the saturation light amounts L _A and L _{B of the} AF imaging elements 32A and 32B being different, but the focus evaluation value corresponding to the light amount is captured. Since the elements cannot be matched and the difference in the focus evaluation value changes according to the amount of light, it is difficult to completely align the characteristics of the AF image sensors 32A and 32B.

  For example, when the focus evaluation value peaks obtained when a specific subject is photographed are adjusted in advance so as to be aligned between the image sensors, for example, as shown in FIG. 9, from each of the AF image sensors 32A and 32B. In some cases, the levels of the obtained video signals 80A ′ and 80B ′ coincide with each other to obtain curves A and B having the same size as shown in FIG. However, this is limited to specific shooting conditions. When the amount (amplitude) of the noise components 82A ′ and 82B ′ included in the video signals 80A ′ and 80B ′ changes due to the change in the amount of light, the video signal 80A ′, The levels of 80B 'do not match, and curves A and B having different sizes can be obtained as shown in FIG. As a result, the accuracy of focusing is reduced. In particular, when a high-luminance subject is photographed, the difference between the focus evaluation values obtained from the AF image sensors 32A and 32B is large, and the problem becomes more prominent.

Therefore, in the autofocus system according to the present embodiment, as an adjustment method for aligning the characteristics of the image pickup devices 32A and 32B, when the white chart is taken as a subject, the saturation light amount L _A of each AF image pickup device 32A and 32B after the L _B makes a step of performing matching each AF imaging devices 32A to, 32B gain adjustment between the imaging element (gain adjustment step) (see FIG. 8), the focus evaluation value is the imaging device in accordance with the amount A step of performing correction processing (correction processing step) is performed so as to match each other.

In this correction processing step, a correction value (obtained from a predetermined correction function f (x) for one or both of the focus evaluation values obtained from the AF image sensors 32A and 32B ( (Corresponding to the difference in focus evaluation values) is added to perform correction processing so that the same focus evaluation value is obtained when the light quantity is the same. Note that the average luminance in the AF area that varies according to the amount of light is used as the variable x. When correction processing is performed on both focus evaluation values, a plurality of correction functions f _a (x) and f _b (x) respectively corresponding to the AF imaging elements 32A and 32B are used.

  FIG. 10 is a diagram excerpted from a part of the graph shown in FIG. 8, and the inclination straight lines 90A and 90B correspond to the inclination straight lines of the graphs showing the white chart characteristics of the AF imaging elements 32A and 32B, respectively. is there. In the example shown in the figure, the difference between the focus evaluation values obtained from the AF image sensors 32A and 32B is composed of a part ax and a fixed value part b, which are proportional to the light amount. In this case, the correction function f (x) is The sum ax + b can be expressed by N (ax + b) obtained by multiplying the number N of pixels in the AF area (ie, f (x) = N (ax + b)). The correction coefficients a and b are values determined individually depending on the combination of the image pickup elements used as the AF image pickup elements 32A and 32B, and optimal values are appropriately set according to the characteristics after gain adjustment. The correction function f (x) is not limited to the above-described example, and may be any function corresponding to the difference between the focus evaluation values obtained from the AF imaging elements 32A and 32B.

  FIG. 11 is a diagram schematically illustrating a process in which the focus evaluation value is corrected in the correction processing step. As shown in the figure, in the correction processing step, first, the average luminance (luminance per pixel) x in the AF area is calculated. Then, after multiplying the average luminance x by the correction coefficient a, the correction coefficient b is further added to obtain a correction value ax + b per pixel. Further, a correction value N (ax + b) to be added to the focus evaluation value is obtained by multiplying the correction value ax + b per pixel by the number N of pixels in the AF area. Then, the corrected focus evaluation value can be calculated by adding the correction value N (ax + b) to the focus evaluation value to be corrected.

  Next, a specific processing procedure of the CPU 10 will be described using the flowchart of FIG. As shown in the flowchart of FIG. 12, when the CPU 10 acquires the focus evaluation values E1 and E2 of chA and chB from the AF circuit 30 (step S10), the CPU 10 obtains the average luminances X1 and X2 in the AF area (step S12). . Subsequently, correction coefficients a1, b1, a2, and b2 for correcting the focus evaluation values E1 and E2 are acquired (step S14). The correction coefficients a1, b1, a2, and b2 correspond to the correction coefficients a and b described above, and are stored in advance in the memory 22 of FIG. The CPU 10 obtains these correction coefficients a1, b1, a2, and b2 by accessing the memory 22.

  Next, the focus evaluation values E1 'and E2' after correction of the focus evaluation values E1 and E2 are calculated according to the following equations (step S16).

E1 ′ = E1 + N (a1 × X1 + b1)
E2 ′ = E1 + N (a2 × X2 + b2)
Then, the CPU 10 performs focus adjustment based on the optical path length difference based on the corrected focus evaluation values E1 ′ and E2 ′ obtained as described above.

As described above, according to the present embodiment, only gain adjustment is performed so that the saturated light amounts L _A and L _{B of the} AF image pickup devices 32A and 32B coincide with each other in the adjustment stage before manufacture and shipment. In addition, since the correction processing is performed so that the focus evaluation values according to the amount of light coincide with each other, it is possible to completely align the characteristics of the AF image pickup devices 32A and 32B. As a result, focus detection by the optical path length difference method can be stably performed with high accuracy.

  FL: Focus lens, ZL: Zoom lens, I: Aperture, FA, ZA, IA ... Amplifier, FM, ZM, IM ... Motor, FP, ZP, IP ... Potentiometer, 10 ... CPU, 18 ... Focus demand, 20 ... Zoom Demand, 30 ... AF circuit, 32 ... AF image sensor, 34 ... A / D converter, 36 ... Gate circuit, 38 ... High pass filter, 40A, 40B ... Adder circuit, 50 ... Camera body, 60 ... Shooting lens, 62 ... Half mirror, 64 ... Light splitting optical system, 68 ... Color separation optical system, 70 ... Image sensor for video

Claims (4)

A subject image is picked up by a plurality of autofocus imaging elements arranged at different positions of the optical path length, and based on a focus evaluation value indicating the contrast height of the subject image obtained by the image pickup, In the method of adjusting the characteristics of the image sensor in an autofocus system that performs automatic focus adjustment by controlling the focus,
A gain adjustment step of performing gain adjustment of at least one of the plurality of image sensors so that the amount of light at which a video signal obtained from each image sensor becomes saturated when the white chart is a subject,
A correction processing step for performing correction processing on the focus evaluation value obtained from at least one of the image sensors so that the focus evaluation values obtained from the respective image sensors match after the gain adjustment step;
The characteristic adjustment method of the image pick-up element characterized by including these. In the characteristic adjustment method of the image sensor according to claim 1,
The image sensor characteristic adjustment method, wherein the correction process step performs a correction process using a correction function that determines a difference in focus evaluation values obtained from each image sensor. A subject image is picked up by a plurality of autofocus imaging elements arranged at different positions of the optical path length, and based on a focus evaluation value indicating the contrast height of the subject image obtained by the image pickup, In the device for adjusting the characteristics of an image sensor in an autofocus system that performs automatic focus adjustment by controlling focus,
Gain adjusting means for performing gain adjustment of at least one of the plurality of image sensors so that the amount of light at which a video signal obtained from each image sensor becomes saturated when the white chart is a subject,
After the gain adjustment is performed by the gain adjustment unit, a correction processing unit that performs a correction process on the focus evaluation value obtained from at least one of the image sensors so that the focus evaluation values obtained from the respective image sensors coincide with each other. When,
An image sensor characteristic adjusting apparatus comprising: In the characteristic adjustment device of the image sensor according to claim 3,
The image sensor characteristic adjustment apparatus, wherein the correction processing means performs correction processing using a correction function that determines a difference in focus evaluation values obtained from each image sensor.

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