JP2005345948A - Automatic focusing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To allow an automatic focusing device that exerts focus control, based on an image signal, to perform accurate, high-speed focusing operation free from wrong focusing judgement, even in a very blurred state. <P>SOLUTION: The automatic focusing device includes an imaging means for producing an image signal from an optical image of a photographic lens; a first detecting means for detecting high-region components from the image signal and then outputting a first detection result; a second detecting means for detecting the components of a luminance difference from the image signal and then outputting a second detection result; a first information creating means for creating first information from the first detection result and the second detection result; and a control means having a differential calculating means for differentiating the information created by the first information-creating means, and used for controlling the focal point of the optical lens, based on the information created by the first information creating means and the differential calculating means. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an autofocus device that performs a focusing operation using a high-frequency component of an image signal.

  Conventionally, in an autofocus device that performs a focusing operation using a high-frequency component of an image signal, an image is extracted from the image signal by specifying a region, subjected to filtering processing such as bandpass, and the high-frequency component of the signal And the autofocus operation is performed with the position where this signal (hereinafter referred to as the AF evaluation value) is maximized.

  This method is advantageous in terms of cost and space because it does not require a dedicated sensor or optical system for focus detection.Furthermore, since the focus detection operation is performed using the image sensor, focusing accuracy is also improved. It is expensive and widely used in video cameras.

  The general characteristics of this AF evaluation value will be described with reference to FIGS.

  13 and 14 are graphs showing the AF evaluation value and the luminance difference in the AF area. FIG. 13 shows a case where a high contrast edge chart with a reflectance of 90: 2 is used, and FIG. 14 shows the reflectance. It is a graph at the time of using a 90:80 low contrast edge chart.

  In each figure, the horizontal axis is the defocus amount, the left vertical axis is the evaluation value, the right horizontal axis is the maximum brightness difference in the AF area, (A) is the AF evaluation value, and (B) is the maximum in the AF area. Represents the luminance difference.

  The AF evaluation value (A) indicates a maximum value when the defocus amount on the horizontal axis is 0, that is, in the most focused state.

  On the other hand, the brightness difference (B) in the AF area is small in the area where the defocus amount is large because the high brightness portion and the low brightness portion of the chart are mixed, and the image becomes sharper as the defocus amount is reduced. The brightness difference increases, and the maximum value is shown in the most in-focus state.

  As shown in these graphs, since the AF evaluation value varies depending on the contrast of the subject, it is impossible to determine whether the AF evaluation value is close to the in-focus position using only the absolute value of the AF evaluation value.

  However, paying attention to the correlation between the AF evaluation value (A) and the luminance difference (B) in these figures, the AF evaluation value (A) is divided by the luminance difference (B), so that it is substantially constant regardless of the contrast of the subject. JP-A 06-268896 discloses that an evaluation value can be obtained.

  15 and 16 show normalized AF evaluation values obtained by dividing the AF evaluation values (A) of FIGS. 13 and 14 by the luminance difference (B). As shown in these figures, by dividing the AF evaluation value by the luminance difference, a substantially constant AF evaluation value can be obtained in the vicinity of the focus regardless of the contrast of the subject.

  However, the above conventional method basically assumes a video camera, and the size of the image sensor used is small (the diagonal size is about several millimeters), so the maximum defocus amount (lens at the tele end of the lens) Is at an infinite position, and the defocus amount when the closest subject is viewed) is at most about 1 mm, so there is no particular problem in AF operation in a large blur state. When adapted to a digital camera using a diagonal size (20 mm or more in diagonal direction), the maximum defocus amount is extremely large, and a high defocus area (the left area in FIGS. 14 and 15) has high contrast. Even in the subject, the brightness difference becomes small, and as a result, the normalized AF evaluation value obtained by dividing the AF evaluation value by the brightness difference becomes large. Problems occur that result in the in-focus judgment.

  In terms of specific numerical values, in a 1/4 inch type image pickup device that is generally used as an image pickup sensor for a video camera, the diagonal direction is only about 4.5 mm. The focal length of a lens for a video camera corresponding to a 300 mm telephoto lens with a silver salt camera (diagonal size 43 mm) is only about 32 mm.

Using this CCD, the defocus amount from an infinite position when the subject distance is 2 m is obtained. Defocus amount = lens focal length × subject distance / (subject distance−lens focal length = 0.52 mm)
The normalized evaluation values shown in FIG. 15 and FIG. 16 are regions that monotonously decrease even in a large blurred state, so that it is not possible to make an in-focus determination by mistake.

  On the other hand, in the case of an imaging element called an APS-C size that is often used in interchangeable lens digital SLR, the vertical size of the sensor is 15 mm, the horizontal size is 23 mm, and the diagonal size is 27 mm. . Therefore, since the screen size ratio with respect to the 135 size (diagonal 43 mm) is 27/42 = 0.64, the 135 size 300 mm telephoto lens corresponds to 300 mm × 0.64 = 192 mm.

Therefore, when the focal length of the imaging lens is 200 mm and the distance of the subject is 2 m, the defocus amount from the infinite position is
Defocus amount = lens focal length × subject distance / (subject distance−lens focal length) −lens focal length = 22.2 mm
It becomes.

  Looking at the normalized evaluation value when the defocus amount is 22 mm from the normalized evaluation value graphs shown in FIGS. 15 and 16, the normalized evaluation value increases regardless of the large blurred state, and erroneously despite the large blurred state. There arises a problem of determining the focus.

  Also, focusing on the vicinity of the focus, the AF evaluation value changes abruptly in the vicinity of the focus. Therefore, in order to detect the focus peak, the lens is moved empirically by approximately Fδ, and the peak of the AF evaluation value is obtained. If you don't find it, the focus accuracy will deteriorate.

  For example, when using a lens with a focal length of 200 mmF value 1.8 and driving the lens in the in-focus direction from a position with a defocus amount of 22 mm, assuming that δ = 33 μm, Fδ = 33 μm × Since 1.8 = 59.4 μm, it is necessary to calculate the AF evaluation value by driving the lens 0.0594 [mm] / 22 [mm] = 370 times before reaching the in-focus position. When a 60 Hz image is captured and the AF evaluation value is calculated, it takes 370 × 1/60 = 6.17 seconds to reach the in-focus position.

  SUMMARY OF THE INVENTION The present invention has been made in view of the above, and an object of the present invention is to provide an automatic focusing device that performs focusing control based on an image signal, and does not cause an erroneous focusing determination even in a large blurred state. Another object of the present invention is to provide an automatic focusing device capable of high-speed focusing operation.

  In order to achieve the above object, in the present invention, an imaging means for generating an image signal from an optical image of a photographing lens, and a first detection means for detecting a high frequency component from the image signal and outputting a first detection result A second detection means for detecting a luminance difference component from the image signal and outputting a second detection result; a first for generating first information from the first detection result and the second detection result; Information generating means and a differential calculating means for differentiating the information generated by the first information generating means, and based on the information generated by the first information generating means and the differential calculating means, the optical lens And a control means for performing focus control.

  Further, the present invention is characterized by having a focusing control device that moves the lens at a high speed until the vicinity of the focus is detected, and changes the lens driving speed when the vicinity of the focus is detected, and performs the focusing operation accurately.

(Function)
This realizes an accurate automatic focusing device that does not make an erroneous focus determination even in the large defocus state that occurs when a telephoto lens is attached to a large image sensor, and detects the vicinity of the focus Until this time, the lens is driven at a high speed, and when the vicinity of the focus is detected, the lens drive speed is changed, and the AF is accurately focused, whereby the focusing operation can be performed at a high speed.

  As described above, according to the present invention, the imaging means for generating the image signal from the optical image of the photographing lens, and the first detection means for detecting the high frequency component from the image signal and outputting the first detection result. A second detection means for detecting a luminance difference component from the image signal and outputting a second detection result; a first for generating first information from the first detection result and the second detection result; Information generating means and a differential calculating means for differentiating the information generated by the first information generating means, and based on the information generated by the first information generating means and the differential calculating means, the optical lens And a control means for performing focus control.

  Moreover, until the vicinity of the focus is detected, the lens is moved at a high speed, and when the vicinity of the focus is detected, the driving speed of the lens is changed, and the focus control device that performs the focus operation accurately enables a large-size image sensor. It was possible to realize an accurate automatic focusing device that does not cause an erroneous focus determination even in a large defocus state that occurs when a telephoto lens is mounted.

(First embodiment)
Details of the first embodiment of the present invention will be described below with reference to the drawings.

  FIG. 1 is a block diagram showing the overall configuration of a camera system implemented by applying the present invention to an electronic camera. In the figure, 1 is a photographic lens, 2 is a diaphragm for adjusting the amount of light, 3 is a CCD as an image sensor, 4 is an amplifier for amplifying the image signal of the CCD, and 5 is for converting the image output of the image sensor 3 into digital data. An A / D converter 6 designates an area from a digitized image signal, calculates an AF evaluation value, performs color composition from each pixel information, performs gamma processing, and creates a compressed image. A signal processing circuit 7 is an LCD driving circuit for displaying the output of the image signal processing circuit on the LCD monitor 8.

  Reference numeral 9 denotes a focusing motor for driving the imaging lens 1 in the optical axis direction for focusing. Reference numeral 10 denotes a driving circuit for driving the focusing motor 9. Reference numeral 11 denotes an aperture driving motor for driving the diaphragm 2. Reference numeral 12 denotes a drive circuit for driving the aperture drive motor 11. In this example, the focusing motor and the aperture drive motor are composed of stepping motors. Therefore, if the initial position is determined, the position of the focusing lens or the position of the aperture can be managed as an absolute position. Reference numeral 13 denotes a CCD drive circuit for driving the CCD 3 which is an image pickup device, and reference numeral 14 denotes a memory for storing the taken image. A microcomputer 15 controls the AF operation and the entire operation. Reference numeral 16 denotes a lens position detection SW, 17 is a close end pattern, and 18 is an infinite end pattern, which suppresses movement outside the range as the lens is positioned.

  Next, FIG. 2 is a block diagram showing an AF evaluation signal generator in the image signal processing circuit 6. In the figure, 61 is a gate circuit, 62 is a timing generator for extracting an image signal of an area set as an AF area from all image signals, 63 is a known digital low-pass filter, and 64 is a known high-pass filter. The delay circuit 65 includes a shift register and a subtraction circuit 66. 67 is a known absolute value circuit, 68 is a maximum value hold circuit for an AF evaluation value generated from one line of the image signal, 69 is a maximum luminance hold circuit for one line of the image signal, and 70 is an image signal. A minimum luminance hold circuit in one line, 71 is an AF memory for storing the evaluation value maximum value, maximum luminance, and minimum luminance of each line in the AF calculation area in the image signal. Output.

  Next, the AF area of the image sensor 3 will be described with reference to FIGS. 3 and 4.

  3 in FIG. 3 is the entire imaging area of the imaging device 3, and 21 is the AF area. Although it is not necessary to limit the size and position of this area, if it is too wide, it becomes easy to be drawn on the background with a small subject. A certain area is set as an AF area.

  FIG. 4 is an enlarged view of the AF area 21 of FIG. 3, which is two-dimensionally configured with a predetermined pixel size. In this example, AF processing is performed for each horizontal line.

  The output of the image sensor is amplified by the amplifier 4 from the pixel on the left side of the top line of the sensor and converted into a digital signal by the A / D converter 5 and then the A / D input terminal in the image signal processing circuit. A signal is input to the gate circuit 60. At this time, the timing generator 61 designates the AF area of the screen, and when it becomes a necessary area, the gate circuit 60 is opened and the image signal is transmitted to the rear low pass filter 63. When the capture of the AF area for one line is completed, the gate circuit 60 is closed again, and each data held by the AF evaluation value maximum value hold circuit 68, the maximum luminance hold circuit 69, and the minimum luminance hold circuit 70 is stored in the AF memory 71. To be transferred. Therefore, the AF memory 71 stores the AF evaluation value maximum value, maximum luminance, and minimum luminance of each line in the AF area.

  Next, FIGS. 5 and 6 show flowcharts of an AF control flow programmed in the microcomputer 15.

  When an unillustrated AF start button is turned on, each memory data is initialized as an AF initialization process (S100). The close end SW16 and the infinite end SW17 are read, and if the lens has come to the close end, the process branches to S102. If the lens hits the infinite end, the process branches to S103, and if it is not in the contact state, the process branches to S106 (S101). When it hits the nearest end, when the focusing motor is being driven, the driving of the focusing motor is stopped, the driving direction of the motor is changed to the infinite direction, and the inversion count that is a counter of the number of inversions in the driving direction is incremented by one. (S102). When it hits the infinite end, when the focusing motor is being driven, the driving of the focusing motor is stopped, the driving direction of the motor is changed to the closest direction, and the inversion count that is a counter of the number of inversions in the driving direction is incremented by 1 ( S103). If it hits the infinite end and the number of inversions is 2 or more, the process proceeds to S105 to end the AF operation, and if it is less than 2 times, the process proceeds to S106 (S104). If the number of inversions is 2 or more, that is, if in-focus cannot be achieved even if the entire area is searched from the closest direction to the infinite direction, an in-focus indication is displayed on the monitor LCD 8 and the AF operation is terminated (S105).

  On the other hand, when the AF operation is continued, the maximum evaluation value, the maximum luminance, and the minimum luminance of all the lines in the AF area are read from the AF memory 70 of the image signal processing circuit 6 (S106). Next, the AF evaluation value maximum value is divided by the difference between the maximum luminance and the minimum luminance for each line, AF normalization processing is performed, the calculated normalization evaluation values of each line are added, and the result is divided by the number of pixel lines in the AF area. This is the normalized evaluation value for this time. (S108). Next, the AF evaluation value obtained in S106 is differentiated once based on the focus lens driving amount. That is, the previous AF evaluation value is subtracted from the current AF evaluation value, and the current lens position is subtracted from the previous lens position.

  FIG. 7 is a diagram showing the differentiated AF evaluation value. 7A shows a normalized AF evaluation value obtained by dividing the above-described AF evaluation value by a luminance difference, and FIG. 7B shows a signal obtained by differentiating the AF evaluation value once.

  Since this primary differential signal is detected as a larger value as the change in the AF evaluation value is larger, normalization is performed in a region where the defocus amount is large (a region where the defocus amount is 15 mm or more on the left side in FIG. 7). Even in a region where the AF evaluation value (A) is gently raised, a differential signal is hardly generated, and a differential signal is suddenly generated in a region near the focus. Therefore, if this differential signal is detected, it is possible to easily detect that it is in the vicinity of the in-focus state.

  FIG. 8 is an enlarged view of the in-focus vicinity portion of FIG. In the figure, (A), (B) and (C) are the same as those in FIG. The point (P0) or (P1) where the slope of the primary differential signal (B) is 0 indicates the inflection point of the AF evaluation value (A). In other words, this is a point at which the projection changes from upward to downward, and the AF evaluation value (A) indicates the very vicinity of the focal point. The point (P2) at which the primary differential signal (B) becomes 0 indicates that the AF evaluation value (A) is an inflection point and indicates a focal point.

  Next, when the AF evaluation value differentiation process is completed, the AF count, which is an AF process number counter, is incremented by 1 (S109).

  If the AF count is less than 2, that is, if the AF process has only been performed once, the AF evaluation values cannot be compared, so the process branches to S120, and if it is 2 times or more, the process branches to S111 (S110).

  The current normalized evaluation value and the MAX evaluation value are compared. If the current AF evaluation value is larger, the process branches to S112, and if smaller, the process branches to S114 (S112). The current normalized evaluation value is stored as a MAX evaluation, and the lens position at that time is stored as a MAX lens position. As described above, since the focusing motor is composed of a stepping motor in the present embodiment, if the lens is driven until it hits the infinite end SW when the power is turned on and the initial positioning is performed, the absolute position of the lens is the number of driving steps of the stepping motor thereafter. This driving step is stored as the position of the focusing lens (S113). If the evaluation value increase count is less than the predetermined value nMAX, the process branches to S115, and if it is greater than or equal to nMAX, the process branches to S116 (S114). The evaluation value increase count is increased by 1 (S115). If the evaluation value decrease count is greater than 0, the process branches to S116, and if it is greater than 0, the process branches to S118 (S116). The evaluation value decrease count is decreased by 1 (S117).

  When the inflection point of the first-order differential signal obtained in S108 is detected, the AF mode is set to the near focus mode (S119).

  The driving speed is determined according to the normalized evaluation value. In other words, when the evaluation value is small, it is far from the in-focus state, so that the drive speed during image capture is fast, and when the evaluation value is large, the drive speed is close to the in-focus state. (S120).

  The driving speed of the focusing motor 9 is controlled in accordance with the set driving speed, and the operation returns to step 102 and this operation is repeated until in-focus (S121).

  Next, processing when the current evaluation value is decreased from the previous evaluation value in the branch from step 111 will be described. If the evaluation value decrease count is smaller than the predetermined value nMIN, the process branches to S123, and if it is equal to or greater than nMIN, the process branches to S124 (S122). The evaluation value decrease count is increased by 1 (S123). If the evaluation value increase count is greater than 0, the process branches to S125, and if it is less than 0, the process branches to S126 (S124). The evaluation value increase count is decreased by 1 (S125).

  If the AF mode is the search mode, the process branches to S127. If the AF mode is the near focus mode, the process branches to S129 (S126). If the evaluation value decrease count is equal to or greater than the predetermined value TH3, the process branches to S128. If the evaluation value decrease count is smaller than TH3, the process branches to S120, and the normal drive process is repeated (S127). If the evaluation value decreases for a predetermined number of times TH3 or more, it is far from the in-focus direction. Therefore, in order to reverse the focusing direction, the driving motor is stopped and the driving direction is set in the opposite direction, and the evaluation value decreases. The count and the evaluation value increase count are reset to 0 (S128). On the other hand, if the AF mode is the near focus mode at the branch from S126, if the evaluation value decrease count is equal to or greater than the predetermined value TH2, that is, if the evaluation value decreases a predetermined number of times, the focus peak is surely passed. The process branches to S130, and if it is equal to or smaller than the predetermined value TH2, the process branches to S120, and the normal driving process is repeated (S129).

  For driving to the in-focus position, a difference between the current focus position and the focus position at the maximum evaluation value stored in S113 is obtained as a focus drive amount (S130).

  The focus drive is stopped, the drive direction is reversed, and focus drive is performed with the focus drive amount obtained in S130 (S131). The focus display is displayed on the liquid crystal monitor 8, and the AF operation is terminated (S132).

  By executing the above operation, a primary differential signal is created from the AF evaluation value signal, and a change in the primary differential signal is detected to detect the vicinity of the in-focus state. Can focus on the subject quickly and reliably.

(Second Embodiment)
Next, a second embodiment of the present invention will be described.

  In the first embodiment, the in-focus vicinity is detected using the primary differential signal of the AF evaluation value. However, in the second embodiment, based on the information generated by performing the secondary differentiation of the AF evaluation value signal. A reliable AF operation can be performed.

  Since the hardware embodiment is the same as the first embodiment, only the operation of the software will be described.

  9 and 10 show a flowchart of the AF control flow in the second embodiment programmed in the microcomputer 15.

  When an unillustrated AF start button is turned on, each memory data is initialized as an AF initialization process (S200). The closest end SW16 and the infinite end SW17 are read, and if the lens is in contact with the close end, the process branches to S202. If the lens is in contact with the infinite end, the process branches to S203, and if not, the process branches to S206 (S201). When it hits the nearest end, when the focusing motor is being driven, the driving of the focusing motor is stopped, the driving direction of the motor is changed to the infinite direction, and the inversion count that is a counter of the number of inversions in the driving direction is incremented by one. (S202). When it hits the infinite end, when the focusing motor is being driven, the driving of the focusing motor is stopped, the driving direction of the motor is changed to the closest direction, and the inversion count that is a counter of the number of inversions in the driving direction is incremented by 1 ( S203). If it hits the infinite end and the number of inversions is 2 or more, the process proceeds to S205 to end the AF operation, and if it is less than 2 times, the process proceeds to S206 (S204). If the number of inversions is 2 or more, that is, if in-focus cannot be achieved even if the entire area is searched from the closest direction to the infinite direction, an in-focus indication is displayed on the monitor LCD 8 and the AF operation is terminated (S205).

  On the other hand, when the AF operation is continued, the maximum evaluation value, maximum luminance, and minimum luminance of all the lines in the AF area are read from the AF memory 70 of the image signal processing circuit 6 (S206). Next, the AF evaluation value maximum value is divided by the difference between the maximum luminance and the minimum luminance for each line, AF normalization processing is performed, the calculated normalization evaluation values of each line are added, and the result is divided by the number of pixel lines in the AF area. The normalized evaluation value for this time is used (S208). Next, the AF evaluation value obtained in S206 is differentiated once based on the focus lens driving amount. That is, the previous AF evaluation value is subtracted from the current AF evaluation value, and the current lens position is subtracted from the previous lens position.

  FIG. 11 is a diagram showing the differentiated AF evaluation value. (A) in FIG. 11 is a normalized AF evaluation value obtained by dividing the above-described AF evaluation value by the luminance difference, and (B) is a signal obtained by differentiating the AF evaluation value once. (C) is obtained by differentiating the AF evaluation value twice. That is, it is obtained by differentiating the primary differential signal (B) differentiated once more.

  Since this primary differential signal is detected as a larger change in the AF evaluation value, it is normalized in a region where the defocus amount is large (region where the defocus amount is 15 mm or more on the left side in FIG. 11). Even in a region where the AF evaluation value (A) is gently raised, a differential signal is hardly generated, and a differential signal is rapidly generated in a region near the focus. Therefore, if this differential signal is detected, it is possible to easily detect that it is in the vicinity of the in-focus state.

  FIG. 12 is an enlarged view of the in-focus vicinity portion of FIG. In the figure, (A), (B), and (C) are the same as those in FIG. The point (P0) or (P1) where the slope of the primary differential signal (B) is 0 indicates the inflection point of the AF evaluation value (A). In other words, it is a point that switches from convex upward to convex downward, and as the AF evaluation value (A), the point (P2) where the primary differential signal (B) indicating the very vicinity of the focal point is 0 is the AF evaluation value ( A) shows the inflection point and shows the focal point.

  Next, inflection points (P3) and (P4) of the secondary differential signal (C) indicate inflection points of the primary differential signal (B).

  It can be seen that (P3) and (P4) are located outside the inflection points (P0) and (P2) of the primary differential signal (B) with reference to the focal point.

  Accordingly, by detecting the inflection point of the secondary signal, it is possible to detect that the in-focus vicinity has been reached at a point faster than the detection of the inflection point of the first derivative.

  Next, when the AF evaluation value differentiation process ends, the AF count, which is the AF process count, is incremented by 1 (S209).

  If the AF count is less than 2, that is, if the AF process has only been performed once, the AF evaluation values cannot be compared, so the process branches to S220, and if it is 2 times or more, the process branches to S211 (S210).

  The current normalized evaluation value and the MAX evaluation value are compared. If the current AF evaluation value is larger, the process branches to S212, and if smaller, the process branches to S214 (S212). The current normalized evaluation value is stored as a MAX evaluation value, and the lens position at that time is stored as a MAX lens position. As described above, since the focusing motor is composed of a stepping motor in the present embodiment, if the lens is driven until it hits the infinite end SW when the power is turned on and the initial positioning is performed, the absolute position of the lens is the number of driving steps of the stepping motor thereafter. This driving step is stored as the position of the focusing lens (S213). If the evaluation value increase count is less than the predetermined value nMAX, the process branches to S215, and if it is greater than nMAX, the process branches to S216 (S214). The evaluation value increase count is increased by 1 (S215). If the evaluation value decrease count is greater than 0, the process branches to S216, and if it is greater than 0, the process branches to S218 (S216). The evaluation value decrease count is decreased by 1 (S217).

  When the inflection point of the secondary differential signal obtained in S208 is detected, the AF mode is set to the near focus mode (S219).

  The driving speed is determined according to the normalized evaluation value. In other words, when the evaluation value is small, it is far from the in-focus state, so that the drive speed during image capture is fast, and when the evaluation value is large, the drive speed is close to the in-focus state. (S220).

  The driving speed of the focusing motor 9 is controlled according to the set driving speed, and the operation returns to S202 and this operation is repeated until in-focus (S221).

  Next, processing when the current evaluation value has decreased from the previous evaluation value in the branch from S211 will be described. If the evaluation value decrease count is smaller than the predetermined value nMIN, the process branches to S223, and if it is equal to or greater than nMIN, the process branches to S224 (S222). The evaluation value decrease count is increased by 1 (S223). If the evaluation value increase count is greater than 0, the process branches to S225, and if it is 0 or less, the process branches to S226 (S224). The evaluation value increase count is decreased by 1 (S225).

  If the AF mode is the search mode, the process branches to S227. If the AF mode is the near focus mode, the process branches to S229 (S226). If the evaluation value decrease count is greater than or equal to the predetermined value TH3, the process branches to S228. If the evaluation value decrease count is less than TH3, the process branches to S220, and the normal driving process is repeated (S227). If the evaluation value decreases for a predetermined number of times TH3 or more, it is far from the in-focus direction. Therefore, in order to reverse the focusing direction, the driving motor is stopped and the driving direction is set in the opposite direction, and the evaluation value decreases. The count and the evaluation value increase count are reset to 0 (S128). On the other hand, when the AF mode is the near focus mode at the branch from S226, if the evaluation value decrease count is equal to or greater than the predetermined value TH2, that is, if the predetermined number of evaluation values decreases, the focus peak is surely passed. The process branches to step 230, and if it is equal to or smaller than the predetermined value TH2, the process branches to S220, and the normal driving process is repeated (S229).

  For driving to the in-focus position, the difference between the current focus position and the focus position at the maximum evaluation value stored in S213 is obtained as the focus drive amount (S230).

  The focus drive is stopped, the drive direction is reversed, and focus drive is performed with the focus drive amount obtained in S230 (S231). The focus display is displayed on the liquid crystal monitor 8, and the AF operation is terminated (S232).

  By executing the above operation, a secondary differential signal is created from the AF evaluation value signal, and a change in the secondary differential signal is detected to detect the vicinity of the in-focus state. Can focus on the subject quickly and reliably.

  In the above embodiment, the image signal processing circuit 6 corresponds to detection means for outputting the first and second detection results, the microcomputer 15 corresponds to first, second, and differential information generation means, The drive circuit 10 corresponds to control means for performing focus control.

Block diagram of an autofocus device embodying the present invention 1 is a block diagram of an AF evaluation value generation circuit according to a first embodiment of the present invention. 2A and 2B illustrate an AF area of the image sensor according to the first embodiment of the present invention. The figure explaining the detail of AF area | region of the image pick-up element which concerns on the 1st Embodiment of this invention. The flowchart which shows operation | movement of the camera which concerns on the 1st Embodiment of this invention. The flowchart which shows operation | movement of the camera which concerns on the 1st Embodiment of this invention. The figure which shows the 1st derivative signal of AF evaluation value based on 1st Example of this invention. The figure which shows the 1st differential signal of AF evaluation value based on 1st Example of this invention. The flowchart which shows operation | movement of the camera which concerns on the 2nd Embodiment of this invention. The flowchart which shows operation | movement of the camera which concerns on the 2nd Embodiment of this invention. The figure which shows the 1st differential signal of AF evaluation value based on 2nd Example of this invention. The figure which shows the 1st differential signal of AF evaluation value based on 2nd Example of this invention. The figure explaining AF evaluation value information with respect to the defocus amount The figure explaining AF evaluation value information with respect to the defocus amount The figure explaining AF evaluation value information normalized with respect to the amount of defocus of a prior art example The figure explaining AF evaluation value information normalized with respect to the amount of defocus of a prior art example

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image pickup lens 2 Aperture 3 Image pick-up element 4 Amplifier 5 A / D converter 6 Image signal processing circuit 7 CCD drive circuit 8 Monitor liquid crystal 9, 11 Motor 15 Microcomputer

Claims (4)

Imaging means for generating an image signal from the optical image of the taking lens;
First detection means for detecting a high frequency component from the image signal and outputting a first detection result;
Second detection means for detecting a luminance difference component from the image signal and outputting a second detection result, and first information for generating first information from the first detection result and the second detection result Generating means;
Having differential operation means for differentiating the information generated by the first information generation means;
An automatic focusing control device comprising: a control unit that performs focus control of the optical lens based on information generated by the first information generation unit and the differential calculation unit.   2. The automatic focusing control device according to claim 1, wherein the first information generation means obtains the first detection result by dividing the first detection result by the second detection result.   2. The automatic focusing control device according to claim 1, wherein the differential calculation means generates primary differential information output from the first information generation means.   2. The automatic focusing control device according to claim 1, wherein the differential calculation means generates secondary differential information output from the first information generation means.

Images