JP2675807B2 - Imaging device - Google Patents

Description

The present invention relates to an image pickup apparatus for focusing an object on the basis of a video signal.

[Conventional technology]

2. Description of the Related Art Conventionally, in image pickup devices such as video cameras, the focus of the camera is detected by detecting the definition of the shooting screen by the high frequency component of the video signal and controlling the focusing lens position so that the high frequency component is maximized. A method of automatically controlling the state is known. That is, the video signal changes abruptly at the boundary of the subject, and the high frequency component of the video signal increases. It is known that the higher the high frequency component and the higher its level, the closer to the in-focus state.

By the way, when the subject moves relative to the camera when the subject moves or the camera moves while shooting the subject, the movement reduces the high-frequency component, and the focus detection is performed. If the subject moves out of the area, the autofocusing device will focus on other objects, which causes extremely inconvenient problems.Therefore, the movement of the subject is detected, the focus detection area is tracked to the subject, and the subject moves. Also, an automatic tracking device has been proposed which tracks a subject and keeps the subject in focus.

The conventional tracking device stores characteristics such as color and brightness distribution of a subject, compares them with the passage of time, detects movement of the subject from the change, and compares vertical and horizontal correlations at different times. Many methods have been proposed, such as a method of doing.

However, these methods have many problems such that the characteristics cannot be accurately detected depending on the situation of the subject, the configuration is complicated, and a relatively large memory is required.

On the other hand, a method has been proposed in which the difference between the average video signal levels inside and outside the specified area set on the shooting screen is calculated, and the focus detection area is moved so that the difference is maximized. Have been made and have made great achievements.

[Problems to be solved by the invention]

However, as a result of subsequent research, it has become clear that there is room for further improvement of the subject tracking method based on the difference between the average video signal levels inside and outside the designated area.

That is, when the difference in brightness between the subject and the background is small, it is likely to be affected by other objects, the detection accuracy of the subject's movement decreases, and there is a possibility that sufficient tracking performance for the movement of the subject cannot be obtained.

[Means for solving the problem]

The present invention has been made to solve the above-mentioned problems, and is characterized in that focus detection is performed based on a subject image in a focus detection area set in a shooting screen. An image pickup apparatus according to claim 1, wherein the focus detection area is set at a position on the shooting screen where a difference between average luminance levels inside and outside a predetermined area set to be movable in the shooting screen is maximum. Tracking means, a second tracking means for setting the focus detection area at a position where the contrast is maximized in the photographing screen, and the first and the second tracking means according to the difference between the average luminance levels inside and outside the predetermined area. An image pickup apparatus comprising: a control unit that adaptively controls switching of the second tracking unit, and that operates the second tracking unit when the average brightness level is equal to or lower than a predetermined value.

Another feature of the present invention is an image pickup apparatus configured to perform focus detection based on a subject image in a focus detection area set in a shooting screen, wherein First, the position of the focus detection area is set so that the difference between the average luminance levels inside and outside the focus detection area is maximized.
According to the difference between the average brightness level inside and outside the focus detection area, and the second area setting means for setting the focus detection area at the position where the contrast is maximum in the photographing screen. To adaptively control the switching of the first and second area setting means, and to operate the second area setting means when the difference between the average brightness levels is less than a predetermined value. is there.

Another feature of the present invention is an imaging device for detecting a movement of a subject image within a shooting screen to track a predetermined tracking region, wherein in the shooting screen, the tracking region has an average brightness level inside and outside thereof. The first tracking means for moving the tracking area in a direction in which the contrast increases, and the second tracking means for moving the tracking area in the direction in which the contrast increases in the photographing screen; and the average brightness level inside and outside the tracking area. And a control means for adaptively controlling the switching of the first and second tracking means according to the difference between the first and second tracking means, and operating the second tracking means when the difference between the average luminance levels is equal to or less than a predetermined value. On the device.

Another feature of the present invention is that, based on a difference between an average brightness level inside and outside the detection area, area setting means for movably setting a predetermined detection area for extracting a predetermined video signal in the screen, First area control means for controlling the area setting means to control the position of the detection area so that the difference in the average luminance level becomes large, and the area setting means based on an evaluation value regarding the contrast in the detection area. To control the position of the detection area so as to increase the contrast, and adaptively switch between the first area control means and the second area control means. However, when one of the first area control means and the second area control means becomes inoperable, the image pickup apparatus includes the control means for switching the operation to the other.

〔Example〕

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
As shown in FIG. 4, the automatic focusing apparatus of the present invention can set a focus detection area A for focusing on the photographing screen 1 and a tracking gate B for detecting and tracking the movement of the subject. In the tracking area B, the position of the subject is detected, and the focus detection area is aligned with the subject. FIG. 1 is a block diagram showing the construction of an embodiment of an automatic focusing device according to the present invention.

In FIG. 1, 101 is a focusing lens, whose position is adjusted by a motor 105. The image pickup element 102 such as CCD converts the subject image formed on the image pickup surface by the lens 101 into an electric signal and outputs it in the form of a video signal. The amplifier 103 amplifies the video signal from the image pickup device 102, and the process circuit 104 performs predetermined signal processing such as gamma correction, blanking processing and addition of a synchronization signal, and supplies a television signal to the video output terminal Vout. Band pass filter 107
Extracts high-frequency components necessary for focus detection from the video signal output from the amplifier 103. A differentiating circuit and an absolute value circuit for converting its output into an absolute value may be used instead of the band pass filter. The gate circuit 108 supplies the signal in the focus detection area A of the 1-field video signal to the peak value / peak position detection circuit 111 according to the gate pulse from the gate pulse generation circuit 109. When viewed on the shooting screen, this is because only signals within a predetermined area on the shooting screen are extracted and supplied to the peak value / peak position detection circuit 111, and the peak value / peak position detection circuit will be described later. The position showing the highest level in the output of the gate circuit 108 in the field cycle is supplied to the microcomputer 112 as horizontal and vertical position information H and V, and the highest level is supplied to the motor drive circuit 106. The brightness difference detection circuit 110 will also be described later, but the difference between the average brightness levels inside and outside the tracking area B on the imaging screen is calculated by the data signal G from the microcomputer 112, and the data F is supplied to the microcomputer 112. The microcomputer 112 controls the gate pulse generation circuit 109 based on the peak position information and the brightness difference between the inside and outside of the tracking area B to control the position of the focusing area A on the photographing screen. The motor drive circuit 106 determines the motor drive direction based on the peak value of the contrast supplied from the peak value / peak position detection circuit 111 in the field cycle so that the peak value becomes maximum in the manner of so-called hill climbing servo.

Next, details of the peak value / peak position detection circuit 111 will be described with reference to FIG. The output of the gate circuit 108 is supplied to the first peak detection circuit 201.

The peak detection circuit 201 is a circuit that detects a high frequency component by the BPF 107 and holds the peak value of the input signal for each horizontal scanning of the focus detection area. Although FIG. 4 shows the divided state of the photographing screen, the sample and hold circuit 202 determines the output value of the peak detection circuit 201 by the clock having a frequency n times the horizontal scanning frequency f _H corresponding to the horizontal division of FIG. The output is held by the comparison circuit 203, and the output of the sample and hold circuit 202 is compared with the output of the peak detection circuit 201. The comparison circuit 203 outputs a pulse signal that rises at the timing when the output of the peak detection circuit 201 changes. The output change of the peak detection circuit 201 means that the changed portion is a certain kind of boundary of the subject image, and the steeper the change, the closer to the in-focus state.

The counter 204 counts the clock of the frequency nf _H , and the data hold circuit 205 holds the count value of the counter 204 according to the pulse signal from the comparison circuit 203. The hold value H of the data hold circuit 205 is n when the output change of the peak detection circuit 201 (that is, the peak of the output of the BPF 107) is n.
The pulse count number indicates which one of the divided horizontal sections is located. In the illustrated example, when there are a plurality of peaks in the focus detection area A in the horizontal direction, the position of the maximum peak is shown.

The second peak detection circuit 206 is the first peak detection circuit 2
The output of 01 is received and the vertical peak value in the focus detection area is held. The sample and hold circuit 207 and the comparison circuit 208 are the sample and hold circuit 202 and the comparison circuit 20.
Similar to 3, it forms a signal indicating the point of time when the output of the peak detection circuit 206 changes. However, the frequency of the sampling clock to the sample and hold circuit 207 is m times the vertical synchronizing signal frequency f _V (corresponding to the number of divisions in the vertical direction in FIG. 4).
It is. As a result, the output of the comparison circuit 208 indicates in which section in the vertical direction the output of the peak detection circuit 206 has changed.

The counter 209 counts the clock of the frequency mf _V , and the data hold circuit 210 holds the held value of the counter 209 according to the pulse signal from the comparison circuit 208. data·
The hold value V of the hold circuit 210 is the peak detection circuit 206.
Output change (that is, the peak of the output of the BPF 107) indicates which of the m vertical divisions the detected peak is located. In the illustrated example, there are a plurality of vertical peaks in the focus detection area. Sometimes the position of the maximum peak is shown.

Although not shown, the counter 204 is cleared at the start of horizontal scanning, and the peak detection circuits 201 and 206 and the counter 2
09 is cleared at the start of vertical scanning.

The peak value detected by the peak detection circuit 206 is the maximum value of the entire captured image and is supplied to the motor drive circuit 106 as a signal indicating the degree of focus.

Next, details of the brightness difference detection circuit 110 will be described with reference to FIG. In FIG. 3, when the luminance component of the video signal output from the amplifier 103 is supplied to the gate circuit 303, the gate circuit 303 outputs the control signal G from the microcomputer 112.
Gate pulse generation circuit for generating a gate pulse corresponding to a position of a predetermined tracking area B on the photographing screen instructed by
The video signal of the tracking area B within one field according to the gate pulse from 301 is obtained and supplied to the integrating circuit 305, and then to the area correction circuit 307 for normalizing the integrated value with the area of the tracking area. . Further, the inversion / gate circuit 304 is a gate F pulse generation circuit 3 inverted by the inverter 302.
According to the gate pulse from 01, a video signal of a designated area (area excluding the previous tracking area from the entire screen) opposite to the tracking area by the gate circuit 303 in one field is obtained and supplied to the integrating circuit 306. Then, the integrated value is supplied to the area correction circuit 308 for normalizing the integrated value with the area. Since the area correction circuits 307 and 308 have different internal and external areas of the gates, respectively, the outputs of the integration circuits 305 and 306 cannot be compared as they are. Therefore, each integrated value is normalized by the area of the extracted region and a comparison is made. To do.
The subtraction circuit 309 to which the signals output from the area correction circuits 307 and 308 are supplied calculates the difference between the outputs of the area correction circuits 307 and 308, and supplies this difference information to the absolute value circuit 310. The F data output from the absolute value circuit 310 is supplied to the microcomputer 112.

Next, the tracking algorithm executed by the microcomputer 112 will be described with reference to FIGS.

FIG. 5 is a tracking method selection algorithm. In step 501, the difference in average brightness inside and outside the tracking area B (hereinafter referred to as F data) calculated by the brightness difference detection circuit 110 is compared with a predetermined threshold value TH, and F data is TH. When it is larger than TH, it shifts to the brightness difference tracking algorithm of step 502, and when it is smaller than TH, step 503
Shift to the contrast tracking algorithm. FIG. 6 shows a contrast tracking algorithm. In step 601, the peak position is obtained based on the horizontal / vertical coordinates of the peak position on the photographic screen supplied from the peak value / peak position detection circuit 111, and in step 602 it is shown in FIG. The gate pulse generation circuit 109 is controlled so that the center of the focus detection area becomes the peak position obtained in step 601, and the process proceeds to step 501 in FIG. Seventh
The figure shows the luminance difference tracking algorithm. The principle is briefly described before the description of the flow chart. For example, the tracking area B is shifted up, down, left, and right by one division, and the average value of the brightness levels inside and outside the tracking area B at each position is calculated. It is determined that the subject has moved in the direction in which the absolute value of the difference is maximum, and the focus detection area is moved in units of one section. The flow chart of FIG. 7 will be described below. step
At step 701, the F data supplied from the brightness difference detection circuit 110 is fetched, set as F1, and at step 702 a command for shifting the tracking area B to the right by one section on the photographing screen shown in FIG. 4 is issued to the brightness difference detection circuit. Send to 110. F data is fetched again in step 703 and is taken as F2. In step 704, the magnitude relationship between F1 and F2 is calculated and F
When 2> F1, go to step 706, and when F2 ≦ F1, step70
After shifting the tracking area B by one division to the left at 5, step706
The focus detection area is aligned with the tracking area B at. Similarly, in the same manner, the tracking area B is moved according to the result when shifting one section upwards from step 707 to step 712, and the tracking is performed according to the result when shifting one section leftward from step 713 to step 718. The tracking area B is moved according to the result of moving the area B and shifting downward by one section from step 719 to step 724.
After moving, shifts to step 501 in FIG.

By repeating the above operation, the tracking area B is moved so that the brightness difference between the inside and outside thereof is maximized, the object is tracked and the F data thereof is supplied to the microcomputer 112, and the gate circuit 108 causes the microcomputer 112 to The gate pulse generation circuit 109 is controlled in accordance with the instruction of A, and the focus detection area A within one field is controlled according to the gate pulse from the gate pulse generation circuit 109.
The focus detection area A can be set at the position of the tracking area B, and the focus can be kept on the subject even if the subject moves.

In the above embodiment, the tracking area is tracked by the object to detect the position of the object, and the focus detection area is set at that position. However, the focus area and the tracking area are not separately controlled. ,
Even if they are used in the same area, there is no problem in implementing the present invention.

Further, the focus detection area can also be used as another light amount detection area, for example.

〔The invention's effect〕

As described above, according to the imaging apparatus of the present invention, even when the average luminance difference between the subject and the background is small and it is difficult to detect the movement of the subject, the tracking is switched to the peak value to detect the subject. It is possible to reliably track and always reliably focus on the subject.

Further, a large-scale memory or the like for detecting the movement of the subject is not required, which is effective in simplifying the configuration.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of the image pickup apparatus according to the present invention, FIG. 2 is a block diagram showing the internal structure of the peak value / peak position detection circuit in the block diagram shown in FIG. 1, and FIG. FIG. 6 is a block diagram showing the internal structure of the luminance difference detection circuit in the block diagram shown in FIG. 1, FIG. 4 is a diagram for explaining the shooting screen, FIG. 5 is a flow chart showing an algorithm for selecting a tracking method, FIG. Is a flow chart showing a contrast tracking algorithm, and FIG. 7 is a flow chart showing a luminance difference tracking algorithm.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Hiroshi Suda, Hiroshi Suda, 770 Shimonoge, Takatsu-ku, Kawasaki, Kanagawa Canon Inc., Tamagawa Plant (72) Kunihiko Yamada, 770, Shimonoge, Takatsu-ku, Kawasaki, Kanagawa Canon Inc., Tamagawa Business In-house (56) Reference JP-A-1-120180 (JP, A) JP-A-1-71382 (JP, A) JP-A-53-22459 (JP, A)

Claims (4)

(57) [Claims] 1. An image pickup apparatus configured to perform focus detection based on a subject image in a focus detection area set in a shooting screen, the predetermined image pickup device set to be movable in the shooting screen. First tracking means for setting the focus detection area at a position on the shooting screen where the difference between the average brightness levels inside and outside the area is maximum; and within the shooting screen, the first tracking means sets the focus detection area at the position where the contrast is maximum. The second tracking means for setting the focus detection area and the first and second tracking means are adaptively switched and controlled according to the difference between the average brightness level inside and outside the predetermined area, and the average brightness level is predetermined. An image pickup apparatus comprising: a control unit that operates the second tracking unit when the value is less than or equal to a value. 2. An imaging device configured to perform focus detection based on a subject image in a focus detection area set in a shooting screen, wherein the focus detection area of the focus detection area is set in the shooting screen. A first area setting unit that sets the position of the focus detection area so that the difference between the average brightness level of the inside and the outside becomes maximum; and the focus detection area at the position of the maximum contrast in the photographing screen. The second area setting means to be set and the first and second area setting means are adaptively switched and controlled according to the difference between the average brightness levels inside and outside the focus detection area, and the difference between the average brightness levels is When it is less than a predetermined value, the second
An image pickup apparatus comprising: a control unit that operates the area setting unit. 3. An image pickup apparatus for detecting a movement of a subject image within a photographing screen to trace a predetermined tracking area, wherein the tracking area has a large difference in average luminance level between the inside and outside of the tracking area. In accordance with the difference between the average luminance level inside and outside the tracking area, and the first tracking means for moving the tracking area in the direction in which the contrast increases in the photographing screen. Control means for adaptively switching between the first and second tracking means, and operating the second tracking means when the difference between the average luminance levels is equal to or less than a predetermined value. Image pickup device. 4. An area setting means for movably setting a predetermined detection area for extracting a predetermined video signal in a screen, and the area setting means based on a difference between average luminance levels inside and outside the detection area. A first position for controlling the position of the detection area so that the difference between the average luminance levels becomes large.
Area control means, and second area control means for controlling the position of the detection area so as to increase the contrast by controlling the area setting means based on an evaluation value regarding the contrast in the detection area, When the first area control means and the second area control means are adaptively switched and controlled so that one of the first area control means and the second area control means becomes inoperable, the other An image pickup apparatus, comprising: a control unit that switches the operation to.