JP2663452B2 - Automatic focusing device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in an automatic focusing device that converts a subject image into a video signal by a two-dimensional image sensor and focuses a lens based on the video signal. Things. (Background of the Invention) In a video camera, a camera is focused by detecting the definition of a shooting screen based on a high-frequency component of a video signal and controlling the position of a lens so that the definition (high-frequency component) is maximized. A method for automatically controlling the state is known. Specifically, the video signal changes rapidly at the edge of the subject image, and the high-frequency component of the video signal increases. Then, as the high frequency component increases, the subject image is closer to the focused state. Here, FIG. 9 shows a schematic configuration of a conventional automatic focusing apparatus of this type. In FIG. 9, a subject image is formed on an image pickup surface of an image pickup device 2 by a lens 1, and the image is converted into an electric signal (video signal) by the image pickup device 2. The preamplifier 3 arranged in the next stage amplifies the video signal from the image sensor 2, and the process circuit 4 and the band pass filter (BPF)
Output to 5 Upon receiving this signal, the process circuit 4 performs predetermined signal processing and outputs it as a standard TV signal (video signal). On the other hand, the band pass filter 5 extracts a high frequency component from the output from the preamplifier 3, and
Of the signals for one screen (one field or one frame), only signals in a region where focus detection is to be performed are selected and output to the gate circuit 6 that passes the signals. The detection circuit 7 is a gate circuit 6
Is detected, and a signal showing a maximum amplitude value, that is, a peak value is formed at a point where a high frequency component is large in the region. The output signal of the detection circuit 7 represents the degree of focusing of the lens 1, and the greater the value, the closer the focusing state is. The motor drive circuit 8 drives the motor 9 according to the output value of the detection circuit 7 for each photographing screen, and automatically controls the lens 1 to be in focus. By the way, in the above-mentioned conventional automatic focusing apparatus, the video signal passing area (focus detection area) in the gate circuit 6 is
A type set in a wide fixed area on the screen,
There are types that are set at a slightly narrower fixed area at the center of the screen, but these types have the following problems. In other words, in the former type, another subject enters the focus detection area, or the camera moves to move the focus detection area itself, and another subject enters the focus detection area. In some cases, a subject different from the main subject is focused. On the other hand, in the latter type, although the possibility that the above-described subject which is not the main subject enters the focus detection area is low, the possibility that the target main subject exits the focus detection area increases, Reactivation of the focusing operation tends to occur frequently.
This is recognized as an inconvenience of the focusing operation by the photographer, and must be eliminated as much as possible. (Object of the Invention) An object of the present invention is to solve the above-mentioned problems and to provide an automatic focusing apparatus capable of continuously focusing on a main subject of various sizes without being affected by other than the main subject. It is. (Features of the Invention) In order to achieve the above object, the present invention provides an automatic focusing device that automatically controls a focusing state of an optical system based on a video signal obtained in a focusing detection area specified in a shooting screen. In the shooting screen, an area setting means for setting a detection area so that its size is variable, and extracting a luminance signal component in the video signal corresponding to the inside and outside of the detection area, respectively, Area control means for changing the size of the detection area in a direction in which the difference between the component levels increases, and focusing area setting means for setting the size of the focus detection area based on the size of the detection area Focus detecting means for detecting a focus state based on the video signal corresponding to the in-focus detection area. Hereinafter, the present invention will be described in detail with reference to the illustrated embodiments. In the embodiment, as shown in FIG. 2, the photographing screen is divided into n equal parts in the horizontal direction and m equal parts in the vertical direction, and divided into n × m sections. Then, a plurality of sections are set as focus detection areas, and a focus signal is formed within the area. FIG. 1 is a block diagram showing a first embodiment of the present invention, and the same parts as those in FIG. 9 are denoted by the same reference numerals. In FIG. 1, when an imaging signal (luminance component) output from the imaging element 2 via the preamplifier 3 is input to the gate F circuit 11, the gate F circuit 11
The luminance component of the designated area in one field is obtained according to the gate pulse from the gate F pulse generation circuit 26 for generating a gate pulse at the position designated by 24, and the luminance component is applied to the integration circuit 15, and then to the area correction circuit 30. And supply. The inverting gate F circuit 12 operates in accordance with the gate pulse from the gate F pulse generating circuit 26 inverted by the inverter 28 and has a designated area (from the entire screen) opposite to the designated area designated by the gate F circuit 11 in one field. The luminance component of the region other than the specified region is obtained, applied to the integration circuit 16, and subsequently supplied to the area correction circuit 31. Similarly, the gate G circuit 13 obtains a luminance component of a designated region in one field according to the gate pulse from the gate G pulse generation circuit 27 which generates a gate pulse at a position designated by the microcomputer 24, and The inverting gate G circuit 14 sequentially applies the voltage to the area correction circuit 32, and the inverted gate G circuit 14
The luminance component of the designated area opposite to the designated area by the gate G circuit 13 in the field is obtained, and is sequentially applied to the integration circuit 18 and the area correction circuit 33. Here, each area specified as described above, that is, the inner area and the outer area that are divided by the gates F and G, which are the boundaries dividing the screen into two areas, are as shown in FIG. The center positions are the same, and the sizes (the number of sections) are different from each other. Integrators 15, 16 and 1 to which the luminance components of only the areas specified by the gate F circuit 11, the inverting gate F circuit 12, the gate G circuit 13, and the inverting gate G circuit 14 are input.
7, 18 perform integration of the luminance component to obtain an average value of the luminance component in each area. Further, since the area correction circuits 30, 31 and 32, 33 cannot compare the outputs of the integration circuits 15 to 18 as they are, since the areas of the inner and outer regions allocated by the gates F, G are different from each other, An operation is performed in which the values are normalized by the area of the extracted region, and the values are compared with each other. The subtraction circuits 19 and 20 to which the signals output from these area correction circuits 30, 31, 32, and 33 calculate difference information of the average value of the luminance components from the integration circuits 15, 16, 17, and 18, respectively. This difference information is output to absolute value circuits 21 and 22. The absolute value circuits 21 and 22 take the absolute values of the input difference information, and output these absolute values to the microcomputer 24 via the A / D conversion circuit 23. The microcomputer 24 checks which absolute value signal has passed through which gate is larger by inputting the data as described above, and outputs gate information corresponding to the larger value to the gate pulse generation circuit 25. For example, the data sent from the absolute value circuit 21 is F1, the absolute value circuit 22
When the transmitted data is G1, the case where the relationship of F1> G1 is satisfied corresponds to FIG. 4 (B), so it can be estimated that the main subject is large. In this case, the focus detection area is set to be wide. In order to perform this, information indicating that the gate F has been detected is output to the gate pulse generation circuit 25 for setting the focus detection area. That is, since many luminance components are present in the main subject portion, when the main subject is almost contained in the gate, the luminance difference between the inside and outside becomes maximum. Therefore, in the case of F1> G1, it can be seen that the main subject is more accurately contained in the gate F than in the gate G, and it can be determined that the main subject is large. The same can be considered for the case where the relationship of F1 <G1 holds.
Since it corresponds to FIG. (A), it can be estimated that the main subject is small. In this case, in order to set the focus detection area narrower,
Information indicating that the gate G has been detected is output to the gate pulse generation circuit 25. The gate circuit 10 is a gate pulse generation circuit that generates a pulse according to the information from the microcomputer 24 described above.
The video signal of the designated area in one field according to the gate pulse from 25 is passed. For example, gate G
If a pulse corresponding to the information indicating is input,
The narrower area as drawn by the one-dot chain line in FIG. 3 is used as the focus detection area, and when a pulse corresponding to the information indicating the gate F is input, the focus detection area is drawn as the two-dot chain line in FIG. The larger area is set as the focus detection area. As a result, a focus detection area having a size corresponding to the size of the main subject in the screen is set, and it is possible to keep focusing on only the main subject with a high probability. In the embodiment of FIG. 1, before passing through the band-pass filter 5, the size of the main subject in the screen is detected based on the video signal obtained from the image sensor via the preamplifier 3, that is, the luminance signal component. Although the width of the focus detection area is determined correspondingly, the band of the luminance component is actually wide, and the size of the main subject has changed, and some of the frequency bands have changed. However, in the state where the average value of the luminance components is taken, the change may be canceled out and not appear. Therefore, as shown in FIG. 5, a signal component serving as a basis for detecting a change in a main subject to be extracted in regions inside and outside the gates is extracted from the output side of the band-pass filter 5 and a high-frequency component corresponding to a high-frequency side of a luminance component is extracted. Components may be used. In other words, since the high frequency components are distributed in many details and contours of the subject, changes in the main subject that were not reflected in the average value in a wide band such as the luminance component were detected by extracting the high frequency components and comparing them. It is considered possible, and this method is also very effective. In FIG. 5, only a main part for obtaining a signal extracted from each of the gates F and G is shown, and other components are omitted, but the other parts are completely the same as those in FIG. Yes, and the operation is the same. In the above-described embodiment of FIGS. 1 and 5, the size of the main subject is determined by the gates F and G having different widths, and the focus detection area is set accordingly to focus. However, even when the main subject moves in the shooting screen or when the camera is slightly moved, the main subject cannot be focused. In view of this point, the main subject whose position changes in the shooting screen is tracked by each of the gates F and G, and the focus detection area is always adjusted not only by the size of the main subject but also by the position in the screen, It is also possible to adopt a configuration that can surely keep focusing on the main subject. For example,
In the configuration of FIG. 1 (or FIG. 5), the gates F, G
Is shifted up, down, right, and left by one section (in the microcomputer 24), and the absolute value of the difference between the average values of the luminance components (or high-frequency components) obtained in the inside and outside regions at each position If the function of detecting the position of the main subject in the screen and moving the focus detection area to the position is further added, if only the size of the main subject is detected, Instead, even if the position of the main subject in the screen changes, the main subject can be surely kept in focus, and a more automated apparatus can be provided. The operation when the tracking function is added to the microcomputer 24 will be described with reference to the flowchart of FIG. First, the signal from the A / D conversion circuit 23 is read as F data and G data, and these are taken into variables F1 and G1 (step 1). Next, the gates F and G are shifted rightward by one section (this is performed via the gate F pulse generation circuit 26 and the gate G pulse generation circuit 27) (step 2), and the F data and G in the next field are changed. Read the data and
The variables F2 and G2 are fetched (step 3). Then, it is determined whether or not the respective values have a relationship of F2> F1 or G2> G1 (step 4). When it is determined that such a relationship exists (the main subject moves to a position shifted to the right) If it can be estimated that this is the case, the process proceeds to the subroutine shown in FIG. The subroutine is a routine for selecting the size of the focus detection area in accordance with the size of the main subject.
It is determined whether or not G1 is satisfied. If F1> G1, it is understood that the main subject is more accurately captured on the gate F side as described above. Therefore, in this case, the process proceeds to step 6-3 to select the wider focus detection area shown by the two-dot chain line in FIG. If F1> G1, the main subject is properly captured on the gate G side. In this case, the process proceeds to step 6-2, where the narrower focus detection area shown by the one-dot chain line in FIG. select. The setting of the focus detection area is performed via the gate pulse generation circuit 25. In step 4, if the condition of F2> F1 or G2> G1 is not satisfied (the case where the main subject does not change its position and remains at the original position), the process proceeds to step 5, and FIG. The process proceeds to a subroutine shown in FIG. The subroutine is also a routine for selecting the size of the focus detection area according to the size of the main subject. In step 5-1 it is determined whether or not F2> G2. As described above, it can be seen that the main subject is more accurately captured on the gate F side. Therefore, in this case, the process proceeds to step 5-3 to select the wider focus detection area shown by the two-dot chain line in FIG. If F2> G2, the main subject is more accurately captured on the gate G side. In this case, the process proceeds to step 5-2, and the narrower focus detection area shown by the dashed line in FIG. Select Thereafter, the process proceeds to step 7, in which the gates F and G are shifted leftward by one section, that is, returned to the previous state. In step 8, the position of the focus detection area is adjusted to the gate F or the gate G. Similarly, in steps 9 to 16, the focus detection area is adjusted to the gate position according to the result of shifting upward by one section in the next two fields,
In steps 17 to 24, the in-focus detection area is adjusted to the gate position corresponding to the result obtained by shifting leftward by one section in the next two fields, and in steps 9 to 16, the next two shields are used. The focus detection area is adjusted to the gate position according to the result of the shift downward by one section. In steps 13, 21, and 29, the same operation as the subroutine performed in step 5 is performed, and in steps 14, 22, and 30, the same operation as the subroutine performed in step 6 is performed. Thereafter, the same operation is repeated. As described above, the gates F and G are shifted in the screen, and the focus detection area is moved in a direction in which the luminance difference (or the difference between high-frequency components) inside and outside each gate is increased. By adding a new operation of tracking the focus detection area according to the position change to the microcomputer 24, not only the size of the focus detection area almost matches the size of the main subject described above, but also the Also suitable for main subjects whose position may change. This is based on the same idea as in the case of determining the size of the main subject described above. For example, since many luminance components are detected from the main subject portion, the two large and small gates F and G have inside and outside the respective gates. By moving the gates F and G so that the average luminance difference always becomes large and adjusting the focus detection area to this, the focus detection area always corresponds to the position change of the main subject on the screen. Can be set. Therefore, in this case, the microcomputer 24 sends to the gate pulse generation circuit 25 not only the signal indicating the gate F or the gate G corresponding to the size of the subject in the screen, but also the gate corresponding to the position of the main subject. F or gate G
Is output. The gate circuit 10 passes the video signal in the designated area according to the gate pulse from the gate pulse generation circuit 25 that generates a pulse according to the instruction of the microcomputer 24 described above. Accordingly, even when the main subject moves in the screen, it is possible to always follow the main subject and to surely keep the main subject in focus. FIG. 7 is a block diagram showing a fourth embodiment of the present invention, in which a focus detection area is set by detecting a luminance component having a relatively wide band and having a wide adaptation range for various subjects. The method of FIG. 1 and the method of setting a focus detection area by detecting a high-frequency component capable of detecting a change in a subject that does not appear as a difference in the average value of the luminance components, that is, the method of FIG. The method of the embodiment shown in FIG. 5 can be automatically selected according to the situation at that time. 1 and 5 have the same reference numerals. The difference from these embodiments is that the gate F circuit 11
From the input side of the band-pass filter 5 (to extract the luminance component) and the output side (to extract the high-frequency component) from the input side of the band-pass filter 5 to select the signal supplied to the inverting gate G circuit 14 by switching the analog switch SW I'm going. Further, the microcomputer 24 here has a function of detecting the size of the subject and its position in the screen, performing control so as to match the focus detection area with the size, and also performing switching control of the analog switch SW. It is assumed that Hereinafter, the operation will be described with reference to the flowchart of FIG. When the focus detection operation is started, in step 1-1, first, the analog switch SW is switched to the input side of the band-pass filter 5, that is, the contact Y side, in order to extract a luminance component, and inside and outside the gates F and G at that time. The values based on the difference between the average values of the detected luminance components are read into variables FY and GY, respectively (step 1-2). Subsequently, the analog switch SW is set to the output side of the band-pass filter 5 to extract the high-frequency component.
That is, it is switched to the contact H side (step 1-3), and values based on the difference between the average values of the high-frequency components detected inside and outside the gates F and G at that time are read into variables FH and GH, respectively (step 1-4). Next, proceed to step 1-5 to change the variables FH, GH, FY, GY
Is determined to be the largest, and if the variable FH or
If GH is the maximum, the process proceeds to step 1-8, where the contents of the variables FH and GH are stored in the variables F1 and G1, respectively, and then the process proceeds to step 2. If the variable FY or GY is the maximum in step 1-5, the process proceeds to step 1-6, in which the analog switch SW is switched to the contact Y to set the detection mode based on the luminance component. After the contents of the variables FY and GY have been stored in Thereafter, the operations from step 2 to step 32 are the same as the operations in FIG. 6 described above, and the description thereof will not be repeated. According to the embodiment shown in FIGS. 1 to 8, the luminance components of the video signals obtained in the inner and outer regions of the gates F and G respectively determine the absolute value of the difference between the average values of the high-frequency components. The size of the focus detection area is set according to the gate F or the gate G corresponding to, so that it is possible to keep focusing on a main subject of various sizes with a high probability. Become. In the embodiment shown in FIGS. 6 to 8, the focus detection area is set in consideration of not only the size of the main subject but also the position of the main subject in the screen. Even if the camera itself moves or the camera moves, it is possible to keep focusing with high probability. Further, as shown in FIGS. 7 and 8, the analog switch SW is switched to the corresponding side by judging which component of the luminance component or the high frequency component is more advantageous, and the focus detection area is determined. Is set, it is possible to continue focusing with a high probability regardless of the shooting environment and subject conditions at that time. (Correspondence between Invention and Embodiment) In this embodiment, the gate F circuit 11 is switched to the inversion gate G.
Up to the circuit 14, the gate F pulse generation circuit 26 and the gate G pulse generation circuit 27 are included in the area setting means of the present invention.
To the A / D conversion circuit 22 and the microcomputer 24 correspond to the area control means, and the gate pulse generation circuit 25 corresponds to the focus area setting means. (Effects of the Invention) As described above, according to the present invention, an automatic focusing device that automatically controls a focusing state of an optical system based on a video signal obtained in a focusing detection area specified in a shooting screen. In the shooting screen, an area setting means for setting a detection area so that its size is variable, and extracting a luminance signal component in the video signal corresponding to the inside and outside of the detection area, respectively, Area control means for changing the size of the detection area in a direction in which the difference between the component levels increases, and focusing area setting means for setting the size of the focus detection area based on the size of the detection area And focus detection means for detecting a focus state by the video signal corresponding to the focus detection area, so that the main subject of various sizes is continuously received without being affected by other than the main subject. Can be focused. In addition, since the size of the detection area, that is, the focus detection area, is changed so that the level difference between the luminance signal components inside and outside the detection area becomes large, the main subject can be accurately captured regardless of the background. , An accurate focus detection operation can be performed.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing a first embodiment of the present invention, and FIG.
FIG. 3 is a diagram showing a divided state of the photographing screen, FIG. 3 is a diagram for explaining a relationship between each gate for detecting the size of the main subject and a selected focus detection area, and FIGS. 4 (A) and 4 (B). FIG. 5 is a diagram for explaining the size determination operation of the main subject in the screen, FIG.
6 is a block diagram of a main part showing a second embodiment of the present invention, FIGS. 6 (A) to 6 (C) are flowcharts showing the operation of the third embodiment of the present invention, and FIG. FIG. 8 is a block diagram showing a fourth embodiment, FIG. 8 is a flowchart showing the operation thereof, and FIG. 9 is a block diagram of a conventional automatic focusing apparatus. 1 ... Lens 2 ... Imaging element 5 ... Band pass filter 7 ... Detection circuit 8 ... Motor drive circuit 9 ...
Motor, 10 gate circuit, 11 gate F circuit, 12
... Inverting gate F circuit, 13 ... Gate G circuit, 14 ... Inverting gate G circuit, 15-18 ... Integration circuit, 19,20 ... Subtraction circuit, 21,22 ... Absolute value circuit, 23 ... A / D conversion circuit, 24 ……
Microcomputer, 25 gate pulse generation circuit,
26 gate F pulse generation circuit, 27 gate G pulse generation circuit, 30 to 33 area correction circuit, SW analog switch.

Continuation of front page    (72) Inventor Kunihiko Yamada               770 Shimonoge, Takatsu-ku, Kawasaki-shi, Kanagawa               Inside the Tamagawa Office of Canon Inc.                (56) References JP-A-60-213175 (JP, A)

Claims (1)

(57) [Claims] In an automatic focusing device that automatically controls the focusing state of the optical system based on a video signal obtained in a focus detection area specified in a shooting screen, the size of the detection area in the shooting screen is variable Region setting means for setting, and extracting a luminance signal component in the video signal corresponding to the inside and outside of the detection region, and increasing the size of the detection region in a direction in which the level difference of the luminance signal component increases. Area control means for changing; focus area setting means for setting the size of the focus detection area based on the size of the detection area; and a focus state based on the video signal corresponding to the focus detection area. An automatic focusing device, comprising: a focus detecting means for detecting. 2. The area control means is configured to change a size of the detection area in a direction in which a level difference of a high-frequency component on a high frequency side of the video signal component corresponding to inside and outside of the detection area increases. 2. The automatic focusing device according to claim 1, wherein: 3. The area setting means sets at least two large and small areas overlapping each other, and the area control means sets a level of the luminance signal component corresponding to the large area and a luminance signal component corresponding to the small area. 2. The automatic focusing apparatus according to claim 1, wherein a size of the detection area is changed in a direction in which a difference from a level increases.