JP2547619B2 - Imaging device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to a video camera that automatically adjusts exposure.

(B) Conventional Technology In a video camera, control of an image pickup signal level (exposure) by a diaphragm, a gain, etc. is a very important issue as well as focus detection.

2. Description of the Related Art Conventionally, an automatic exposure adjustment mechanism has been used, which detects the average brightness level of an imaging screen, the level of a peak value, etc., and based on that, controls the gain by controlling the gain. In this method, when a high-luminance portion such as a light source exists in the screen, or conversely, the background is dark, the main subject may not be properly exposed due to the influence of the surroundings.

In order to solve this, there is a technique such as Japanese Patent Laid-Open No. 62-110369 (H04N 5/243). This takes advantage of the tendency that the main subject is often located in the center of the screen, and the imaging screen is divided into the central part and the peripheral part other than that, and the brightness level of each is obtained and the ratio of the two is obtained. The gain is controlled and the level of the image pickup signal is changed to obtain proper exposure for the main subject in the center of the screen.

(C) Problems to be Solved by the Invention According to the above-described conventional technique, the gain of the AGC circuit through which the imaged video signal passes is controlled by the ratio of the brightness levels of the central portion and the peripheral portion of the screen so that the central portion of the screen is always displayed. In order to obtain the optimum exposure for a certain main subject, there is a significant brightness difference between the center of the screen and the peripheral part, for example, if the central part is brighter than the peripheral part, the peripheral part is significantly underexposed, On the contrary, if the central part is darker than the peripheral part, the peripheral part is remarkably overexposed.

Further, when the brightness level in the priority area is extremely small, the S / N is deteriorated and the brightness level is frequently changed due to the influence of noise, and the exposure control becomes unstable.

(D) Means for Solving the Problems The present invention places the main subject of the priority area set in the screen during exposure adjustment in the proper exposure range, and determines the relative relationship between the brightness levels of the priority area and the non-priority area. When the target level for exposure adjustment is subtly changed or the target level to be compared with the target level is calculated, the non-priority area of the priority area brightness level is determined by the relative relationship between the priority level and non-priority area brightness levels. It is characterized in that the target level is obtained from both brightness levels by changing the weighting amount with respect to the brightness level, and that the brightness level is replaced with a fixed value for an area having an extremely small brightness level.

(E) Operation Since the present invention is configured as described above, the brightness levels of the priority area and the non-priority area are compared, and as a result, the main subject in the priority area is exposed within a range where proper exposure can be obtained. By changing the target level of, it is possible to reduce the overexposure / insufficiency that occurs in the screen.
Further, the influence of noise when the luminance level is low is reduced, and optimal exposure control can be performed.

(F) Example An example of the present invention will be described below with reference to the drawings.

FIG. 1 is a circuit block diagram of this embodiment. Reference numeral (1) denotes a video camera unit, which includes a focus motor (4) that drives a focus ring (3) that supports and moves the focus lens (2) in the optical axis direction, and an optical aperture mechanism (6) that controls exposure. An iris motor (7) for driving the aperture mechanism (6) and an imaging circuit (8) having a solid-state imaging device (CCD) for converting subject light into an imaging video signal are arranged.

The luminance signal in the captured video signal obtained by the imaging circuit (8) is sent to a high-pass filter (HPF) (9), a low-pass filter (LPF) (11), and a sync separation circuit (12).

The vertical synchronization signal (VD) and the horizontal synchronization signal (HD) separated from the luminance signal by the synchronization separation circuit (12) are supplied to a switching control circuit (13) for setting a sampling area.

The switching control circuit (13) is a vertical / horizontal synchronization signal (VD)
(HD) and a fixed oscillator output as a clock for driving the CCD, a rectangular sampling area (A1) in the center of the screen as shown in FIG. ) 4 times the sampling area (A2)
And the sampling area (A) around this area (A2)
3) Select signal (S) so that (A4) (A5) (A6) can be set
2) is output to the selection circuit (15) at the subsequent stage, and HPF
(9) Switching signal (S1) to select output or LPF (11) output
Is supplied to the switching circuit (14).

The switching circuit (14) receives the switching signal (S1) and continues to select the HPF (9) output for a predetermined period, for example, 32 fields, and selects the LPF (11) output only for 1 field for every 32 fields. After that, this switching operation is repeated in the same cycle.

The selection circuit (15) outputs the output of the HPF or LPF selected by the switching circuit (14) based on the selection signal (S2) to the integrated circuits (16) (17) ... (21) according to the sampling area. Selectively output to. That is, each filter output regarding the first sampling area (A1) is output to the integration circuit (16), each filter output regarding the second sampling area (A2) is output to the integration circuit (17), and the third to sixth sampling areas (A3) ) (A4) (A5) (A6) filter output is
The signals are output to the integrating circuits (18), (19), (20), and (21), respectively.

The integrating circuit (16) includes an A / D converter (22), an adder (23),
The A / D converter (22) consists of a memory circuit (24), and the A / D converter (22) sequentially converts each filter output passing through the selection circuit (15) to A / D
D-convert and output to the adder (23). The adder (23) forms a digital integrator together with the preceding A / D converter (22) and the succeeding memory circuit (24), and outputs the output of the memory circuit (24) and the output of the A / D converter (22). The result of the addition is supplied to the memory circuit (24) again. The memory circuit (24) is reset for each field, and holds the output of the adder (23), that is, one field of the digital conversion value of the level of the luminance signal that has been filtered for the first sampling area (A1). .

The integrating circuits (17), (18),... (21) have exactly the same configuration as the integrating circuit (16), and the memory circuits incorporated in each of the integrating circuits have the current information related to each sampling area. The integrated value for one field of the level of the luminance signal that has passed through the filter selected in the field is retained. The integrated value of each of these memory circuits is collectively stored in a memory circuit (25) at a subsequent stage.

The cutoff frequency of HPF (9) is specifically 200 KHz
The band of ~ 2.4MHz is allowed to pass, and the cutoff frequency of the LPF (11) is set to allow the band of 0 ~ 2.4MHz to pass. Note that 2.4 MHz is an extremely high frequency that is not directly related to the luminance signal, and its value is not so significant.
The HPF (9) only needs to be able to extract a band of 200KHz or more.
(11) may be substantially omitted, and the imaging luminance signal may be directly supplied to the switching circuit (14) when the LPF (11) is selected.

Therefore, the high band or low band component of the luminance signal that has passed through either the HPF (9) or the LPF (11) is digitally integrated for one field and stored as an integrated value of the current field for each sampling area. It will be stored in the circuit (25). Here, of the integrated values stored in the memory circuit (25), the integrated value of the low-frequency component when the LPF (11) is selected is normalized per unit area to obtain an exposure evaluation value for exposure control, and The integral value of the high frequency component when the HPF (9) is selected is processed by a microcomputer (26) at the subsequent stage as a focus evaluation value for focus control.

These evaluation values are processed in software by the microcomputer (26), and based on the processing results, a command is issued to the focus motor control circuit (27) to drive the focus motor (4) to move the focus lens (2). The iris motor (7) is driven by driving the iris motor (7) by operating the iris motor (7) by operating the auto-focus operation so that the focus evaluation value becomes maximum, and by issuing a command to the iris motor control circuit (28). Thus, automatic exposure adjustment can be performed so that the exposure evaluation value becomes a predetermined value.

Next, the main routine of the auto focus operation and the auto iris operation of the microcomputer (26) will be described with reference to the flowchart of FIG.

When the video camera enters the operating state, the microcomputer (26) executes the main routine of FIG. 3 for each field.

First, in STEP (30), the integrated value for one field in each sampling area in the current field is read from the memory circuit (25) into the microcomputer (26).

Next, the counter (AE-CNT) provided for performing the auto focus operation and the auto iris operation in a time-division manner is decremented, that is, decremented by 1 (STEP (32)) to determine whether the counter value is 0 or not. Then, if the counter value is not 0 (step (33)), the auto focus operation is executed, and the auto iris operation is executed only when the counter value is 0. The autofocus operation is performed by executing an AF routine (35) for holding the focus lens (2) at the in-focus position based on a focus evaluation value which is an integral value of the output of the HPF (9).

During the execution of the AF routine, the integral value (DA) of the first and second sampling areas (A1) and (A2) when HPF (9) is selected
TA (1)) (DATA (2)) is taken out as the focus evaluation value (X ₍₁₎ ) (X ₍₂₎ ) of each area in the current field, and the first sampling area (A1) is designated as the focus area first. Then, the focus motor (4) is driven to displace the focus lens (2), and the focus evaluation value X ₍₁₎ in the first sampling area (A1) is changed for each field, that is, the focus evaluation value X _{(1) )} each time is updated by comparing the focus evaluation value in the current field and the previous field, in a direction which the focus evaluation value increases to connect the rotation of the focus motor (4), the mountain apex of, that is, the maximum evaluation value Is detected, and when this position is reached, this position is set as the focus position, the focus motor (4) is stopped, and the focus lens (2) is reached.
Is fixed to complete the focusing operation.

Further, although the lens position changed from the far point to the near point at the time of detecting the peak of the mountain, a clear peak of the mountain could not be detected in the focus evaluation value X ₍₁₎ in the first sampling area (A1). 2
The maximum evaluation value of the focus evaluation value X _{(2) in} the sampling area (A2) is larger per unit area of the area than the maximum evaluation value of the focus evaluation value X ₍₁₎ in the first sampling area (A1). In this case, the second sampling area (A2) is designated as the focus area, and thereafter, the lens position at which the focus evaluation value X ₍₂₎ takes the maximum evaluation value is set as the focus position, and this lens position is held and focused. Complete the operation.

Furthermore, in the AF routine, even after reaching the peak of the mountain, once fixing the lens at this position and completing the focusing operation, the change in the focus evaluation value is monitored, and if the focus evaluation value changes greatly, A subject change monitoring operation is performed in which the subject moves and moves out of the focus area, and the focusing operation is restarted from the beginning. In this monitoring operation, if the focusing operation is ended with the first sampling area (A1) as the focus area, the monitoring operation is first performed for this first sampling area (A1), and the focus evaluation of the first sampling area (A1) is performed. When a large change occurs in the value X ₍₁₎ , the focus evaluation value of the second sampling area (A2)
It is determined whether the change in X ₍₂₎ occurs, when caused to instruct the resumption of the focusing operation, but a significant change in this focus evaluation value X ₍₂₎ does not occur, a main object As shown in FIG. 12, it is assumed that the mere movement from the position of the chain line to the position of the solid line, that is, the position outside the first sampling area (A1) in the second sampling area (A2),
The focus area is switched from the first sampling area (A1) to the second sampling area (A2), and the monitoring operation is continued.

When the above-mentioned AF routine ends, the counter (AE-CN
T) is decremented by 1 to determine whether the counter value becomes 0 (STEP (36)). If the counter value becomes 0, the microcomputer (26) sends a control signal to the switching control circuit (13). Is issued, a switching signal (S1) is issued to the switching circuit (14) so as to select the LPF (11), and the LPF (11) is selected (STEP (37)). When the LPF (11) is selected in this way, it waits until the evaluation value obtained by the selection is read.

On the other hand, if the auto iris operation is selected in STEP (33), the AE routine (3
8) is executed, and thereafter, the counter (AE-CNT) is returned to the initial state (STEP (39)), the filter is selected to HPF (9) (STEP (40)), and the evaluation value of the next field is evaluated. Wait for integration. Here, the initial state of the counter (AE-CNT) is 3
This is a state in which an initial value “32” is set for calculating an exposure evaluation value based on a luminance signal that has passed through the LPF (11) every two fields.

Next, the auto iris operation will be described with reference to a flowchart. The counter (AE-
When the count value of the CNT reaches zero, that is, when 32 fields have elapsed since the start of the focusing operation, the auto iris (A
E) The routine is executed as shown in FIG. First, integration of one field of the luminance signal passing through the LPF (11) in the first, third to sixth sampling areas (A1), (A3),. The values DATA (1), DATA (3),... DATA (6) are normalized by the area of each area, that is, the values of the first, third to sixth sampling areas (A1), (A3),. Area (SM
1) The integral value per unit area obtained by dividing by (SM3) ... (SM6) is used as the exposure evaluation value Z ₍₁₎ , Z ₍₃₎ ... in each area.
Calculated as STEP (200 ₎ as Z ₍₆₎ .

However, the second sampling area (A2) is defined as an area including the first sampling area (A1) and used for the focusing operation as described above. However, in the exposure control operation, the area corresponding to each exposure evaluation value is used. Are independent areas. Therefore, the exposure evaluation value Z ₍₂₎ is defined as the exposure evaluation value of the area excluding the first sampling area (A1) from the second sampling area (A2). That is, Z ₍₂₎ = ｛DATA (2) −DATA
(1) It is calculated as {/ {(SM2)-(SM1)}}.

Next, the average value in all areas, Is calculated as the average exposure evaluation value (Z _A ) in STEP (201).

Next, a target evaluation value (Z _T ) to be controlled is determined by representing the luminance level of this screen. First, the first sampling area (A1) used for the focus area assuming that the main subject exists in the autofocus operation described above.
The priority for exposure evaluation value Z ₍₁₎ the average exposure evaluation value of the first sampling area (A1) (Z _A), and determines whether or not entered within a predetermined allowable range, both Absolute value of log ratio of exposure evaluation value If it is determined in STEP (202) that is within the predetermined value (a), the exposure evaluation value Z ₍₁₎ is set as the target evaluation value (Z _T ) in STEP (203), and Is outside the range of the predetermined value (a), and the larger second sampling area (A2) is designated as the focus area in the autofocus operation described above, the STEP
When judged in (204), it is judged whether or not the exposure evaluation value Z ₍₂₎ is within a predetermined range with respect to the average exposure evaluation value (Z _A ), Is determined to be within the predetermined value (a) in STEP (205), the exposure evaluation value Z ₍₂₎ is set as the target evaluation value (Z _T ) in STEP (206).

Further to STEP (205) Is not satisfied, or Is not less than the predetermined value (a) and the focus area is designated as the first sampling area (A1), the average exposure value among the exposure evaluation values Z _(i) (i = 1 to 6) of each area. Within a predetermined range for the evaluation value (Z _A ), that is, Is calculated as the target evaluation value (Z _T ) in STEP (207). If the exposure evaluation values in all areas are not within the specified range, STEP (29
0), the first sampling area (A
To 1) exposure evaluation value Z of the ₍₁₎ target evaluation value (Z _T). Furthermore S
In TEP (208), the maximum value among the exposure evaluation values Z _(i) (i = 1 to 6), that is, Z ₍₁₎ , Z ₍₂₎ , Z ₍₃₎ , ... Z ₍₆₎ , is set to Zmax. , Set the minimum value as Zmin as the value required for exposure determination.

In STEPs (202), (205), and (207), it is determined whether each exposure evaluation value is within a predetermined allowable range with respect to the average exposure evaluation value (Z _A ), or is a value greatly different outside the range. In making the determination, there is no problem if the ratio between the two is simply used. However, in the present embodiment, the dynamic range of the ratio between the two is considered and the logarithmically compressed data is compared with the predetermined value (a). .

As described above, the target evaluation value, which is the exposure evaluation value of the area used when performing the auto iris operation among the exposure evaluation values of the plurality of sampling areas, is the exposure evaluation value Z _{( 1)} is prioritized, and there is an extremely high brightness part such as a light source or an extremely low brightness part such as dark green, that is, an abnormal brightness part in this first sampling area (A1), and the average evaluation value (Z _A ) When the logarithmic compression value of the ratio is not within the range of the predetermined value (a), if the focus area is the second sampling area (A2), the exposure evaluation value Z ₍₂₎ of this area is prioritized. Further, when an abnormal luminance portion also exists in the second sampling area (A2), the average value of the exposure evaluation values of the area where the abnormal luminance portion does not exist is set as the target evaluation value, and the corresponding area is used for the auto iris operation. Used.

Based on the values set as described above, the aperture is first determined based on the flowchart of FIG. STEP (21
First, the logarithm of the ratio between the target evaluation value (Z _T ) and the maximum value (Zmax) And the logarithm of the ratio between the target evaluation value (Z _T ) and the minimum value (Zmin) And calculate LOG, the difference between the two. Is derived as the brightness / darkness discrimination value (D). The brightness / darkness determination value (D) is a parameter for determining whether the main subject, which is the basis of the target evaluation value (Z _T ), is relatively bright or dark in the screen. The main subject is bright and the target evaluation value (Z _T ) Is relatively large if is relatively large Becomes larger, Becomes smaller and the lightness / darkness discrimination value (D) becomes larger. Conversely, when the target evaluation value (Z _T ) is relatively small, the preceding term becomes smaller, the latter term becomes larger, and the light / dark discrimination value (D) becomes smaller.

The reason why the logarithm of the ratio of the evaluation values is used in the calculation of the light / dark discrimination value (D) is that the recognition of the brightness in human vision is usually such that the actual brightness level of the subject is exponential, for example, It is noted that the visual brightness changes linearly when the level increases from 2 times to 4 times to 8 times.

The discrimination value (D) is a predetermined value (b) in STEP (211) and (212).
(B> 0), that is, when it is determined that | D | <b, the upper limit of the target value (Z _T ) for controlling the target evaluation value (Z _T ) is determined to be intermediate brightness in the screen. Z _U ) and the lower limit (Z _L ) are set to (V) and (v) in STEP (213), respectively.
When the determination value (D) is determined to be equal to or more than + b, the upper limit (Z _U ) and the lower limit (Z _L ) are determined to be relatively bright in STEP (214).
Are defined as (U) and (u) respectively. Further, the discrimination value (D) is-
When it is determined to be equal to or less than b, the upper limit (Z _U ) and the lower limit (Z _L ) are set to be relatively dark (W) in STEP (215).
(W). Here, the upper and lower limits are U
By providing the relationship between VW and uvw in advance, a target range corresponding to the relative brightness of the target evaluation value (Z _T ) in the screen can be obtained.

The above-mentioned predetermined value (b) is a limit value at which the luminance level of the main subject can be visually recognized as being extremely bright or extremely dark with respect to the luminance level of the entire screen, and is obtained experimentally in advance. Have been.

Next, in STEPs (216) and (217), the target evaluation value (Z _T ) is compared with the upper and lower limits (Z _U ) and (Z _L ) of the target value, and Z _U > Z _T > Z _L is established. Then, it is determined that the proper exposure has been obtained, the ailes motor (7) for driving the optical diaphragm mechanism (6) is stopped, the current diaphragm is maintained, and the target evaluation value (Z _T ) is set to the upper limit (Z _T ). _U ) If it is larger, it is overexposed
At (219), the diaphragm mechanism drives the iris motor (7) in the direction to close the diaphragm amount by one step, and conversely, if the target evaluation value (Z _T ) is smaller than the lower limit (Z _L ), it is determined that the exposure is insufficient and STEP is performed. At (218), the iris motor (7) is driven in the direction in which the aperture amount is opened by one step. Incidentally, the iris motor (7) is constituted by a stepping motor.

During the adjustment of the aperture amount by the iris motor (7),
AGC amplifier (30) that amplifies the captured video signal in STEP (222)
The gain of 1) is fixed to a constant value (gain may be 0) (this state is called the AGC operation OFF state). In addition, when it is difficult to properly perform exposure only by adjusting the amount of incident light, that is, in STEP (220), it is determined that the aperture mechanism is opened while the subject repeats STEP (218) with extremely low brightness. If the correct exposure cannot be obtained even after reaching this state, the AGC amplifier (301) is activated in STEP (221),
The amplification gain is made variable, and the gain is increased or decreased according to the level of the input imaged video signal to amplify until the output reaches a constant level (this state is called the AGC operation ON state).

The open state of the optical aperture mechanism (6) is detected by monitoring the total rotation amount (the total number of steps) of the iris motor (7) or mechanically detecting the operation of the optical aperture mechanism (6) itself. It is possible.

FIGS. 7 to 9 show specific examples in which the upper limit and the lower limit of the target value are delicately changed in accordance with the magnitude of the light / dark discrimination value (D) to perform the exposure adjustment. In each figure, the target evaluation value (Z _T ) is obtained from the first sampling area (A1) that is the focus area, the main subject exists in this first sampling area (A1), and the brightness level of the main subject is It corresponds to the target evaluation value (Z _T ).

In the figure, the horizontal axis represents the actual brightness level of the entire subject including the main subject and the background, which has not been subjected to exposure adjustment. The brightness area of the entire screen is indicated by (L) (indicated by an arrow). Are shown by (輝 度). The vertical axis represents the luminance level of the captured video signal after exposure adjustment has been performed after passing through the aperture mechanism (6) and the AGC amplifier (301), and is a permissible level that can be recognized as a high-quality video by human eyes. The appropriate exposure range (M), which is the range, is indicated by an arrow.

Here, FIG. 7 shows that the relationship | D | <b holds between the light / dark discrimination value (D) and the predetermined value (b), and the target evaluation value (Z _T ), that is, the actual luminance level of the main subject (▽ ) Is located substantially at the center of the luminance area (L) of the entire screen, and the main subject has relatively intermediate brightness. FIG.
-B holds, the actual luminance level (▽) of the main subject is at a slightly lower position in the area (L), and the main subject is relatively dark. FIG. 9 shows the relationship of D> + b. The actual luminance level of the main subject is in the region (L)
This is a case in which the main subject is at a slightly higher position and the main subject is relatively bright.

In each figure, (P) is a type of conventional example, and the brightness of the imaged video signal after exposure adjustment by all subjects when the method of performing exposure adjustment based only on the average brightness level of the entire screen is adopted. This is a level area, and the actual brightness level of all the subjects and the brightness level of the imaged video signal at this time have a relationship shown by a straight line (p). By matching the average value (AV) (the middle point of P) of this area (P) with the optimum value (m) which is the middle point of the proper exposure range (M), the proper exposure range (M) for the entire screen is displayed. Can be located in the approximate center, but as shown in FIGS. 8 and 9, the actual luminance level (▽) of the main subject is the actual luminance area (L) of the entire screen.
If the position is relatively low or high, the imaging brightness level of the main subject is (t1), which is outside the proper exposure range (M), and the main subject is underexposed.

Further, (Q) is a kind of conventional example, and is based on all the subjects when a method of matching the image pickup luminance level of the main subject or the image pickup luminance level of the area including the main subject with the optimum value (m) is adopted. That is, it is the brightness level region of the imaged video signal of the entire screen, and the actual brightness level of all the subjects and the imaged brightness level at this time have a relationship shown by a straight line (q). According to this method, the optimum exposure is obtained for the main subject, but in the case of FIGS. 8 and 9, the other screens such as the background are largely out of the proper exposure range, and the image is dim or white and has a dusty appearance. Screen.

(R) is the luminance level area of the captured video signal of all subjects in the method of the present embodiment, and the relationship between the actual luminance level of the entire screen and the luminance level of the captured video signal after exposure adjustment is indicated by a straight line (r). Becomes As will be described later, the target value is slightly changed by shifting the straight line (r) in the vertical direction.

In the flowchart of FIG. 5, if the absolute value of the lightness / darkness determination value (D) is within the range of the predetermined value (b) and the brightness is intermediate with respect to the entire screen, the upper and lower limits of the target value ( V) (v), the diaphragm mechanism operates so that the target evaluation value (Z _T ) including the main subject is located between the upper limit and the lower limit (V) (v), and FIG. As shown in, the image pickup brightness level (t3) of the main subject matches the optimum value (m) like the region (Q), and the image pickup brightness level region (R) of the entire screen of all the subjects is the proper exposure range (M). Position the lens at the approximate center, and the proper exposure is adjusted.

When a relationship of D <-b is established between the brightness determination value (D) and the predetermined value (b), and it is recognized that the luminance level of the main subject is relatively dark, the upper and lower limits of the target value of the target evaluation value are set. (Z _U ) and (Z _L ) are smaller than (V) and (v) respectively (W)
(W), the aperture mechanism is operated, and the target evaluation value (Z _T ) is positioned above and below the lower limit (Z _U ) (Z _L ), whereby the straight line (r) in FIG. By shifting the imaging brightness level of the main subject near the lower limit of the proper exposure range (M) by shifting it downward, the imaging brightness level region (R) of the entire screen is matched as much as possible with the proper exposure range (M). The main subject is provided with a sufficiently high-quality and proper exposure, and the other screens are also large, and a good screen is obtained without departing from the proper exposure range (M).

Further, D> + between the light / dark discrimination value (D) and the predetermined value (b).
When the relationship of b is established and the brightness level of the main subject is recognized to be relatively bright, the upper limit and the lower limit (Z _U ) (Z _L ) of the target evaluation value are larger than (V) and (v), respectively. By changing to (U) and (u) and operating the diaphragm mechanism, the straight line (r) in FIG. 8 is shifted upward so that the imaging brightness level of the main subject is positioned near the upper limit of the proper exposure range (M). At the very least, by matching the imaging brightness level region (R) of the entire screen with the proper exposure range (M) as much as possible, it is possible to obtain a proper visual exposure of the main subject with sufficient visual quality, and to obtain another screen. Larger exposure range (M)
画面 得 画面 外 な く な く 外.

Next, the gamma value determination will be described with reference to the flowchart of FIG. First, in STEP (230), the screen contrast (△) is derived as the ratio of the maximum value (Zmax) and the minimum value (Zmin) of the exposure evaluation values, and the contrast (△) is calculated using a preset reduction function f (△). The calculation is performed by substituting Δ) for changing the correction gamma (γ) to an optimum value. Specifically, γ = a ₀ LOG (Zmax / Zmin) + b ₀ = a ₀ LOG (△) + b ₀ (where a ₀ and b ₀ are constants, and the target correction gamma (γ) is derived in STEP (231) using the formula a ₀ <0, b ₀ <0) To be done.

Here, the subject has extremely low brightness in STEP (232), and the AGC amplifier (30) in STEP (221) in the flowchart of FIG.
If the gain in 1) is not fixed to a fixed value and it is determined that the normal AGC operation is ON, then in STEP (233), the correction gamma (γ) is felt by a predetermined amount (d ₁ ), By compressing the screen contrast, the signal level of a subject with substantially low brightness is raised.

Further, in STEP (234), the light / dark judgment value (D) of the target evaluation value (Z _T ) (normally, the exposure evaluation value of the priority focus area) is out of the range of the predetermined value (b), that is, D
When <-b or D> + b, the correction gamma (γ) is reduced by a predetermined amount (d ₂ ) in STEP (235) to compress the screen contrast. For example, when D <−b holds and the brightness level of the main subject, that is, the target evaluation value is significantly lower than the brightness level of the entire screen, the exposure adjustment is performed by the optical diaphragm mechanism (6), As shown in FIG. 8 (R), the brightness level of the main subject is positioned near the lower limit of the proper exposure range (M), and the brightness area of the entire cross section is positioned in the approximate center of the proper exposure range (M). Although the device was devised so that proper exposure could be obtained for both the main subject and the entire screen, the high-brightness region (r ₀ ) after exposure adjustment shown in (R) should be outside the proper exposure range (M). Up to.
Therefore, at this time, when the screen contrast is compressed by reducing the correction gamma (γ) by a predetermined amount (d ₂ ) as described above, the straight line (r) becomes a curved line (r ′) as shown in FIG. ), The luminance area of the entire screen changes from (R) to (R ′), and the luminance area of the entire screen is adjusted to proper while the luminance level of the main subject is located near the lower limit of the proper exposure range (M). It is possible to substantially match the exposure range (M), and the exposure adjustment by the optical diaphragm mechanism (6) is further corrected to realize proper exposure.

Further, even if D> + b holds and the luminance level of the main subject is significantly higher than the luminance level of the entire screen, as shown in (R) of FIG. r ₁ ) remains outside the proper exposure range (M), and at this time also, the screen contrast is compressed by decreasing the correction gamma (γ) by the predetermined amount (d ₂ ), as shown in FIG. Then, the straight line (r) changes like the curve (r ″), the brightness area of the entire screen changes from (R) to (R ″), and the brightness level of the main subject is changed to the proper exposure range (M).
It is possible to make the brightness area of the entire screen substantially coincide with the appropriate exposure range (M) while being positioned near the upper limit of, so that the exposure adjustment by the optical aperture mechanism (6) is further corrected to realize an appropriate exposure. Excessive exposure of the luminance portion and insufficient exposure of the low luminance portion are prevented.

The luminance regions (L) (R) and the straight line (r) in FIGS. 8 and 10 are the same, and the luminance regions (L) (R) and the straight line (r) in FIGS. 9 and 11 are the same. Are the same. The correction gamma (γ) value determined in this manner is used for the gamma correction circuit (302)
If the correction gamma (γ ₀ ) is significantly different from the previous correction gamma at the time of supply, the screen will be corrected at once and the screen will be unsightly, and the correction gamma will gradually change. Need to be done.

Therefore, in STEP (236), the correction gamma (γ) in the current field is compared with the correction gamma (γ ₀ ) previously determined, that is, 32 fields before, and the correction gamma in the current field is compared. If is larger, STEP (241)
, The correction gamma is increased by one step (dγ), and if the previous correction gamma (γ ₀ ) is larger,
In STEP (242), the correction gamma for one step (d
γ). Here, the one step (dγ) is set by dividing the difference between the maximum value and the minimum value that the correction gamma (γ) can take into n equal parts (n: natural number). γ) will change in n steps.

When switching the correction gamma (γ), it is effective to change the correction gamma (γ ₀ ) in one direction from the previous correction gamma (γ ₀ ). When the correction gamma is approaching, the brightness level of the screen slightly changes due to camera shake or the like, and the correction gamma fluctuates up and down at every switching according to this, resulting in complicated switching. Then, in order to prevent this complicated switching, the change direction of the previous correction gamma and the current change direction are compared in STEPs (237) and (238) according to the state of the flag (SX). Jump over STEP (239) (240) and proceed to STEP (241) (242). If different, difference | γ ₀ between correction gamma (γ ₀ ) (γ) between previous time and current field
Hysteresis is provided by changing the correction gamma only when −γ | is a predetermined value (C) or more at which correction is recognized to be essential.

A control signal corresponding to the gamma for correction determined in this way is input to a gamma correction circuit (302) connected downstream of the AGC amplifier (301), and is amplified based on the input signal of the imaging video signal based on the control signal. The ratio is changed and the optimal gamma correction is performed, so that even for a subject having a high screen contrast, appropriate brightness can be obtained over the entire screen. The information video signal gamma-corrected by the gamma correction circuit (302) is displayed on a CRT (not shown) or recorded by a VTR (not shown).

By the way, when the area set on the screen is very dark, the low-level picked-up video signal passes through the amplifier circuit in the pick-up circuit (8), which deteriorates the S / N and causes an error in the brightness level value. Grows. Therefore, when the brightness level of the captured video signal is A / D converted and calculated as the exposure evaluation value Z _i (i = 1 to 6) for each area as in the above-described embodiment, the exposure evaluation value is extremely large. When the value is small, the error of the evaluation value itself becomes large, and even when the same subject is imaged under the same condition, the exposure evaluation value constantly changes in a small value region and is not stable. Therefore, when the exposure is controlled by the ratio of the evaluation values of the respective areas as in the above-described embodiment, the aperture amount by the aperture mechanism (6) frequently changes according to the noise, which may result in a very unstable screen. is there.

Therefore, as shown in FIG. 13, STEP (200) in FIG.
Exposure evaluation value replacement routine (250) is inserted between P (201), and exposure evaluation value Z for each area calculated in STEP (200)
_(i) If there is an extremely small value in (i = 1 to 6), a change that frequently occurs in response to the noise of the extremely small exposure evaluation value does not affect the exposure and the γ correction. It is necessary to devise a method of previously replacing the exposure evaluation value of the area with a fixed value. In the exposure evaluation value replacement routine (250), the exposure evaluation value Z _(i) (i = 1 to 6) is set in STEP (251).
The fixed value (h ₀ ) set in advance in STEP (252) for those judged to be below the limit value (Pm)
Replace with After only the extremely small exposure evaluation value is replaced with the fixed value (h ₀ ) in this way, STEP (20
1) It is possible to prevent exposure control and γ correction from being affected by a change in the exposure evaluation value that frequently occurs due to the influence of noise by executing the flowcharts described below. Note that the limit value (Pm) is a value that can be recognized when the exposure evaluation value changes significantly due to noise when the luminance level is extremely small, and the exposure control starts to be adversely affected. The fixed value (h ₀ ) is h ₀ = Pm
Or Is a value less than or close to the limit value (h ₀ ), and both values are experimentally obtained in advance.

In the above embodiment, the target evaluation value (Z _T ) is selected when there is no abnormal brightness part in the first sampling area (A1).
When judged by EP (202), Z _T = Z ₍₁₎ is set and the exposure evaluation value Z ₍₁₎ in the first sampling area (A1) is prioritized, and the abnormal brightness is detected in the first sampling area (A1). Exists and the focus area is the second sampling area (A2)
Then, if there is an abnormal brightness part in this area (A2), STEP
When it is judged in (205), Z _T = Z ₍₂₎ is set and the exposure evaluation value Z ₍₂₎ of the area excluding the first sampling area (A1) from the second sampling area (A2 ₎ is prioritized.

However, if the priority of the center of the screen is increased, the peripheral part is underexposed if the central part is brighter than the peripheral part, and the peripheral part is overexposed if the central part is brighter than the peripheral part. Further, due to the entrance and exit of the subject in the priority area in the center, the brightness level of the priority area changes even though the subject is the same on the entire screen, and the exposure of the entire screen becomes unstable.

Therefore, a method of changing the priority of the screen center in the target evaluation value that is the basis of the exposure control according to the brightness difference between the screen center and the peripheral portion is effective for optimum exposure control. Therefore, another embodiment in consideration of this point is shown in FIG.
In FIG. 14, the same parts as those in FIG. In the flowchart of FIG. 14, when the priority areas are designated as the first or second sampling areas (A1) and (A2) in STEPs (202) and (205), the target evaluation value calculation routine considering the above points ( 300) (30
1) is executed.

This target evaluation value calculation routine (300) (301)
As shown in the figure, the logarithmic compression value of the ratio of the exposure evaluation values Z ₍₁₎ and Z ₍₂₎ used in STEP (202) (205 ₎ to the average exposure evaluation value (Z _A ). Or The relationship between the predetermined value (b ₀ ) and the predetermined value (c ₀ ) is determined in STEP (310) (311). Here, a> b ₀ > c ₀ is established between the predetermined value (b ₀ ) (c ₀ ) and the predetermined value (a).

For example, in STEP (202), the first sampling area (A1) is designated as the priority area, and in STEP (310) Is determined to be larger than the predetermined value (b ₀ ), the function (f)
Substituting the exposure evaluation values Z ₍₁₎ , Z ₍₂₎ , ... Z ₍₆₎ of each area into, the target evaluation site (Z _T ) is calculated, If judged, Z ₍₁₎ , Z ₍₂₎ , ... Z ₍₆₎ is substituted into the function (g), and If it is determined that Z ₍₁₎ is assigned to the function (h), the calculation is performed. here Has a property that it becomes larger as the brightness difference between areas becomes larger. When the brightness difference is extremely large, the function (f) is used, and when it is slightly smaller than this, the function (g) is used. Further, when there is almost no difference in brightness, it is calculated using the function (h).

Functions (f), (g), and (h) are f (Z ₍₁₎ , Z ₍₂₎ , ..., Z ₍₆₎ ) = (Z ₍₁₎ + Z ₍₂₎ +… + Z ₍₆₎ ) / 6 = Z _T g (Z ₍₁₎ , Z ₍₂₎ , ..., Z ₍₆₎ ) = (2Z ₍₁₎ ＋ Z ₍₂₎ ＋ ・ ・ ・ ＋ Z ₍₆₎ ) / 7 = Z _T h (Z _{(1 )} , Z ₍₂₎ , ..., Z ₍₆₎ ) = Z ₍₁₎ = Z _T.

As is clear from these calculation methods, the exposure evaluation value Z _{(1) at the} target evaluation value (Z _T ) increases as the brightness difference increases.
Reduce the effect of. That is, the priority of the first sampling area (A1) which is the priority area is lowered.

Similarly, when the second sampling area (A2) is designated as the priority area in STEP (205), the target evaluation value (Z _T )
As the brightness difference between areas increases in the calculation routine (301), the function for calculating the target evaluation value (Z _T ) is (h) →
Switching from (g) to (f). However, the calculation routine (30
1) is shown in the same flow chart as the routine (300), but Z ₍₁₎ and Z ₍₂₎ are replaced in the arithmetic expression. That is, f (Z ₍₂₎ , Z ₍₁₎ , Z ₍₃₎ , ・ ・ ・, Z ₍₆₎ ) ＝ (Z ₍₂₎ ＋ Z ₍₁₎ ＋ Z ₍₃₎ ＋＋＋ Z ₍₆₎ ) / 6 ＝ Z _T g (Z ₍₂₎ , Z ₍₁₎ , Z ₍₃₎ , ‥, Z ₍₆₎ ) ＝ (2Z ₍₂₎ ＋ Z ₍₁₎ ＋ Z ₍₃₎ ＋＋＋ Z ₍₆₎ ) / 7 ＝ _{Z T h (Z (2)} , Z (1), Z (3), ‥, Z (6)) is calculated as _{= Z (2) = Z T} .

As described above, as the brightness difference, which is the ratio of the brightness level of the priority area to the entire screen, increases, the weighting amount of each exposure evaluation value in the target evaluation value (Z _T ) is switched in stages, and the screen with a large brightness difference is displayed. Also prevents overexposure or underexposure of the non-priority area due to excessive correction, reduces changes in the target evaluation value due to movement of the subject, and reduces unstable changes in exposure. Based on the target evaluation value calculated by any of the functions (f), (g), and (h) as described above, STEP
(208) The exposure control is performed as in the first embodiment in the subsequent flow charts.

When selecting the calculation formula for calculation by STEP (310) (311), the condition of STEP (310) (311) is set, for example, three times (3
The unstable exposure control can be alleviated by executing the switching of the arithmetic expression when the field is continuously satisfied.

By the way, as shown in Figures 14 and 15, the target evaluation value (Z _T )
Is calculated based on the functions (f) (g) (h), And the weighting ratio of the exposure evaluation values Z ₍₁₎ , Z ₍₂₎ , ..., Z ₍₆₎ of each area, and And the weighting ratio of the exposure evaluation values Z ₍₁₎ , Z ₍₂₎ , ..., Z ₍₆₎ of each area are as shown in FIGS. 16 and 17. That is, the weighting ratio of each exposure evaluation value in the target evaluation value (Z _T ) changes stepwise according to the three regions with the predetermined values (b ₀ ) and (c ₀ ) as threshold values. Therefore, When is a value near the predetermined value (b ₀ ) (c ₀ ), the function to be used is frequently switched due to a small change in the screen due to camera shake, movement of the subject, etc., and the target evaluation value (Z _T ) Fluctuates greatly.

This causes fluctuations in the exposure as it is, causing unstable screens and sometimes hunting.

Therefore, as a method of improving this point, another embodiment that executes the routine of FIG. 18 is effective instead of the target evaluation value calculation routine of FIG. For example, when the first sampling area (A1) is designated as the priority area in STEP (202) and the target evaluation value (Z _T ) is calculated in STEP (300), the calculation of FIG. 18 is performed. The routine is executed. First, at STEP (401) Is used as a variable (x) and is substituted into six continuous weighting functions f _{i (X)} (i = 1, 2, ... 6) for each area to determine the weighting ratio by each exposure evaluation value. These six functions (However, x = 0 to ∞) is always established, and as shown in Fig. 19, it changes in a smooth curve according to the variable (x), and changes stepwise as shown in Fig. 16. There is no such thing. Then ST
In EP (402), the variable (x) is substituted into the function f _{i (X} ) to calculate the weighting rate d _(i) (i = 1 to 6) of the exposure evaluation value of each area, and STEP (403) At Based on the arithmetic expression of, the weighting rate d _{(i) for} each area (i = 1
6), the exposure evaluation values Z _(i) are weighted and averaged to obtain the target evaluation value (Z _T ).

Similarly, when the second sampling area (A2) is designated as the priority area in STEP (205), the target evaluation value calculation routine (301) described above in FIG. Is a variable (x), and as shown in FIG. 20, the function f in FIG.
_The calculation is performed in the routine of FIG. 18 by replacing _{1 (X)} with f _{2 (X)} .

By continuously changing the function fi _(X) with respect to the variable (x) in this way, the change of the target evaluation value (Z _T ) can be made smooth with respect to the change of the screen, and a stable screen can be obtained. It will be possible.

(G) Effect of the Invention As described above, according to the present invention, the brightness level of the priority area of the screen is prioritized over other areas to maximize the overexposure or underexposure of the non-priority area. It also reduces the instability of the screen. Further, the influence of noise generated when the luminance level is low is reduced, and stable exposure control is performed.

[Brief description of drawings]

1 to 13 relate to an embodiment of the present invention, FIG. 1 is an overall circuit block diagram, FIG. 2 is an explanatory diagram of area division,
Figure 3 is a flow chart of the main routine, and Figure 4 is AE.
FIG. 5 is a flow chart of a routine, FIG. 5 is a flow chart of determination of the aperture amount, FIG. 6 is a flow chart of γ setting for correction,
7, 8 and 9 are characteristic diagrams relating to exposure adjustment,
10 and 11 are characteristic diagrams relating to γ correction, FIG. 12 is a diagram for explaining movement of the main subject, and FIG. 13 is a flowchart of the exposure evaluation value replacement routine. See also Figure 14, Figure 15,
FIG. 18 is a flow chart of another embodiment.
FIG. 17 is a diagram showing changes in the weighting ratio for the routine of FIG. 15, and FIGS. 19 and 20 are diagrams showing changes in the weighting ratio for the routine of FIG. (26) ... microcomputer (level detection means),
(6) …… Optical aperture mechanism (exposure control means), (Z _U ) ……
Upper limit of target value (target brightness level), (Z _L ) ...... Lower limit of target value (target brightness level).

Claims (2)

(57) [Claims] 1. A level detecting means for detecting a brightness level of a picked-up video signal for each of a plurality of areas including a priority area set by dividing an image pickup screen, and a weighting amount set for each of the plurality of areas. In the above, weighting means for weighting the brightness level of each of the plurality of areas, and exposure control means for controlling the exposure so that the target level calculated from the brightness levels of the weighted areas approaches the target brightness level. In the case of weighting by the weighting means, when the brightness difference between the priority area and another area is small, the weighting amount of the priority area is made larger than the other area, and conversely when the brightness difference is large, An imaging apparatus, wherein the weighting amount of a priority area is reduced so as to approach the other area. 2. A level detecting means for detecting a brightness level of a picked-up image signal for each of a plurality of areas set by dividing an imaged screen, and a target level calculated from a brightness level of each area is a target brightness. Exposure control means for controlling the exposure so as to approach the level, and when there is a brightness level below the limit value among the brightness levels for each area detected by the level detection means, the brightness level of the corresponding area is set in advance. An image pickup device characterized by replacing with a fixed level that has been set.