JPH0256180A - Image pickup device - Google Patents

Abstract

PURPOSE:To decrease the excess and insufficiency of exposure between a priority area and the luminance level of the whole screen by changing a correcting gamma value by the relation between the luminance level of the priority area and the luminance levels of the other areas. CONSTITUTION:The output picture of an image pickup circuit is divided into plural areas A2-A6 including a priority area A1 and the luminance level of each divided area is detected by a switching circuit 14, a selecting circuit 15 and an integrating circuit 16 and inputted to a microcomputer 26. The microcomputer 26 controls an iris motor 7 so that the luminance level of the above priority area A1 may coincide with a target level, detects a screen contrast from the luminance level of each area above and determines the correcting gamma value by the contrast. The gamma value is changed by the relation between the luminance level of the priority area A1 and the luminance levels of the other areas A2-A6. Based on the correcting gamma value, a gamma correcting circuit 302 is controlled.

Description

DETAILED DESCRIPTION OF THE INVENTION (A) Field of Industrial Application The present invention relates to an imaging apparatus such as a video camera that includes an exposure adjustment means and a gamma correction mechanism.

(1) Prior Art In an imaging device such as a video camera, it is an important element to obtain an appropriate imaging luminance signal level (brightness) for a subject. This includes the absolute level (average brightness) and relative level (contrast) of the imaging signal within the screen.

The former is appropriately adjusted by an exposure adjustment mechanism such as an optical diaphragm and an AGC circuit, and the latter is appropriately adjusted by a gamma (7) correction mechanism.

To explain in more detail, there is an exposure adjustment mechanism that is widely accepted and is achieved by controlling the optical aperture of a lens or the like and the amplification factor of an amplifier that amplifies the captured video signal level. However, there was a problem in that the main subject could not be properly brightened when the screen included a high-brightness area such as a light source or when the background was very dark.

To solve this problem, an exposure compensation method has been proposed that takes advantage of the fact that the main subject is placed in the center of many screens. For example, JP-A-62-11
Publication No. 0369 (HO4N 5/243) discloses that the screen is divided into two areas, a central area and a peripheral area, and the signal level of the captured video signal in each area is detected as an evaluation value, and the evaluation value is calculated based on the evaluation value of the peripheral area. If you want to give weight to the evaluation value of the central region, the aperture amount of the lens and the amplification gain of the imaged video signal are controlled according to the ratio of both evaluation values (1:0). Techniques are disclosed for increasing the contribution of .

By the way, regarding the dynamic range of subject brightness,
The size of current image sensors is quite small, and that of display devices such as CRTs is even smaller. Therefore, as mentioned above, controlling the absolute level of the brightness signal alone cannot avoid saturation in high-brightness areas and blackout in low-brightness areas, making it difficult to obtain appropriate brightness for the entire subject. It is.

Therefore, in normal imaging devices, the photoelectric conversion characteristics (gamma characteristics) of the imaging device are In order to ensure that the overall gamma characteristic of the system from the image pickup device to the display device is always 1 based on the nonlinear electro-optical conversion characteristics of the display device, a technology has been adopted that performs gamma correction within the circuit on the camera side.

(c) Problems to be Solved by the Invention As in the prior art (Japanese Unexamined Patent Publication No. 62-110369), the central area where 11 subjects are present is set as a priority area, and the brightness level of this area matches the target level. If you perform exposure adjustment in such a way that the center area is extremely dark relative to the entire screen including the periphery, if you control this center area to the optimal brightness level, the non-priority areas in the periphery will become significantly darker. If the brightness is controlled to the optimum value when the image is relatively bright, the peripheral areas will be severely underexposed.

Furthermore, if the brightness level in the husband area is extremely low, the S/N ratio will deteriorate and the brightness rail will frequently fluctuate due to the influence of noise, making exposure control unstable.

(d) Means for Solving the Problems The present invention detects the brightness level of the captured video signal for each of a plurality of areas including priority J and rear set by dividing the imaging screen, and detects the brightness level of the captured video signal in the priority area. In addition to adjusting the exposure so that the brightness level matches the target level, the screen contrast is detected from the brightness level of each area, and the gamma value for correction is determined from this contrast. The correction gamma value is changed depending on the relationship with the brightness level of other areas, and for areas where the brightness level is extremely low, the brightness level is replaced with a fixed value.

(E) Function Since the present invention is configured as described above, when there is a large difference between the brightness level of the priority area and the entire screen, the screen contrast is compressed and overexposure and underexposure of the non-priority area is reduced. Ru. Furthermore, the influence of noise when the brightness level is low is reduced, making it possible to perform optimal exposure control.

Kube) Example An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a circuit block diagram of this embodiment.

(1) is the video camera section, and the focus lens (2
), an optical diaphragm mechanism (6) that controls exposure, and an iris motor (7) that drives this diaphragm mechanism (6). ) and an imaging circuit 8) having a solid-state imaging device (CCD) that converts subject light into an imaged video signal.

The luminance signal in the imaged video signal obtained by the imaging circuit (8) is processed through a bypass filter (HPF) (9), a low pass filter (LPF) (tt), and a sync separation circuit (1).
2).

The vertical synchronization signal (VD) and horizontal synchronization signal (HD) separated from the luminance signal by the synchronization separation circuit (12) are supplied to the switching control circuit (13) in order to set the sample area.

The switching control circuit (13) outputs a vertical/horizontal synchronizing signal (VD
>(HD) and a fixed oscillator output that serves as a clock for driving the CCD, as shown in Figure 2, a rectangular sampling area (A1) is created in the center of the screen, and the area including this area (At>) is The selection signal (S2) is sent to the subsequent selection circuit so that a sampling area (A2) that is four times larger than (A1) and sampling areas (A3), (A4), (A5), and (A6) can be set around this area (A2). (1
5), and is also output to HPF (9) output and L P F
(11) A switching key (51) for selecting an output is supplied to the switching circuit (14).

The switching circuit (14) receives the switching signal (Sl) and continues to select the HPF (9) output for a predetermined period, for example, between 32 fields, and selects the LP output for only one field every 32 fields.
F(11) output is selected, and this switching operation is repeated at the same cycle thereafter.

Based on the selection signal (S2), the selection circuit (15) converts the output of the HPF or LPF selected by the switching circuit (14) into the integration circuit (16) (1) according to the sampling area.
7)... Selectively output to 21). That is, each filter output related to the first sampling area (A1) is sent to the integration circuit (16), each filter output related to the second sampling area (A2) is sent to the integration circuit (<17), and the following is sent to the third integration circuit (16).
The filter outputs related to the sixth sampling area (A3)<A4) (A5 area (A6)) are respectively output from the integrating circuit (1).
8) (19) (20) (21).

The integration circuit (16) includes an A/D converter (22) and an adder (2
3), consists of a memory circuit (24), and the A/D converter (22) sequentially A/D converts each filter output that passes through the selection circuit (15) and sends it to the adder (23). Output.

The adder (23) constitutes a digital integrator together with the A/D converter (22) in the previous stage and the memory circuit (24) in the latter stage, and connects the output of the memory circuit (24) and the output of the A/D converter (22). The power O is calculated and the addition result is sent to the memory circuit (24) again.
supply to the The memory circuit (24) can be reset for each field and holds one field of the output of the adder (23), that is, the digitally converted value of the level of the luminance signal that has passed through the filter, for the first sampling area (A1). become.

Regarding the integration circuits (17), (18)...(21),
It has exactly the same configuration as the integrating circuit (16), and the memory circuit built into each integrating circuit stores the level of the luminance current that has passed through the filter selected in the current field for each sampling area. The integral value for one field will be held. The integral value of each of these memory circuits is calculated by the memory circuit (25) at the subsequent stage.
It is stored in groups.

Specifically, the cutoff frequency of HP F(9) is 20
Allows passage of band from 0KHz to 2.4MHz, LP
The cutoff frequency of F(11) is set to allow passage of a band of 0 to 2.4 MHz. In addition, 2.4M
Hz is an extremely high frequency that is not directly related to the luminance signal, and its value has little meaning, and I(PF(9) is 2
It is sufficient if the band above 00KHz can be extracted, and LPF (1
1) 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-frequency or low-frequency component of the luminance (g) that has passed through either HP F (9) or LPF (11) can be digitally integrated for one field, and the current field can be integrated for each sampling area. will be stored in the memory circuit (25) as an integral value.

Here, among the integral values stored in the memory circuit (25), the integral value of the low frequency component when L P F (11) is selected is normalized per unit area and used as an exposure evaluation value for exposure control. , and when the HPF (9) is selected, the integral value of the high frequency component can be processed by a subsequent microcomputer (26) as a focus evaluation value for focus control.

These evaluation values are processed by software by the microcomputer (26), and based on the processing results, a command is issued to the focus motor control circuit (27>) to control the focus motor (
4> to advance and retreat the focus lens (2),
The autofocus operation is executed so that the focus evaluation value is maximized, and a command is issued to the iris motor control circuit (28) to drive the iris motor (7) and operate the optical diaphragm mechanism (
6), automatic exposure adjustment becomes possible so that the exposure evaluation value becomes a predetermined value.

Next, referring to the flowchart in Figure 3, the microcontroller (2
6) The main routine of the autofocus operation and auto iris operation will be explained.

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

First, at 5TEP (30), the integrated value for one field in each sampling area in the current field is read into the microcomputer (26) from the memory circuit (25).

Next, the counter (A E-CNT) provided for performing autofocus operation and auto iris operation in a time-sharing manner is decremented, that is, 1 is subtracted to 5 TEP (32))
, to determine whether the counter value is 0 or not S T E
P(33)), if the cursor angle is not 0, an autofocus operation is executed, and an auto iris operation is executed only when the counter value is 00. Autofocus operation is H
AF for holding the focus lens (2) at the in-focus position based on the focus evaluation value, which is the integral value of the PF (9) output.
This can be accomplished by executing routine (35).

During the AF routine execution, when HPF (9) is selected,
The integral values (DATA (1)) (DATA (2)) of the first and second sampling areas (At) (A2) are calculated by multiplying the focus evaluation value (X (1)) of each area in the current field by First, specify the first sampling area (A1) as the focus area, and then turn the focus motor
4) to displace the focus lens (2),
Focus evaluation value X in the first sampling area (A1)
Regarding (1), for each field, that is, the focus evaluation value
Every time (+) is updated, the focus evaluation value of the current field and the previous field are compared, and the rotation of the focus motor (4) is continued in the direction in which the focus evaluation value becomes larger. Detects the position that becomes the evaluation value, and when this position is reached, the focus motor (4) sets this as the focusing position.
is stopped, the focus lens (2) is fixed, and the focusing operation is completed.

In addition, even though the lens position changed from the far point to the near point when detecting the top of the mountain, the first sampling
A clear peak of the mountain could not be detected in the focus evaluation value X (I), and the focus evaluation value X in the second sampling area (A2)
If the maximum evaluation value in (1) is larger per unit area of the area than the maximum evaluation value of the focus evaluation value X < I in the first sampling area (A1>), the second
The Zumbling area (A2) is designated as the focus area, and henceforth, the focus evaluation value is X. The lens position where , takes the maximum evaluation value is set as the in-focus position, and this lens position is held to complete the focusing operation.

Furthermore, in the AF routine, even after the lens reaches the top of the mountain and the focusing operation is completed by temporarily fixing the lens at this position, the change in focus evaluation value is monitored, and if the focus evaluation value changes significantly, , an object change monitoring operation is performed in which the object moves and leaves the focus area and the focusing operation is restarted from the beginning. In this monitoring operation, when the focusing operation is completed with the first sampling area (A1) as the focus area, the monitoring operation is first performed on this first sampling area (A1), and if the first sampling area (A1) is When a large change occurs in the focus evaluation value X (1), the second sampling area (A2)
Determine whether a change has occurred in the focus evaluation value X(!,
When this occurs, an instruction is given to restart the focusing operation, but this focus evaluation value X0. If there is no significant change in , the main subject moves from the position of the chain line to the position of the solid line, that is, within the second sampling area (A2) and away from the first sampling area (A1), as shown in Figure 12. Assuming that the focus area is simply moved laterally to the position, the focus area is changed from the first sampling area (A1) to the second sampling area (A1).
A2) and continue the monitoring operation.

When the above AF routine is completed, the counter (AE-C
NT) is 1fj, and it is determined whether the counter value becomes 0 or not (STEP (36)). If it becomes 0, the microcomputer (26) controls the switching control circuit (13).
Control number 18 is issued, and in response to this, the switching circuit (14
) has a switching signal (Sl) to select the LPF (11).
is issued, and the selection of L P F (11) is made (S
T E P (37)). Thus L P F (11)
Once selected, wait for the evaluation value obtained by this selection to be loaded.

On the other hand, when the auto iris operation is selected at 5TEP (33), the AE routine (38) which is the basis of the auto iris operation is executed, and then the counter (AE-CNT
) to the initial state (STEP (39)), select the filter to HP F (9) (STEP (40)
), waits for the evaluation value of the next field to be integrated. Here, the initial state of the counter (AE-CNT) is a state where the initial value "32'" is set in order to calculate the exposure evaluation value based on the luminance signal that passes through LPF (11) every 32 fields. say.

Next, the auto iris operation will be explained according to a flowchart. At 5TEP (38) of the main routine, the counter (
When the curvature of the auto-iris (AE-CNT) reaches zero, that is, 32 fields have elapsed since the start of the focusing operation, the auto-iris (AE) routine is executed as shown in FIG. First, the 1st, 3rd to 6th sampling areas (At) read in 5TEP (30) of the main routine
(A3)...In (A6), the integral value DATA(1
), DATA(3), ... DATA(6) is normalized by the area of each area, that is, the first, third to sixth
The integral value per unit area obtained by dividing the area (SMI) (5M3)...(5M6) of the Zumbling Area (At) (A3)...(A6) is the exposure evaluation value for each area. Calculated in S T E P (200) as Z (1), Z (1: l...Z (,,).

However, as mentioned above, the second sampling area (A2) was defined as the area that included the first sampling area (A1) and was used for the focusing operation, but in the exposure control operation, the area corresponding to each exposure evaluation value are separate areas. Therefore, the exposure evaluation value Z(!, is the second sampling area (!)
A2) is defined as the exposure evaluation value of the area excluding the first sampling area (A1). That is, Z(*, ■(DA
TA(2)-DATA(1))/((5M2)-(SM
It can be calculated as I)).

+Z(1)+Z)+Z(+,+Z(6)+Z<*,)
is the average exposure evaluation value (Z A ) and 1. Te S T E
P (201) l Knee C [put out.

Next, a target evaluation value (Z7) that represents the brightness level of this screen and is to be controlled is determined. First, in the autofocus operation described above, the first sampling area (A1
), and the exposure evaluation value Z(+) of this first sampling area (A1) is relative to the average exposure evaluation value (ZA).
It is determined whether the exposure evaluation values are within a certain permissible range, and if the exposure evaluation values are within the pair (a), S T E P
(202), 5TEP (203)
), this exposure evaluation value Z(1, is the target evaluation value (2 lenses), and the larger second sampling area (A2) is specified as the focus area in the autofocus operation described in ILOG. E P (20
When it is determined in step 4), if the exposure evaluation value 2 (,) is within a predetermined range (a) with respect to the average exposure evaluation value (ZA), S T E P ( 205
), this exposure evaluation value 2 (1) is set as the target evaluation value (zt) in 5TEP (206).

is not satisfied, or when the ILOG cass area is designated as the first sampling area (At), the exposure evaluation value Z(1) low 1 to 6 of each area is
Of these, a predetermined value (a) is calculated for the average exposure evaluation value (zA).
Add the average of the following to the target evaluation value <zy) and get 5T
Calculated using EP (207). In addition, if the exposure evaluation values in all areas are not within the specified range, S T E P
When it is determined in (290), the exposure evaluation value z(1) of the first pulling area (AI) is set as the target evaluation value (Za). Furthermore, in S T E P (208), the maximum value among the sequential exposure evaluation values Z (1) (i-1 to 6) is Z
mix, and the minimum value is set as Zmin as a value necessary for exposure determination.

In S T E P (202) (205 > (207)), each exposure evaluation value is within the preset tolerance range with respect to the average exposure evaluation value (ZA), or is a value that is significantly different from the average exposure evaluation value (ZA). Simply use the ratio of the two to determine whether l/
There is no problem even if the ratio is 1, but in this embodiment, taking into consideration that the dynamic range of the ratio between the two is extremely wide, the ratio is logarithmically compressed and then compared with the predetermined value (a).

As described above, when executing the auto eye 1, 1 scan operation among the exposure evaluation values of multiple sampling areas, the target evaluation value, which is the exposure evaluation value of the area used, is of the first sampling area (A1). Exposure evaluation value Z(+) is prioritized, and if there are extremely high brightness areas such as light sources and extreme low brightness areas such as deep green in this first sampling angle (Al), that is, abnormal brightness areas, the average evaluation value If the logarithmic compression value of the ratio to (2, 1) is not within the range of the predetermined (i(a)), and the focus area is the second pull area (A2), the exposure evaluation value Z(.

Prioritize. Furthermore, this second sampling area (A2)
If there is an abnormal brightness part in
The average value of the exposure evaluation values of the area where no aperture part exists is set as the target evaluation value, and the area corresponding to this is used for the auto iris operation.

With the aperture set as described above, the aperture is first determined based on flowchart 1 in FIG. 5TEP(
In step 210), first, the logarithm 1.0 of the ratio between the target evaluation value (21) and the minimum value (Z min ) is derived. This brightness/darkness discrimination value (D> is the target evaluation value (21
) is a parameter that determines whether the main subject is relatively bright or dark in the screen.
becomes larger. Conversely, when the object evaluation value (Z□) is relatively small, the former term becomes small, the latter term becomes large, and the brightness discrimination value (D) becomes small.

The reason why the logarithm of the ratio of evaluation values is used when calculating this brightness/darkness discrimination value (D) is that human vision normally recognizes brightness because the brightness level of the actual subject is exponential, for example, the brightness level We focus on the fact that when the value increases from 2 times to 4 times to 8 times, the visual brightness changes linearly.

Discriminant value <D at S T E P (211) (212>)
) is within the range of the predetermined value (b) (b>O), that is, ID
When it is determined that I<b holds, it is assumed that the brightness in the screen is intermediate, and the upper limit (ZU) and lower limit (2,) of the target value for controlling the target evaluation value (zd) are set as S T E P (
213), respectively (V) and (v), and the discriminant value (D
> is judged to be more than +b, it is considered relatively bright and the L limit <ZU) and the D limit (ZL) are set as S T E P (21
4) as defined in (U) and (u), respectively. Furthermore, the discriminant value (D>
When it is determined that -bI2J is below, the upper limit (Zo) and lower limit (zL) are set as relatively dark.
215), respectively (W) and (w). By setting the upper and lower limits in advance to have the relationships U≧V)W and u>V>W, the relative brightness within the screen of the target evaluation value (z, r) can be adjusted. A corresponding target range will be obtained.

Note that the above-mentioned predetermined value (b) is the limit value when the brightness level of the main subject can be visually recognized as being significantly brighter or significantly darker than the brightness level of the entire screen,
It has been experimentally determined in advance.

Next S T E P (216) (217) 4: Set the target evaluation value (2 guns) and the target value upper and lower limits (ZU), (ZL
), and if Z,>Zt>ZL holds, it is determined that proper exposure has been obtained.1. The isle smoke (7) that drives the optical aperture mechanism (6) is maintained in a stopped state, and the current aperture! : Maintain, target evaluation value (ZT) is the upper limit (ZU)
If it is larger, it is considered overexposed, and S T E P
At (219), the aperture mechanism drives the iris motor (7) in a direction to close the aperture amount by one step, and conversely, if the target evaluation value (ZT) is smaller than the lower limit (ZL), it is determined that the exposure is insufficient and S T E At P (218), the iris motor (7) is driven in the direction of opening the aperture amount by one step.

Note that the iris motor (7) is constituted by a stepping motor.

While adjusting the aperture amount using this iris motor (7),
The gain of the AGC amplifier (301) that amplifies the captured video signal at T E P (222) is fixed at a constant value (the gain may be -0) (this state is called the AGC operation OFF state), and the incident If it is difficult to obtain proper exposure by simply adjusting the light intensity, that is, if the subject is extremely low brightness and
While repeating TEP (218), it is determined in STEP (220) that the aperture mechanism is in the open state, and if proper exposure cannot be obtained even if this state is reached, then STEP (221) at AGC amplifier (
301), its amplification gain is made variable, and the gain is increased or decreased depending on the level of the input imaged video signal, and the output is amplified until it reaches a constant level (this state is referred to as the AGC operation state N). state).

The open state of the optical diaphragm mechanism (6) can be determined by observing the total rotation amount (total number of steps) of the iris motor (7) or by mechanically detecting the operation of the optical diaphragm mechanism (6) itself. Detectable.

As mentioned above, specific examples of the case where exposure It is executed by subtly changing the upper and lower limits of the target value according to the magnitude of the brightness discrimination value (D>) are shown in FIGS. 7 to 9. In the figure, the target evaluation value <z7) is obtained from the first sampling area (A1) which is the focus area, the main subject exists in this first sampling area (A1), and the brightness level of the main subject is obtained from the target evaluation value ( Corresponds to Z7).

In the figure, the horizontal axis is the actual brightness level of all subjects including the main subject and background without exposure adjustment, and the brightness area of the entire screen is indicated by (L) (indicated by arrow 0). The actual brightness level is indicated by ( ). The vertical axis is the brightness level of the captured video signal after passing through the aperture mechanism (6) and AGC a/b (301) and exposure adjustment, which is recognized as a high-quality video by human vision. The appropriate exposure range (M>, which is the allowable range) is indicated by an arrow.

Here, in FIG. 7, the relationship IDI<b holds between the brightness discrimination value (D) and the predetermined value (b), and the target evaluation value <21>,
In other words, the actual brightness level () of the main subject is located approximately at the center of the brightness area (L) of the entire screen, and the main subject has a relatively intermediate brightness. D<
-b holds true, the actual brightness level () of the main subject is at a slightly lower position in area (L), and the main subject is relatively dark. Figure 9 shows the relationship p>-B+. The actual brightness level of the main subject is the area (L)
The main subject is relatively bright.

In each figure, (P) is a type of conventional example, which is the brightness of the captured video signal after exposure adjustment for all subjects when a method of performing exposure adjustment based only on the average brightness level of the entire screen is adopted. This is a level region, and the relationship between the actual brightness level of all objects and the brightness level of the captured video signal at this time is shown by a straight line (p). The average value (A
By matching V ) (midpoint of P) to the optimum value (m), which is the midpoint of the proper exposure range (M), the proper exposure range (M) can be positioned approximately at the center for the entire screen. However, as shown in Figures 8 and 9, the actual brightness level () of the main subject is different from the actual brightness area of the entire screen (L>
If the position is relatively low or high, the imaging brightness level of the main subject will be (tl), which will be out of the appropriate exposure range (M), and the main subject will be underexposed.

In addition, (Q) is a type of conventional example, and when a method is adopted in which the imaging brightness level of the main subject or the imaging brightness level of the area containing this main subject is matched to the optimal value (m), That is, this is the brightness level region of the imaged video signal of the entire screen, and the actual brightness level of all objects and the imaged brightness level at this time have a relationship shown by a straight line (q).

Using this method, the main subject can be properly exposed, but in the case of Figures 8 and 9, other areas such as the background are significantly out of the appropriate exposure range, resulting in dim or white areas. It becomes a screen.

(R) is the brightness level region of the imaged video signal for all subjects in the method of this embodiment, and the relationship between the actual brightness level of the entire screen and the brightness level of the imaged video signal after exposure adjustment is shown by the straight line (r). becomes. As will be explained later, this straight line (
By shifting r) in the vertical direction, the target value can be slightly changed.

In the flowchart of FIG. 5, if the absolute value of the brightness discrimination value (D) is within the range of the predetermined value (b) and the brightness is intermediate to the entire screen, the upper and lower limits of the target value are set ( V
) (v), the aperture mechanism operates so that the target evaluation value (zl) that includes the main subject is located between the upper and lower limits (V) and (v), as shown in Figure 7. Similarly to the area (Q), the imaging brightness level (t3) of the main subject matches the optimum value (m), and the imaging brightness level area (R) of the entire screen for all subjects is approximately the appropriate exposure range (M). The camera is placed in the middle of the room and the exposure is adjusted appropriately.

When the relationship D<-b holds between the brightness discrimination value (D) and the predetermined value (b), and the brightness level of the main subject is recognized to be relatively dark, the upper and lower limits of the target value of the object evaluation value are set. (
ZL+) (ZL) respectively (V) (W) smaller than (v)
)(w), operate the diaphragm mechanism, and position the target evaluation value (ZT) within the upper and lower limits (ZL), thereby moving the straight line (r) in Fig. 7 downward. Adjust the imaging brightness level of the main subject to the appropriate exposure range (M)
to match the imaging brightness level area (R) of the entire screen to the appropriate exposure range (M) as much as possible.
By doing so, it is possible to obtain a proper exposure of sufficiently good visual quality for the main subject, and to obtain good pictures on other pictures without significantly deviating from the proper exposure range (M).

Furthermore, when the relationship D>10 holds between the brightness discrimination value (D) and the predetermined value (b), and the brightness level of the main subject is recognized to be relatively bright, the target value of the object evaluation value is
By changing the lower limits ('l Ll) (Z L) to (U) and (u) which are larger than (V) and (v), respectively, and activating the aperture mechanism, the straight line (r) in Fig. 8 is moved upward. By shifting the imaging brightness level of the main subject to near the upper limit of the appropriate exposure range (M) and matching the imaging brightness level area (R) of the entire screen to the appropriate exposure range (M>), the main subject can be photographed. Appropriate exposure with sufficiently high visual quality can be obtained, and good images can be obtained on other screens without exceeding the appropriate exposure range (M>).

Next, the determination of the gamma value will be explained based on the flowchart of FIG. First, in S T E P (230), the screen contrast (△) is set to the maximum value (Z) of the exposure evaluation values.
max ) and the minimum value (Zmin),
, the calculation is performed to change the correction gamma (7) to an appropriate value by substituting the contrast (△) into the preset reduction function f(△). 7 = aeL OG(Zmax/Zmin)+
b a = a e L OG (△) + b.

(However, ao and b6 are constants, and the target correction gamma (7) is derived in S T E P (231) using the formula ao<0, b, <o).

Here, in S T E P (232), the subject is of extremely low brightness, and S T E P in the flowchart of FIG.
If it is determined in step (221) that the gain of the AGC amplifier (301) is not fixed to a constant value and normal AGC operation is ON, the correction gamma (7 ) by a predetermined amount (dl) and compressing the screen contrast, the signal level of a subject with low brightness is substantially raised.

In addition, the target evaluation value (Z
T) (usually the exposure evaluation value of the prioritized focus area), when the brightness discrimination value (D) is within the range of the predetermined value (b), that is, D<-b or D>+b, S
In T E P (235), the correction gamma (7) is reduced by a predetermined amount (d,) to compress the screen contrast.1 For example, if D<-b holds, the brightness level of the main subject, that is, the target evaluation value. When the brightness level of the main subject is extremely low relative to the brightness level of the entire screen, the exposure is adjusted by the optical aperture mechanism (6), and the brightness level of the main subject is adjusted as shown in (R) in Figure 8. The camera is positioned near the lower limit of the appropriate exposure range (M), and the brightness area of the entire screen is positioned approximately at the center of the appropriate exposure range (M), so that appropriate exposure can be obtained for both the main subject and the entire screen. was done, but (R
) Exposure 01S! The latter high brightness region (r,) remains outside the proper exposure range <M>. At this time, if the screen contrast is compressed by reducing the correction gamma (7) by a predetermined amount (d,) as described above, the straight line (r) changes to a curved line (r') as shown in FIG. ), and the brightness area of the entire screen changes from (R) to (R゛)
The brightness level of the main subject changes to the appropriate exposure range (M
), it is possible to make the brightness area of the entire screen approximately match the appropriate exposure range (M), and further correct the exposure adjustment by the optical diaphragm mechanism (6) to obtain the appropriate exposure. Realized.

Furthermore, even if D〉+b holds true and the brightness level of the main subject is extremely high relative to the brightness level of the entire screen, the low brightness area after exposure adjustment ( r,) remains outside the proper exposure range (M>), and at this time, by reducing the correction gamma (7) by a predetermined amount (d,), the screen contrast is compressed, as shown in Figure 11. , the straight line (r) changes like a curved line (r''), the brightness area of the entire screen changes from (R) to (R'), and the brightness level of the main subject changes to the appropriate exposure range (M
), it is possible to substantially match the appropriate exposure range (M) for the me area of the entire screen, and further correct exposure m* by the optical diaphragm mechanism (6) to achieve proper exposure. , overexposure of high brightness areas and underexposure of low brightness areas can be prevented.

In addition, the brightness region (L>(R), straight line (
r) are the same, and the luminance region (
L) (R), straight! (r) are the same. The correction gamma (7) value thus determined is sent to the gamma correction circuit (302).
If the correction gamma (7 degrees) differs significantly from the previous correction gamma (7°), correction will be applied to the screen at - degrees, resulting in an unsightly screen, so the correction gamma will gradually change. It is necessary to change to.

Therefore, in S T E P (236>), the correction gamma (7) in the current field is compared with the correction gamma (7°) detected last time, that is, detected 32 fields ago, and the correction gamma (7°) in the current field is compared. If the correction gamma is larger, increase the correction gamma by one step (d7) in 5TEP (241), and set the previous correction gamma <7°.
If it is larger, the correction gamma is decreased by one step (d7) in S T E P (242). Here, one step (d7) is the correction gamma (7)
It is set by dividing the difference between the maximum value and the minimum value that can be taken into n equal parts (n: natural number), and thereby the correction gamma (7) changes in n steps.

When switching the correction gamma (7), it is effective to change it continuously every 32 fields in order to make a large change in one direction from the previous correction gamma (7°), but it is effective to change it continuously every 32 fields. When the correction gammas are close to each other, the brightness level of the screen changes slightly due to manual play, etc., and the correction gammas follow this and vibrate up and down each time the change is made, resulting in complicated switching. Therefore, in order to prevent this complicated switching, the previous correction gamma change direction and the current change direction are flagged (SX) at 5TEP (237 bar 238).
If they are the same, then 5TEP (239
) (240) and S T E P (241)
(242), and if they are different, the correction gamma is applied only when the difference 17e-71 between the correction gamma D,>(y>) in the previous and current field is greater than or equal to a predetermined value (C) at which correction is recognized as essential. Hysteresis is created by varying the .

A control signal corresponding to the correction gamma thus determined is connected to the downstream stage of the AGC amplifier (301)! Based on this, the amplification factor is changed according to the input level of the imaged video signal, and optimal gamma correction is executed, even for subjects with high screen contrast. Appropriate brightness can be obtained across the entire screen. Gamma correction times % The captured video signal subjected to gamma correction in (302) is displayed on a CRT (not shown) or recorded on a VTR (not shown).

By the way, when the area set on the screen is very dark, a low-level captured video signal passes through the amplifier circuit in the imaging circuit (8), resulting in a deterioration of the S/N ratio and an error in the brightness level value. becomes larger.

Therefore, as in the above embodiment, the brightness level of the captured video signal is A/D converted to obtain the exposure evaluation value Z + (+
-1 to 6), if this exposure evaluation value is extremely small, the error in the evaluation value itself will be large, and even if the same subject is imaged under the same conditions, the 6n output evaluation value will be a small value. Therefore, if the exposure is controlled by the ratio of the evaluation values of each area as in the above embodiment, the aperture amount by the aperture mechanism (6) will change frequently depending on the noise, resulting in a very There is a risk that the screen may become unstable.

Therefore, as shown in Fig. 13, STE P (20
An exposure evaluation value head change routine (250) is inserted between S T E P (0) and S T E P (201), and S T E P (2
Exposure evaluation value Z(1)(
If there is an extremely small value in i = l to 6), the appropriate value should be set in advance so that changes that frequently occur due to the noise of this extremely small exposure evaluation value will not affect the exposure or 7 correction. It is necessary to devise a way to replace the exposure evaluation value of the area with a fixed value. In this exposure evaluation value replacement routine (250), the exposure evaluation value 2 (
1) For those (i-1 to i-6) that can be determined to be less than the limit value (Pi), replace them with a fixed value <h,) set in advance in STE P (252). After only the extremely small exposure evaluation value is replaced with the fixed value (h,), S T E P (20
1) By executing the subsequent flowcharts, changes in the exposure evaluation value that frequently occur due to the influence of noise can be prevented from affecting exposure control and 7 corrections. The limit value (Pm) is a value that can be recognized when the exposure evaluation value changes due to noise becomes noticeable when the brightness level is extremely low, and the exposure control begins to be adversely affected, and the fixed value (ho) is
e '' P m or , both of which are values determined experimentally in advance.

(G) Effects of the Invention As described above, according to the present invention, when a specific area of the screen is prioritized and all exposure adjustment is performed based on the brightness level in this area, the effect occurs in areas other than the priority area. Overexposure and underexposure are reduced by gamma correction, making it possible to properly expose the entire screen. It also occurs when the brightness level is low. The influence of noise is reduced,
Stable exposure control is achieved.

[Brief explanation of the drawing]

The drawings all relate to one embodiment of the present invention, and FIG. 1 is an overall circuit block diagram, FIG. 2 is an explanatory diagram of area division, FIG. 3 is a flowchart of the main routine, and FIG. 4 is an AE shield.
Figure 5 is a flowchart for determining the aperture amount, Figure 6 is a flowchart for Oki Masayo 7 settings, Figures 7, 8 and 9 are characteristic diagrams related to exposure adjustment, Figures 10 and 11. 12 is a diagram illustrating the movement of the main subject, and FIG. 13 is a flowchart of the exposure evaluation value replacement routine. (26)...Microcomputer (level detection means), (302)...Gamma correction circuit.

Claims (2)

[Claims] (1) Level detection means for detecting the brightness level of the captured video signal for each of a plurality of areas including the priority area set by dividing the imaging screen, and a level detection means for detecting the brightness level of the captured video signal so that the brightness level of the priority area matches the target level. and a gamma correction means that detects screen contrast from the brightness level of each area, determines a correction gamma value based on the screen contrast, and performs gamma correction, An imaging device characterized in that the correction gamma value is changed depending on the relationship between the brightness level and the brightness level of another area. (2) level detection means for detecting the brightness level of the captured video signal for each of a plurality of areas including the priority area set by dividing the imaging screen; and a gamma correction means that detects screen contrast from the brightness level of each area, determines a correction gamma value based on the screen contrast, and performs gamma correction, and the level detection means When there is a brightness level of the imaged video signal for each area detected in the area that is below the limit value,
An imaging device characterized by replacing the brightness level of a corresponding area with a preset fixed level.