JP2003153073A - Imaging device, exposure control method, program, and computer-readable storage medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform convergence to an appropriate exposure at a comfortable speed to a photographer all the time irrespective of a size in a variation in subject brightness. SOLUTION: A system controller 12 selects one of an exposure target value Ev1 of average photometry, an exposure target value Ev2 of center-weighted photometry, and an exposure target value Ev2 of evaluated photometry; uses the value as an exposure target value EvT; performs a photometric operation at a predetermined time interval; inputs the exposure target value EvT to n FIFO buffers (step S23); and detects a variation in subject brightness on time series, based on the data to judge the presence or absence of a variation in subject brightness. Then, according to the judgment result on a variation in subject brightness, a time constant under feedback AE control is changed. Thus, it is possible to flexibly change a time constant according to a variation in subject brightness, thereby achieving convergence to an appropriate exposure at a comfortable speed to the photographer all the time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image pickup apparatus, an exposure control method, a program, and a computer-readable storage medium.

[0002]

2. Description of the Related Art In an image pickup device such as a digital still camera, an electronic viewfinder is provided so that the composition and exposure state at the time of actual photographing can be confirmed as a finder by displaying the output from the image pickup device on a display device. An imaging device having (hereinafter, EVF) has been proposed.

In an image pickup apparatus such as a digital still camera, a method has been proposed in which the exposure level is calculated by photometrically measuring the subject brightness based on the image pickup signal output from the image pickup device.

As the photometric method of these image pickup devices, in order to measure the subject brightness, a predetermined coefficient is used based on an image pickup signal of a specific region of the screen or an image pickup signal of a plurality of divided screen regions to center the screen. Center-weighted photometry for deriving the target luminance by weighting the partial area as a center, and evaluation photometry for deriving the target luminance using a specific algorithm based on the information of each area are known.

Further, as disclosed in Japanese Patent Publication No. 06-071319, there is known an exposure control method in which when the target brightness changes, the exposure is linearly and stepwise controlled to converge to the target brightness value. Has been.

A detailed description will be given below. <Explanation of photometry of each frame> In the system controller in the image pickup apparatus such as a digital still camera, A shown in FIG.
The brightness values YA, YB, and YC integrated for each of the divided screen areas B and C are acquired.

The photometric processing inside the system controller will be described below. If the areas of the screen areas A, B, and C are Sa, Sb, and Sc, respectively, the luminance value Ya per unit area of the screen areas A, B, and C will be described. , Yb, and Yc are expressed by the following formula (1) to
It is obtained by (3). Ya = YA / Sa (1) Yb = YB / Sb (2) Yc = YC / Sc (3)

Further, as shown in the following equations (4) to (6),
The difference from the predetermined brightness level reference value Yref is logarithmically calculated, and the difference from the proper brightness level of each frame is obtained as ΔEvA, ΔEvB, and EvC, respectively. ΔEvA = log ₂ (Ya / Yref) (4) ΔEvB = log ₂ (Yb / Yref) (5) ΔEvC = log ₂ (Yc / Yref) (6)

On the other hand, Av0 is a value obtained by converting the aperture diameter set in the mechanical shutter that also serves as the aperture during exposure into the aperture value Av.
When the exposure time converted into the shutter speed Tv is Tv0, Ev0, which is the set exposure value Ev at the time of exposure, is obtained by the following equation (7). Ev0 = Av0 + Tv0 (7)

Exposure value Ev of each frame (screen areas A, B, C)
Can be obtained by Ev_a = Ev0 + ΔEvA (8) Ev_b = Ev0 + ΔEvB (9) Ev_c = Ev0 + ΔEvC (10) as shown in the following equations (8) to (10).

<Explanation of Average Photometry> Each of the A, B, and C regions is weighted according to its area, and the brightness level of the entire screen is calculated by the following equation (11) and is Ev1. Ev1 = Ev0 + (ΔEvA × Sa + ΔEvB × Sb + ΔEvC × Sc) / (Sa + Sb + Sc) (11)

<Explanation of center-weighted photometry> In addition, A, B,
C Predetermined weighting factors kWeiA and kWei for each region
Let Ev2 be the luminance level of the entire screen obtained by the following equation (12) using B and kWeiC. Ev2 = Ev0 + (ΔEvA × kWeiA + ΔEvB × kWeiB + ΔE vC × kWeiC) / (kWeiA + kWeiB + kWeiC) (12) Here, the weighting factors kWeiA, kWeiB, and kWe.
iC is (kWeiA / Sa)> (kWeiB / Sb)> (kW
By configuring so that the relationship of eiC / Sc) is established, it is possible to give the character of center-weighted photometry.

<Explanation of evaluation photometry> In addition, A, B and B,
The brightness differences ΔBA and ΔCB in each area of C are expressed by the following equation (13),
Obtained as shown in (14), the exposure correction value α by evaluation photometry is calculated from the values of ΔBA and ΔCB. ΔBA = Ev_b-Ev_a ... (13) ΔCB = Ev_c-Ev_b ... Backlight correction is performed by increasing the exposure correction value α. The exposure correction value α is corrected, and the target brightness level obtained by the following equation (15) is Ev3. Ev3 = Ev2-α (15)

Ev1, Ev2, E thus obtained
By setting v3 as the exposure target value in each of the average metering mode, the center-weighted metering mode, and the evaluation metering mode, various metering methods can be provided.

<Determination of Exposure Target Value> As shown in FIG. 12, the system controller determines the exposure target value Ev1 for the average photometry and the central portion emphasis according to the photometry mode selected by the photographer through the operation unit. One of the exposure target value Ev2 for photometry and the exposure target value Ev3 for evaluation photometry is selected, and the selected value is set as the exposure target value EvT. For example, when the photographer sets the evaluation metering as the metering mode, the following formula (1
As shown in 6), EvT = Ev3 (16).

<Description of Control of Feedback AE> The control of the feedback AE will be described below with reference to the flowchart of FIG. Difference Δ between the target exposure value EvT obtained as described above and the current exposure control value Ev0
Find Ev. ΔEv = EvT−Ev0 (17)

If | ΔEv | is within a predetermined proper exposure range kEvRange (for example, ± 0.5 steps) (step S131), the current exposure control value Ev.
0 is set as it is to the next exposure value EvNext (step S132).

| ΔEv | is the proper exposure range kEvRang
If it is outside the range of e (step S131), it is determined whether ΔEv is positive or negative (step S133). When ΔEv is positive, the exposure value obtained by subtracting the predetermined value kEvChg from the current exposure control value Ev0 is set as the next exposure value EvNext as shown in the following equation (18) (step S
134), if ΔEv is negative, as shown in the following equation (19), from the current exposure control value Ev0 to the predetermined value kEvChg
The exposure value added by just is set as the next exposure value EvNext (step S135). When | ΔEv |> kEvRange and ΔEv> 0 EvNext = Ev0-kEvChg (18) When | ΔEv |> kEvRange and ΔEv <0 EvNext = Ev0 + kEvChg (19)

The next exposure value EvNext obtained as described above is applied to, for example, a program diagram as shown in FIG. 14, and the aperture value and shutter speed obtained therefrom are used as the next aperture value AvNext and the next aperture value AvNext, respectively. The shutter speed is TvNext.

In the exposure control for the next photometry, the system controller sets the aperture value of the mechanical shutter that also serves as the aperture to AvNext, and picks up the electronic shutter pulse and the readout pulse so that the photocharge is accumulated for the exposure time of TvNext. Control to supply to the device. The signal read in the above state is converted into a brightness level signal for the next photometry and a signal for the finder output.

As described above, the output signal from the image sensor is used to determine whether the current exposure value is a proper value, and if it is not proper, the next exposure value is increased by a predetermined value kEvChg on the positive or negative side. By repeating the movement to the predetermined interval T, it is possible to always converge to a proper exposure gently.

A predetermined value kEvCh of the exposure change amount at this time
By setting g and the predetermined interval T, the time constant is configured as shown in the following equation (20). Time constant = predetermined interval T / kEvChg (20)

[0023]

However, in the above exposure control, even when the subject brightness changes slowly,
Even if the subject brightness changes drastically, the exposure follows only at the same speed, so there is a problem especially when the subject brightness changes drastically. That is, when the subject brightness changes rapidly, it takes a long time to converge to the proper exposure when the time constant is set to a large value.
There arises a problem that an image with proper exposure is not easily displayed on the EVF display. On the other hand, when the time constant is set to a small value, there is a problem that the EVF display becomes uncomfortable for the photographer due to a sharp change in brightness on the EVF display and hunting.

Further, when the subject target brightness is calculated by performing center-weighted photometry or evaluation photometry, if there is a subject having a large brightness difference from the peripheral part in the center of the screen, as shown in FIG. 15, for example. When the subject moves between the photometric frames, the target brightness EvT changes significantly. As a result, the brightness changes in time series on the EVF even if the photographer does not change the direction of the camera. In this case, when the time constant is set small, the brightness change on the EVF display is sharp. EVF due to hunting
There is a problem that the display becomes uncomfortable for the photographer.

The present invention has been made in order to solve such a problem, and in the EVF display mode, whether the subject brightness change is large or small, the exposure is always converged to the proper exposure at a comfortable speed for the photographer. The purpose is to Furthermore, in the case of obtaining the target luminance of the subject by the center-weighted photometry or the evaluation photometry, the hunting that is likely to occur in the feedback AE control when the target luminance changes greatly such as the subject moves between the photometry frames in the screen. It is an object of the present invention to prevent the above and prevent the brightness change in the EVF display from converging to the proper exposure at a comfortable speed.

[0026]

An image pickup apparatus of the present invention is an image pickup apparatus including an image pickup element for converting an optical image into an electric signal and a display section for displaying an image signal output from the image pickup element. And a target brightness level calculating means for calculating a target brightness level of the screen by using the brightness level derived by the first photometric means, Exposure control means for controlling exposure with a predetermined time constant so that the brightness level derived by the photometric means converges to the brightness level calculated by the target brightness level calculating means, and the exposure control means derives by the first photometric means. And a time constant changing means for changing the time constant according to the difference between the brightness level and the brightness level calculated by the target brightness level calculating means.

Another feature of the image pickup device of the present invention is that the difference value between the brightness level derived by the first photometric means and the brightness level calculated by the target brightness level calculation means. Is observed in time series, and the time constant is changed according to the change in the difference. Further, the exposure control means is to reduce the time constant as the difference increases. Further, the first photometric means obtains the subject brightness level in the screen by performing predetermined weighting on the brightness levels respectively obtained from the divided areas in the screen, and by the weighting different from that of the first photometric means. A second photometric means for obtaining the subject brightness level in the screen is provided, and the time constant is changed according to the brightness level derived by the second photometric means. Also,
The point is that the brightness level derived by the second photometric means is observed in time series, and the time constant is changed according to the change.

The exposure control method of the present invention is an exposure control method in an image pickup apparatus comprising an image pickup device for converting an optical image into an electric signal and a display section for displaying an image signal output from the image pickup device. , A first photometric procedure for obtaining a subject brightness level in the screen, a target brightness level calculation procedure for calculating a target brightness level of the screen using the brightness level derived by the first photometric procedure, and the first An exposure control procedure for controlling exposure with a predetermined time constant so that the brightness level derived by the photometric procedure converges to the brightness level calculated by the target brightness level calculation procedure;
It is characterized in that it has a time constant changing procedure for changing the time constant according to the difference between the brightness level derived by the photometric procedure and the brightness level calculated by the target brightness level calculating procedure.

Another feature of the exposure control method of the present invention is that the difference between the brightness level derived by the first photometric procedure and the brightness level calculated by the target brightness level calculation procedure is calculated. The value is observed in time series, and the time constant is changed according to the change in the difference. The exposure control procedure is to reduce the time constant as the difference increases. In the first photometric procedure, the subject brightness level in the screen is acquired by performing predetermined weighting on the brightness levels obtained from the divided areas in the screen, and the brightness level different from that in the first photometric procedure is used. Second to obtain the subject brightness level in the screen
And has the point that the time constant is changed according to the brightness level derived by the second photometric procedure.
In addition, the luminance level derived by the second photometric procedure is observed in time series, and the time constant is changed according to the change.

The program of the present invention is characterized in that it causes a computer to function as each unit of the above-mentioned image pickup apparatus. Another program of the present invention is characterized by causing a computer to execute each procedure of the exposure control method. The computer-readable storage medium of the present invention is characterized in that any one of these programs is stored.

[0031]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of an image pickup apparatus, an exposure control method, a program, and a computer-readable storage medium according to the present invention will be described below with reference to the drawings.

(First Embodiment) FIG. 1 shows the configuration of a digital still camera which is an image pickup apparatus according to the present embodiment. In the figure, reference numeral 1 denotes an optical lens for forming an optical image on an image pickup element, which includes a focus adjusting focus lens (not shown). Reference numeral 2 denotes a diaphragm / mechanical shutter that has both a diaphragm function and a shutter function. Reference numeral 3 is a drive circuit for each part of the mechanical system including the optical lens 1 and the mechanical shutter 2 that also serves as a diaphragm. Reference numeral 4 denotes an image pickup device that converts the subject image formed by the optical lens into an electric signal.

Reference numeral 5 is a timing signal generating circuit (hereinafter referred to as TG) which generates a timing signal necessary for operating the image pickup device 4. Reference numeral 6 denotes an image sensor drive circuit that amplifies the signal from the TG 5 to a level at which the image sensor can be driven. 7 is a CDS for removing output noise of the image sensor 4
It is a preprocessing circuit including a circuit and an amplifier circuit. 8 is A / D
It is a converter. Reference numeral 9 is an image pickup signal processing circuit.

Reference numeral 10 is a recording medium, for example PCMCI
A standard memory card, hard disk, etc. are used. Reference numeral 11 is an interface circuit for recording a signal on the recording medium 10.

Reference numeral 12 denotes a system controller (hereinafter referred to as a syscon) which is a CPU for controlling the mechanical and operation sections and the image pickup signal processing section. Reference numeral 13 is an operation unit for externally controlling the camera.

Reference numeral 14 is a display signal processing circuit for displaying on a display device. Reference numeral 15 is a D / A converter. Reference numeral 16 is a display device used as an electronic viewfinder.

In the digital still camera configured as described above, when the photographer operates the operation section 13 to start the finder display operation, the mechanical system drive circuit 3 is driven by the control of the syscon 12 to drive each circuit. Turn on the power.

Next, the aperture / mechanical shutter 2 is opened with a predetermined initial aperture diameter to start the exposure of the image pickup device 4, and the electronic shutter pulse and the read pulse are set so that the photocharge is accumulated for a predetermined initial exposure time. Is supplied from the TG 5 to the image sensor 4 via the image sensor drive circuit 6.

The signal read in the above state is converted into a brightness level signal for photometry and a signal for finder output through the preprocessing circuit 7 and the A / D converter 8 and by the image pickup signal processing circuit 9. To be done. Brightness level signal is syscon 1
2, the syscon 12 determines the exposure amount according to the brightness level, derives the aperture and shutter speed according to the exposure amount, and according to the values, the aperture / mechanical shutter 2 and electronic shutter for the next exposure. Control the shutter.

After that, photometry is repeated for each field,
Control the exposure. The finder output signal is sent through the D / A converter 15 and the display signal processing circuit 14 to the display device 1.
6, the subject being photographed is displayed on the display device 16.

The photometric operation in the digital still camera of the first embodiment will be described below. The image pickup signal processing circuit 9, as shown in FIG.
The brightness values Ys1 to Ys36 integrated every 1 to S36 are sent to the syscon 12. The areas S1 to S36 all have the same area, and the brightness values Ys1 to Ys36 can be regarded as brightness values per unit area.

Next, the photometric processing inside the syscon 12 will be described. As shown in the following formula (21), the difference from the predetermined brightness level reference value Yref is logarithmically calculated, and the difference from the proper brightness level of each frame is set as ΔEv_Sn (n = 1 to 36). Desired. ΔEv_Sn = log ₂ (Ysn / Yref) (21)

On the other hand, the aperture diameter set in the mechanical shutter 2 that also serves as the aperture at the time of exposure is converted into an aperture value Av, which is Av0,
When the exposure time converted to the shutter speed Tv is Tv0, the set exposure value Ev0 at the time of exposure is given by the following equation (22).
Is required. Ev0 = Av0 + Tv0 (22)

Exposure value E of each frame (screen areas S1 to S36)
v is calculated | required by Ev_Sn = Ev0 + (DELTA) Ev_Sn (n = 1-36) ... (23), respectively, as shown in following formula (23).

<Explanation of Photometry of Each Frame> Next, the luminance values Ys1 to Ys36 integrated for each screen area of the divided screen areas S1 to S36 shown in FIG. 3 are shown by the hatched portions in FIGS. Let YA, YB, and YC be the sums calculated for each part.
It can be regarded as equivalent to the brightness values of the screen areas A, B, and C shown in FIG. 11, respectively, and the exposure target value E of the average photometry is obtained.
v1 can be derived. Further, the exposure target value Ev2 for center-weighted photometry and the exposure target value Ev3 for evaluation photometry can be derived by using the same method as described above.

<Determination of Exposure Target Value> As shown in FIG. 12, the syscon 12 determines the exposure target value E of the average photometry according to the photometry mode selected by the photographer through the operation unit 13.
One of v1, the exposure target value Ev2 of the center-weighted photometry, and the exposure target value Ev3 of the evaluation photometry is selected, and the selected value is set as the exposure target value EvT. For example, when the photographer sets the evaluation metering as the metering mode, the above formula (1
As shown in 6), the exposure target value Ev3 of the evaluation photometry is set as the exposure target value EvT.

<Detection of Change in Subject Luminance> As shown in FIG. 2, the syscon 12 performs the photometric operation at intervals of a predetermined time t (for example, 30 ms) (steps S21 and S2).
2), the exposure target value EvT is set to n FIFOs (first-i
(n first-out) buffer (step S23) and always stores the latest n photometric data (FIG. 7).
See).

Then, the absolute value ΔBvCn of the difference between the data BvC0 acquired this time and the data BvCn acquired n times before in the FIFO buffer, and the data BvC acquired this time.
Absolute value ΔBv of the difference between 0 and the data BvCm n-1 times before
Cm is calculated (the following formulas (24) and (25)) (step S
24). ΔBvCn = | BvCn−BvC0 | (24) ΔBvCm = | BvCm−BvC0 | (25)

The larger value of ΔBvCn and ΔBvCm is selected to be ΔBvC (steps S25 and S2).
6, S27). When the value of ΔBvC is equal to or larger than a predetermined value (for example, one step) (step S28), it is determined that “subject luminance has changed” and a predetermined time T (for example, 500 ms).
The countdown timer A is started (if timer A is already counting, restart) (step S29).
When the counting is completed for the predetermined time T, the timer A is stopped.

After detecting the subject brightness change in time series, the syscon 12 determines whether or not the timer A is counting, and if the timer A is counting, "the subject brightness change is present" within a predetermined time. If it is not counting, it is determined that there is no change in subject brightness within a predetermined time, and it is determined whether there is a change in subject brightness.

<Change of Time Constant> When it is determined that “subject brightness has changed” in the above determination of whether or not the subject brightness has changed, a predetermined value kEvChg used in the feedback AE control described above (the above equation (18)). , (19)), the time constant is reduced by increasing the value, and when it is determined that there is no change in subject brightness (or a slight change), a predetermined value k
The time constant is increased by decreasing the value of EvChg. As a result, the time constant can be adaptively changed according to the subject brightness change amount, and when the subject brightness change is large or small in the EVF display mode, the exposure is always converged to the proper exposure at a comfortable speed for the photographer. It becomes possible.

(Second Embodiment) The second embodiment will be described below. The configuration of the digital still camera is the same as that of the first embodiment, and the feedback AE control is different from that of the first embodiment, and the difference will be mainly described below.

<Description of Control of Feedback AE> FIG. 8
The control of the feedback AE will be described with reference to the flowchart of FIG. As shown in the above equation (17), the difference ΔEv between the calculated exposure target value EvT and the current exposure control value Ev0 is calculated.

If .vertline..DELTA.Ev.vertline. Is within the predetermined proper exposure range kEvRange (for example. +-. 0.5 step) (step S81), the current exposure control value Ev0.
Is set as it is to the next exposure value EvNext (step S82).

| ΔEv | is the proper exposure range kEvRang
If it is outside the range of e (step S81), the following equation (26)
As shown in, the exposure value obtained by subtracting the value obtained by multiplying ΔEv by the predetermined coefficient kCoef from the current exposure control value Ev0 is set as the next exposure value EvNext (step S8).
3). EvNext = Ev0−ΔEv × kCoef (26)

As described above, it is determined whether or not the current exposure value is an appropriate value using the output signal from the image sensor, and if it is not appropriate, the next exposure value is brought closer to the exposure target value by ΔEv × kCoef. By repeating this at a predetermined interval T, it becomes possible to always converge to a proper exposure gently.

By setting the coefficient kCoef of the exposure change amount and the predetermined interval T at this time, the time constant is configured as shown in the following equation (27). Time constant = predetermined interval T / kCoef (27)

<Change of time constant> Further, the system controller 12
Depending on ΔEv, as shown in FIG. 9, kCoe
Change the value of f. For example, when | ΔEv | is larger than 0.1, the value of kCoef is set to 0.5, and | ΔEv |
When is 0.1 or more, the value of kCoef is set to 1. That is, when | ΔEv | is large, the value of kCoef is made small, and the time constant is made large so that it converges slowly. When | ΔEv | is small, the value of kCoef is made large and the time constant is made small. Make it smaller and converge faster.
This makes it possible to prevent hunting that tends to occur in the feedback AE operation when the value of ΔEv is large, and the EVF display mode is appropriate at a comfortable speed for the photographer regardless of whether the subject brightness change is large or small. It is possible to focus on the exposure.

(Third Embodiment) The third embodiment will be described below. The coefficient kCoef is changed as in the second embodiment, but the changing method is different, and the difference will be mainly described below.

<Creation of Weighting Values Centered on C Frame> Each of the areas A, B and C shown in FIG. 11 has a predetermined weighting coefficient k.
E is the luminance level of the entire screen obtained by using WeiAr, kWeiBr, and kWeiCr by the following equation (28).
vR. EvR = Ev0 + (ΔEvA × kWeiAr + ΔEvB × kWeiBr + ΔEvC × kWeiCr) / (kWeiAr + kWeiBr + kWeiCr) (28) Here, the weighting factors kWeiAr, kWeiBr, k
WeiCr is (kWeiAr / Sa) <(kWeiBr / Sb) <
By configuring so that the relationship of (kWeiCr / Sc) is established, it is possible to give a photometric character with more weight to the peripheral portion of the screen.

<Detection of Change in Subject Luminance> Syscon 12
Performs the photometry operation at intervals of a predetermined time t (for example, 30 ms), inputs the EvR value into the n FIFO buffers regardless of the photometry mode selected by the photographer through the operation unit 13, and always updates the latest value. Save the data of the photometric results of n times.

Then, the absolute value ΔBvCn of the difference between the data BvC0 acquired this time and the data BvCn acquired n times before in the FIFO buffer, and the data BvC0 acquired this time.
And the absolute value ΔBvC of the difference between n−1 times before data BvCm
m is calculated (the following formulas (29) and (30)). ΔBvCn = | BvCn−BvC0 | (29) ΔBvCm = | BvCm−BvC0 | (30)

The larger value of ΔBvCn and ΔBvCm is selected to be ΔBvC. When the value of ΔBvC is equal to or greater than a predetermined value (for example, one step), it is determined that “subject luminance has changed” and the countdown timer A for a predetermined time T (for example, 500 ms) is activated (the timer A is already counting). If so, restart). When the counting is completed for the predetermined time T, the timer A is stopped.

After detecting the subject brightness change in time series in this way, the syscon 12 determines whether or not the timer A is counting, and if the timer A is counting, "subject brightness change" is given within a predetermined time. If it is not counting, it is determined that there is no change in subject brightness within a predetermined time, and it is determined whether there is a change in subject brightness.

<Change of time constant> Furthermore, the system controller 12
In addition to the range of the value of ΔEv, as shown in FIG.
Change the value of oef. For example, as shown in FIG. 10, when the absolute value of ΔEv is larger than 0.5 and “the subject luminance has changed”, the value of kCoef is set to 0.
5, the value of kCoef is set to 0.25 when “no change in subject brightness”. That is, when ΔEv is relatively large, the value of kCoef is increased when “subject luminance change is present” and the time constant is reduced so that convergence is fast, and when “subject luminance change is not present”, kCoef is set. Decrease the value of and increase the time constant so that it converges slowly. As a result, it is possible to adaptively change the time constant according to the change in the photometric brightness value with weight placed on the peripheral portion of the screen.

Therefore, when the subject brightness is obtained by the center-weighted photometry or the evaluation photometry, the target brightness is large even if the framing of the camera is not changed, such as when the subject moves between the photometry frames in the screen. If it changes,
It is possible to prevent hunting that is likely to occur in the feedback AE operation, and to converge to a proper exposure at a comfortable speed without causing a rapid brightness change in EVF display.

(Other Embodiments) In order to operate various devices so as to realize the functions of the above-described embodiments, a computer in an apparatus or system connected to the various devices is operated in the above-described embodiment. Supply the program code of software to realize the function of
What was carried out by operating the above-mentioned various devices according to the program stored in the computer (CPU or MPU) of the system or apparatus is also included in the category of the present invention.

In this case, the program code itself of the software realizes the functions of the above-described embodiments, and the program code itself constitutes the present invention. As a transmission medium of the program code, a communication medium (a wired line such as an optical fiber or a wireless line) in a computer network (LAN, WAN such as the Internet, a wireless communication network, etc.) system for propagating and supplying the program information as a carrier wave. Etc.) can be used.

Further, means for supplying the program code to a computer, for example, a recording medium storing the program code constitutes the present invention. A flexible disk, a hard disk, an optical disk, a magneto-optical disk, a CD-ROM, a magnetic tape, a non-volatile memory card, a ROM, or the like can be used as a recording medium for storing the program code.

Moreover, not only the functions of the above-described embodiments are realized by executing the supplied program code by the computer, but also the OS (operating system) or the other in which the program code is operating in the computer. It goes without saying that the program code is also included in the embodiment of the present invention when the functions of the above-described embodiment are realized in cooperation with the application software of the above.

Furthermore, after the supplied program code is stored in the memory provided in the function expansion board of the computer or the function expansion unit connected to the computer, the function expansion board or function expansion unit is instructed based on the instruction of the program code. It goes without saying that the present invention also includes a case where the CPU or the like included in the above-mentioned performs some or all of the actual processing and the functions of the above-described embodiments are realized by the processing.

It should be noted that the shapes and structures of the respective portions shown in the above-mentioned embodiments are merely examples of the embodiment in carrying out the present invention, and the technical scope of the present invention is thereby provided. It should not be construed as limiting. That is, the present invention can be implemented in various forms without departing from the spirit or the main features thereof.

[0073]

As described above, according to the present invention, the correct exposure can be always converged at a speed comfortable to the photographer regardless of whether the subject luminance change is large or small.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a digital still camera which is an image pickup apparatus according to the present embodiment.

FIG. 2 is a flowchart showing an operation of detecting a change in subject brightness.

FIG. 3 is a diagram showing divided areas of a screen.

FIG. 4 is a diagram showing divided areas of a screen.

FIG. 5 is a diagram showing divided areas of a screen.

FIG. 6 is a diagram showing divided areas of a screen.

FIG. 7 is a diagram for explaining a relationship of data in and out of a FIFO buffer.

FIG. 8 is a flowchart for explaining control of feedback AE.

FIG. 9 is a diagram showing a relationship between a range of ΔEv and a coefficient kCoef in the second embodiment.

FIG. 10 is a diagram showing a relationship between a range of ΔEv and a coefficient kCoef in the third embodiment.

FIG. 11 is a diagram showing divided areas of a screen.

FIG. 12 is a flowchart for explaining a photometry result selecting operation according to a photometry mode.

FIG. 13 is a flowchart for explaining control of feedback AE.

FIG. 14 is a diagram showing an example of a program diagram.

FIG. 15 is a diagram for explaining a state in which a subject is moving between photometry frames.

[Explanation of symbols]

1 Optical lens 2 Mechanical shutter that doubles as an aperture 3 Drive circuits for each part of the mechanical system 4 image sensor 5 Timing signal generation circuit 6 Image sensor drive circuit 7 Preprocessing circuit 8 A / D converter 9 Imaging signal processing circuit 10 recording media 11 Interface circuit 12 System controller 13 Operation part 14 Display signal processing circuit 15 D / A converter 16 Display

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Katsumi Iijima             3-30-2 Shimomaruko, Ota-ku, Tokyo             Non non corporation F-term (reference) 2H002 DB25                 5C022 AA13 AB03 AB17 AC03 AC41                       AC52 AC69                 5C024 BX01 CX56 CX66 DX04 EX11                       EX31

Claims (13)

[Claims] 1. An image pickup apparatus comprising: an image pickup device for converting an optical image into an electric signal; and a display section for displaying an image signal output from the image pickup device, wherein the image pickup device obtains a subject brightness level within a screen. No. 1 photometric means, target brightness level calculation means for calculating the target brightness level of the screen using the brightness level derived by the first photometric means, and the brightness level derived by the first photometric means is Exposure control means for controlling exposure with a predetermined time constant so as to converge to the brightness level calculated by the target brightness level calculation means, brightness level derived by the first photometric means, and the target brightness level calculation means An image pickup apparatus comprising: a time constant changing unit that changes the time constant according to a difference from the brightness level calculated by. 2. The value of the difference between the brightness level derived by the first photometric means and the brightness level calculated by the target brightness level calculation means is observed in time series, and the difference value is observed according to the change in the difference. The image pickup apparatus according to claim 1, wherein the time constant is changed. 3. The image pickup apparatus according to claim 1, wherein the exposure control unit decreases the time constant as the difference increases. 4. The first photometric means obtains the subject brightness level in the screen by performing a predetermined weighting on the brightness level obtained from each of the divided areas in the screen. The second photometric means for obtaining the subject brightness level in the screen by different weighting is provided, and the time constant is changed according to the brightness level derived by the second photometric means. Imaging device. 5. The image pickup apparatus according to claim 4, wherein the brightness level derived by the second photometric means is observed in time series, and the time constant is changed according to the change. 6. An exposure control method in an image pickup apparatus comprising: an image pickup device for converting an optical image into an electric signal; and a display section for displaying an image signal output from the image pickup device. A first photometric procedure for obtaining a level, a target brightness level calculation procedure for calculating a target brightness level of the screen using the brightness levels derived by the first photometry procedure, and a first photometric procedure derived An exposure control procedure for controlling exposure with a predetermined time constant so that the brightness level converges to the brightness level calculated by the target brightness level calculation procedure, a brightness level derived by the first photometric procedure, and the target An exposure control method comprising: a time constant changing procedure for changing the time constant according to a difference from the brightness level calculated by the brightness level calculating procedure. 7. The value of the difference between the brightness level derived by the first photometric procedure and the brightness level calculated by the target brightness level calculation procedure is observed in time series, and the difference value is observed according to the change in the difference. The exposure control method according to claim 6, wherein the time constant is changed. 8. The exposure control method according to claim 6, wherein in the exposure control procedure, the time constant is decreased as the difference increases. 9. The first photometric procedure obtains a subject brightness level in a screen by performing predetermined weighting on brightness levels obtained from divided areas in the screen, and the first photometric procedure is 7. A second photometric procedure for obtaining a subject brightness level in a screen by different weighting, wherein the time constant is changed according to the brightness level derived by the second photometric procedure. The exposure control method described. 10. The exposure control method according to claim 9, wherein the brightness level derived by the second photometric procedure is observed in time series, and the time constant is changed according to the change. 11. A program for causing a computer to function as each unit of the image pickup apparatus according to claim 1. 12. A program for causing a computer to execute each procedure of the exposure control method according to claim 6. 13. A computer-readable storage medium on which the program according to claim 11 or 12 is stored.