JPS63306777A - Image pickup device - Google Patents

Abstract

PURPOSE:To execute suitably exposure control and focus control also by controlling the moving of a camera by using the signal of one of the plural pictures generated from the same object different in exposure quantity as reference. CONSTITUTION:A sample holding circuit 26 and a switch 29 are provided in order that control signals to control an automatic diaphragm adjusting AE action are limited to only one of the plural images different in exposure quantity. A sampling pulse is formed from a vertical blanking VELK, a 1/2 frequency divider 24 forms such signals as inverting at every VELK signal which are lead to the contact (a) of the switch 29. Also an output from the divider 24 is inverted by an inverter 28 and is lead to the contact (b) of the switch 29. When a switch 22 selects its contact (a), sampling pulses for which odd-field, 1/1000sec accumulating signal made as a reference for AE loop control are impressed to the circuit 26. Inversely, when the contact (b) is selected, pulses for which 1/60sec accumulating signal used as the reference for AE loop control are impressed to the circuit 26.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an imaging device having a substantially wide dynamic range.

[Conventional technology]

Imaging devices are widely used as video camera units such as camera-integrated VTRs and still video cameras. Video cameras that use image pickup tubes or solid-state imaging elements have a narrower dynamic range than traditional silver-halide photographic systems, and as a result, when backlit, etc., whites and darks are crushed (a common term for areas with extremely high or low brightness levels). ) etc. occur.

With conventional video cameras, in such cases, the aperture can be opened by about two stops either manually or by operating the backlight compensation button.
The amount of light was being adjusted.

However, even when such backlight compensation is performed appropriately,
Even if the main subject has the proper exposure, overexposure will occur in the background, leaving the screen with only a white background.

In other words, the narrow dynamic range of the imaging device cannot be solved by simply adjusting the light amount so that the exposure amount of the main subject is appropriate, as in conventional devices. For example, in a conventional imaging device that uses a line scanner to convert a still image into an electrical signal, it is considered that a single screen is synthesized from a plurality of screens obtained from the same subject with different exposure amounts.

[Problem that the invention seeks to solve]

However, such imaging devices are intended for still images, and cannot provide moving images with a wide dynamic range.

In view of this situation, the present applicant has proposed an imaging device that can obtain a video signal with a substantially wide dynamic range, but the present invention provides an imaging device that can also appropriately control exposure and focus. The purpose is to present.

[Means for solving problems]

An imaging device according to the present invention is an imaging device that synthesizes one appropriate screen from a plurality of screens with different exposure amounts from the same subject, and which combines any one screen among the plurality of screens with different exposure amounts. It is characterized by controlling the camera operation based on the signal.

[Effect]

By controlling camera operations such as exposure control and focus adjustment using one signal from multiple screens with different exposure amounts as a reference, camera operation control does not become unstable and accurate operation can be achieved. You can expect it.

〔Example〕

Hereinafter, one embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a block diagram of the overall configuration when the present invention is applied to a camera-integrated VTR.

In FIG. 1, 100 is a camera section, 200 is a processing section,
300 is a recording section. In the camera unit 100, the light beam entering from the optical system 101 is limited in light amount by the aperture 102, and is imaged on the image sensor 103. The image sensor 103 is composed of a picture tube, a semiconductor image sensor such as MOS, or COD. The focus drive circuit 107, the aperture drive circuit 106, and the image sensor drive circuit 105 respectively control the optical system 101, the aperture 102, and the image sensor 1 under the control of the camera control circuit 108.
Drive 03. The camera signal processing circuit 104 is a well-known circuit that performs T-correction and other processing similar to the signal processing circuit of a normal video camera.

The video signal output from the camera section 100 is processed by the processing section 20.
0 is converted into a digital signal by the A/D converter 201,
The arithmetic circuit 202 performs pixel data conversion, which will be described later.
The D/A converter 203 converts the signal back to an analog signal, and the recording unit 3
60.

204 is an image memory for calculation in the calculation circuit 202, and 205 is its addressing circuit. The addressing circuit 205 writes data into the image memory 204 in response to a timing signal from the control circuit 108 of the camera unit 100.
Outputs read address control signal.

In the recording section 300, the analog signal from the D/A converter 203 is recorded on the VTR recorder 3.1 using a known method.

Next, the operation of the image sensor 103 will be explained. Figure 3 is NTS
Taking the C signal as an example, the field index (Fl
) signal is a signal for distinguishing between an odd (ODD) field and an even (EVEN) field that constitute one frame. The v3□ signal is a vertical blanking signal, and H
The (high) period corresponds to the effective screen, and the L (low) portion corresponds to the vertical blanking period. TpuLsa is the image sensor 103
This is a signal for controlling the charge accumulation time of, for example, a CCD.
In the case of an image sensor, this is a pulse for reading out pixel output to a vertical transfer CCD. The iris gate signal is used as a reference video signal for automatic exposure, which will be described later.
This signal specifies whether to use the /1000 second accumulation signal or the 1/6o second accumulation signal.

In the illustrated example, 171,000 during the vertical blanking period.
1/1000 of that in the next valid screen period.
Outputs second accumulation signal. Then, charge is accumulated for substantially 1760 seconds during the effective screen period immediately after the 1/1000 second accumulation period, and the 1760 second accumulation signal is output during the effective screen period of the next field. In this way, two types of light intensity signals (1/1000 seconds and 1760 seconds) are alternately output for each field.

In the above example, it is a combination of 1/1000 seconds and 1160 seconds, and the light amount changes by about 4 steps (24 times).
For example, in the case of a camera using a CCD image sensor, EVEN
If you adjust the exposure to the main subject based on the 1/60 second accumulation time in the field, the EVEN field tends to cause overexposure in the background, but if you reduce the light intensity by 4 steps (OD
In the D field, blackout often occurs on the main subject. Note that this example assumes that the exposure is adjusted to the background side during backlight correction, and of course, it may be set to a value other than 1/1000 seconds depending on the situation.

In the present invention, such blown-out highlights and/or blown-up shadows in one field are actively utilized to improve the screen. It is replaced with a corresponding portion (no blackout or overexposure occurs because the exposure is different), and the signals of both fields are combined to form a final video signal. The basic idea will be explained with reference to FIG. In FIG. 4, the main subject is schematically shown as a vertically long rectangle.

In FIG. 4, the through image (T) refers to the direct output of the image sensor 103, and the memory (M) image or memory output refers to the signal of the previous field once stored in the image memory 204. In the through image, the ODD field In each case, the backlit main subject becomes blown out in black, and in each EVBN field, the background becomes blown out. Furthermore, since the memory image consists of a signal delayed by one field period, blown-out highlights and blown-out shadows occur in a different field from the through-the-lens image.

Therefore, by appropriately combining the through-the-lens image and the memory image, a good image without blown-out highlights or blown-out shadows can be obtained. That is, for each field, the signals of the live view image and the memory image are compared with a predetermined threshold value, and if the signal is larger than the threshold value, it is set as 1, and if it is smaller than the threshold value, it is set as 0, and blown-out highlights or blown-out shadows are determined for each pixel.

Figure 6 shows the relationship between the threshold, the brightness value of the pixel, and the field. In Figure 6 (a), the horizontal axis is the brightness level, and the vertical axis is 1.
Shows the frequency of appearance of each brightness level in the 100 pages.

As shown in FIG. 6(a), the threshold Thl is set so as to be able to determine blown-up shadows, and the threshold Th2 is set so as to be able to determine blown-out highlights. In other words, an image below Thl is determined to be blown-up shadows, and an image above the threshold Th2 is determined to be blown-out highlights. Figure 6) shows the relationship between each field and the threshold, as shown above.
Since overexposure and underexposure occur alternately in the ODD field and the EVEN field, the threshold for determining this is also changed for each field.

In this way, it is possible to determine which pixel part of which field has a blocked-up shadow or a blocked-up highlight, and by using the judgment result, it is possible to select a pixel signal with an appropriate exposure amount for the through image and the memory image6. Take the AND of A and judgment B, and in the ODD field, select the through image signal for pixels whose AND is 1, and select the memory image signal for pixels whose AND is O. S-i! By creating the opposite relationship in the VEN field, a selection flag as shown in FIG. 4 can be obtained. The picture at the bottom of FIG. 4 shows a composite image based on the selection flag. In this figure, we assumed that the main subject was moving at a constant speed, and confirmed the effect of time axis shift on the image, but it can be seen that the resulting video is sufficient for practical use.

FIG. 5 shows that the threshold value Th1. A detailed configuration block diagram of a circuit portion forming a comparison with Th2 and a selection flag is shown.

The Th switching control signal is a signal in which H "Ill" is inverted for each field, like the Fl signal, and is applied to the second threshold generation circuit 52 via the dark value generation circuit 53 and the inverter 51 . The dark value generation circuits 52 and 53 generate the threshold value Thl or T of the relationship shown in Figure 6 according to the switching signal.
Generate h2. Comparison circuits 54 and 55 respectively compare the memory image and through image with the threshold values from the dark value generation circuits 52 and 53, and output signals A and B. and gate 5
6 performs a logical product of the A signal and B signal and outputs a selection flag signal. The switch 57 is switched in accordance with the selection flag signal to select a memory image or a through image signal.

Figure 7 shows a gradation characteristic diagram. The solid line in Figure 7 (a) is the characteristic diagram of a normal video camera. The input/output is linear up to 100χ, and for inputs beyond that (100 to 400
χ), there is a relationship with a gentle slope called the KNEE characteristic. Assuming that this point of change is Pl, this point of change shifts to position P2 during high-speed shutter operation. However, Pl
is 1760 seconds, and P2 is 1/250 of the 2-step exposure change.
Suppose it is seconds. In the case of a difference of four stages as described above, the relationships (1) and (5) in FIG. 7(d) are obtained. By the way, (1) in Figure 7(d) is 1/60 second, and (2) is 17125 seconds.
seconds, (3) is 1/251) seconds, (4) is 11500 seconds,
(5) is a characteristic diagram when the time is 1/1000 seconds. A characteristic with a desired curve is synthesized from two characteristics with different slopes.

Figure 7<b) shows an example of composite characteristics when changing the darkness value for overexposure and underexposure determination, and the characteristics of (1) to (3) change the threshold Th2 for overexposure determination from a low value. FIG. 7(C) shows how the position for selecting the high-speed shutter side changes to the high-brightness side by pixel switching by the switch 57 when the value is sequentially changed to higher values. Characteristics (2)
(2) is the same as (2) from Figure 7, which shows the composite characteristics when various calculation methods are selected based on
(1) is the composite characteristic when the average value is used, and (3) is the composite characteristic when subtraction processing is performed using an appropriate coefficient.

FIG. 2 shows a more detailed configuration block diagram of the camera unit 100. 20 is a known AE! which receives a signal (for example, a brightness signal) from the camera signal processing circuit 104 and calculates a control signal for exposure control! IIJ circuit, 22 is a known AF*]i circuit that outputs a control signal for focusing control, and 24 is a 1/2 frequency divider circuit that divides the vertical blanking signals (■, □) into two. 26.27 is a sample and hold circuit, 28
is an inverter, and 29.30 is a switch for selecting which of the output of the 172 frequency divider circuit 24 or its inverted signal by the inverter 28 determines the sampling timing. The outputs of the sample and hold circuits 26 and 27 are applied to the aperture drive circuit 106 and the focus drive circuit 107, respectively, to perform automatic exposure control and automatic focus adjustment.

As described above, when signals from a plurality of screens having different exposure amounts are obtained within one field, it is necessary to partially change the camera signal processing. That is, AE (automatic aperture adjustment),
This is a case where internal imaging signals are used in each control system such as AF (automatic focus adjustment) and AWB (automatic white balance adjustment). Therefore, as a main example, we will use the AE
Explain the process. The signal obtained from the image sensor 103 is
For AEf#Ii, it is sent from the camera signal processing circuit 104 to the AE control circuit 20, and the AEwi control circuit 20
11]? A control signal is provided to the aperture drive circuit 106 so that the serve loop of Il is activated. This control signal is
The output of the image sensor 103 is changed to fall within an appropriate dynamic range, that is, the aperture 102 is closed down when it is bright and the aperture 102 is opened when it is dark.

However, if the amount of light changes at a periodicity such as every field, appropriate AE operation cannot be expected.

This is because the response speed of the AE servo is much longer than changes in the field or frame period, and settles at a halfway value. To avoid this, the control signal for the AE operation should be limited to only one of the plurality of exposure images. In FIG. 2, a sample and hold circuit 26 is provided, and any one (for example, 1760 seconds)
The sample timing is defined by the switch 29 so that only the control signal corresponding to the screen is selected.

In FIG. 2, a sampling pulse is formed by the vertical blanking (vm□) signal, and the 1/2 frequency divider 24 forms a signal that is inverted for each VILX signal, and this is applied to the a contact of the switch 29. The output of the frequency divider 24 is inverted by the inverter 28 and the signal is sent to the switch 29 b.
Connect to the contacts.

If the a contact side is selected with the switch 22, the ODD field and the 1/1000 second accumulation signal are used as the sampling pulses that serve as the reference for AE loop control.
6, and if you select the B contact side, the 1/60 second accumulation signal becomes the sampling signal that becomes the reference for AE loop control.
A pulse is applied to sample and hold circuit 26. A
The same applies to the AF control circuit 22, sample/hold circuit 27, and switch 30 for F@@. A.W.
Illustration of BIllllI was omitted.

The video camera's operation loop is set to have a response time of a few seconds, avoiding sudden changes in the screen. Therefore, for example, if the exposure time is switched between 1/1000 seconds and 1760 seconds for each field, the AE loop will show the same response as when the exposure time is approximately 1/250 seconds continuously. Since this can be regarded as a general error, it can be solved by adding an offset bias to the AE loop according to the difference in exposure amount. FIG. 8 shows an example of the modified configuration. 80 is a bias generation circuit that generates the bias; 81 is an adder that adds the bias to the AE loop;
82 is an adder that adds a similar offset bias to the AF loop. The same applies to AWB.

Next, another detailed example of the control circuit 108 is shown in FIG. 9. A master clock generator 40 generates a master clock for internal use in the control circuit 108 in accordance with an external reference signal. Clock generator 41 for 1/1000 shutter
generates a high-speed clock according to its master clock, and the clock generator 42 for the 1/60 shifter generates a low-speed clock according to its master clock. The switch 45 is switched for each field and alternately applies the outputs of the clock generators 41 and 42 to the drive circuit 105. AE! The 1ljl signal generator 43 generates an AEitllil signal for aperture control based on the video signal from the camera signal processing circuit 104. Control signal holding circuit 4
4 holds the control signal for one field.

The switch 46 switches for each field, and
The output of the No. 11 signal generator 43 and the holding signal from the control signal holding circuit 44 are alternately applied to the aperture control circuit 106.

A switching signal generator 47 controls switching of switches 45,46. Switches 45 and 46 are switched synchronously.

In this embodiment, a clock generator is provided for low speed and high speed, and the clocks are switched by the output signal of a switching signal generator that generates a signal for each field, which simplifies the circuit configuration and operation. This effect is particularly suitable for videos.

〔Effect of the invention〕

As can be easily understood from the above explanation, according to the present invention, even in backlit situations, it is possible to take pictures in which not only the main subject but also the background is properly exposed, thereby substantially expanding the dynamic range. sell. Moreover, the basic operations of the camera can be performed accurately.

[Brief explanation of drawings]

Figure 1 shows a camera-integrated VTR using an embodiment of the present invention.
2 is a specific configuration block diagram of the control circuit 108 of the camera unit shown in FIG. 1, FIG. 3 is an operation timing chart of the image sensor, and FIG. 4 is a conceptual diagram of image processing according to the present invention. , FIG. 5 is a concrete block diagram of the arithmetic circuit 202 shown in FIG. 8
This figure is a modified example of the configuration of FIG. 2, and FIG. 9 is a block diagram of another example of the configuration of the control circuit 108. 100--Camera section 200--Processing section 300...-
Recording department

Claims (1)

[Claims] An imaging device that synthesizes one appropriate screen from multiple screens with different exposure amounts from the same subject, and controls camera operation based on a signal from one of the multiple screens with different exposure amounts. An imaging device characterized by: