JPH0575931A - Image pickup device - Google Patents

Abstract

PURPOSE:To make it possible to apply the image pickup device to many image input devices by practically expanding a dynamic range with a simple and economical processing circuit and reading out a signal from an optional picture element. CONSTITUTION:The image pickup device using a random access type image pickup element is provided with an exposure control means for setting up a short exposure time and transferring an obtained picture element signal to an image memory 350 in a picture element area having much irradiation light to the element 200 and setting up a long exposure time and transferring an obtained picture element signal to the memory 350 in a picture element area having little irradiation light to the element 200 and the picture element signals stored in the memory 350 are successively transferred.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image pickup device, and more particularly to an image pickup device having a substantially wide dynamic range.

[0002]

2. Description of the Related Art An image pickup device is widely used as a video camera unit such as a VTR with a built-in camera and a still video camera. A video camera that uses an image pickup tube or a solid-state image sensor has a narrower dynamic range than a conventional silver halide photography system, and therefore, underexposure or underexposure (a common name for parts with extremely high or low brightness levels). And so on. In the conventional video camera, in such a case, the aperture is opened by about 2 apertures manually or by operating the backlight compensation button to adjust the light amount.

However, even when such a backlight correction is appropriately performed, even if the main subject has an appropriate exposure amount, whiteout occurs in the background, resulting in a screen with only the white background. That is, narrowing the dynamic range of the image pickup device cannot be solved only by adjusting the light amount so that the exposure amount of the main subject becomes appropriate as in the conventional device.

To solve this problem, there is a method of expanding the dynamic range by performing exposure twice, for example. This method uses a high-speed shutter operation (for example, 1/60 sec.
It is replaced by the pixel signal imaged at 1000 seconds). With this method, the exposure time differs by about 16 times, so the dynamic range can be expanded by 16 times.

[0005]

However, the method of expanding the dynamic range by the above-described two exposures has the following problems.

For example, in a movie camera for shooting a moving image, a normal exposure signal and a high-speed shutter signal are read out for each field. Therefore, when two image signals are combined, the combined signal is an image for one field in two fields. It is only a signal. Therefore, the same combined signal is output from the memory or the like during the two-field period, which causes a problem that the dynamic resolution is lowered.

Further, both of the two exposures are performed by scanning the image pickup device in a predetermined sequence, so that the next scanning cannot be performed until all the signals have been output. .. In many cases, the area where the image pickup element is saturated is a very small part of the image pickup screen, and the signal replacement for improving the dynamic range over the above two image pickup signals requires only a small amount of data. That is, an image is composed of a lot of unnecessary information, and it is uneconomical to output all two image pickup signals and perform image processing as in the conventional case.

In view of these problems, it is an object of the present invention to provide an image pickup apparatus which has a wide dynamic range, is simple in image processing, and can obtain a normal moving image.

[0009]

The image pickup device of the present invention is obtained by setting a short exposure time in a pixel region where a large amount of light is applied to the image pickup device in an image pickup device using a random access type image pickup device. The pixel signal of the memory is transferred to the memory, the exposure time is set to be long in the pixel area where the light amount irradiated to the image sensor is small, and the pixel signal of the memory is transferred to the memory. Is sequentially transferred.

[0010]

In the image pickup apparatus of the present invention, the area where the image pickup element is saturated is a very small part of the image pickup screen, and the signal replacement for improving the dynamic range is better than two image pickup signals with a small amount of data. Paying attention to the good point, information is transferred to the memory by shortening the exposure time in the pixel area where the amount of light emitted to the image sensor is large, and long in the pixel area where the amount of light emitted to the image sensor is small. And the pixel signals in the memory are sequentially transferred to obtain areas with different exposure amounts in one screen, and the imaging device is not saturated even if a bright subject that is saturated by the imaging device is imaged. It is possible to control.

[0011]

Embodiments of the present invention will be described in detail below with reference to the drawings.

First, the structure of the image pickup device used in the present invention will be described. FIG. 6 is a block diagram showing a unit circuit of an example of the image pickup device used in the present invention. FIG. 7 is a basic drive timing chart of the unit circuit of FIG.

In FIG. 6, reference numeral 100 denotes a unit circuit portion, which constitutes one photoelectric conversion element. Reference numeral 10 is a photodiode serving as a photoelectric conversion unit, 20 is a transfer MOS transistor, and 30 is a reset MOS transistor. In addition,
The photodiode 10 is reset ((A) in FIG. 7) by the transfer MOS transistor 20 and the reset MO.
This is performed by controlling conduction of the S transistor 30 with drive pulses φ _R1 and φ _C.

Further, 40 is a transfer MOS transistor, 5
Reference numeral 0 is a capacitor, and 60 is a read transistor. The base potential of the read transistor 60 can be controlled via the capacitor 50 by the drive pulse φ _R2 .

To transfer the accumulated charges photoelectrically converted by the photodiode 10 ((B) in FIG. 7), the transfer MOS transistor 20 and the transfer MOS transistor 40 are conduction-controlled by drive pulses φ _R1 and φ _R2. Made by The transferred charges are transferred to the parasitic base capacitance (not shown) of the read transistor 60 and the capacitance 5 serving as charge holding means.
It is temporarily stored at 0. When this accumulated signal is read from the read transistor 60 to the output signal line 65 ((C) in FIG. 7), a positive drive pulse φ _R2 is applied to the capacitor 50 to bring the read transistor 60 into the forward bias state. At this time, when the transfer MOS transistor 70 connected to the output signal line 65 is made conductive by the drive pulse φ _T , an emitter current flows from the read transistor 60 to the temporary storage capacitor 80, and an emitter voltage corresponding to the base potential appears.

To clear the electric charge remaining at the base of the read transistor 60 ((D) in FIG. 7), first, the reset MOS transistor 30 and the transfer MOS transistor 40 are made conductive by the drive pulses φ _C and φ _R2. As a reset (period T _D1 ). Next, drive pulse φ _VC
To make the output line reset MOS transistor 90 conductive and make the emitter a constant potential, and apply a positive drive pulse φ _R2 to the capacitor 50 to set the read transistor 60 in a forward bias state to discharge the electric charge remaining in the base ( The transient refresh operation) and the reset operation are completed (period T _D2 ).

As described above, the driving pulses φ _R1 , φ _R2 ,
By changing the timings of φ _C , φ _T , and φ _VC , it is possible to perform the basic operation of the image sensor, from the reset operation of the photodiode to the accumulation operation, and from the transfer of the accumulated charge to the reading operation.

FIG. 8 is a schematic view of an XY type image pickup device in which the above unit circuits are arranged. Here, for simplification, only 2 × 2 4 elements are shown. As shown in FIG. 8, the XY type image sensor includes two row decoders (L, R) 1.
10, 120, two column decoders (U, D) 130, 1
40, a readout circuit 150, an output amplifier 160, and a photoelectric conversion element 100. Each decoder 110, 12
0, 130, 140 are a plurality of input pulses (φ _Ln , φ _Rn ,
φ _Cn , φ _On ) outputs the desired selected drive pulse. It is possible to reset any photodiode 10 by the combination of the driving pulses of the row decoder 110 and the column decoder 130.

The row decoder 110 and the row decoder 120 are also provided.
The accumulated charge accumulated in the photodiode 10 is transferred to the read transistor 60 by the combination of the driving pulses. Further, by the drive pulse of the row decoder 120, the accumulated charge is amplified and transferred from the read transistor 60 of any row to the temporary storage capacitor 80 (C _T ) via the output signal line 65.

An arbitrary read transistor 6 is selected by a combination of driving pulses of the column decoder 130 and the row decoder 120.
The base of 0 is reset, the transient refresh operation of the read transistor 60 of any row is performed by the drive pulse and the drive pulse φ _VC from the row decoder 120, and the signal temporarily stored in the read circuit 150 is stored in the column decoder 140.
Thus, an arbitrary signal is transferred to the horizontal output line and is output to the outside via the output amplifier 160.

Next, the structure of the image pickup apparatus of the present invention will be described.

FIG. 1 is a block diagram showing an embodiment of an image pickup apparatus of the present invention using the above image pickup element. In the figure, 310 is an image pickup optical system, 320 is a diaphragm for controlling the amount of light incident on the image pickup device, and 200 is an XY type image pickup device shown in FIG. The light beam incident from the imaging optical system 310 is a diaphragm 3
The amount of light is limited by 20, and an image is formed on the image sensor 200.
The diaphragm 320 and the imaging optical system 310 (lens in the figure) are driven by a drive circuit 390 controlled by a control signal from the image processing unit 360. The signal processing circuit 330 is a known circuit that performs gamma correction and other video signal processing. This signal is converted into a digital signal by the A / D converter 340 and recorded in the image memory 350.

The signal from the image memory 350 is transferred to the image processing section 360. The image processing section 360 is an address section,
It includes an arithmetic processing unit, an arithmetic memory unit, a control unit, and the like, and determines a signal level described later, converts a signal level, transfers a scan address for random control of the image sensor 200, and the imaging optical system 310 ( It generates control signals for the lens (focal length) and diaphragm 320. Image processing unit 3
Reference numeral 60 transfers the scan pattern to the random scan address circuit 370 based on the sensor scan method selection and the sensor signal level determination result. The random scan address circuit 370 randomly scans the image sensor 200 for an address signal via the scan interface 380. By this random scan, the image sensor 200
Input data is sent to the row decoders (L, R) 110, 120 and the column decoders (U, D) 130, 140, and the charges accumulated in the photodiodes 10 are transferred ((B) in FIG. 7).
The accumulated charges are read (C in FIG. 7), the photodiode 10 is reset (A in FIG. 7), the read transistor 60 is reset (D in FIG. 7), and the like.
The exposure control means is the image processing unit 360, the random scan address circuit 370, the scan interface 38.
It is composed of zero.

FIG. 2 is a control flow chart of the image sensor 200, and FIG. 3 is a flow chart relating to processing of pixel signals output from the image sensor 200.

In FIG. 2, when the operation of the image pickup apparatus is started (500), first, the scan of the image pickup device 200 is selected (502). As a scanning method,
For example, (1) Pixel accumulation (T _S1 =
1/60 seconds) and the pixel is saturated in the storage time of T _S1 , the pixel storage with a short storage time (T _S2 = 1 /
For example, 1000 seconds) and the storage time of each pixel is different in one screen. (2) At the first time, all the signals accumulated at T _S1 are read out, and at the second time, only the pixels saturated at the first time are T _S2. For example, there is a method of performing the accumulation for the time, and reading out only the signal of the pixel whose accumulation time is changed (3) A method of changing the accumulation time (T _S2 ) only for the pixels in a certain predetermined area. A detailed description of the scanning method will be given later.

When the scan is selected (502), the scan pattern is transferred from the image processing section 360 to the random scan address circuit 370 (504). An address is transferred from the random scan address circuit 370 to the scan interface 380 (506), and the operation of each pixel of the image sensor 200 is controlled via this scan interface 380.

First, in the image pickup device 200, the charge accumulated in the photodiode 10 of the selected pixel (X, Y) is transferred to the read transistor ((B) in FIG. 7) (50).
8).

Next, the signal of the pixel is read from the image pickup device 200 ((C) of FIG. 7), that is, the signal is output (510). This read operation ((C) of FIG. 7)
When 510 is completed, the reset operation of the photodiode 10 ((A) of FIG. 7) and the reset operation of the read transistor 60 ((D) of FIG. 7) are performed (512). Each operation of the image pickup device 200 is performed for each pixel or each horizontal pixel column by the random scan address operation (504).

Other than the read operation ((C) in FIG. 7) 510, the accumulated charges of a plurality of horizontal pixel columns can be transferred, the photodiode 10 can be reset, and the read transistor 60 can be reset.

After the signal is read ((C) in FIG. 7) (510), the read signal is processed by the signal processing circuit 330,
Data is taken into the image memory 350 via the A / D converter 340 (514), and the image processing unit 360 performs arithmetic processing and the like (516). When the reset operation is completed, the same operation is repeated again.

Next, the flow chart of FIG. 3 will be described.

The flow chart shown in FIG. 3 illustrates the process 516, and illustrates the operation of the exposure control means according to the present invention.

First, it is judged whether the image signal from the image memory 350 is the signal of the accumulation time T _S2 (6
00). Here, if the signal is T _S2 , it is transferred to the level conversion section (602) and the signal level is judged (604). If the pixel signal is at the low level V _L or higher, subsequently, the pixel storage time is set to T _S2 .
The pixel address (X, Y) is stored. Low level V
If it is smaller than _L , the pixel accumulation time is set to T _S1 (61
4).

In the level conversion section, a calculation of T _S2 / T _S1 times is performed (602), but since the dynamic range of the output device is generally narrow, coefficient processing of knee (KNEE) processing is further performed.

If the pixel signal is not T _{S2 in} the judgment 600, the signal is transferred as output data (610), and the signal level is judged, that is, saturation is detected (V _H or more) (606). If the signal is saturated, the storage time of the pixel is set to T _S2, and therefore the pixel address (X, Y) is stored (608). If the signal is not saturated, the pixel accumulation time is set to T _S1 (616).

This address is reflected in the random scan address circuit 370 from the image processing section 360, and the photodiode 10 is reset ((A) in FIG. 7).

After the output data is transferred (610), it is input to the D / A converter 400 to be converted into an analog signal (612).

The exposure time control by random scanning will be described below.

4 and 5 are explanatory diagrams of exposure time control by random scanning, and FIG. 4 is a schematic diagram of an image pickup screen,
FIG. 5 is an explanatory diagram of vertical scanning.

Point A and point B in FIG. 4 indicate the start and end points of vertical scanning, and abc in the screen.
In the pixel area Z _A indicated by d, the amount of incident light is much stronger than in the surrounding area, and the normal TV (TV) rate (exposure time 1/60
In second), the pixels inside it are saturated.

FIG. 5 is an explanatory diagram for shortening the exposure time of the pixels in the pixel area Z _A to, for example, 1/600 second.
In FIG. 5, the T ₁ period is a long exposure period (exposure time T _S1 ). At the time when the exposure of the exposure period T ₁ is completed, the photodiode in the region Z _A is saturated, and the photodiode in the pixel region Z _B accumulates electric charges at a level that is not saturated.

In the T ₁₂ period, first, the readout transistors of the pixels (pixel regions Z _A and Z _B ) in the entire region are reset ((D) in FIG. 7), and the residual charges are removed.

Next, the charge accumulated in the pixel region Z _B that is not saturated in the T ₂ period is transferred to the charge holding portion of the read transistor ((B) in FIG. 7).

The periods T ₃ , T ₄ , and T ₅ are operations for short-time exposure for preventing the pixel region Z _A from being saturated. First,
The photodiode is reset in the period T ₃ ((A) in FIG. 7), short-time exposure is performed in the period T _4, and the accumulated charge in the pixel region Z _A is transferred to the charge holding portion of the read transistor in the period T ₅ ( 7B) is performed.

The long exposure signal accumulated in the effective period and the short exposure signal thus accumulated in the blanking period are temporarily held in the charge holding portion, and these signals are stored in the next T ₆ period. Is output to the outside through the read transistor. Although resetting the photodiode is a known technique, electric charges are discharged to the element substrate by the reset pulse.

Next, an example using a CCD type image pickup device will be described as another example of the image pickup device used in the present invention. As a known example of a CCD capable of randomly controlling charge transfer from a photodiode to a vertical register, there is JP-A-2-234583. In this CCD, the transfer gate is of the XY type so that the charge transfer to the vertical register can be selectively performed.

FIG. 9 is a block diagram showing a row decoder and a column decoder provided in the above-mentioned known XY CCD.

The photodiode 700 is connected to the row decoder 701 via a horizontal selection line 705, and is connected to the gate electrode in the horizontal direction, and to the column decoder 702 via a vertical selection line 704, in the vertical direction. The configured gate electrode is provided in parallel. When the driving voltage is applied to both gate electrodes at the same time, only the charge accumulated in the photodiode 700 is applied to the vertical register 703.
Transferred to. The accumulated charge of the unselected photodiode 700 remains unchanged. The charges of the vertical register 703 are sequentially transferred to the horizontal register 704 by a plurality of vertical transfer pulses (φV _(n) ), and output to the outside through the output amplifier. The row decoder 701 and the column decoder 702 output desired drive pulses selected by respective input pulses (φV _Sn , φH _Sn ). φ _RS is a board reset pulse.

10 and 11 are drive timing charts of the CCD type image pickup device shown in FIG. Note that FIG. 10 is mainly applied to a movie camera or a still video camera, and FIG. 11 is applied to a still video camera.

In FIGS. 10 and 11, φV_{Sn (ZB)} , Φ
H_{Sn (ZB)} Is the pixel area Z in the low illuminance area _B Control input
Ruth, φV_{Sn (ZA)} , ΦH_{Sn (ZA)} Is the pixel area in the high illuminance area
Z_AIs an input pulse for controlling.

In FIG. 10, among the charges exposed during the period T ₁ , the signal charges in the pixel region Z _B which is not saturated are:
During the T ₂ period, the pulses φV _{Sn (ZB)} and φH _{Sn (ZB)} become high level and are transferred to the vertical register 703.

Next, during the period T ₃ , the pulse φ _RS becomes high level, the photodiode 700 is reset, and during the period T ₄ , exposure for the pixel region Z _A is performed.

Next, in the T ₅ period, pulses φV _{Sn (ZA)} , φH
_{Sn (ZA)} becomes high level and the signal of the pixel area Z _A is transferred to the vertical register 703. At this point, the signals of each pixel are all transferred to the vertical register 703.

During the next T ₃ ′ period, the photodiode 700
Are reset to shift to the exposure period of the T ₁ period.

The signal charges transferred to the vertical register 703 are output to the outside through the horizontal register 704 within the effective period (T ₆ period).

[0056] In the timing of Fig. 11, to reset the photodiode 700 in the period T _3, T ₄ period (T _S2 h) after (post-exposure), the vertical register 703 f the pixel signals of Z _A region in the period T ₅ Transfer and T ₁ period (T _S1 hour)
After a lapse of time (after exposure), the pixel signal of the Z _A area is transferred to the vertical register 703 in the T ₂ period.

The signal charge of the vertical register 703 is output to the outside in the next T ₆ period.

[0058]

As described above, according to the image pickup apparatus of the present invention, the exposure time of any pixel can be changed, so that the dynamic range can be substantially widened by a simple and economical processing circuit. You can Further, since the signal can be read from any pixel, it can be applied to many image input devices.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of an image pickup apparatus of the present invention.

FIG. 2 is a control flowchart of the image sensor.

FIG. 3 is a flowchart showing processing of a pixel signal output from an image sensor.

FIG. 4 is an explanatory diagram of exposure time control by random scanning, and is a schematic diagram of an imaging screen.

FIG. 5 is an explanatory diagram of exposure time control by random scanning, which is an explanatory diagram of vertical scanning.

FIG. 6 is a configuration diagram showing a unit circuit of an example of an image sensor used in the present invention.

7 is a basic drive timing diagram of the unit circuit of FIG.

8 is a schematic diagram of an XY type image sensor in which the unit circuits of FIG. 6 are arranged.

FIG. 9 is a configuration diagram in the case where a row decoder and a column decoder are provided in an XY CCD.

FIG. 10 is a drive timing chart of the image sensor shown in FIG. 9 applied to a movie camera or a still video camera.

11 is a drive timing diagram of the image sensor shown in FIG. 9 applied to a still video.

[Explanation of symbols]

10 Photodiodes, 20 Transfer MOS Transistors, 30 Reset MOS Transistors, 40
Transfer MOS transistor, 50 capacitance, 60 read transistor, 65 output signal line, 70 transfer M
OS transistor, 80 storage capacitor, 90 output line reset MOS transistor, 100 unit circuit section,
110 row decoder L, 120 row decoder R,
130 column decoder U, 140 column decoder D, 200
XY type image pickup device, 310 image pickup optical system, 320
Aperture, 330 signal processing circuit, 340 A / D converter, 350 image memory, 360 image processing unit,
370 Random scan address circuit, 380 scan interface, 390 drive circuit, 400
D / A converter.

Claims (1)

[Claims] 1. An image pickup device using a random access type image pickup device, wherein an exposure time is set to be short in a pixel region where a large amount of light is irradiated to the image pickup device, and the obtained pixel signal is transferred to a memory, An image pickup apparatus having an exposure control unit for setting a long exposure time in a pixel region with a small amount of irradiation light to the memory and transferring the obtained pixel signals to the memory, and sequentially transferring the pixel signals of the memory. ..