JPH06197286A - Image pickup unit - Google Patents

Abstract

PURPOSE:To obtain a picture with a wide dynamic range independently of the presence of saturation of each picture element. CONSTITUTION:A time count means 14a measures a time till a signal quantity stored to each picture element 11 of a solid-state image pickup element 1 reaches a prescribed signal quantity. When the signal quantity stored in each picture element 11 of the solid-state image pickup element 1 reaches a prescribed signal quantity, the total stored quantity for each picture element within the prescribed time is calculated based on time information generated by the time count means 14a. Thus, the saturation of the stored charge is prevented and the dynamic range is extended.

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, it is suitable for use in an image pickup device using a solid-state image pickup device to expand the dynamic range.

[0002]

2. Description of the Related Art Conventionally, many inventions relating to the expansion of the dynamic range in an image pickup device using a solid-state image pickup device have been filed. As an example of the conventional technique, for example,
In Japanese Patent Laid-Open No. 63-98286, one field period of the television signal mode is divided into a plurality of periods, and signals accumulated in each divided period are added to prevent saturation of accumulated charges and to increase the dynamic range. A method of expanding is disclosed.

Further, in Japanese Patent Application Laid-Open No. 61-158279, the charge storage time is set to different times of short and long, and when an overflow occurs in the long storage time, the signal is removed to shorten the storage time. A method of improving signal overflow and blooming is disclosed.

[0004]

However, in the former invention proposed in Japanese Unexamined Patent Publication No. 63-98286, S / N is deteriorated due to mixing of noise by reading a signal a plurality of times. However, there is a problem that the dynamic range is reduced due to that. In the latter Japanese Patent Laid-Open No. 61-158279, there is a problem that the storage gate signal becomes complicated. Further, in the pixel which has overflowed, there is a defect that the accumulation time is different from other pixels and is shorter than the charge amount of the pixel which does not overflow. In view of the above problems, it is an object of the present invention to obtain an image with a wide dynamic range regardless of whether or not each pixel is saturated.

[0005]

The image pickup device of the present invention compares these two types of signals by comparing the signal amount accumulated for each pixel of the solid-state image pickup device with a predetermined signal amount set in advance. Determination means for determining the amount of the amount, timing means for measuring the time until the signal amount accumulated for each pixel reaches a predetermined signal amount, and the accumulated signal amount is larger than the predetermined signal amount. For the pixel determined by the determination means to be,
And a calculating means for calculating the accumulated signal of the corresponding pixel based on the time information obtained from the time measuring means.

Another feature of the present invention is that
By comparing the signal amount accumulated for each pixel of the solid-state image pickup device with a predetermined signal amount, it is determined whether or not the signal amount accumulated for each pixel has reached a predetermined signal amount. And a resetting means for resetting the accumulated signal for each pixel according to the determination result of the determining means.

[0007]

Since the present invention measures the time until the signal amount accumulated for each pixel of the solid-state image pickup device reaches a predetermined signal amount by providing the clocking means, the accumulation is performed for each pixel of the solid-state image pickup device. When the signal amount thus reached reaches a predetermined signal amount, it becomes possible to calculate the total accumulated amount for each pixel within a predetermined time based on the measurement value of the time measuring means.

Further, the signal amount accumulated for each pixel of the solid-state image pickup device is compared with a predetermined signal amount, and whether the signal amount accumulated for each pixel reaches a predetermined signal amount. Since it is determined whether or not the accumulated charge is reset for each pixel in accordance with the determination result, each image is determined by the number of resets within a predetermined time and the signal amount accumulated after the predetermined time. It is possible to calculate the total accumulated signal of

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the image pickup apparatus of the present invention will be described below with reference to the accompanying drawings. 1 and 2 show a first embodiment of an image pickup device of the present invention, FIG. 1 is a schematic configuration diagram of the image pickup device, and FIG. 2 is a characteristic diagram showing a relationship between an accumulation time and a signal amount. In FIG. 1, 11 is a photocell for accumulating electric charges in one pixel of the image pickup device 1, and 13 is a signal indicating that when the signal amount accumulated in the photocell 11 exceeds a predetermined signal amount. The discriminating means 14 is a microcomputer, and the microcomputer 14 measures the time from the start of accumulation until the signal is derived from the discriminating means 13 for each pixel 1
I have 4a.

Next, how the signal charges are accumulated in the photocell 11 will be described in two cases with reference to FIG. First, explaining the first case, this is the case exceeds accumulated signal amount during a predetermined storage time (t _s) is a predetermined amount of signal (V _1).

In this case, the signal amount increases along the first straight line l ₁ . Then, the accumulated signal amount is a predetermined signal amount V ₁
Then, the microcomputer 14 measures the time t ₁ until the predetermined signal amount V ₁ is reached by the signal from the discriminating means 13. The threshold signal amount V ₁ is usually S / N
In order to improve as much as possible, a value close to the saturation signal amount V _sat of the photocell 11 is set. Therefore, after the accumulated signal amount exceeds the predetermined signal amount V ₁ , the saturated signal amount V _sat is reached in a short time.

After that, when the time has elapsed and a predetermined storage time (t _s ) has been reached, the signal storage is terminated. The predetermined storage time t _s is one field period (1/60 _s) in a camera-integrated recorder or the like, and is a shutter speed of 1/500 s in an electronic still camera, for example.

In this case, the microcomputer 14 generally calculates the accumulated signal amount V _i of the photocell 11 from the following (Equation 1). Vi = V ₁ × t _s / t ₁ (Equation 1)

Further, when the storage signal amount V _i during a predetermined storage time t _s does not exceed a predetermined signal amount V _i is as follows. That is, the signal accumulated in the photocell 11 along the straight line l ₂ has a signal amount V ₂ after a predetermined accumulation time t _s.
Reach Therefore, the accumulated signal amount V _i of the photocell 11 in this case is calculated by the following Expression 2. Vi = V ₂ (Equation 2) (where V ₁ ≧ V ₂ )

Generally, when there is a high-luminance portion in the subject, a correction for controlling the inclination of the photoelectric conversion characteristic in the high-luminance region of the output of the image sensor, that is, so-called knee correction is considered. Next, the concept of implementing the knee correction in the present invention will be described with reference to FIG.

The signal amount V from the image sensor, which is the horizontal axis of FIG.
_i changes linearly according to the light input as described above, and is calculated by the above-described Equation 1 or Equation 2. Here, the inclination is changed in the high-luminance portion where the signal amount is equal to or higher than the predetermined signal amount V ₁ ′, and the signal amount after knee correction is obtained by the following equation. , V _e> 'In the case of _{V e = V 1' V 1} + α (t s / t 1 · V 1'- V 1 ') ··· ( Equation 3) where, 1 ≧ α ≧ 0

In the case of V _e ≦ ₁ V ₁ , V _e = V ₁ ′ (Equation 4) Further, by varying the coefficient α of Equation 3 as a function of time t ₁ , various knee corrections can be performed. It becomes possible to call. For example, alpha = is substituted into equation 3 as _{t 1 / t s, V e} = V 1 '+ α (t s / t 1 · V 1'- V 1') = V 1 '+ t 1 / t s · (t _{s / t 1 · V 1'-} V 1 ') = V 1' + V 1 '-t 1 / t s · V 1' = (2-t 1 / t s) · V 1 '( However, V _e> V ₁ ')

Then, as shown in FIG. 4, at t ₁ → 0,
A curve for V _e = 2V ₁ ′ is drawn, and the accumulated signal amount is V ₁ ′.
The faster the time t ₁ to reach, that is, the higher the brightness, the more the signal amount is compressed, and a better knee characteristic can be obtained.

Next, a second embodiment of the image pickup apparatus of the present invention will be described with reference to the drawings. 5 and 6 show a second embodiment of the present invention, FIG. 5 is a schematic configuration diagram, and FIG. 6 is a characteristic diagram. In FIG. 5, 11 is a photocell for accumulating charges in one pixel, 12 is reset means for resetting the charges accumulated in the photocell 11, and 13 is a photocell 1.
According to the amount of signal accumulated in 1 (V ₁ in FIG. 2),
It is a determination means for operating the reset means 12. Also,
Reference numeral 14 is a microcomputer that records the number of resets and the signal amount V _O from the photocell 11 in the circuit system 1 configured as described above.

Next, with reference to FIG. 6, the manner in which charges are accumulated in the photocell 11 of this embodiment will be described. The signal generated by irradiating the photocell 11 with light is
It increases along the time along the straight line l ₁ . Then, when the predetermined signal amount V ₁ is reached, the discriminating means 13 is activated to reset the electric charge accumulated in the photocell 11 (time t ₁ ).

The photocell 11 in which the accumulated charge is reset in this manner starts charge accumulation again after the time t ₁ and increases the signal amount along the straight line l ₂ . And
When the signal amount V ₁ is reached again at time t ₂ , the signal amount is reset again. The photocell 11 having the electric charges reset again starts accumulating electric charges again after the time t ₂ and increases the signal amount along the straight line l ₃ .

Here, when the predetermined charge accumulation end time t ₃ is reached, the amount of signals accumulated after the time t ₂ is set to V ₂ and the charge accumulation is terminated. At that time, the signal amount V ₀ read from the photocell 11 is V ₀ = V ₂ . By the way, in a normal video camera or the like, the time (0 to t ₃ ) from the start of charge accumulation to the end thereof is one field (1/60 s) at the television rate.

Such charge accumulation operation is performed in each photocell 11 of the image pickup device, and the signal V ₀ of each photocell 11 is read out after the charge accumulation is completed. Next, the microcomputer 14 checks the number N of resets in each photocell 11, and calculates the total accumulated signal amount V of each photocell 11 by the following arithmetic expression.
Calculate _i . V _i = V ₁ × N + V ₂

The total accumulated signal amount V ₁ is reset as the saturated output of the photocell 11 is closer to the photocell 1.
The number of 1s and the number of resets N decrease. Further, since also reduces computation time of total accumulated signal amount V _i, the total accumulated signal amount V _i is a value close to the saturation output as possible is set.

Next, as a more detailed embodiment, BASI
A configuration example using the S imaging sensor will be described with reference to FIG. 7. In FIG. 7, 1 is a circuit system corresponding to each pixel, and S is an aperture bit of the image sensor corresponding to the photocell 11 in FIG.

The capacitor electrode a of each bit S is connected to the terminal 10
A common positive voltage is applied to the collector electrode b. The electrode c of the reset MOS transistor is grounded, and the gate electrode d is connected to the terminal 105. Further, the emitter electrode e ₁ bit S is connected to the vertical line L _1, the vertical line L ₁
Is a charge storage capacitor C ₁ via a transistor Ta.
And the output signal line 110 through the transistor T ₁ .

The output signal line 110 is grounded via the reset transistor Ts ₁ . The gate electrode of the transistor T ₁ is connected to the parallel output terminal of the scanning circuit 106. The shift pulse φ _sp is input to the scanning circuit 106 via the terminal 101, and the transistor T ₁ is controlled by the scanning circuit 106 to be turned on.

The vertical line L ₁ is grounded via the transistor Tb. The gate electrode of the transistor Tb is commonly connected to the terminal 104. Also,
The emitter electrode e ₂ of the opening bit S is connected to the line 111, and the line 111 is grounded via the transistor Ts. Further, the gate electrode of the transistor Ts is connected to the terminal 104.

The reset operation of the bit S in such a configuration will be described. Terminal 10 from the microcomputer 14
When the signal φ _res is applied to 5, the reset M of the bit S
The OS transistor is turned on, the accumulated charges in the p base region of the bit S are removed, and the potential becomes constant.

Subsequently, when the signal φ _vrs is applied to the terminal 104, the transistors Tb and Ts are turned on and the emitter electrodes e ₁ and e ₂ are grounded.
Further, when the pulse φ _r for initialization is applied to the terminal 103, the accumulated charge in the p base region is removed as already described. The above is the reset operation.

In order to start the accumulation operation of the optical signal from this state, the application of the signal φ _res to the terminal 105 is stopped, and the shift pulse φ _sp is applied to the scanning circuit 106 via the terminal 101 ( The reset MOS transistor is turned off by the microcomputer 14).

As a result, first, the photoelectric conversion operation corresponding to the amount of light incident on the bit S is started. Next, in order to accumulate the charges generated by the above-described operation in the capacitor C ₁ , the application of the signal φ _vrs to the terminal 104 is first stopped. As a result, the transistors Tb and Ts are turned off, and the emitter electrodes e ₁ and e ₂ are in a floating state. Subsequently, the signal φ _t is applied to the terminal 102 by the microcomputer 14, which turns on the transistor Ta.

Next, when a read pulse φ _r is applied to the terminal 103, a signal corresponding to the amount of incident light is read from the bit S through the vertical line L ₁ and stored in the capacitor C ₁ . After that, when the signal φ _t indicating the end of storage is applied to the terminal 102, the transistor Ta is turned off, and the storage operation to the capacitor C ₁ ends.

When the shift pulse φ _sp is applied to the terminal 101, the scanning circuit 106 causes the transistor T
Transistor T turned on by turning on ₁
The electric charge of the capacitor C ₁ corresponding to ₁ is sent out as the image signal V _O via the output terminal 110. Also,
Immediately thereafter, when the signal φ _hrs is applied to the terminal 113 by the microcomputer 14, the transistor Ts ₁ is turned on accordingly, and the residual charge on the output signal line 110 is removed.

Further, the detection operation of the signal Vp is performed in parallel with the accumulation operation. That is, the signal φ _r applied to the terminal 103 during the above operation causes the signal from the bit S to be read out to the line 111 and the comparator CNP.
It is output to the non-inverting input terminal (+) of.

On the other hand, the reference voltage V ₁ is supplied to the inverting input terminal (-) of the comparator CNP, the signal Vp is compared with the reference voltage V ₁ in the comparator CNP, and the signal Vp is changed to the reference voltage V _1. Microcomputer 14
An "H" level signal is output to. The microcomputer 14
At that time, in order to reset the accumulated charge of the bit S, the above reset operation is performed and the number of resets is stored.

The image pickup apparatus of the present invention is not limited to the above-mentioned embodiment and can be realized by other configurations. That is, in the above-described embodiment, the microcomputer 14 receives the output of the comparator CNP, which is the discriminating means, and generates the pulse φ _res for resetting. However, the output of the comparator CNP is received and the reset pulse is generated. Hardware such as a clock for controlling may be provided. Further, the form of the image pickup device is not limited to BASIS, and any form of image pickup device does not impair the gist of the present invention.

[0038]

As described above, according to the present invention, when the signal amount accumulated for each pixel of the image pickup device reaches a predetermined signal amount, the time until the signal amount is reached is measured. By doing so, an image with a wide dynamic range can be obtained regardless of whether or not each pixel is saturated.

Further, according to the invention of claim 2, the calculation using time in claim 1 is performed by V _e = V _e = V ₁ ′
By carrying out the equation + α (t _s / t ₁ V ₁ ′ −V ₁ ′), it is possible to prevent white crushing in the high luminance portion. Further, by setting the coefficient α in the above equation as a function of time t ₁ , it is possible to provide a better knee characteristic.

Further, according to the invention of claim 3, since the predetermined signal amount in the equation in claim 2 is used as the threshold value, when the accumulated amount of the photocell 11 does not reach the threshold value, Since it is not necessary to calculate the accumulated amount, the calculation time by the microcomputer can be reduced.

Further, according to the invention of claim 4, the signal amount accumulated for each pixel of the solid-state image pickup device is compared with a predetermined signal amount, and the signal amount accumulated for each pixel is predetermined. Since it is determined whether or not the signal amount reached is reached and the accumulated charge is reset for each pixel as a result of the determination, the number of resets within a predetermined time period and the accumulated amount after a predetermined time period are accumulated. It is possible to calculate the total accumulated signal for each image from the signal amount, and it is possible to prevent an overflow and to expand the dynamic range of the image pickup apparatus.

[Brief description of drawings]

FIG. 1 is a block diagram showing a schematic configuration of an image pickup apparatus according to a first embodiment of the present invention.

FIG. 2 is a characteristic diagram showing a relationship between a signal amount accumulated in one pixel and time.

FIG. 3 is a characteristic diagram showing an accumulated signal amount after knee correction.

FIG. 4 is a characteristic diagram showing an accumulated signal amount after knee correction.

FIG. 5 is a block diagram showing a schematic configuration of an image pickup apparatus according to a second embodiment of the present invention.

FIG. 6 is a characteristic diagram showing the relationship between the amount of signal accumulated in one pixel and time.

FIG. 7 is a circuit diagram showing a circuit configuration for one pixel of an image pickup device embodying the present invention.

[Explanation of symbols]

 11 Photocell 12 Reset Means 13 Judgment Means 14 Microcomputer 14a Timer

Claims (5)

[Claims] 1. A discriminating means for discriminating the magnitude of these two kinds of signal amounts by comparing a signal amount accumulated for each pixel of the solid-state image pickup device with a preset predetermined signal amount, The time measuring means for measuring the time until the accumulated signal amount reaches a predetermined signal amount for each pixel, and the pixel for which the judging means judges that the accumulated signal amount is larger than the predetermined signal amount. On the other hand, an image pickup device comprising: a calculation unit that calculates an accumulation signal of the pixel based on time information obtained from the time measurement unit. 2. A calculation performed by the calculating means is performed by the equation _{V e = V 1 '+ α} (t s / t 1 V 1' below-V ₁ '), in the above formula, V _e · be time alpha · · · coefficients up ... reaching one pixel signal amount V ₁ of the '... predetermined signal quantity t _s · · · accumulation time _{t 1 ··· V 1' (0} ≦ α ≦ 1) The imaging device according to claim 1, wherein 3. The image pickup apparatus according to claim 1, wherein the predetermined signal amount V ₁ ′ in the formula described in claim 2 has the same magnitude as a preset threshold value. 4. A signal quantity accumulated for each pixel of the solid-state image pickup device is compared with a predetermined signal quantity, and whether the signal quantity accumulated for each pixel reaches a predetermined signal quantity or not. An image pickup apparatus, comprising: a determination unit that determines whether or not the reset signal and a reset unit that resets the accumulated signal for each pixel according to a determination result of the determination unit. 5. The total accumulated signal for each pixel is calculated from the number of resets for each pixel within a predetermined time and the amount of signal accumulated after the lapse of the predetermined time. The imaging device described.