JPH0723283A - Image pickup device - Google Patents

Abstract

PURPOSE:To expand a dynamic range by amplifying the video signal output part corresponded every block so that the amplification factor of an amplifier means may be equal to the reciprocal of the extinction factor and enabling the output of a video signal which is faithful to an image pickup object. CONSTITUTION:When the signal output part of a picture element, for instance, is extincted by a light control element 2 by the extinction factor of 1/alpha (alpha is a positive number 2 1) for the output every picture element in accordance with the adjusting amount (extinction amount) of a light quantity adjusting means 13, this device has a signal amplifier means 7 composed so that this signal output part may be amplified alpha times. As a result, the output which is linear to the light quantity of an object is obtained as the output of the means 4 at the dynamic range which is wider than the dynamic range specific to an image pickup element 3. Thus, a video signal which is high in resolution and is faithful also for both contrast objects is possible to be reproduced and video reproducibility can be remarkably improved.

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 which is configured to greatly expand the dynamic range of the image pickup device and to obtain an extremely faithful video signal.

[0002]

2. Description of the Related Art Basically, an image pickup device for converting light into a voltage has a dynamic range specific to the image pickup device. For this reason, when the light amount deviates from the dynamic range and the light amount becomes excessive, the photoelectric conversion unit of the image sensor is saturated, causing smear or blooming phenomenon and significantly deteriorating the image. Conventionally, when an optical image is converted into an electrical signal by using this type of image sensor, in order to increase the light amount, a light amount adjusting means such as a diaphragm function or a neutral density filter is used to detect the light incident on the entire surface of the image sensor. The light quantity was reduced at a constant level.

Further, in a device (TV camera or the like) whose output level is regulated, signals exceeding 100% of the regulated value are electrically compressed by a limiter characteristic as shown in FIG. I was outputting. Note that FIG. 2 shows limiter characteristics when the input relative light amount is taken on the horizontal axis, and as an example, it is assumed that the photoelectric conversion unit is saturated with a relative light amount that is five times the specified value. The vertical axis of FIG. 2 represents the output level, but in general, the normal use range (the range where the relative light intensity in the figure is 0 to 1) corresponds linearly to the output, and when the relative light intensity exceeds 1, compression is performed. It is designed so that a mold limiter can be applied.

Incidentally, as a light quantity adjusting means, Japanese Patent Laid-Open No.
-35081 describes an imaging light quantity control device using a liquid crystal capable of controlling the light transmission characteristics for each divided area of the imaging device. Regarding the control method, the pulse of the one-shot circuit is determined according to the comparison result of the level comparator. By controlling the output time, the image pickup light amount is controlled to be constant, and an image with no contrast appears in the incident light amount region above a predetermined level.

Further, in Japanese Laid-Open Patent Publication No. 5-122614, a similar image pickup light amount control device and an image sensor capable of nondestructive read or high-speed read are used to read at least once during the exposure period, and the amount of transmitted light is determined according to the result. Is controlled, and cannot be controlled when the photoelectric conversion unit is saturated due to excessive light amount before the first reading.

[0006]

As described above, according to the conventional method, it is possible to somehow electrically obtain the output by applying an electrical limiter if the incident light amount level can be handled within the dynamic range peculiar to the image pickup device. When extremely strong light that deviates from the dynamic range peculiar to the element is incident, it is impossible to convert the light into an electric signal of a level corresponding to the light.

Further, in the control method disclosed in the above-mentioned Japanese Patent Laid-Open No. 63-35081, since the incident light amount region having a predetermined level or higher becomes an image without contrast, it may be far from the actual image depending on the imaged contents. It becomes a thing.

Further, the above-mentioned Japanese Patent Laid-Open No. 5-122614
In the control method disclosed in Japanese Patent Laid-Open Publication No. JP-A-2004-242, when the photoelectric conversion unit is saturated due to excessive light amount before the first reading, the photoelectric conversion unit is saturated because the light amount exceeds the dynamic range. This causes smear and blooming phenomena, and significantly deteriorates the image.

The present invention eliminates these drawbacks and provides an image pickup camera capable of outputting a video signal faithful to an image pickup target from a bright subject to a dark subject without saturation of a photoelectric conversion unit and capable of significantly widening a dynamic range. The purpose is to provide.

[0010]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a light quantity adjustment comprising a dimming element corresponding to a block in which one or a plurality of photoelectric conversion parts are grouped in front of an imaging element. Means are combined and the adjustment amount of the light amount adjusting means is selectively fed back according to the video signal output of each pixel corresponding to each block so that the output of each image pickup device falls within its own dynamic range. The output of each pixel is controlled according to the adjustment amount (light reduction amount) of the light amount adjusting means, for example, a signal output of a certain pixel is 1 / α (α is 1 or more by a light control element. If the extinction rate is a positive number),
By having the signal amplifying means configured to amplify the signal output by α times, the output of the signal amplifying means is linear with respect to the light amount of the subject in a dynamic range that is significantly wider than the dynamic range specific to the image sensor. It is designed so that various outputs can be obtained.

[0011]

As a result, in an image pickup apparatus which is picking up an image of a subject group having a remarkable difference in brightness and darkness, the incident light amount is changed with respect to a photoelectric conversion unit which is picking up a bright subject part which exceeds a dynamic range peculiar to the image pickup element. The light intensity is reduced according to the intensity of the light, and the amount of incident light is controlled so that each photoelectric conversion unit does not deviate from its dynamic range. The light amount is controlled so as not to impair the sensitivity peculiar to the image pickup device in a state close to the open state. For this reason, it is possible to realize an image pickup apparatus which has a high resolution for both bright and dark subjects, can reproduce a faithful video signal, and can significantly improve the video reproducibility.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG. The image of the subject collected by the lens 1 is captured by the image sensor 3 via the light control element 2. In addition, the light control element 2
May have any structure as long as the amount of transmitted light can be changed, such as a liquid crystal. Further, it is desirable that the light control element 2 and the image pickup element 3 have a close contact structure.

The output 101 of the image pickup device 3 is shaped into a video signal 102 by the signal processing unit 4, converted into a digital signal 103 by the AD converter 5, and applied to the α multiplication circuit 7 and the arithmetic processing unit 10. The output of the α-times multiplication circuit 7 is converted back to an analog signal by the DA converter 8 as necessary, and output from the output terminal 9 as a video signal.

Here, in the arithmetic processing unit 10, the digital signal 103 has a signal level corresponding to a light amount larger than a light amount (A) defined in a range not exceeding the dynamic range peculiar to the image pickup device 3. In this case, it is detected as an overflow, and the latter part 11 of the coefficient storage unit 11 is detected.
Based on the coefficient signal 105 of b, the coefficient value α is increased by a predetermined ratio and the result is output to the pre-stage unit 11a of the coefficient storage unit 11. Further, the digital signal 103 is smaller than the specified light amount A, and based on the coefficient signal 105, the coefficient value α is reduced by a predetermined ratio within a range not smaller than “1” and multiplied by 1 / α times. But the result is light intensity A
If the signal level corresponds to a smaller light amount level, it is detected as an underflow, the coefficient value α is reduced by the above-mentioned predetermined ratio, and the result is output to the front stage section 11a of the coefficient storage unit 11.

The arithmetic processing unit 10 repeats the above processing for each signal corresponding to each pixel. It is desirable that this repetition period is, for example, every frame.

The coefficient storage unit 11 holds the output of the calculation result of the calculation processing unit 10 in the pre-stage unit 11a. The contents of the front-stage part 11a are transferred to the rear-stage part 11b in the above-described repetition cycle, for example, for each frame. This operation may be realized by dividing the holding area of the coefficient storage unit 11 into two and alternately switching the functions of the front stage section and the rear stage section.

The dimming element control circuit 13 outputs a light amount control signal 106 for controlling the dimming amount of the corresponding dimming element 2 based on the coefficient signal 105 corresponding to each pixel. In the α-times multiplication circuit 7, each pixel is multiplied by α times by the coefficient value α of the coefficient signal 105, and the result is output.

The operation of the above configuration will be described for one line with reference to FIGS. 3 and 4. 3 and 4, the horizontal axis represents the time axis, the positive axis of the vertical axis represents the light quantity, and the negative side represents the light quantity control signal. As described above, the level A in the figure represents the amount of light defined within the range that does not exceed the dynamic range peculiar to the image sensor 3.

In FIG. 3, the solid line a is an example of the amount of incident light applied to the image pickup device 3 first, and the solid line e is an example of the control voltage finally applied to the light control device 2. It should be noted that b and d show the state in the middle of control, and the amount of incident light finally added to the image sensor 3 is shown by c.

As a concrete operation, in the first sweep,
Assuming that all the coefficient values corresponding to each pixel stored in the coefficient storage unit 11 are initialized to “1”, the light amount indicated by a enters the image sensor 3. In this example, since the amount of incident light is within the dynamic range of the image sensor (below the A level) until time x, the arithmetic processing unit 10 does not perform the overflow detection operation. However, after the time x, the arithmetic processing unit 10 detects an overflow, so that x to x'of the coefficient storage unit 11 is detected.
A coefficient value increased by a predetermined ratio, for example, "2" is stored in the storage area corresponding to the period.

As a result, in the second sweep, the control signal as shown in d is applied to the dimming element 2. However, since the light quantity such as b is still applied to the image sensor 3 in the second sweep, the arithmetic processing unit 10 again performs the overflow detection operation during the period y to y ′, which corresponds to the period y to y ′ of the coefficient storage unit 11. The storage area stores a coefficient value increased by a predetermined ratio, for example, "3".

As a result, in the third sweep, a control signal such as e is applied to the dimming element 2, so that all the incident light amounts fall within the dynamic range (A level or less) as shown in c. In this state, the output of the AD converter 5 is α
In the multiplication circuit 7, the x-y period is doubled and the y-y 'period is 3 times.
Since it is amplified twice during the period y ′ to x ′, the output of the α multiplication circuit 7 is very similar to the incident light amount a.

Next, the underflow detection operation when the brightness of the subject sharply decreases from the state after the overflow detection operation of FIG. 3 described above will be described with reference to FIG. This starts the explanation from the final state in FIG. The dotted line of c is the amount of incident light applied to the image sensor 3 at this time. Immediately after this, it is assumed that the brightness of the subject suddenly changes, and for example, the amount of incident light becomes 1/3 at the next sweep. g indicates the amount of incident light at this time.

Therefore, the amount of incident light becomes equal to or lower than the signal level corresponding to A, but the value of the coefficient signal 105 of the coefficient storage unit 11 is "up to the time x and after the time x '.
In this case, the arithmetic processing unit 10 does not detect an underflow because it is 1 ". However, during the period from x to x ', the coefficient value is"
Since it is 3 "or" 2 "(not" 1 "), in this case, the arithmetic processing unit 10 subtracts the value and, for example, the coefficient value α
If it is 3, reduce it to 2 and if it is 2, reduce it to 1
Since it is determined that the level does not exceed the level of A even when multiplied by a multiple or a unity, detection operation is performed as an underflow, and the storage area corresponding to the period y to y'of the coefficient storage unit 11 is reduced by a predetermined ratio. The coefficient value, eg, “2”, corresponding to the x to y period and the y ′ to x ′ period, stores the coefficient value reduced by a predetermined ratio, eg, “1”.

Since the underflow detection operation is performed until the coefficient value α becomes as small as possible to the smallest value, for example, "1", in the next sweep, the incident light amount is until the y time and after the y'time, the coefficient storage unit. Since the value of the coefficient signal 105 of 11 is "1", the underflow is not detected, but the period y to y'is "2". Therefore, the arithmetic processing unit 10 reduces the value, for example, the coefficient value α to "2". It is determined that the level does not exceed the level of A even if the amount of incident light is multiplied by 1 times by reducing from "1" to "1". Therefore, the detection operation is performed as an underflow, and the storage corresponding to the period y to y'of the coefficient storage 11 is performed. In the area,
A coefficient value reduced by a predetermined ratio, for example, "1" is stored.

As a result, a flat control signal as indicated by h is generated by the above-mentioned underflow detection operation.
In addition, the total amount of incident light falls within the dynamic range (A level or less) as shown in f, and the dynamic range of the image sensor is used more widely than in g, which improves the image reproducibility. To do.

In the above example, the photoelectric conversion section and the cell of the light control element correspond to each other on a pixel-by-pixel basis, but a plurality of photoelectric conversion sections corresponding to a plurality of pixels are connected to one cell of the light control element. The light amount may be controlled by.

Further, in the above example, the operation has been described as a monochrome image pickup device, but it is clear that the same idea can be applied to a single-plate color camera, a color camera using a plurality of image pickup elements, and the like. However, in consideration of color balance, it is desirable to give a control signal to a plurality of image pickup devices forming pixels so as to obtain the same dimming performance.

When a part of the subject is expected to deviate from the dynamic range, an interface circuit with a personal computer or another image pickup device is provided so that a numerical value can be set in the coefficient storage 11 from the outside. It is also possible to use it for various kinds of imaging such as reproducing only a part of the image clearly, faithfully expressing a part of the entire gradation range, or giving a special effect.

Further, an image change predicting means is newly provided,
The amount of change in the coefficient value may be controlled according to the prediction result.

In the above embodiment, the analog signal is partially converted into the digital signal for description, but the digital circuit may not be used and the analog circuit may be used.

A frame memory can also be used depending on the configuration.

[0033]

As described above, according to the present invention,
With the same function as having a diaphragm function for each photoelectric conversion unit, it is possible to provide an image pickup apparatus that can respond to a dynamic range that is far superior to conventional ones.

[Brief description of drawings]

FIG. 1 is a block diagram showing the overall configuration of the present invention.

FIG. 2 is a diagram showing one characteristic of a conventional analog limiter.

FIG. 3 is a diagram showing an example of an output state for incident light according to the present invention.

FIG. 4 is a diagram showing another example of an output state for incident light according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 lens 2 light control element 3 image sensor 5 AD converter 7 α multiplication circuit 8 DA converter 10 arithmetic processing unit 11 coefficient memory 13 light control element control circuit 14 reset signal input terminal

Claims (2)

[Claims] 1. In an image pickup apparatus, a light amount adjusting means for adjusting the light amount of light entering each block is provided for each block in which one or a plurality of photoelectric conversion units of an image pickup device are grouped. Place it in front of the light side,
A means for amplifying a video signal output corresponding to each block by an amplification factor for a video signal which is an output signal of the image pickup device, and dimming the incident light quantity dimmed by the light quantity adjusting means. The image pickup device is characterized in that the video signal output corresponding to each of the blocks is amplified so that the amplification rate of the amplification means becomes equal to the reciprocal of the extinction rate. 2. The image pickup apparatus according to claim 1,
It is characterized in that a light amount adjusting means for adjusting the extinction ratio is provided for each of the blocks so that the incident light amount of the image pickup device is settled within the dynamic range in consideration of the dynamic range peculiar to the image pickup device. Imaging device.