JP2003009007A - Solid-state imaging device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solid-state imaging device which generates a picture signal of a high dynamic range, in which no highlight area is missed regardless of a large difference of brightness in a subject image, with one image pickup. SOLUTION: A solid-state imaging device photoelectrically converts a subject image formed on an image pickup face to generate a picture signal, and a member in which the transmittance for visible rays can be partially changed is arranged on the image pickup face side of the solid-state imaging device. It is preferable that the member in which the transmittance for visible rays can be partially changed is a liquid crystal panel in which the liquid crystal density can be partially changed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid-state image sensor, and more particularly to a solid-state image sensor capable of generating an image signal having a high dynamic range.

[0002]

2. Description of the Related Art In an image pickup apparatus that digitally processes image data, such as a digital still camera that handles a still image or a digital video camera that handles a moving image, an optical image obtained through an image pickup optical system such as an image pickup lens is used by a solid state image pickup device. The image signal obtained by photoelectric conversion is digitally processed.

As such a solid-state image pickup element, a CCD (Charge Coupled Device) formed by arranging a large number of light receiving elements (pixels) on an image pickup surface is generally used.

[0004]

When a subject image is picked up by using such a solid-state image pickup device, if there is a large difference in brightness between the inside and outside of the room in the picked-up image, the room You can see the phenomenon that the outer part is too bright and blows white. This is because the charge accumulated by photoelectric conversion in the pixel corresponding to the bright portion exceeds a certain amount and causes overflow. Figure 6
It is a figure which shows the output value with respect to the incident light amount in the conventional solid-state image sensor. Thus, when the amount of incident light exceeds a certain amount, an overflow occurs, and as a result, the effective amount of incident light is limited to a narrow range, and the dynamic range becomes narrow.

In order to avoid such a phenomenon, conventionally, during exposure control, a diaphragm is used to reduce the light amount of the entire subject image, and an electronic shutter is used to discard the electric charge on the way. Since the whole control is applied, the whole image tends to be dark, etc.
After all, the expansion of the dynamic range has not been realized.

Further, as proposed in, for example, Japanese Patent Laid-Open No. 63-306778, an image signal of underexposure and an image signal of overexposure are generated for the same subject, and these image data are generated. There is also known a method of obtaining a single image with an expanded dynamic range by synthesizing two images, but the exposure amount for the same subject is at least 2 for under eyes and over eyes.
Since the exposure work needs to be performed once, there is a problem that the imaging time becomes longer accordingly.

Therefore, the present invention provides a solid-state image pickup device capable of generating an image signal having a high dynamic range in which a highlight does not fly even if there is a large difference in lightness and darkness in a subject image by one-time image pickup. The challenge is to provide.

[0008]

The invention according to claim 1 for solving the above-mentioned problems is a solid-state image pickup device for photoelectrically converting a subject image formed on an image pickup surface to generate an image signal, In the solid-state image pickup device, a member whose transmittance of visible light can be partially changed is arranged on the image pickup surface side of the solid-state image pickup device.

According to a second aspect of the present invention, the member whose transmittance of visible light can be partially changed is a liquid crystal panel whose liquid crystal concentration can be partially changed. Is a solid-state image sensor.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below.

FIG. 1 is a partially cutaway perspective view showing a solid-state image pickup device according to the present invention. The solid-state image sensor 1 is a substrate 1
A large number of pixels 12 each composed of a light receiving element and constituent parts (not shown) are two-dimensionally arranged in the XY directions on the substrate 1, and a large number of terminals 13 are provided on the back surface of the substrate 11. The substrate 11, the pixel 12 and the electrode terminal 13 constitute a conventionally well-known CCD 10.

A surface formed by each pixel 12 constitutes an image pickup surface of a subject image, and a frame 14 is provided in front of this image pickup surface.
The frame 14 is provided with a member whose visible light transmittance can be partially changed.

The member whose transmittance of visible light is partially changeable serves as a so-called shutter for partially changing the incident amount of visible light from the subject image to each pixel 12. Although any member may be used as long as it has a function, in the present embodiment, the liquid crystal panel 15 is used because it is easy to control the transmittance by partially changing the density. This liquid crystal panel 15
A protective cover for protecting the image pickup surface of the CCD 10 can also be used. In FIG. 1, the liquid crystal panel 15 is shown with a part cut away.

In this liquid crystal panel 15, cells 15a are arranged in a lattice pattern between substrates (not shown) capable of transmitting visible light,
Liquid crystal is sealed in each cell 15a.
The density of the liquid crystal inside is partially changeable (Fig. 2).

The size of each cell 15a in the liquid crystal panel 15 may be set such that one cell 15a corresponds to each of a plurality of pixels, for example, four pixels 12, but each pixel 1a.
It is preferable to provide each two in a one-to-one correspondence because more detailed control can be performed. In this embodiment, the latter example is shown.

An address is assigned to each cell 15a, and by designating the address,
For example, two cell groups C1 indicated by diagonal lines in FIG.
The liquid crystal density is increased by turning on each cell 15a forming C2. In each of the cells 15a in the cell groups C1 and C2 whose liquid crystal concentration is increased in this way, the visible light transmittance of the liquid crystal panel 15 is lower than that of each cell 15a in the OFF state as shown in FIG. The amount of light incident on each pixel 12 corresponding to each cell 15a in the ON state is reduced.

The liquid crystal density changed for each cell 15a is not limited to a uniform one, but the density can be adjusted for each cell 15a by appropriately increasing or decreasing according to the amount of incident light on each pixel 12. It is preferable that

Further, in FIG. 1, 16 is a liquid crystal panel 1.
5 is a terminal for controlling the liquid crystal density of each cell 15a in FIG.

As described above, according to the solid-state image pickup device 1, even if there is a large difference in brightness in the subject image, the amount of incident light imaged on the image pickup surface of the CCD 10 in the liquid crystal panel 15 is large. Pixel 12 corresponding to the highlight part
It is possible to increase the liquid crystal concentration of the cell 15a corresponding to the above and partially reduce the transmittance of visible light, and to reduce the amount of incident light to the pixel 12 corresponding thereto. Therefore, the transmittance of the pixel 12 can be changed according to the amount of incident light.
As shown in (A), the relationship between the output value and the incident light amount has a plurality of inclinations. By switching this inclination according to the output, the range of the effective incident light amount can be widened, and the dynamic range can be expanded. As a result, it is possible to generate an image signal having a high dynamic range with a single image pickup, without causing a phenomenon in which an image obtained is partially blown white as in the related art.

It is preferable to add an offset to the output value when changing the transmittance of visible light with respect to the pixel 12 corresponding to the highlight portion where the amount of incident light is large. By doing so, as shown in FIG. 4B, the output value with respect to the amount of incident light is maintained in continuity, so that at the time of subsequent signal processing of the output signal from the solid-state imaging device 1,
Since it is not necessary to detect which pixel has changed the transmittance, it is possible to simplify the processing work.

An example of a control system for picking up a subject image using the solid-state image pickup device 1 will be described with reference to the block diagram shown in FIG. Here, AE (Automatic Exposu)
re: automatic exposure) circuit, an example is shown in which the liquid crystal density of the liquid crystal panel 15 is feedback-controlled from the brightness of a subject image once captured.

Visible light that has entered the solid-state image pickup device 1 through an image pickup optical system including a lens group (not shown) passes through the liquid crystal panel 15 and forms a subject image on the image pickup surface of the CCD 10. Here, the CCD 1 on which the subject image is formed on the imaging surface
Driven by the CCD driver 3 which is driven and controlled by the control unit 2, 0 photoelectrically converts the light amount of each pixel 12 and outputs the accumulated charge as an image signal to the AE circuit 4.

The AE circuit 4 detects the brightness of each pixel 12 in the subject image from the image signal output from the CCD 10 and outputs the detection signal to the control unit 2.

The control unit 2 discriminates from the brightness detection signal sent from the AE circuit 4 for each pixel 12 which pixel 12 has an incident light quantity above a certain level, and at the same time, the pixel 1
The transmittance of visible light to be reduced from the incident light amount in 2 is calculated, and the degree of the liquid crystal density of the liquid crystal panel 15 in the portion corresponding to the pixel 12 is calculated from the calculated value. Next, the liquid crystal panel 15 corresponding to the determined pixels 12
Cell 15a is selected, and the information of the address value of the cell 15a and the density value of the liquid crystal of the cell 15a is output to the liquid crystal driver 5.

The liquid crystal driver 5 adjusts and controls the liquid crystal density of each cell 15a corresponding to the address value sent from the control unit 2 so as to be a specified density, and passes through the liquid crystal panel 15 to cause each CCD 10 to pass. The transmittance of visible light incident on the pixel 12 is partially reduced.

After the partial density adjustment control of the liquid crystal panel 15, the AE circuit 4 again passes through the liquid crystal panel 15 and forms each pixel 1 of the object image formed on the image pickup surface of the CCD 10.
The brightness of each of the two is detected, and if there is a pixel 12 whose incident light amount is equal to or higher than a certain level according to the detection result, the same processing as above is repeated. In addition, as a result of the detection, when the incident light amount in the pixel 12 whose visible light transmittance has been reduced becomes a certain level or less, the image signal output from the CCD 10 is output to thereby obtain an image having a high dynamic range. A signal is generated.

A control system using such a solid-state image pickup device 1 is
It can be applied as a control system of an image sensor in a digital still camera that handles still images and a digital video camera that handles moving images.

[0028]

According to the present invention, a solid-state image pickup capable of generating an image signal having a high dynamic range in which a highlight does not fly even if there is a large difference in light and shade in a subject image by one-time image pickup. An element can be provided.

[Brief description of drawings]

FIG. 1 is a perspective view in which a solid-state image sensor is partially cut away.

FIG. 2 is a partial front view of a liquid crystal panel.

FIG. 3 is a partial sectional view of a solid-state image sensor.

4A and 4B are diagrams showing a relationship between an incident light amount and an output value of the solid-state image sensor according to the present invention.

FIG. 5 is a configuration block diagram showing a control system using a solid-state image sensor.

FIG. 6 is a diagram showing a relationship between an incident light amount and an output value of a conventional solid-state image sensor.

[Explanation of symbols]

1: Solid-state image sensor 10: CCD 11: substrate 12: Pixel 13: Terminal 14: frame 15: Liquid crystal panel 15a: cell 16: Terminal 2: Control unit 3: CCD driver 4: AE circuit 5: LCD driver

Continued front page    F term (reference) 2H088 EA25 EA32 EA37 MA02 MA13                 4M118 AA02 AB01 BA10 GC01 GC14                       GC20 HA04                 5C022 AA00 AC55 CA00                 5C024 CX46 EX56 GY01

Claims (2)

[Claims] 1. A solid-state imaging device for photoelectrically converting an object image formed on an imaging surface to generate an image signal, wherein visible light transmittance is partially changed on the imaging surface side of the solid-state imaging device. A solid-state imaging device, in which possible members are arranged. 2. The solid-state image pickup device according to claim 1, wherein the member whose transmittance of visible light can be partially changed is a liquid crystal panel whose liquid crystal concentration can be partially changed.