JPS62141868A - Uneven picture correcting circuit - Google Patents

Abstract

PURPOSE:To obtain a uniform picture by subtracting a signal component comprising a dark current from an image pickup signal outputted from a solid-state image sensor so as to eliminate the image pickup signal thereby correcting uneven picture due to uneven signal component due to the dark current. CONSTITUTION:The signal component SD comprising the dark current stored in a frame memory 7 in advance is subtracted at each picture element from the image pickup signal SO outputted from the solid-state image sensor 1 and an image pickup signal SO' eliminated with the signal component SD is obtained from a subtractor 6. Thus, a uniform picture without uneven picture due to the unevenness of the signal component SD caused by the dark current is obtained. For example, when the picture by the image pickup signal SO has an uneven picture as shown in figure A, since the picture by the signal component SD is as shown in figure B, the picture by the image pickup signal SO' is a uniform picture without uneven picture as shown in figure C.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an image unevenness correction circuit that corrects image unevenness caused by dark current flowing through a solid-state image sensor.

[Summary of the invention]

The present invention provides an image unevenness correction circuit for correcting image unevenness due to unevenness of signal components due to dark current flowing on each pixel of a solid-state image sensor, in which signal components due to dark current for each predetermined pixel block are stored in a memory, By subtracting the memory output from the imaging signal of the solid-state image sensor,
Corrects image unevenness caused by uneven signal components due to dark current,
This allows a uniform image to be obtained.

[Conventional technology]

2. Description of the Related Art Conventionally, solid-state imaging devices configured using a solid-state image sensor formed of, for example, a CCD (charge-coupled device) have been proposed. In this case, if there is unevenness (dark unevenness) in the dark current flowing through each pixel, unevenness will occur in the signal component due to the dark current included in the imaging signal, resulting in unevenness in the image.

[Problem that the invention seeks to solve]

In recent years, with the demand for higher sensitivity, the gain ff of AGC amplifiers has increased, and this image unevenness has become a problem. This image unevenness is noticeable on dark screens.

For example, in a photographing device using a plurality of solid-state image sensors, countermeasures such as using a combination of sensors with similar dark current unevenness trends have been taken, but these have not been sufficient.

In view of this point, the present invention corrects image unevenness due to unevenness in signal components due to dark current, thereby making it possible to obtain a uniform image.

[Means for solving problems]

The present invention includes a memory (7) that stores signal components SD due to dark current for each predetermined pixel block (for example, for each pixel) of a solid-state image sensor (1). And an image signal S output from the solid-state image sensor (1). By subtracting the output of the memory (7) from the output of the memory (7), image unevenness due to unevenness of the signal component sD due to dark current is corrected.

[Effect]

In the above configuration, the imaging signal S is output from the solid-state image sensor (1). Since the output of the memory (7), that is, the signal component sD due to the dark current is subtracted, the image signal so' after the subtraction process no longer contains the signal component due to the dark current, and this signal component has no unevenness. Even if there is, image unevenness will no longer occur.

[Embodiment] Hereinafter, an embodiment of the present invention will be described with reference to FIG.

In the figure, (1) is a solid-state image sensor, for example, a well-known interline transfer type CCD image sensor as shown in FIG. 2 is used.

In FIG. 2, Ql is each light receiving part arranged in a matrix corresponding to each pixel in an odd field, and Ql is each light receiving part arranged in a matrix corresponding to each pixel in an even field. A light receiving section, (to) h each of the above light receiving sections ea
(24) is a horizontal transfer register section provided on the output side of the vertical transfer register section (a);
(C) and (C) are respective topology sections provided between each light receiving section e◇, (A) and the vertical transfer register section (to).

Based on the vertical synchronization signal, the transfer sections f-) and (a) of the solid-state image sensor (1) are opened at the beginning of the odd and even fields, and the odd and Even field signal charges are transferred to the vertical transfer register unit. and,
The signal charge transferred to the vertical transfer register unit at the beginning of each field is sequentially transferred to the horizontal transfer register unit (c) for one horizontal line every horizontal period by the vertical transfer lock synchronized with the horizontal synchronization signal. and sequentially read out via this horizontal transfer register section. That is, the image signal is output from this horizontal transfer register section.

In addition, on the front side of the solid-state image sensor (1), for example, a color filter (2) and an iris mechanism (3) as shown in FIG.
) and a lens system (4) are arranged, and a solid-state image sensor (
1) outputs red, green, and real dot signals in sequence.

The imaging signal So from the solid-state image sensor (1) is supplied to a sample and hold circuit (5), and after the signals obtained from each light receiving section are sampled and held, the signal So is sent to a subtracter (6).
).

In addition, the subtracter (6) receives a signal component sD, which is caused by the dark current of each pixel of the solid-state image sensor (1), read from the frame memory (7) made of, for example, FROM, and is input to the D/A converter. and Gui control amplifier (9)
Supplied via. Reading of the frame memory (7) or the rough signal component SO is performed in synchronization with the imaging signal So output from the solid-state image sensor (1) under the control of the controller α6.

Incidentally, writing of the signal component SD into the frame memory (7) is performed as shown in FIG. In FIG. 4, parts corresponding to those in FIG. 1 are marked with the same symbol, and detailed explanation thereof will be omitted.

That is, the solid-state image sensor (1) captures an image in a completely black state. At this time, solid-state image sensor (1)
A signal component SD due to dark current is output from .

Ru. This signal component SD is supplied to the frame memory (7) via the sample-and-hold circuit (5) and the ψ converter at-, and is sequentially written, for example, pixel by pixel. Writing to the frame memory (7) is performed under the control of the controller (6) in synchronization with the output of the solid-state image sensor (1).

Returning to Figure 1, (13 is the solid-state image sensor (1)
The temperature detection signal ST from this temperature sensor α1 is supplied to the controller (10).The temperature characteristics of the dark current of the solid-state image sensor (1) are as shown in FIG. It is known that the dark current changes greatly depending on the temperature. For example, the amount of dark current changes from T0 to D4 from T to T4. In this way, since the amount of dark current changes greatly depending on the temperature, the signal component sD due to the dark current
will also change proportionately. Therefore, although not mentioned above, the signal component sD is stored in the frame memory (7) at a high temperature (for example, T4), and the gain is controlled by the controller αQ based on the detection signal sT from the temperature sensor α→. Ann f (9)
The gain of the frame memory (7) is controlled, and the level of the signal component sD from the frame memory (7) is corrected according to the temperature.

In the subtracter (6), the solid-state image sensor (
1) imaging signal S. Then, the signal component sD due to the dark current read out from the frame memory (7) is subtracted, and the subtracter (6) produces an image signal S from which the signal component SD has been removed.
. ′ is obtained. This imaging signal S. ' is AGC amplifier α
- is supplied to the sample and hold circuit (to).

As mentioned above, the output of the solid-state image sensor (1) is red,
The green and blue points are 11111 primary signals, sampled and held sequentially at each color signal position, and the red,
Green and blue primary color signals R, G, and B are output.

These three primary color signals R, G, and B are supplied to the matrix circuit α via the white balance amplifier α→ and the gamma correction circuit α. Then, a luminance signal Y and a red color difference signal RY are output from this matrix circuit α.

The blue difference signal B-Y is supplied to the color encoder α■,
From this color encoder (to) to terminal -, for example, NT
An SC-based composite color video signal Sv is output.

As described above, in this example, the imaging signal S is output from the solid-state image sensor (1). The signal component SD due to the dark current stored in advance in the frame memory (7) is subtracted for each pixel, and the subtractor (6) outputs an image signal S from which the signal component SD has been removed. ′ is obtained. Therefore, according to this example, the image 1 due to the unevenness of the signal component S due to the dark current
A uniform image without unevenness can be obtained. For example, when the image produced by the imaging signal S0 has unevenness as shown in FIG. 6A, the image produced by the signal component SD becomes as shown in FIG. This results in a uniform image with no image unevenness.

In the example shown in FIG. 1, the signal component SD due to the dark current of each pixel of the solid-state image sensor (1) is stored in the frame memory (7), and the signal component SD from the image signal S0 output from the solid-state image sensor (1) is stored in the frame memory (7). , the signal component Sr) from the frame memory (7) is subtracted pixel by pixel, but
When considering image unevenness correction for a large area, the signal component SD due to the dark current of each predetermined pixel block of the solid-state image sensor (1) is stored in the memory, and
) is output from the image signal S. The signal component SD from the memory may be subtracted for each predetermined pixel block. In this case, a two-dimensional low-pass filter may be disposed after the ψ converter Qυ in FIG. 4, and the signal component SD of each predetermined pixel block subjected to two-dimensional processing may be stored in advance in the memory. This makes it possible to reduce memory capacity.

Next, FIG. 7 shows another embodiment of the present invention,
This allows the user to correct image unevenness at any desired time. In FIG. 7, parts corresponding to those in FIG. 1 are designated by the same reference numerals, and detailed explanation thereof will be omitted.

In the figure, an imaging signal S from a solid-state image sensor (1). is the subtracter (
6).

Further, the subtracter (6) receives a signal component SD, which is caused by the dark current of each pixel of the solid-state image sensor (1), read from the frame memory (1) made of, for example, a RAM, and is input to the D/A converter 0. ]). Signal component S from this frame memory (g). The image signal S output from the solid-state image sensor (1) is read out under the control of the controller Oa. This is done in sync with the

The iris mechanism (3) is controlled by the controller 0, and is brought into a light blocking state when, for example, an automatic reset type push button switch (c) connected to the controller 0 is turned on. When the iris mechanism (3) is in the light blocking state, the solid-state image sensor (1) outputs a signal component SD due to dark current. This signal component SD is supplied to a frame memory (g) via a sample and hold circuit (5) and a converter (b), and is sequentially written, for example, pixel by pixel. Writing to the frame memory (1) is performed under the control of the controller 2 in synchronization with the output of the solid-state image sensor (1).

In this way, when the push button switch (G) is turned on, the signal component SD due to the dark current at that time is written into the frame memory (G). Then, when the push button switch (to) returns to OFF, the iris mechanism (3) is returned to the light passing state as described above, and the solid-state image sensor (
1) is the imaging signal S. At the same time, the signal component SD is read out from the frame memory (7) under the control of the controller 0.

In the subtracter (6), the image signal S of the solid-state image sensor (1) is input. Thus, the signal component SD due to the dark current read out from the frame memory (7) is subtracted, and the subtracter (6) obtains an imaging signal 80' from which the signal component SD has been removed. The rest of the structure is the same as the example shown in FIG.

Also in the example of FIG. 7, the subtracter (6) outputs the image signal S from which the signal component SD has been removed. ', it is possible to obtain a uniform image free from image unevenness caused by unevenness in the signal component SD due to dark current. Furthermore, according to the example in FIG. 7, the signal component SD at the time when the user turns on the push button switch (to) is written and stored in the memory, so that image unevenness can be corrected at the time the user desires. becomes possible.

In the example shown in FIG. 7, the signal component SD due to the dark current for each pixel of the solid-state image sensor (1) is stored in the frame memory (1), and correction is performed for each pixel. When considering image unevenness correction for a large area, correction may be performed for each predetermined pixel block. In this case, in FIG. 7, a two-dimensional low and p4 filter is placed after the converter (b), and the signal component SD of each predetermined pixel block subjected to two-dimensional processing is stored in advance in the seven-mole (1). good. This makes it possible to reduce memory capacity.

In the example shown in Fig. 1 above, if there is sufficient memory capacity, it is possible to prepare a plurality of memories storing signal components SD due to dark current under each temperature, and to switch between them according to the output of the temperature sensor (2). You can also do this. Furthermore, in addition to the above-described embodiments, the correction methods shown in FIG. 1 and FIG. 7 may be used in combination. Furthermore, the above embodiment is an example applied to a so-called single-plate type in which one solid-state image sensor is used, but a two-plate or three-plate type in which two or three solid-state image sensors are used. The same can be applied to

Furthermore, the above embodiment is an example in which the solid-state image sensor (1) is of the interline transformer 77 type.
The present invention can be similarly applied to frame transfer systems. Further, although the above-mentioned embodiment is an example constructed using a solid-state image sensor (1) formed of a CCD, the present invention can be constructed using another solid-state image sensor formed of a MOS or the like. The same can be applied to

〔Effect of the invention〕

According to the present invention described above, since the signal component due to dark current is subtracted and removed from the imaging signal output from the solid-state image sensor, image unevenness due to uneven signal component due to dark current can be effectively eliminated. It can be corrected and a uniform image can be obtained.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an example of the present invention, Fig. 2 is a block diagram of an example of a solid-state image sensor, Fig. 3 is a block diagram of a color filter, and Figs. Diagram for explanation,
FIG. 7 is a configuration diagram showing another embodiment of the present invention. (1) is a solid-state image sensor, (6) is a subtractor, (7)
is frame memory, (9) high gain control amplifier, ! IO) is a controller, and α] is a temperature sensor.

Claims (1)

[Claims] A memory is provided for storing a signal component due to a dark current for each predetermined pixel block of the solid-state image sensor, and the output of the memory is subtracted from the image pickup signal of the solid-state image sensor to eliminate image unevenness due to unevenness of the signal component due to the dark current. An image unevenness correction circuit that performs image unevenness correction.