JP2000101925A - Pixel defect correction device and method for ccd image pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To correct the pixel defect that is caused by a temperature white flaw. SOLUTION: Position data showing the position of a defective pixel of a CCD image pickup device 3, that is causes a temperature white flaw, are stored in an lock-up table(LUT). The position data show the position of a defective pixel that causes a temperature white flaw, in response to the environmental temperature and shutter speed set in a photographing mode. A defect correction circuit 5 specifies a defective pixel signal, corresponding to the temperature white flaw contained in a pixel signal Pix that is read out the device 3 in a photographing mode, based on the position data corresponding to the actual environmental temperature and shutter speed set in a photographing mode and then corrects the specified defective pixel signal. Thus, the defective pixel can be corrected depending on the occurrence characteristic of the temperature white flaw, that varies dynamically in matching with the temperature or shutter speed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a pixel defect correction device and a pixel defect correction method for correcting a pixel defect of a CCD image sensor.

[0002]

2. Description of the Related Art Conventionally, various types of pixel defects called black flaws, white flaws during lightening, and white flaws in temperature have been known as factors that hinder the performance improvement of CCD image pickup devices.

[0003] A pixel defect called a black flaw is generated by blocking light incident on a pixel due to dust or the like adhering to a light incident surface of the pixel. A pixel defect called a white defect at the time of light is caused by a partial loss of original optical characteristics due to a defect of a color microfilter or a microlens formed on a light incident surface of a pixel. Pixel defects called thermal white flaws are caused by crystal defects of a semiconductor wafer or the like.

[0004] Of these pixel defects, black defects and light-time white defects are static defect factors that occur independently of the operating environment of the CCD image sensor, and are in keeping with the progress of VLSI technology in the manufacturing process. That improvement has been taken.

[0005]

However, unlike the black flaw and the bright white flaw, the temperature white flaw is a dynamic white flaw having a greater effect as the temperature of the CCD imaging device rises and the exposure time becomes longer. It is a serious defect factor, and its generation is also non-uniform.

For example, as a problem due to temperature white flaws,
When the exposure time of the CCD image sensor is increased for photographing in a low illuminance environment such as at night, a noise component is generated in a defective pixel corresponding to a temperature white defect, and a bright point is generated in a reproduced image due to the noise component. As a result, there is a problem that image degradation is caused. Further, as the environmental temperature increases, the above-mentioned noise component increases, which causes image deterioration.

[0007] C that suppresses the occurrence of such thermal white flaws
As a CD image sensor, a cooled CCD image sensor equipped with a cooling device for suppressing the generation of a dark current having a strong temperature dependency is known, but this cooled CCD image sensor is an expensive night-vision camera or bioanalysis. Since it is a special camera applied to an ultra-high-sensitivity camera, it is difficult to mass-produce or downsize the camera, and there is a problem that it cannot be applied to a consumer camera.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has a pixel defect correction device and a pixel defect correction device capable of correcting a temperature white defect without providing a special auxiliary device such as a cooling device. The aim is to provide a method.

[0009]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention relates to a pixel defect correction device for a CCD image pickup device for correcting a white defect of a temperature of a CCD image pickup device. A storage unit for storing in advance correction information obtained by specifying based on the environmental temperature and the shutter speed, and a defective pixel signal corresponding to a temperature white defect in a pixel signal read from the CCD image sensor at the time of photographing, Defect correction means for specifying a defect pixel signal based on the correction information in the storage means corresponding to an actual environmental temperature and a shutter speed at the time of photographing, and performing defect correction on the specified defective pixel signal.

In a method for correcting a pixel defect of a CCD image sensor for correcting a temperature white defect of a CCD image sensor, correction information for specifying a defective pixel causing a temperature white defect is corrected based on an environmental temperature and a shutter speed. Determined in advance, a defective pixel signal corresponding to a temperature white defect in a pixel signal read from the CCD image sensor at the time of shooting, based on the correction information corresponding to the actual environmental temperature and shutter speed at the time of shooting, Defect correction is performed on the specified defective pixel signal.

According to the pixel defect correcting device and the pixel defect correcting method of the CCD image pickup device, when normal photographing is performed under a so-called normal temperature environment and under a generally set shutter speed, Thermal white flaws do not appear so noticeably, and temperature white flaws appear remarkably when taken under high temperature environment or under low shutter speed,
Defect correction of temperature white flaws is performed according to the dynamic generation characteristics of temperature white flaws.

[0012] Thus, when photographing in which thermal white flaws do not appear so remarkably, unnecessary (excessive) defect correction is not performed, so that image quality degradation is prevented, and high-temperature environments or low-temperature flaws in which thermal white flaws become remarkable are prevented. When photographing is performed at a shutter speed, temperature white flaws are reliably corrected.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a configuration when applied to a digital camera.

In FIG. 1, a CCD image pickup device 3 is provided behind an image pickup lens system 1 and a mechanical shutter 2. Further, an output terminal of the CCD imaging device 3 is connected to a pre-circuit 4 having a pre-amplifier circuit and an A / D converter, and a defect correction circuit 5 is connected to an output terminal of the pre-circuit 4. And these mechanical shutter 2 and CCD
The image sensor 3, the pre-circuit 4 and the defect correction circuit 5 operate in synchronization with timing control signals C1 to C4 output from the timing generation circuit 7 in accordance with an instruction from the central control circuit 6 having a microprocessor.

The timing control signal C1 is based on the shutter timing of the mechanical shutter 2 and the shutter speed S.
Set. The timing control signal C2 controls the image pickup operation of the CCD image pickup device 3 so that each signal charge generated in many pixels formed in the CCD image pickup device 3 is
The data is converted into a pixel signal Pix corresponding to the pixel arrangement and read out in a dot-sequential manner.

The timing control signal C3 causes the pre-circuit 4 to perform a process synchronized with the dot sequential reading, amplify each pixel signal Pix read from the CCD image pickup device 3 to a level capable of signal processing, and perform digital pixel Data D
ix.

The timing control signal C4 causes the defect correction circuit 5 to perform a pixel defect correction process in synchronization with the above-described dot-sequential reading timing. That is, the defect correction circuit 5 performs the pixel defect correction on the digital pixel data Dix ′ corresponding to the information of the defective pixel stored in the lookup table LUT described later among the digital pixel data Dix transferred from the pre-circuit 4. The correction is made.

The central control circuit 6 is provided with a look-up table LUT comprising a read-only memory (ROM) in which information on defective pixels is stored in advance, and a digital pixel output via the defect correction circuit 5 A frame memory 8 for storing data, an AE sensor 9 for detecting exposure, a temperature sensor 10, and a strobe unit 11 are connected.

FIG. 2 shows a memory map of the lookup table LUT. In the figure, a lookup table LUT is provided with first to fourth correction information storage areas (A) to (D) for storing four types of position data.

In the first correction information storage area (A), position data (X) indicating the position of each defective pixel causing a black defect is stored.
a1, Ya1), (Xa2, Ya2)... are stored. That is, due to dust adhering to the light incident surface of the pixel,
Correction information for correcting a pixel defect (black defect) caused by blocking incident light on the pixel is stored as position data of the defective pixel.

In the second correction information storage area (B), position data (Xb1, Yb1), (Xb2, Yb2)... Indicating the position of each defective pixel causing a white defect during lightening are stored.
That is, a pixel defect (white defect at the time of light) caused by partially losing the original optical characteristics due to a defect of a color micro filter or a micro lens formed on a light incident surface of a pixel is corrected. Correction information for
It is stored as position data of a defective pixel.

The third correction information storage area (C) and the fourth correction information storage area (D) are used to correct a pixel defect (temperature white flaw) caused by a crystal defect or the like of a semiconductor wafer. The correction information includes position data (Xc1, Yc1), (Xc2, Y) indicating the position of each defective pixel causing a temperature white defect.
c2) ... and position data (Xd1, Yd1), (Xd2, Yd2) ...
Respectively.

That is, the third correction information storage area (C)
The shutter speed S of the mechanical shutter 2 at the time of photographing is higher than a predetermined boundary shutter speed Sth (S ≦ Sth), and the environmental temperature T is lower than the predetermined boundary temperature Tth (T ≦ Tth). When the position data (Xc1,
Yc1), (Xc2, Yc2)... Are stored.

Note that the shutter speed S and the boundary shutter speed Sth refer to the exposure time of the shutter. Therefore, S ≦
Sth means that the shutter exposure time S is shorter than a predetermined boundary exposure time Sth (however, S = Sth is included).

On the other hand, in the fourth correction data storage area (D), the shutter speed S of the mechanical shutter 2 during photographing is lower than the boundary shutter speed Sth (S> St).
h) or the environmental temperature T is higher than the boundary temperature Tth (Tt
Position data (Xd1, Yd1), (Xd2, Yd2) indicating the position of a defective pixel that causes a temperature white defect when h <T).
Is stored. As described above, S> Sth means that the shutter exposure time S is longer than a predetermined boundary exposure time Sth (however, S = Sth is excluded).

However, the position data (Xc1, Yc1), (Xc2, Yc2) of the third correction information storage area (C) and the position data (Xd1, Yd1) of the fourth correction information storage area (D),
(Xd2, Yd2)... Indicate defective pixels that do not overlap with each other.

That is, in the defective pixel which causes the temperature white defect, the noise component increases as the shutter speed S increases, and the noise component increases by about 2 every time the temperature rises by 8 ° C.
It has the property of increasing by a factor of two. Therefore, S ≦ Sth
In addition, a defective pixel that causes a temperature white defect when T ≦ Tth also occurs as a defective pixel when S> Sth or Tth <T. Further, when S ≦ Sth and T ≦ Tth, pixels that do not cause temperature white spots are S> Sth or Tth <
At time T, there is a pixel which becomes a defective pixel for the first time and causes a temperature white defect.

Then, when S> Sth or Tth <T, position data (Xd1, Yd
By storing only (1), (Xd2, Yd2)... In the fourth correction information storage area (D), the position data (Xc1, Yc1), (Xc2, Yc2)
Are not overlapped with the defective pixels corresponding to (Xd1, Yd1), (Xd2, Yd2),... In the fourth correction information storage area (D).

Then, the frequency of occurrence of defective pixels that cause temperature white flaws when the environmental temperature T and the shutter speed S are variously changed is measured. The upper limit of the ambient temperature of the
The boundary shutter speed Sth and the boundary temperature Tth are determined in consideration of the characteristic characteristic of the temperature white flaw that the amount of the noise component generated by the temperature white flaw increases about twice every time the temperature rises by 8 ° C. I have. For example, the boundary shutter speed Sth is set to 1/15 second, and the boundary temperature Tth is set to 50 ° C.

Next, the pixel defect correcting operation of the digital camera having the above configuration will be described. First, the central control circuit 6 determines the environmental temperature T at the time of shooting based on the measurement output of the temperature sensor 10, and further, in the automatic exposure mode,
The shutter speed S is automatically determined based on the measurement output of the AE sensor 9 and the presence / absence of strobe shooting. In the manual exposure mode, the shutter speed S specified by the operator is set.

Further, the central control circuit 6 determines the ambient temperature T and the boundary temperature Tth, the shutter speed S and the boundary shutter speed S
th, and the condition for defect correction is S ≦ Sth
In addition, it is determined whether T ≦ Tth, S> Sth or Tth <T.

As shown in FIG. 3, S ≦ Sth and T ≦ Tth
(Hereinafter, referred to as a first defect correction condition), defect correction is performed based on the position data stored in the first to third correction information storage areas (A) to (C). ,
If S> Sth or Tth <T (hereinafter, referred to as a second defect correction condition), the above-described positions stored in the first to fourth correction information storage areas (A) to (D) are used. Initial setting is performed so that defect correction is performed based on the data.

Then, in synchronism with the pressing of the shutter release button by the operator, each timing control signal C1 to C4 is output from the timing generation circuit 7, and the photographing is performed at the above shutter speed S. Further, a pixel signal Pix generated at each pixel of the CCD image sensor 3 is converted into digital pixel data Dix by the pre-circuit 4 and transferred to the frame memory 8 via the defect correction circuit 5.

Here, when the first defect correction condition is initially set, the defect correction circuit 5 stores the digital pixel data Dix ′ read from the defective pixel in the first to third correction information storage areas (A). (C) to identify based on the position data stored.

Then, the normal digital pixel data Dix is stored in the frame memory 8 as it is, and the digital pixel data Dix ′ corresponding to the pixel defect is stored in the frame memory 8.
Normal digital pixel data Dix read before and after that
After performing a defect correction such as replacing the simple average value of the pixel data with the digital pixel data Dix ′ or multiplying the digital pixel data Dix ′ by a predetermined weighting coefficient, the digital pixel data Dix ′ is stored in the frame memory 8.

On the other hand, when the second defect correction condition is initially set, the defect correction circuit 5 stores the digital pixel data Dix ′ read from the defective pixel in the first to fourth correction information storage areas (A ) To (D) are identified based on the position data stored therein, and the same defect correction as in the case of the first defect correction condition is performed. That is, when the second defect correction condition is initially set, in addition to the defect correction based on the position data in the first to third correction information storage areas (A) to (C), the fourth correction is performed. Defect correction based on position data in the information storage area (D) is additionally performed.

As described above, according to the present embodiment, the correction of the pixel defect is performed in synchronization with the readout timing of the pixel signal Pix, so that the delay of the photographing process can be prevented.

Further, since the defect correction is performed on the digital pixel data Dix using the environmental temperature T and the shutter speed S as parameters, the temperature white defect which is a dynamic defect factor is accurately corrected, and the image quality is improved. Can be done.

In particular, under the first defect correction condition, the defect correction of the temperature white defect is performed based on the correction information in the third correction information storage area (C). Under the second defect correction condition, the third and third defect correction conditions are used. Since the defect correction of the temperature white defect is performed based on the correction information in the correction information storage areas (C) and (D) of No. 4, the defect correction according to the temperature white defect generation characteristic can be performed.

That is, the temperature white flaw does not appear so remarkably when normal photographing is performed under a normal temperature environment and under a generally set shutter speed, and is different from that in normal photographing. It has a characteristic that becomes remarkable when shooting is performed under an environment or a low shutter speed. Then, the defect correction condition of the temperature white defect is changed to the boundary temperature T.
Since the first and second defect correction conditions are divided on the basis of th and the boundary shutter speed Sth, defect correction can be performed in accordance with the temperature white spot generation characteristic.

As a result, during normal photographing, unnecessary (excessive) defect correction is not performed, so that image quality deterioration can be prevented, and when photographing is performed in a high-temperature environment or a low shutter speed, the temperature is low. White scratches can be reliably corrected.

In the above description, the case where the boundary temperature Tth and the boundary shutter speed Sth are set one by one to perform the defect correction of the temperature white defect has been described.
The defect correction may be performed based on a plurality of correction conditions divided by a plurality of threshold temperatures and a plurality of boundary shutter speeds Sth. According to such a configuration, more precise defect correction can be performed in accordance with the temperature white spot generation characteristics.

The above lookup table LUT
Has been described above, the position data of the defective pixel is stored in advance, but the present invention is not limited to such a configuration. For example, correction data of a bit string composed of flag data “1” indicating a defective pixel and flag data “0” indicating a normal pixel is stored in a semiconductor memory in correspondence with the arrangement of pixels formed in the CCD image sensor 3. The defective pixel signal read from the defective pixel may be specified by sequentially counting up the address of the semiconductor memory in synchronization with the read timing of the pixel signal Pix.

A look-up table storing correction information or the above-mentioned semiconductor memory may be provided in association with the central control circuit in the camera. However, a look-up table storing correction information specific to each CCD image pickup device may be provided. A table or the like may be integrated with the CCD image sensor in advance. Thus C
When a lookup table or the like is integrated with the CD imaging device, reliable correction information can be obtained for each CCD imaging device even if the characteristics of pixel defects differ for each CCD imaging device due to inter-device variations or the like. For this reason, it is not necessary to perform an adjustment for specifying a defective pixel for each CCD image pickup device in the camera manufacturing process, and it is possible to obtain an effect that the manufacturing process can be simplified.

[0045]

As described above, according to the present invention, when normal photographing is performed under a so-called normal temperature environment and under a generally set shutter speed, the temperature white flaw is not so large. The temperature white flaw defect correction is performed in accordance with the dynamic generation characteristic of the temperature white flaw, in which the temperature white flaw appears remarkably when photographing is performed in a high temperature environment or a low shutter speed without being noticeable. Since the correction is performed, it is possible to reliably and appropriately correct the defect of the temperature white spot.

Further, when photographing in which thermal white flaws do not appear so remarkably, unnecessary (excessive) defect correction is not performed, so that image quality deterioration can be prevented and high temperature environments in which thermal white flaws become remarkable. Alternatively, when photographing is performed at a low shutter speed, temperature white flaws can be reliably corrected.

Further, since white spots in temperature can be corrected without providing a special device such as a conventional cooled CCD image sensor, mass production and miniaturization are possible. Can be applied to

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of an embodiment in which the present invention is applied to a digital camera.

FIG. 2 is an explanatory diagram showing a memory map of a lookup table storing correction information.

FIG. 3 is an explanatory diagram showing correction conditions for pixel defects.

[Explanation of symbols]

 2. Mechanical shutter 3. CCD image pickup device 5. Defect correction circuit LUT ... Look-up table

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5C024 AA01 CA05 CA09 EA01 FA01 FA09 FA11 GA11 HA24 HA25 5C077 LL02 LL13 MM03 PP05 PP43 PP77 PQ08 PQ23

Claims (5)

[Claims] 1. A pixel defect correction device for a CCD image pickup device for correcting a temperature white defect of a CCD image pickup device, wherein the correction is performed by specifying a defective pixel causing a temperature white defect based on an environmental temperature and a shutter speed. Storage means for storing information in advance; and a storage means for storing a defective pixel signal corresponding to a temperature white defect in a pixel signal read from the CCD image pickup device at the time of shooting, corresponding to an actual environmental temperature and a shutter speed at the time of shooting. And a defect correcting unit for performing a defect correction on the specified defective pixel signal based on the correction information therein. 2. A pixel defect correction device for a CCD image pickup device for correcting a temperature white defect of a CCD image pickup device, wherein a defective pixel causing a temperature white defect when photographing is performed at a normal environmental temperature and a normal shutter speed is specified. First
Storage means for storing beforehand correction information and second correction information for specifying defective pixels that cause white spots in the image when photographing is performed at a high environmental temperature or a low shutter speed. A defective pixel signal corresponding to the temperature white defect in the read pixel signal is specified based on the first and second correction information in the storage unit corresponding to the actual environmental temperature and the shutter speed at the time of the photographing. ,
A defect correction unit that performs defect correction on the specified defective pixel signal. 3. The apparatus according to claim 1, wherein said storage means is integrated with said CCD image pickup device. 4. A method for correcting a pixel defect of a CCD image sensor for correcting a temperature white defect of a CCD image sensor, comprising: correcting information for identifying a defective pixel causing a temperature white defect based on an environmental temperature and a shutter speed. A defective pixel signal corresponding to a temperature white defect in a pixel signal read out from the CCD image sensor at the time of shooting is specified in advance based on the correction information corresponding to the actual environmental temperature and shutter speed at the time of shooting, A defect correction method for a CCD image pickup device, comprising: performing a defect correction on the specified defective pixel signal. 5. A pixel defect correction method for a CCD image pickup device for correcting a temperature white defect of a CCD image pickup device, wherein a defective pixel causing a temperature white defect when photographing is performed at a normal environmental temperature and a normal shutter speed is specified. First
, And second correction information for specifying a defective pixel that causes a temperature white defect when a photograph is taken at a high environmental temperature or a low shutter speed, and a pixel signal read out from the CCD image pickup device at the time of photographing The defective pixel signal corresponding to the medium temperature white defect is specified based on the first and second correction information corresponding to the actual environmental temperature and the shutter speed at the time of the photographing. A pixel defect correction method for a CCD image pickup device, wherein defect correction is performed.