JP4097332B2 - Pixel defect correction apparatus and pixel defect correction method for CCD image sensor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
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]
[Prior art]
Conventionally, various pixel defects called black scratches, bright white scratches, and thermal white scratches are known as factors that hinder the performance improvement of CCD image pickup devices.
[0003]
A pixel defect called a black flaw occurs when incident light on the pixel is blocked due to dust or the like adhering to the light incident surface of the pixel. Pixel defects called white defects at the time of light are caused by partial loss of original optical characteristics due to defects in color microfilters and microlenses formed on the light incident surface of the pixels. Pixel defects called temperature white scratches are caused by crystal defects of a semiconductor wafer.
[0004]
Among these pixel defects, black scratches and bright white scratches are static defect factors that occur regardless of the operating environment of the CCD image sensor, and improvements can be made in step with the progress of VLSI technology in the manufacturing process. Has been taken.
[0005]
[Problems to be solved by the invention]
However, temperature white scratches, unlike black scratches and bright white scratches, are dynamic defect factors that increase as the temperature of the CCD image sensor increases and the exposure time increases. Occurrence is also uneven.
[0006]
For example, as a problem due to temperature white scratches, if the exposure time of the CCD image sensor is increased in order to shoot in a low-light environment such as at night, a noise component is generated in a defective pixel corresponding to the temperature white scratch, and this noise component As a result, a bright spot is generated in the reproduced image, resulting in a problem of image deterioration. In addition, as the environmental temperature increases, the above noise components increase, leading to image degradation.
[0007]
As a CCD image pickup device that suppresses the occurrence of such white scratches, a cooled CCD image pickup device that includes a cooling device for suppressing the occurrence of dark current that is strongly temperature dependent is known. The element is a special device that is applied to expensive night vision cameras and ultra-high sensitivity cameras for bioanalysis, etc., so it is difficult to mass-produce and miniaturize it, and it cannot be applied to consumer cameras. .
[0008]
The present invention has been made in view of such problems, and provides a pixel defect correction apparatus and a pixel defect correction method capable of correcting temperature white scratches without providing a special auxiliary device such as a cooling device. The purpose is to do.
[0009]
[Means for Solving the Problems]
In order to achieve such an object, the present invention is a pixel defect correction device for a CCD image sensor that corrects temperature white defects in the CCD image sensor, and shoots under a first defect correction condition at a normal ambient temperature and a normal shutter speed. If the image is taken under the second defect correction condition with a high ambient temperature or a low shutter speed, the defective pixel that causes the temperature white defect is identified. Storage means for preliminarily storing second correction information that does not overlap with the first correction information for identifying the defective pixel signal corresponding to the temperature white defect in the pixel signal read from the CCD image sensor at the time of shooting. , wherein when the actual ambient temperature and the shutter speed during shooting is the first defect correction condition is determined based only on the first correction information in said storage means, said shooting Specified based on the actual ambient temperature and the first correction information and the second correction information in said storage means when the shutter speed is the second defect correction conditions when was the specific Defect correction means for performing defect correction on the defective pixel signal is provided.
[0010]
Further, in a pixel defect correction method for a CCD image sensor that corrects temperature white defects in the CCD image sensor, temperature white defects are generated when photographing is performed under the first defect correction condition at a normal environmental temperature and a normal shutter speed. First correction information for specifying a defective pixel, and first correction information for specifying a defective pixel that causes a temperature white defect when shooting is performed under a second defect correction condition with a high ambient temperature or a low shutter speed. Previously obtained non-overlapping second correction information, and the defective pixel signal corresponding to the temperature white defect in the pixel signal read from the CCD image pickup device at the time of shooting is determined based on the actual environmental temperature and shutter speed at the time of shooting. in the first, if a defect correction condition specified based only on the first correction information, the actual environmental temperature and shutter speed the second defect correction conditions at the time of the photographing If that was to perform the first specified based on the correction information and the second correction information, the identified defective pixel signal defect corrected for.
[0011]
According to the pixel defect correction device and the pixel defect correction method for these CCD image sensors , normal imaging is performed under a first defect correction condition under a so-called normal temperature environment and a generally set shutter speed. In such a case, the temperature white scratches do not appear so prominently, and the temperature white scratches appear prominently when shooting is performed under the second defect correction condition in a high temperature environment or under a low shutter speed. In accordance with the dynamic generation characteristics, temperature white defect defect correction is performed.
[0012]
As a result, unnecessary (excessive) defect correction is not performed at the time of shooting under the first defect correction condition in which temperature white scratches do not appear so conspicuously, so image quality deterioration is prevented and temperature white scratches are noticeable. When shooting is performed under the second defect correction condition under the appearing high temperature environment or low shutter speed, the temperature white defect is reliably corrected.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing a configuration when applied to a digital camera.
[0014]
In the figure, a CCD imaging device 3 is disposed behind an imaging lens system 1 and a mechanical shutter 2. Furthermore, a pre-amplifier 4 and a pre-circuit 4 having an A / D converter are connected to the output terminal of the CCD image pickup device 3, and a defect correction circuit 5 is connected to the output terminal of the pre-circuit 4. The mechanical shutter 2, the CCD image pickup device 3, the pre-circuit 4 and the defect correction circuit 5 are supplied to timing control signals C1 to C4 output from the timing generation circuit 7 in accordance with instructions from the central control circuit 6 having a microprocessor. Operates synchronously.
[0015]
The timing control signal C1 sets the shutter timing and shutter speed S of the mechanical shutter 2. The timing control signal C2 controls the image pickup operation of the CCD image pickup device 3 to convert each signal charge generated in a large number of pixels formed in the CCD image pickup device 3 into a pixel signal Pix corresponding to the pixel arrangement. To read out dot-sequentially.
[0016]
The timing control signal C3 causes the pre-circuit 4 to perform processing synchronized with point-sequential readout, amplifies each pixel signal Pix read from the CCD image pickup device 3 to a level at which signal processing is possible, and converts it into digital pixel data Dix. Convert it.
[0017]
The timing control signal C4 causes the defect correction circuit 5 to perform pixel defect correction processing in synchronization with the dot sequential readout timing. That is, the defect correction circuit 5 performs pixel defect on the digital pixel data Dix ′ corresponding to information on defective pixels stored in a lookup table LUT to be described later, among the digital pixel data Dix transferred from the front circuit 4. Correction is applied.
[0018]
The central control circuit 6 includes a look-up table LUT composed of a read-only memory (ROM) in which information on defective pixels is stored in advance, and further stores digital pixel data output via the defect correction circuit 5. A frame memory 8 for detecting the exposure, an AE sensor 9 for detecting exposure, a temperature sensor 10 and a strobe unit 11 are connected.
[0019]
FIG. 2 shows a memory map of the lookup table LUT. In the figure, the lookup table LUT is provided with first to fourth correction information storage areas (A) to (D) for storing four types of position data.
[0020]
In the first correction information storage area (A), position data (Xa1, Ya1), (Xa2, Ya2)... Indicating the position of each defective pixel causing black flaws is stored. That is, correction information for correcting pixel defects (black flaws) caused by blocking incident light on the pixel due to dust or the like adhering to the light incident surface of the pixel is the position data of the defective pixel. It is remembered.
[0021]
In the second correction information storage area (B), position data (Xb1, Yb1), (Xb2, Yb2)... Indicating the position of each defective pixel that causes white defects at the time of light is stored. That is, a pixel defect (white defect at light) caused by partial loss of original optical characteristics due to a defect of a color microfilter or microlens formed on the light incident surface of the pixel is corrected. Correction information is stored as defective pixel position data.
[0022]
In the third correction information storage area (C) and the fourth correction information storage area (D), there is correction information for correcting pixel defects (temperature flaws) caused by crystal defects of the semiconductor wafer. Are stored as position data (Xc1, Yc1), (Xc2, Yc2)... And position data (Xd1, Yd1), (Xd2, Yd2).
[0023]
That is, in the third correction information storage area (C), the shutter speed S of the mechanical shutter 2 at the time of shooting is higher than the predetermined boundary shutter speed Sth (S ≦ Sth), and the environmental temperature T is predetermined. Further, position data (Xc1, Yc1), (Xc2, Yc2)... Indicating the position of the defective pixel causing the temperature flaw when the temperature is lower than the boundary temperature Tth (T ≦ Tth) is stored.
[0024]
The shutter speed S and the boundary shutter speed Sth refer to the shutter exposure time. Therefore, S ≦ Sth means that the exposure time S of the shutter is shorter than the predetermined boundary exposure time Sth (including S = Sth).
[0025]
On the other hand, in the fourth correction data storage area (D), the shutter speed S of the mechanical shutter 2 at the time of shooting is lower than the boundary shutter speed Sth (S> Sth), or the environmental temperature T is higher than the boundary temperature Tth ( Position data (Xd1, Yd1), (Xd2, Yd2)... Indicating the position of a defective pixel that causes a temperature white defect when Tth <T) is stored. Similarly to the above, S> Sth means that the exposure time S of the shutter is longer than the predetermined boundary exposure time Sth (except S = Sth).
[0026]
However, the position data (Xc1, Yc1), (Xc2, Yc2)... In the third correction information storage area (C) and the position data (Xd1, Yd1), (Xd2,. Yd2)... Indicates defective pixels that do not overlap each other.
[0027]
That is, a defective pixel that causes a white spot in the temperature has a characteristic that the noise component increases as the shutter speed S increases, and the noise component increases approximately twice each time the time temperature increases by 8 ° C. For this reason, a defective pixel that causes a white temperature defect when S ≦ Sth and T ≦ Tth occurs as a defective pixel when S> Sth or Tth <T. In addition, when S ≦ Sth and T ≦ Tth, a pixel that does not generate a temperature white defect becomes a defective pixel only when S> Sth or Tth <T, and causes a temperature white defect.
[0028]
Therefore, only the position data (Xd1, Yd1), (Xd2, Yd2)... Which become the first significant defective pixels when S> Sth or Tth <T is stored in the fourth correction information storage area (D). , Defective pixels corresponding to the position data (Xc1, Yc1), (Xc2, Yc2)... In the third correction information storage area (C), and (Xd1, Yd1 in the fourth correction information storage area (D). ), (Xd2, Yd2)... Are not overlapped with defective pixels.
[0029]
Then, when the environmental temperature T and the shutter speed S are changed variously, the frequency of occurrence of defective pixels causing white flaws is actually measured, and the normal environmental temperature when the digital camera is used is obtained as a result of the actual measurement. Boundary shutter speed Sth and boundary temperature, taking into account the characteristic of temperature white scratches, such as the upper limit temperature of the temperature and the amount of noise components generated by temperature white scratches increasing by about twice each time the temperature rises by 8 ° C Tth is decided. For example, the boundary shutter speed Sth is set to 1/15 seconds, and the boundary temperature Tth is set to 50 ° C.
[0030]
Next, the pixel defect correction operation of the digital camera having such a 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, automatically based on the measurement output of the AE sensor 9 and the presence or absence of flash photography. In the manual exposure mode, the shutter speed S designated by the operator is set.
[0031]
Further, the central control circuit 6 compares the environmental temperature T and the boundary temperature Tth, the shutter speed S and the boundary shutter speed Sth, respectively, and whether the condition for defect correction corresponds to S ≦ Sth and T ≦ Tth, or S> It is determined whether Sth or Tth <T is satisfied.
[0032]
As shown in FIG. 3, when S ≦ Sth and T ≦ Tth (hereinafter referred to as the first defect correction condition), the first to third correction information storage areas (A) to (C) are stored. When the defect is corrected based on the stored position data and S> Sth or Tth <T (hereinafter referred to as the second defect correction condition), the first to fourth correction information storage areas are used. Initial setting is performed so that defect correction is performed based on the position data stored in (A) to (D).
[0033]
Then, in synchronization with the pressing of the shutter release button by the operator, timing control signals C1 to C4 are output from the timing generation circuit 7, and shooting is performed under the shutter speed S described above. Further, the pixel signal Pix generated in each pixel of the CCD image pickup device 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.
[0034]
Here, when the first defect correction condition is initially set, the defect correction circuit 5 converts the digital pixel data Dix ′ read from the defective pixel into the first to third correction information storage areas (A) to (C). ) Is identified based on the position data stored in (1).
[0035]
The normal digital pixel data Dix is stored in the frame memory 8 as it is, and for the digital pixel data Dix ′ corresponding to the pixel defect, the simple average value of the normal digital pixel data Dix read before and after the digital pixel data Dix ′ After performing defect correction such as replacement with the data Dix ′ or multiplying the digital pixel data Dix ′ by a predetermined weighting coefficient, the data is stored in the frame memory 8.
[0036]
On the other hand, when the second defect correction condition is initialized, the defect correction circuit 5 converts the digital pixel data Dix ′ read from the defective pixel into the first to fourth correction information storage areas (A) to ( Identification is performed based on the position data stored in (D), and defect correction similar to that in the case of the first defect correction condition is performed. That is, when the second defect correction condition is initially set, the fourth correction is performed in addition to the defect correction based on the position data in the first to third correction information storage areas (A) to (C). Defect correction based on position data in the information storage area (D) is additionally performed.
[0037]
As described above, according to the present embodiment, the pixel defect is corrected in synchronization with the readout timing of the pixel signal Pix, so that a delay in the photographing process can be prevented.
[0038]
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, it is possible to accurately correct the temperature white defect, which is a dynamic defect factor, and to improve the image quality. it can.
[0039]
In particular, under the first defect correction condition, temperature white defect defect correction is performed based on the correction information in the third correction information storage area (C), and under the second defect correction condition, the third and fourth corrections are performed. Since the defect correction of the temperature white defect is performed based on the correction information of the information storage areas (C) and (D), the defect correction according to the generation characteristic of the temperature white defect can be performed.
[0040]
That is, temperature white scratches do not appear so prominently when normal shooting is performed under a normal temperature environment and under a generally set shutter speed, or under a high temperature environment different from normal shooting or It has a characteristic that it becomes prominent when shooting is performed under a low shutter speed. The defect correction conditions for temperature white scratches are divided into first and second defect correction conditions based on the boundary temperature Tth and the boundary shutter speed Sth. Correction is possible.
[0041]
As a result, since unnecessary (excessive) defect correction is not performed during normal shooting, image quality degradation can be prevented, and when white images are shot under a high temperature environment or a low shutter speed, temperature white scratches can be prevented. It can be corrected reliably.
[0042]
In the above description, the case where the boundary temperature Tth and the boundary shutter speed Sth are set one by one to correct the defect of the temperature white defect has been described. However, the boundary temperature Tth and the boundary shutter speed Sth are each plural. It is also possible to perform defect correction based on a plurality of correction conditions that are set one by one and divided by the plurality of boundary temperatures and boundary shutter speeds. According to such a configuration, it is possible to perform more precise defect correction that matches the generation characteristics of temperature white scratches.
[0043]
Moreover, although the case where the position data of the defective pixel is previously stored in the lookup table LUT has been described, 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 the semiconductor memory in correspondence with the pixel arrangement formed in the CCD image pickup device 3. Then, 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 readout timing of the pixel signal Pix.
[0044]
Further, a lookup table storing correction information or the above-described semiconductor memory may be provided along with the central control circuit in the camera, but a lookup table storing correction information unique to each CCD image pickup device may be provided. It may be previously integrated with the CCD image sensor. When a lookup table or the like is integrated with the CCD image pickup device in this way, reliable correction information can be obtained for each CCD image pickup device even if the characteristics of pixel defects differ for each CCD image pickup device due to variations between elements. For this reason, it is not necessary to make an adjustment for specifying a defective pixel for each CCD image pickup device in the camera manufacturing process, and an effect that the manufacturing process can be simplified can be obtained.
[0045]
【The invention's effect】
As described above, according to the present invention, when normal photographing is performed under the first defect correction condition under a so-called normal temperature environment and under a generally set shutter speed, the temperature white defect is detected. In the dynamic generation characteristic of temperature white scratches, in which temperature white scratches appear prominently when shooting is performed under the second defect correction condition in a high temperature environment or at a low shutter speed. In addition, since the defect correction of the temperature white defect is performed, the defect correction of the temperature white defect can be surely and appropriately performed.
[0046]
Furthermore, unnecessary (excessive) defect correction is not performed at the time of shooting under the first defect correction condition in which temperature white scratches do not appear so conspicuously, so that image quality deterioration can be prevented, and temperature white scratches can be prevented. When shooting is performed under the second defect correction condition under a high temperature environment or a low shutter speed that appears prominently, it is possible to reliably correct the temperature white defect.
[0047]
Furthermore, temperature white scratches can be corrected without providing a special device such as a conventional cooled CCD image sensor, so that mass production and miniaturization are possible, and this is particularly applicable to consumer imaging devices and the like. be able to.
[Brief description of the drawings]
FIG. 1 is a block diagram showing 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 sensor 5 ... Defect correction circuit LUT ... Look-up table

Claims (3)

In a pixel defect correction apparatus for a CCD image sensor that corrects temperature white scratches on the CCD image sensor,
When shooting is performed under a first defect correction condition at a normal environmental temperature and a normal shutter speed , first correction information for specifying a defective pixel that causes a white spot in temperature and a second at a high environmental temperature or a low shutter speed . Storage means for preliminarily storing second correction information that does not overlap with the first correction information for specifying a defective pixel that causes a temperature white defect when photographing is performed under the defect correction condition of
The defective pixel signal corresponding to the temperature white defect in the pixel signal read from the CCD image pickup device at the time of shooting is stored if the actual environmental temperature and shutter speed at the time of shooting are the first defect correction conditions. If the actual environmental temperature and shutter speed at the time of shooting are the second defect correction conditions, the first correction in the storage means is specified based on only the first correction information in the means. A defect correction unit that is identified based on the information and the second correction information, and performs defect correction on the identified defective pixel signal;
A pixel defect correction apparatus for a CCD image sensor, comprising: 2. A pixel defect correction apparatus for a CCD image pickup device according to claim 1, wherein the storage means is integrated with the CCD image pickup device. In a pixel defect correction method for a CCD image sensor that corrects temperature white scratches on the CCD image sensor,
When shooting is performed under a first defect correction condition at a normal environmental temperature and a normal shutter speed , first correction information for specifying a defective pixel that causes a white spot in temperature and a second at a high environmental temperature or a low shutter speed . And second correction information that does not overlap with the first correction information that identifies defective pixels that cause temperature white scratches when shooting is performed under the defect correction conditions of
The defective pixel signal corresponding to the temperature white defect in the pixel signal read out from the CCD image pickup device at the time of shooting is determined as the first defect correction condition when the actual environmental temperature and the shutter speed are the first defect correction conditions . It specified based only on the first correction information, when the actual ambient temperature and the shutter speed during the shooting is the second defect correction condition based on the first correction information and the second correction information Identify
A defect correction method for a CCD image pickup device, wherein defect correction is performed on the specified defective pixel signal.

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