JP2001036819A - Image pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image pickup device capable of performing good smear compensation not to generate a failure such as generation of a new fixed pattern noise even when a pixel fault exists in a vertical OB. SOLUTION: This image pickup device is constituted so that a generation processing of a reference signal for smear removal by removing the defective pixel information from the output signal of the vertical OB pixel by providing a CCD imaging device 5, a fault removing part 8-1 to remove defective pixel information from an output signal of a vertical OB pixel of the imaging device, a compensation reference signal generating part 8-2 to generate a reference signal to compensate a valid image signal of the imaging device from the output signal of the vertical OB pixel from which the defective pixel information is removed and an image signal compensating part 8-3 to subtract a compensation reference signal from the valid image signal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image pickup apparatus, and more particularly to an image pickup apparatus having a pseudo signal correction function.

[0002]

2. Description of the Related Art Conventionally, in a solid-state imaging device using a CCD image sensor, a phenomenon peculiar to the CCD image sensor is as follows.
There is a problem of image quality deterioration due to a smear phenomenon that occurs when intense light enters. In other words, this phenomenon is due to the fact that the charge that has not been trapped in the original charge storage region crosses the potential barrier and leaks into the vertical transfer path. For example, in the case of a spotlight, vertical stripes extend up and down the spotlight, and, for example, in the case of a subject in which a high-brightness portion such as a landscape including the sky is spread horizontally, the entire screen has flare. A white-out image is obtained.

[0003] As a method of correcting this phenomenon, attention is paid to the fact that smears occur at substantially the same level in the vertical direction from the principle of generation, and the vertical OB (optical black) which is a light-shielded accumulation pixel area outside the effective pixel area is focused on. : Optical black)
Is used as a smear removal reference signal, and this is subtracted from the pixel output signal of the effective screen.
No. 67038 discloses a known method. Particularly, in the disclosure of this publication, line information (corresponding to one line pixel) obtained by adding and averaging (average for every 12 pixels in the vertical direction) a vertical OB signal composed of a plurality of lines (12 lines in the embodiment). Average data) is used as a smear removal reference signal to reduce the influence of random noise included in the reference signal and prevent new fixed pattern noise from being generated due to smear correction. I am careful.

[0004] Further, the image pickup device has a pixel defect due to a manufacturing problem. This includes a white pixel defect that produces an output larger than the original output level due to the presence of a so-called dark current, and a black pixel defect that produces an output smaller than the original output level due to leakage or transfer failure. Any of the levels that are problematic in actual use,
These techniques are called white flaws and black flaws, respectively, and a technique for complementing information (defect compensation) using output information of a neighboring pixel without using output information of the pixel at the time of imaging signal processing has been widely used. .

[0005]

Here, considering that a conventional smear correction technique described in, for example, the above-mentioned Japanese Patent Application Laid-Open No. 7-67038 is applied to an actual image pickup device, a pixel defect exists in the vertical OB. In this case, a new streak-like fixed pattern noise is generated due to this. That is, for example, if a white flaw is present, a smear removal reference signal is generated regardless of the presence or absence of smear, so that a black vertical streak is generated in the image.If a black flaw is present, smear is generated when smear is generated. Since no rejection reference signal is generated,
Smears remain without being removed, resulting in white vertical streaks. In the smear correction technique disclosed in the above-mentioned publication, the average of a plurality of lines is taken, but the effect of one pixel defect is reduced to some extent (one-half of the number of lines), but does not provide an essential solution.

In order to solve this problem fundamentally, it is only necessary to select and use an image sensor having no pixel defect in the OB area.
This is associated with the yield of the device, resulting in a high price. In particular,
The defect in the effective pixel area is simply a problem of an isolated point of one pixel. However, in the case of the OB area on the premise of the smear correction, this becomes streak-like fixed pattern noise, and the visibility is much higher. The criteria are not realistic because they have to be strict.

Here, even if one new proposal is applied to the case where the conventional defect compensation for effective pixels is applied to the OB area, the following problem occurs. That is, since there are various restrictions on the defect compensation in the effective pixel area, generally used methods are limited. For example, there are cases where processing must be performed only within one horizontal line due to restrictions on storage elements used for processing. Specifically, pixel data adjacent to the left (or left and right) (in the case of color, adjacent among the same colors) of the defective pixel is often used. In the case of a color element, it is necessary to supplement with the pixel data of the same color filter. Specifically, in the case of a so-called RGB Bayer array of "G checkerboard RB line sequential", since the nearest neighbor pixels of G exist in four diagonal directions, interpolation is performed by any of these four pixels or by the above. Become. In such a case, in any case, the conventionally known technique uses information of pixels having different horizontal addresses for defect compensation. Therefore, assuming that defect compensation for a normal effective pixel is applied to the OB area, data of an OB pixel having a different horizontal address nearby (or data of the effective pixel area depending on the defect compensation method) is included in the smear removal reference signal. ), The correct smear correction is not performed, or new vertical stripe noise is generated.

[0008] As described above, the conventional smear correction technology is as follows.
When a pixel defect exists in the OB area, there is a problem that a new fixed pattern noise is generated instead.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem of the smear correction technique in the conventional image pickup apparatus, and the invention according to claim 1 has a new fixing method even if a pixel defect exists in the vertical OB. It is an object of the present invention to provide an imaging device capable of performing good smear correction without causing a problem such as occurrence of pattern noise. It is another object of the present invention to provide an imaging apparatus capable of performing smear correction reliably and easily without causing a defect by using pixel defect data previously inspected on a predetermined basis.

[0010]

According to a first aspect of the present invention, there is provided an image pickup device, comprising: an image pickup device which receives an output signal of a vertical optical black pixel portion of the image pickup device; Correction reference signal generation means for generating a reference signal for correcting an effective image signal which is an output signal of an effective pixel portion; image signal correction means for subtracting the correction reference signal from the effective image signal; and the correction reference signal When the correction reference signal is generated by the generation means, even if a pixel defect exists in the optical black pixel portion, the defective pixel information for generating the defective pixel information so that the information of the defective pixel is not included in the correction reference signal. The image pickup apparatus is constituted by the defect removing means except for the above.

As described above, the defect removing means is provided to remove the defective pixel information from the vertical OB having a plurality of lines to obtain a reference signal for smear removal.
Therefore, it is possible to realize an imaging apparatus capable of performing good smear correction without causing a problem such as generation of new fixed pattern noise even if a pixel defect exists.

According to a second aspect of the present invention, in the image pickup apparatus according to the first aspect, there is provided storage means for storing pixel defect data relating to the optical black pixel portion, and the defect removing means is provided with the storage means. Is used to remove the defective pixel information using the pixel defect data stored in the storage device. By providing the storage means for storing the pixel defect data relating to the vertical OB used by the defect removal means in this way, for example, the smear removal by removing the pixel defect information using the pixel defect data previously inspected by a predetermined standard at a factory or the like. , And a smear correction can be performed reliably and easily without causing a problem.

[0013]

Next, an embodiment will be described. FIG. 1 is a block diagram showing a digital camera according to a main embodiment of an imaging apparatus according to the present invention. 1 is a lens system, 2 is a lens driving mechanism, 3 is an exposure control mechanism, 4
Is a filter system, 5 is a CCD image sensor, 6 is a CCD driver, 7 is a pre-processing circuit including an A / D converter, 8
Is a digital process circuit that includes a memory as hardware and performs all digital process processing.
9 is a memory card interface, 10 is a memory card, 11 is an LCD image display system, 12 is a system controller including a microcomputer as a main configuration, 13 is an operation switch system,
14 is an operation display system including a display LCD, 15 is a strobe, 16
Is a lens driver, 17 is an exposure control driver, 18 is EEP
ROM.

In the digital camera configured as described above, the system controller 12 performs overall control, and controls the exposure control mechanism 3 and the driving of the CCD image pickup device 5 by the CCD driver 6. Exposure (charge accumulation) and signal reading are performed,
The data is stored in a digital process circuit 8 via a pre-process circuit 7 including a D converter, and all necessary various signal processing is performed in the digital process circuit 8, and then displayed on an LCD image display system 11 or recorded on a memory card 10. Various signal processes performed by the digital process circuit 8 include a smear correction process using output level information of a vertical OB pixel, which is a main part of the present invention. That is, the digital process circuit 8 includes a defect removal unit 8-1 for removing defective pixel information from the output of the vertical OB pixel, and a smear removal reference signal based on the output level of the vertical OB pixel from which the defective pixel information has been removed. A correction reference signal generation unit 8-2 for generating
An image signal correction unit 8-3 for correcting (smear removal) the image signal in the effective pixel area using the smear removal reference signal is provided. The defect removing unit 8-1, the correction reference signal generating unit 8-2, and the image signal correcting unit 8-3 may not always be clearly separated in an actual operation process.
It is shown separately for convenience of explanation and clarification of the concept.

FIG. 2 is a schematic diagram showing a sensor area of the CCD image pickup device 5. The sensor area includes an effective pixel portion EP which is an image pickup area, and an OB (optical black) for determining a vertical and horizontal black reference. VOB and H which are pixel parts)
In this embodiment, the optical black pixel portion OB is a vertical VOB of 12 lines vertically above the effective pixel portion EP and horizontally on the right side of the effective pixel portion EP. HO that is a horizontal OB of 40 pixels in the direction
It is made up of B. These OB areas have a structure in which a light-shielding film is provided on the sensor, and smears also exist in the VOB in the same manner as in the effective pixel portion EP. The imaging output signal obtained from this VOB includes an image output signal obtained from the effective pixel portion EP. A smear signal is included at the same level as the imaging output signal to be obtained. In FIG. 2, reference numerals 102 and 103 denote examples of smears generated when the correction process is not performed.

Note that the digital camera according to the present embodiment has a movie (continuous imaging) operation compatible with an electronic finder for composition determination, and a still (still image imaging) which is the main imaging.
The operation is performed, but in the case of a movie, the exposure time is controlled only by a so-called element shutter by controlling the charge accumulation of the imaging element. In the case of still photography, when it is difficult to use a mechanical shutter together, such as during continuous shooting, the exposure time control of only the element shutter is used. Therefore, in at least such a case, if no correction is performed, smear as described in the above-described related art will occur. Therefore, at least in such a case, the smear correction processing is applied. The smear correction according to the present invention also accompanies the correction even in a case where control can be performed so that smear is not originally generated, such as when a still image of only one frame is captured using an optical shutter such as a mechanical shutter. Since there is virtually no generation of new noise, that is, smear correction is certainly unnecessary, but there is no adverse effect, so that the same smear correction processing can be applied to such a case (of course, no application is possible). This is a design choice), and the camera according to the present embodiment employs a common smear correction process in all cases in order to standardize the process.

Next, camera control by the system controller 12 will be described focusing on processing directly related to smear correction in the digital camera according to the present embodiment.
The EEPROM 18 stores the address of the defective pixel of the image sensor 5 including the OB area, which is obtained in advance by the inspection in the manufacturing process. However, the defect determination criteria for the effective area and the OB area at the time of inspection are different, and the stricter level conditions are applied to the OB area. The address information of the effective area is used for known pixel defect compensation processing, and a description thereof will be omitted.

When an image pickup output signal corresponding to one screen from which signal charges generated by exposure in each of the above operations are sequentially read out is stored in a predetermined memory area of the digital process circuit 7, the correction reference signal generation section 8-2 outputs the signal. A smear removal reference signal is calculated using the output of the VOB which is a vertical OB. Here, if no pixel defect exists, similarly to the prior art described in the above-mentioned publication, 12 pixels having the same horizontal address among the data of the OB pixels having 12 lines (in the following description, the pixel group of 12 pixels) Is referred to as a rod), and an average value is obtained by dividing the sum by 12 pixels. In other words, each rod average value corresponds to one pixel.
The image signal of the line is used as a smear removal reference signal.

The smear correction processing in the present embodiment
A feature of this process is that pixel defects are also considered. That is, prior to obtaining the sum of the rods by the correction reference signal generating unit 8-2, the defect removing unit 8-1 refers to the address data of the defective pixel stored in the EEPROM 18 and finds that the rod has a defective pixel. In this case, except for the pixel data, only the remaining (non-defective) pixel data is sent to the correction reference signal generator 8-2, and the sum thereof is calculated. Then, by dividing this by “12 (the total number of pixels of the rod) minus the number of defective pixels (the number of non-defective pixels of the rod)”, an average value for only the non-defective pixels of the rod is obtained. That is, an image signal of one line in which the average value of only non-defective pixels of each rod corresponds to one pixel is used as a smear removal reference signal. Therefore, the smear correction is not affected by pixel defects in the OB area. At this time, since the data of the defective pixel is removed and the divisor is adjusted according to the data, the weight of each OB line (the non-defective pixel relating to the rod) included in the smear removal reference signal maintains the same ratio. This is excellent in that it does not adversely affect the effect of reducing the influence of random noise.

If this point is not emphasized, it is also possible to replace the defective pixel with another (for example, immediately above or below) non-defective pixel data in the same rod. As This has the advantage that the divisor in the average calculation can be made a constant (to 12 in this example), but since the ratio of non-defective pixels used for replacement is higher than the others, random noise It also has the disadvantage that the effect of reducing the effect is reduced accordingly.

Using the smear removal reference signal thus obtained, the image signal correction section 8-3 performs smear correction on the effective pixel signal. That is, a value obtained by subtracting the smear removal reference signal from each line data of the pixel signal read from the effective pixel portion EP is set as a corrected output. (It will be obvious that the subtraction is performed between data having the same horizontal address.)

The digital camera according to the present embodiment has conventionally known pixel defect compensating means. The digital camera according to the present invention stores the smear-corrected output signal corresponding to the effective pixel portion EP in the EEPROM 18. This processing is performed in the digital process circuit 8 based on the defective pixel address data. At this time, smear correction first
It is meaningful to perform defect compensation later, and simply reversing the defect compensation makes it possible to use the smear phenomenon itself or smear correction when information on a pixel with a different horizontal address from the defective pixel is complementarily applied to the defective pixel. Causes image quality degradation.

As described above, the image signal that has undergone the smear correction and the pixel defect compensation processing is recorded on the memory card 10 or displayed on the LCD image display system 11 through various signal processing as appropriate. The image to be recorded or displayed is a high-quality image in which smear has been corrected, and thus has no apparent smear.

Various embodiments other than the above-described main embodiment are conceivable. As an example, there is one in which the present invention is applied to a so-called movie camera (video movie) mainly for shooting moving images. The camera according to the main embodiment is a so-called digital (still) camera whose main purpose is to shoot a still image. Therefore, if at least one frame of a still image is shot, an optical shutter such as a mechanical shutter is used together (the present invention). It is possible to solve the problem, but in the case of a movie camera, since moving pictures are mainly used, it is common to use an optical shutter including a still image shooting which is an additional function. There are various design requirements, and the effect of the present invention becomes more prominent.

Although several embodiments of the present invention and modifications thereof have been specifically described above, the present invention is not limited to these embodiments and may take any form as long as it is described in the claims. It goes without saying that it is a gain.

[0026]

As described above with reference to the embodiments, according to the present invention, it is possible to realize an imaging apparatus capable of obtaining a smear-corrected high-quality image with no apparent smear. be able to. In particular, according to the first aspect of the present invention, the reference signal for smear removal is obtained by removing information on defective pixels from the vertical OB having a plurality of lines. It is possible to perform good smear correction that does not cause a problem such as generation of a fixed pattern noise. According to the second aspect of the present invention, since the storage unit for storing the pixel defect data related to the vertical OB used by the defect removing unit is provided, for example, the pixel defect data inspected in advance at a factory or the like on a predetermined basis is stored. A reference signal for removing smear, excluding the pixel defect information, is used to perform smear correction reliably and easily without causing a problem.

[Brief description of the drawings]

FIG. 1 is a schematic block diagram showing an overall configuration of a digital camera according to an embodiment of an imaging apparatus according to the present invention.

FIG. 2 is a schematic diagram showing a sensor area of the CCD image pickup device in the embodiment shown in FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Lens system 2 Lens drive mechanism 3 Exposure control mechanism 4 Filter system 5 CCD image sensor 6 CCD driver 7 Pre-process circuit 8 Digital process circuit 8-1 Defect removal section 8-2 Correction reference signal generation section 8-3 Image signal correction section 9 Memory card interface 10 Memory card 11 LCD image display system 12 System controller 13 Operation switch system 14 Operation display system 15 Strobe 16 Lens driver 17 Exposure control driver 18 EEPROM 101 Horizontal transfer path (horizontal shift register) EP Effective pixel part (imaging area) OB) Optical black pixel portion VOB Vertical OB HOB Horizontal OB

Claims (2)

[Claims] 1. An image sensor and a reference signal for correcting an effective image signal which is an output signal of an effective pixel portion of the image sensor from an output signal of an optical black pixel portion in a vertical direction of the image sensor. A correction reference signal generating means, an image signal correcting means for subtracting the correction reference signal from the effective image signal, and a pixel defect in the optical black pixel portion when the correction reference signal is generated by the correction reference signal generating means. An image pickup apparatus, comprising: a defect removing unit that removes the defective pixel information so as to generate the information such that the information of the defective pixel is not included in the correction reference signal even if the pixel exists. 2. A storage device for storing pixel defect data relating to the optical black pixel portion, wherein the defect removing unit removes the defective pixel information using the pixel defect data stored in the storage unit. The imaging device according to claim 1, wherein the imaging device is configured as follows.