JP2011101170A - Smear correction method of ccd type solid-state imaging element, and imaging device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the fixed pattern noise of vertical stripes by smear correction in a CCD type CCD solid-state imaging element. <P>SOLUTION: In this smear correction method of a CCD type solid-state imaging element in which a picked-up image signal read from each of a plurality of pixels mounted with the same color filter is transferred and outputted through two adjacent vertical charge transfer paths, a value obtained by averaging smear signals from an optical black part transferred by the two vertical charge transfer paths is subjected to smear correction as a smear component 14 of the picked-up image signal transferred by the vertical charge transfer paths. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a smear correction method and an imaging apparatus for a CCD solid-state imaging device.

  2. Description of the Related Art A CCD (Charge Coupled Devices) type solid-state imaging device includes a plurality of light receiving elements (photodiodes PD: also referred to as pixels hereinafter) arranged in a two-dimensional array on the surface of a semiconductor substrate. A vertical charge transfer path (VCCD) is formed along the plurality of pixel columns, and a horizontal charge transfer path (HCCD) is formed along the transfer direction end of each vertical charge transfer path.

  The region where the pixels are formed is divided into an effective pixel region in the center and an OB portion (optical black portion: the pixels in the OB portion are covered with a light-shielding film) in the periphery. The true video signal component is obtained by subtracting the black level signal value detected by the pixel in the OB portion from the video signal value detected by the pixel.

  In such a CCD type solid-state imaging device, for example, stray light enters the vertical charge transfer path and smear charges are generated, and a phenomenon that this appears as a bright line in the captured image occurs. The black level signal detected by the pixel in the OB portion between the horizontal charge transfer path and the effective pixel region is not so different between pixels adjacent in the horizontal direction in the OB portion (between the vertical charge transfer paths). However, the smear charge detected in the OB portion has a large difference between the vertical charge transfer paths.

  Therefore, as described in Patent Documents 1 and 2, for example, smear correction is performed to obtain a smear component based on the signal read from the OB unit and subtract the smear component from the captured image signal read from the pixel in the effective pixel region. Will do. This will be described with reference to FIGS.

  FIG. 10 shows a pixel arrangement of a solid-state imaging device in which color filters are arranged in a Bayer arrangement. Each pixel column includes a pixel column in which R (red) filter mounted pixels (hereinafter referred to as R pixels) and G2 (green) filter mounted pixels (hereinafter referred to as G2 pixels) are alternately arranged, and G1 (green). ) Filter-equipped pixels (hereinafter referred to as G1 pixels) and B (blue) filter-equipped pixels (hereinafter referred to as B pixels) are alternately provided. G1 and G2 are both green filters and have the same color, but “1” and “2” are added to distinguish the pixel columns.

  FIG. 11 illustrates a smear component superimposed on each signal of the R pixel, the G1 pixel, the G2 pixel, and the B pixel. The R pixel and the G2 pixel have the same smear component 11 because the signal charge is transferred through the same vertical charge transfer path, and the G1 pixel and the B pixel also have the same smear component because the signal charge is transferred through the same vertical charge transfer path. 12

  FIG. 12 shows video signal components 13R, 13G1, 13G2, and 13B of each pixel, which are detected in a state where they are added to the smear components 11 and 12 shown in FIG. The smear correction is performed on the signal detected in the state of FIG. 12. At this time, as described in Patent Document 1, a predetermined threshold is set and smear correction is turned on / off. Switching control is performed.

  At this time, the threshold value may be set to an intermediate value between the smear components 11 and 12 of the adjacent vertical charge transfer paths. When such a case occurs, as shown in FIG. 13, a smear-corrected video signal component 13R is obtained as the R pixel signal, and a smear component 12 is added to the video signal component 13G1 as the G1 pixel signal. An added signal (that is, a signal that is not subjected to smear correction) is obtained, and a video signal component 13G2 (with smear correction) is obtained as a signal of the G2 pixel, and a smear is added to the video signal component 13B as a signal of the B pixel. A signal (no smear correction) added with the component 12 is obtained.

  As a result, a large signal level difference a occurs between the G1 pixel and the G2 pixel, that is, between adjacent pixels of the same color, and becomes larger than the original signal level difference x between the G1 pixel and the G2 pixel in FIG. That is, by performing smear correction, a large step is generated between the signal of the G1 pixel and the signal of the G2 pixel. This appears as a fixed pattern noise of vertical stripes in the captured image, resulting in an unpleasant image.

  In performing smear correction, for example, as described in Patent Documents 3 and 4 below, there is a technique of performing low-pass filter processing in the horizontal direction when detecting smear components. If low-pass filter processing is performed for detection of smear components, it is possible to unify the determination of smear correction on / off between vertical charge transfer paths of, for example, adjacent five columns or ten columns, which is subjected to low-pass filter processing.

  However, since the phenomenon of smear occurs in units of vertical charge transfer paths, if low-pass filter processing is performed over a wide range, another fixed pattern noise may be generated.

  In recent years, it has become common for solid-state imaging devices to have 10 million pixels or more. For this reason, if the smear component must be low-pass filtered over a wide range, the signal readout is hindered, and in particular, there is a problem that the frame rate of the moving image cannot be increased.

JP 2007-81858 A JP 2008-236191 A Paragraph [0043] of JP-A-2009-100302 Paragraph [0024] of JP-A-2005-159564

  An object of the present invention is to provide a smear correction method and an image pickup apparatus for a CCD solid-state image pickup element capable of suppressing fixed pattern noise caused by smear and enabling high-speed reading of picked-up image signals in a CCD solid-state image pickup element. There is to do.

  The smear correction method for a CCD solid-state image pickup device according to the present invention is a CCD type in which two adjacent vertical charge transfer paths transfer and output a picked-up image signal read from each of a plurality of pixels mounted with the same color filter. A smear correction method for a solid-state imaging device, wherein the picked-up image transferred by the vertical charge transfer path is a value obtained by averaging the smear signals from the optical black portion transferred by the two vertical charge transfer paths. Smear correction is performed as a smear component of the signal.

  An image pickup apparatus according to the present invention includes a CCD solid-state image pickup device in which two adjacent vertical charge transfer paths transfer and output a picked-up image signal read from each of a plurality of pixels equipped with the same color filter, and And smear correction means for performing the smear correction method for the CCD solid-state image pickup device described above.

  According to the present invention, smear correction can be appropriately performed at high speed, and a high-quality subject image can be captured.

It is a functional block block diagram of the imaging device which concerns on one Embodiment of this invention. It is a surface schematic diagram which shows an example of the CCD type solid-state image sensor shown in FIG. It is a figure which shows the OB part used with an effective pixel area | region among the solid-state image sensors shown in FIG. It is a figure explaining the order of the signal output from the solid-state image sensor shown in FIG. It is explanatory drawing of the smear correction method of one Embodiment of this invention. It is a figure explaining the output order from the solid-state image sensor of the smear electric charge which concerns on one Embodiment of this invention. It is a figure explaining the example of calculation of the smear component which concerns on one Embodiment of this invention. It is a figure explaining another example of calculation of a smear component concerning one embodiment of the present invention. It is a figure explaining another example of calculation of a smear ingredient concerning one embodiment of the present invention. It is a figure explaining a Bayer arrangement. It is a figure which shows an example of the smear component added to the output of R pixel of a Bayer arrangement, G1 pixel, G2 pixel, and B pixel. It is a figure which shows the state by which the video signal was added to the smear component shown in FIG. It is a figure explaining the conventional smear correction.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a functional block configuration diagram of an imaging apparatus according to an embodiment of the present invention. The imaging device 20 is connected to a photographing lens 21 that collects incident light from a subject, a CCD solid-state imaging device 22 disposed at an imaging position of the photographing lens 21, and an output of the solid-state imaging device 22. An AFE (analog front end) circuit 23, a signal processing unit (DSP) 24 that performs signal processing on a digital captured image signal output from the AFE circuit 23, and a captured image signal that has undergone image processing by the signal processing unit 24 are JPEG images. A compression / decompression processing unit 25 that compresses or reversely compresses the image, a recording medium 26 that stores the JPEG image, and the like, and a display control that displays a captured image signal on a liquid crystal display unit 28 provided on the rear surface of the imaging apparatus. A circuit 27.

  The AFE circuit 23 performs an A / D circuit that performs correlated double sampling processing (CDS) on the analog captured image signal output from the solid-state image sensor 22, further controls the gain, and then converts it to a digital signal. And a timing generator (TG) for controlling the driving timing of the solid-state imaging device 22.

  The signal processing unit 24 offsets the smear correction unit (smear calculation unit) 24a that subtracts the smear component from the digital captured image signal output from the AFE circuit 23, and the captured image signal after the smear calculation. And a signal processing circuit 24b that generates a captured image signal of a subject by performing known image processing such as gamma correction processing and RGB / YC conversion processing.

  FIG. 2 is a schematic view of the surface of the solid-state imaging device 22 shown in FIG. On the surface of the semiconductor substrate, a plurality of pixels 31 are arranged in a two-dimensional array, in the example shown in a square lattice, and a vertical charge transfer path (VCCD) 32 is formed along each pixel column. ing.

  A horizontal charge transfer path (HCCD) 33 is formed along the transfer direction end of each vertical charge transfer path 32, and the horizontal charge transfer path 33 corresponds to the amount of signal charge transferred to the transfer direction end. An amplifier 34 that outputs a voltage value signal as a captured image signal is provided.

  The solid-state imaging device 22 of the present embodiment will be described on the assumption that primary color filters R, G, and B are arranged in a Bayer arrangement in the same manner as in FIG. 10, but the present invention is not limited to the Bayer arrangement. The present invention can be generally applied to a color filter array in which pixels of the same color exist between pixel columns adjacent in the direction. For example, a horizontal stripe color filter array may be used. Further, the pixel arrangement is not limited to a square lattice arrangement, and can be applied to a so-called honeycomb pixel arrangement in which even-numbered pixel rows are arranged with a ½ pixel pitch shifted from odd-numbered pixel rows.

  The area where the pixels shown in FIG. 2 are formed is divided into a rectangular effective pixel area 35 in the center and a surrounding OB portion 36. The pixels of the OB portion 36 are covered with a light shielding film, and a signal in a state where incident light is not incident is detected.

  The OB portion 36 is provided around the effective pixel region 35. In this embodiment, only the detection signal of the OB portion 36 on the opposite side of the horizontal charge transfer path 33 is used in order to explain smear correction. Therefore, description will be made below with reference to FIG.

  As shown in FIG. 3, the effective pixel region 35 is provided with pixel rows of a first horizontal line, a second horizontal line,..., An nth horizontal line from the horizontal charge transfer path 33 side. The pixel rows of the (n + 1) th line,..., The (n + i) th line of the OB portion 36 are provided.

  Although the terms “vertical” and “horizontal” have been described, this means only “one direction” “a direction perpendicular to this one direction” along the surface of the semiconductor substrate.

  FIG. 4 shows a signal order in which signals from the first line to the n-th line and the n + 1-th line to the n + i-line are read for each vertical synchronization (VD) signal. First, a captured image signal (video signal) in the effective pixel area 35 is read out, and then the signal of the OB unit 36 is read out at the end of one vertical synchronization period, and again in this order by the next vertical synchronization signal. The signal is read out.

  R, G1, G2, and B described in the video signal indicate an R pixel video signal, a G1 pixel video signal, a G2 pixel video signal, and a B pixel video signal, respectively. R, G1, G2, and B described in the OB portion signal are the black level signal of the R pixel in the OB portion, the black level signal of the G1 pixel in the OB portion, and the black level of the G2 pixel in the OB portion, respectively. A signal is a black level signal of the B pixel in the OB portion.

  Since the OB portion (OB portion 36 in FIG. 3) on the opposite side of the horizontal charge transfer path 33 is a signal affected by the smear component, the smear component is obtained from the signal of the OB portion, and the next video signal is obtained. Smear correction is performed by subtracting the smear component. At this time, in this embodiment, the smear component is obtained as follows.

  FIG. 5 is a diagram illustrating a smear component calculation method according to the embodiment of the present invention. FIG. 5A is the same as FIG. 12 and shows output signals of R pixel, G1 pixel, G2 pixel, and B pixel in two adjacent pixel columns, and the smear component of each vertical charge transfer path is shown in FIG. The captured image signal of each pixel is output as a signal added.

  In the conventional case, as shown in FIG. 11, smear components 11 and 12 are detected for each vertical charge transfer path, and on / off of smear correction is determined based on a threshold value. Instead of obtaining the smear components 11 and 12 for each transfer path, as shown in FIG. 5B, a value 14 obtained by averaging the smear components of the vertical charge transfer paths in two columns is obtained as a smear component. The value is also used as a threshold value for determining whether smear correction is on / off.

  Therefore, the same smear component value 14 is subtracted from the output signals (FIG. 5 (a)) of the four columns of four-color pixels R, G1, G2, and B, and the signal after smear correction shown in FIG. 5 (c) is obtained. It has gained. Thereby, the step between the G1 pixel signal and the G2 pixel signal of the same color becomes smaller than the signal difference a in FIG. 13, and vertical stripe noise can be reduced.

  As described above, in this embodiment, the signals of the two horizontal pixels of the OB portion transferred by two adjacent vertical charge transfer paths are added to obtain a smear component, and smear correction is performed. There are two methods.

  The first method is a method of adding signal charges on the horizontal charge transfer path. When charge addition is performed in the solid-state imaging device 22, signal charge of each pixel in the effective pixel region is not added, but signal charge in the OB portion is added. Therefore, it is necessary to provide a smear correction means for switching the signal transfer drive to different drive methods and switching both drive methods. The signal output order in this case is shown in FIG. In this case, the output of the OB unit becomes an added value, the processing load on the AFE circuit 23 is reduced, the processing speed is improved, and the cost of the AFE circuit 23 can be reduced.

  In the second method, smear components 11 and 12 for each vertical charge transfer path are obtained and stored in a line memory or the like, and the smear component 14 is obtained by averaging the adjacent signals 11 and 12 as before. A smear correction means may be provided. This method does not require any contrivance for driving the solid-state imaging device 22, and only the addition average processing load in the AFE circuit 23 is slightly increased. In addition, the following averaging process is also possible.

  For example, when performing the averaging process of two columns of each smear component of the vertical charge transfer path of the first column, the second column, the third column, the fourth column, the fifth column,. 1st column + second column) / 2, (third column + fourth column) / 2,..., But in the second method, (first column + second column) / 2, 2 columns + third column) / 2, (third column + fourth column) / 2,..., And it is possible to calculate a smear component that can further reduce vertical stripe noise.

  In any method, since the averaging processing is performed in two columns, the processing can be performed at a high speed, and the fixed noise pattern of vertical stripes can be reduced.

  Next, the method of the averaging process will be described. As shown in FIG. 7 (a), the red R smear before the averaging is defined as Sr, the green G1 smear as Sg1, the green G2 smear as Sg2, and the blue B smear as Sb. Further, as shown in FIG. 7B, after the averaging, the red R smear is defined as Srave, the green G1 smear is defined as Sg1ave, the green G2 smear is defined as Sg2ave, and the blue B smear is defined as Sbave.

The averaging process is
Slave = (Sr + Sg1) / 2
Sg1ave = (Sr + Sg1) / 2
Sg2ave = (Sg2 + Sb) / 2
Sbave = (Sg2 + Sb) / 2
Calculate as

  Thereby, the signal level difference between the pixel G1 and the pixel G2 is reduced, and the fixed pattern noise is reduced.

FIG. 8 is a diagram for explaining another addition averaging process. The above definition before and after the averaging process is the same, and FIG. 8 (a) is the same as FIG. 7 (a). The averaging process of this embodiment is
Slave = (Sr + Sb) / 2
Sg1ave = (Sg1 + Sg2) / 2
Sg2ave = (Sg1 + Sg2) / 2
Sbave = (Sr + Sb) / 2
Calculate as

FIG. 9 is a diagram for explaining still another averaging process. The above definitions before and after the averaging process are the same, and FIG. 9 (a) is the same as FIG. 7 (a). The averaging process of this embodiment is
Slave = (Sr + Sg1 + Sg2 + Sb) / 4
Sg1ave = (Sr + Sg1 + Sg2 + Sb) / 4
Sg2ave = (Sr + Sg1 + Sg2 + Sb) / 4
Sbave = (Sr + Sg1 + Sg2 + Sb) / 4
Calculate as

  Also by the above, the signal level difference between the pixel G1 and the pixel G2 is reduced, and the fixed pattern noise is reduced.

  As described above, the smear correction method for the CCD type solid-state imaging device according to the present embodiment has the two vertical charge transfer paths adjacent to the captured image signal read from each of a plurality of pixels equipped with the same color filter. Is a smear correction method for a CCD type solid-state imaging device that transfers and outputs a value obtained by adding and averaging the smear signals from the optical black portion transferred by the two vertical charge transfer paths. Smear correction is performed as a smear component of the transferred captured image signal.

  Further, the smear correction method for the CCD solid-state imaging device according to the embodiment is characterized in that the addition averaging is performed by signal processing.

  Further, the smear correction method for the CCD solid-state image sensor according to the embodiment is characterized in that the addition averaging is performed by charge mixing inside the CCD solid-state image sensor.

  In the smear correction method for the CCD solid-state imaging device according to the embodiment, the color filters are arranged in a Bayer array, and the color filters of four pixels closest to each other in a square shape are R, G1, G2, B, and the R pixel and the G1 pixel. The smear components are averaged and the smears of the G2 pixel and the B pixel are averaged to obtain the smear component.

  In the smear correction method for the CCD type solid-state imaging device according to the embodiment, the color filters are arranged in a Bayer array, and the color filters of four pixels closest to each other in a square shape are R, G1, G2, B, and R pixels and B pixels. The smear components are averaged and the smears of the G1 pixel and G2 pixel are averaged to obtain the smear component.

  In the smear correction method for the CCD solid-state imaging device according to the embodiment, the color filters are arranged in a Bayer array, and the color filters of four pixels closest to each other in a square shape are R, G1, G2, B, and the R pixel and the G1 pixel. The smear component is obtained by averaging the smears of the G2 pixel and the B pixel.

  In addition, the imaging apparatus of the embodiment includes a CCD solid-state imaging device that transfers and outputs a captured image signal read from each of a plurality of pixels equipped with the same color filter by two adjacent vertical charge transfer paths; And smear correction means for implementing the smear correction method for a CCD solid-state image pickup device according to any one of the above.

  According to the present embodiment, since smear values are averaged by ignoring colors and smear correction is performed, appropriate smear correction can be performed at high speed without performing erroneous correction due to the magnitude relationship of the smear values for each color, and vertical stripes can be obtained. It is possible to reduce the fixed pattern noise.

  Since the smear correction method for a solid-state imaging device according to the present invention can perform smear correction at high speed, a digital still camera, a digital video camera, a mobile phone with a camera, an electronic device with a camera such as a PDA or a notebook computer, It is useful when applied to general imaging devices such as mirrors.

DESCRIPTION OF SYMBOLS 11, 12, 14 Smear component 20 Imaging device 22 CCD type solid-state image sensor 24 Signal processing part 24a Smear calculating part 31 Pixel 32 Vertical charge transfer path (VCCD)
33 Horizontal charge transfer path (HCCD)
35 Effective pixel area 36 OB section

Claims (7)

  A smear correction method for a CCD type solid-state imaging device in which two adjacent vertical charge transfer paths transfer and output a picked-up image signal read from each of a plurality of pixels mounted with the same color filter. Of a CCD type solid-state imaging device that performs smear correction as a smear component of the imaged image signal transferred by the vertical charge transfer path using a value obtained by adding and averaging smear signals from the optical black portion transferred by the vertical charge transfer path Smear correction method.   The smear correction method for a CCD solid-state image pickup device according to claim 1, wherein the addition averaging is performed by signal processing.   The smear correction method for a CCD solid-state imaging device according to claim 1, wherein the addition averaging is performed by charge mixing inside the CCD solid-state imaging device.   2. The smear correction method for a CCD type solid-state imaging device according to claim 1, wherein the color filters are arranged in a Bayer array, and the color filters of four pixels closest to each other in a square shape are R, G1, G2, B, and R pixels A smear correction method for a CCD type solid-state imaging device that calculates the smear component by averaging the smear of the G1 pixel and the smear of the G1 pixel and averaging the smear of the G2 pixel and the B pixel.   2. The smear correction method for a CCD type solid-state imaging device according to claim 1, wherein the color filters are arranged in a Bayer array, and the color filters of four pixels closest to each other in a square shape are R, G1, G2, B, and R pixels A smear correction method for a CCD type solid-state image pickup device that obtains the smear component by averaging the smears of the B pixel and the B pixel and averaging the smears of the G1 pixel and the G2 pixel.   2. The smear correction method for a CCD type solid-state imaging device according to claim 1, wherein the color filters are arranged in a Bayer array, and the color filters of four pixels closest to each other in a square shape are R, G1, G2, B, and R pixels And a smear correction method for a CCD type solid-state imaging device, which obtains the smear component by averaging the smears of the G1, G2, and B pixels.   7. A CCD solid-state imaging device, wherein two adjacent vertical charge transfer paths transfer and output a captured image signal read from each of a plurality of pixels mounted with the same color filter, and any one of claims 1 to 6 An image pickup apparatus comprising smear correction means for performing the smear correction method for the CCD solid-state image pickup device according to claim 1.

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