JP2004222048A - Solid-state imaging device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solid-state imaging device which obtains signals having correct hues and stable color balance from a main photosensitive area and a sub photosensitive area respectively. <P>SOLUTION: A digital camera 10 supplies image signals successively read out from the main photosensitive area and the sub photosensitive area of a light receiving element to a signal processing part 18, and extents of deviation of spectral sensitivities which colors R, G, and B and colors r, g, and b in a main photosensitivity correction part 70 and a sub photosensitivity correction part 72 corresponding to the main photosensitive area and the sub photosensitive area respectively have, are corrected by a spectral sensitivity correction part 48 provided in the signal processing part 18, and color balance of image signals obtained from the main photosensitive area and the sub photosensitive area in image signals obtained by this correction is adjusted. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a solid-state imaging device, and the present invention relates to a solid-state imaging device that obtains an image having a wide dynamic range using, for example, a solid-state imaging device with a shift in the balance of spectral characteristics.
[0002]
[Prior art]
Some solid-state imaging devices have a light receiving region that converts received light into electric charges, and have a structure that discharges excess charge generated in the light receiving region to the substrate side, that is, a so-called vertical overflow drain structure. . When light is incident on the light receiving region, the solid-state imaging device generates a charge immediately below the light receiving region by light absorption of the substrate. In the vertical overflow drain structure, an overflow barrier region is formed as a barrier in signal charge accumulation. At this time, the charge generated at a position shallower than the overflow barrier flows into the solid-state imaging device. This signal charge flowing in the solid-state image sensor contributes to accumulation of the signal charge.
[0003]
By the way, paying attention to the wavelength of incident light, light having a long wavelength enters deeper than the overflow barrier region, and the incident light is absorbed at this position. For this reason, the generated signal charge flows to the substrate and does not contribute to accumulation of the signal charge (see Patent Document 1). This means that the solid-state imaging device is affected by spectral sensitivity and has wavelength dependency. Specifically, when the spectral sensitivity of the solid-state imaging device is exemplified, the short wavelength side is limited by the absorption characteristics of the film on the silicon substrate. The theoretical limit on the long wavelength side is determined by the forbidden band energy of silicon, and in this case is 1100 nm (see Non-Patent Document 1).
[0004]
Among such spectral sensitivities, in particular, when there is a demand to increase the sensitivity of long wavelengths, it has been proposed that the solid-state imaging device is designed so that the overflow barrier region is formed deep in the substrate (Patent Document 1). .
[0005]
[Patent Document 1]
JP 2000-50755 A
[Non-Patent Document 1]
Supervised by Kotaro Wakui, edited by the Institute of Image Information and Television Engineers, “Design Techniques for Television Cameras”, Corona, 1999, p. 187.
[0006]
[Problems to be solved by the invention]
The present applicant has also proposed a solid-state imaging device in which one light receiving region is divided into a main photosensitive region having a relatively large charge storage capacity and a sub photosensitive region having a relatively small charge storage capacity. In this solid-state imaging device, the main photosensitive region and the secondary photosensitive region are separated from each other by a potential barrier. Here, when the potential depth formed so as to accumulate signal charges in each of the primary photosensitive region and the secondary photosensitive region by the overflow barrier is designed to be the same depth, a completely vertical potential barrier may be formed. desired. However, the formation of such a potential barrier requires a very high voltage to be applied to the secondary photosensitive region, which makes it practically difficult to realize.
[0007]
As a result, the actual overflow barrier becomes a potential barrier having a slope. As a result, the sub-photosensitive region is less deep from the substrate surface, and even if it is attempted to accumulate signal charges for light having a long wavelength, the accumulated capacity becomes small. This indicates that even when the same light is incident on the main photosensitive area and the secondary photosensitive area, the sensitivity of the long wavelength in the secondary photosensitive area is likely to be lower than that of the primary photosensitive area. In consideration of this possibility, it is difficult to form different depths by overflow barriers for the main photosensitive region and the sub-photosensitive region so as to satisfy the requirements.
[0008]
SUMMARY OF THE INVENTION An object of the present invention is to provide a solid-state imaging device capable of solving such drawbacks of the prior art and obtaining a color balance signal having a correct and stable color tone from the main photosensitive region and the secondary photosensitive region.
[0009]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the present invention includes a plurality of light receiving elements, each including a main photosensitive region and a sub photosensitive region having an area smaller than the main photosensitive region, for converting incident light into an electric signal, in a two-dimensional array. And a signal processing means for performing signal processing on the image signal read from the solid-state imaging element, and the signal processing means corrects the spectral sensitivity with respect to the signals of the main photosensitive area and the auxiliary photosensitive area. It includes a sensitivity correction unit.
[0010]
The solid-state imaging device of the present invention supplies image signals sequentially read from the main photosensitive area and the secondary photosensitive area of the light receiving element to the signal processing means, and the sensitivity correction means provided in the signal processing means allows the main photosensitive area and the secondary photosensitive area to be detected. The color balance in the obtained image signal is adjusted by correcting the different spectral sensitivities in each photosensitive region.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Next, an embodiment of a solid-state imaging device according to the present invention will be described in detail with reference to the accompanying drawings.
[0012]
In this embodiment, the solid-state imaging device of the present invention is applied to a digital camera 10. The illustration and description of parts not directly related to the present invention are omitted. In the following description, the signal is indicated by the reference number of the connecting line in which it appears.
[0013]
As shown in FIG. 3, the digital camera 10 includes an optical system 12, an imaging unit 14, a preprocessing unit 16, a signal processing unit 18, a system control unit 20, an operation unit 22, a timing signal generator 24, a driver 26, and a monitor 28. And storage 30.
[0014]
Although not shown, the optical system 12 includes a mechanical shutter, an optical system lens, a zoom mechanism, a diaphragm adjustment mechanism, and an auto focus (AF) adjustment mechanism. The optical system 12 has a function of adjusting the various mechanisms described above for the optical lens and sending incident light to the imaging unit 14.
[0015]
Although not shown, the zoom mechanism adjusts the angle of view of the object scene. The AF adjustment mechanism is a mechanism that automatically adjusts the arrangement of a plurality of optical lenses to adjust the subject to a focused positional relationship. Each of the mechanisms is provided with a motor for moving the optical lens to the position described above. These mechanisms operate in response to a drive signal 32 supplied from the driver 26 to each motor.
[0016]
Although not specifically shown, the aperture adjustment mechanism is an AE (Automatic Exposure) adjustment mechanism that adjusts the amount of incident light, and rotates the ring portion according to a drive signal 34 from the driver 26. The ring part partially overlaps the blades to form a round shape of the iris, and forms the iris so that the incident light beam passes therethrough. In this way, the iris adjusting mechanism changes the aperture of the iris. The aperture adjustment mechanism may be incorporated in the optical system lens as a mechanical shutter.
[0017]
The mechanical shutter has a function of shielding the image capturing unit 14 from being irradiated with light except when photographing and determining an exposure time depending on the start and end of exposure. As the mechanical shutter, for example, there is a focal plane type used in a single-lens reflex camera. In this method, the shutter curtain runs vertically or horizontally, and exposure is performed with a slit formed at this moment. Further, as described above, a lens shutter type may be used. The mechanical shutter opens and closes the shutter according to the drive signal 36 supplied from the driver 26.
[0018]
Although not shown, the imaging unit 14 includes a solid-state imaging device in which an optical low-pass filter and a color filter are arranged. The optical low-pass filter is a filter that makes the spatial frequency of incident light equal to or lower than the Nyquist frequency. The solid-state imaging device is a charge coupled device (CCD), and the light receiving surface of one light receiving device is divided into a main photosensitive region having a large light receiving area and a sub photosensitive region having a small light receiving area. A transfer gate (TG) for reading the signal charge accumulated in each of the photosensitive regions to the vertical transfer path is provided. The solid-state imaging device will be further described later. A drive signal 38 is also supplied from the driver 26 to the solid-state imaging device. The drive signal 38 is a horizontal drive signal φH, a vertical drive signal φV, an OFD (Over Flow Drain) signal, or the like corresponding to the operation mode of the solid-state imaging device. The imaging unit 14 outputs an analog voltage signal 40 obtained from the solid-state imaging device to the preprocessing unit 16. The solid-state imaging device reads the signal charge first from the main photosensitive region in consideration of the saturation amount, and then reads the signal charge from the following photosensitive region. In the solid-state imaging device, signal charges in each region are independently interlaced and read out in the order described above with respect to one light receiving device.
[0019]
The preprocessing unit 16 includes a correlated double sampling (CDS) circuit, a gain adjustment amplifier (GCA), and an A / D converter (Analog-to-Digital Converter) for noise removal. It is. A CDS pulse 42 is supplied as a sampling signal from the timing signal generator 24 to the CDS circuit, and a conversion clock signal 44 is supplied to the A / D converter. The preprocessing unit 16 outputs all of the imaging data obtained by performing noise removal, waveform shaping, and digitization to the supplied analog signal 40 to the signal processing unit 18 as digital data 46.
[0020]
As shown in FIG. 1, the signal processing unit 18 includes a spectral sensitivity correction unit 48, an image addition unit 50, a histogram calculation unit 52, a gamma conversion unit 54, a synchronization processing unit 56, a correction unit 58, and a compression / decompression processing unit 60. A card interface unit 62, an image reduction unit 64, and image memories 66 and 68.
[0021]
The spectral sensitivity correction unit 48 includes a main photosensitive correction unit 70 and a secondary photosensitive correction unit 72. The main photosensitive correction unit 70 has a function of correcting the spectral sensitivity with respect to a signal obtained from the main photosensitive region, that is, pixel data. The sub-photosensitive correction unit 72 has a function of correcting the spectral sensitivity with respect to the signal obtained from the sub-tourist area, that is, pixel data.
[0022]
More specifically, as shown in FIG. 2, the main photosensitive correction unit 70 includes an offset unit 74, a linear matrix (LMTX: Linear MaTriX) unit 76, and a white balance (WB: Gain Balance) gain unit 78. The correction unit 72 also includes an offset unit 80, an LMTX unit 82, and a WB gain unit 84. The main photosensitive correction unit 70 and the secondary photosensitive correction unit 72 perform the same processing except that the correction target is pixel data from the primary photosensitive area and pixel data from the secondary photosensitive area. Each part mentioned above is demonstrated below.
[0023]
The offset units 74 and 80 have a function of correcting so-called black float, for example, the black level increases with long exposure. That is, it is a function of reducing the level of the increase so that the black reference level (pedestal level) becomes constant.
[0024]
The LMTX units 76 and 82 each have a function of eliminating color overlap in the spectral sensitivity of the solid-state imaging device, and have an arithmetic function to realize this function. The color overlap in the spectral sensitivity means an overlapping region of the spectral characteristics of the color G with respect to the spectral characteristics of the color R and the color B in this embodiment. The LMTX units 76 and 82 receive from the pixels of the color G adjacent to or adjacent to the target color R and B pixels so that the spectral characteristics of the colors R and B are correctly expressed. An operation is performed to multiply the pixel data by a constant and subtract the multiplication result from the target pixel data. The target pixel data is R (x, y), B (x, y), r (x, y), b (x, y), constants L_RG, L_BG, L_rg, L_bg, located around the object Pixel data G of color G (x + 1, y), corrected pixel data R _c (X, y), B _c (X, y), r _c (X, y), b _c If (x, y), the operations are
[0025]
[Expression 1]
R _c (X, y) = R (x, y) −L_RG * G (x + 1, y) (1)
B _c (X, y) = B (x, y) −L_BG * G (x + 1, y) (2)
r _c (X, y) = r (x, y) −L_rg * G (x + 1, y) (3)
b _c (X, y) = b (x, y) −L_bg * G (x + 1, y) (4)
It becomes.
Here, it is preferable that the constants L_RG and L_BG of the main photosensitive area and the constants L_rg and L_bg of the secondary photosensitive area in the calculation have a relationship of L_RG <L_rg and L_BG> L_bg. This is because the short wavelength component included in the signal of color r in the secondary photosensitive region is less than the short wavelength component included in the signal of color R in the primary photosensitive region, and the long wavelength component included in the signal of color b in the secondary photosensitive region. Is larger than the long wavelength component included in the signal of color B in the main photosensitive region.
[0026]
The WB gain units 78 and 84 each have a function of adjusting the spectral sensitivity by correcting the WB gain of the photosensitive area according to the color by the correction amount for the WB gain of the main photosensitive area. The correction amount α is a red correction value, and the correction amount β is a blue correction value. However, this correction function cannot perform strict correction for a light source having a remarkably large bright line, for example. However, this correction function is suitable at least for a light source having a broad constant color temperature.
[0027]
By definition, the gain r_gain for the color r from the secondary photosensitive area is α * R_gain, and the gain b_gain for the color b from the secondary photosensitive area is β * B_gain. The gain is defined as the ratio of the color G to each color (R_gain = G / R, B_gain = G / B, r_gain = g / r, b_gain = g / r). This definition corresponds to a detection frame described later. Therefore, the correction amounts α and β are set as predetermined color temperatures, for example, at a color temperature of 5000K.
[0028]
[Expression 2]
α (5000) = (R / G) / (r / g) = (R / r) * (g / G) (5)
β (5000) = (B / G) / (b / g) = (B / b) * (g / G) (6)
Calculate from Actually, in the image quality adjustment process at the time of camera manufacture, for example, correction amounts α and β are calculated for a light source having a color temperature of 5000K. This calculated value is stored.
[0029]
Furthermore, the WB gain units 78 and 84 may divide the image into a plurality of regions and perform gain correction using the correction amounts α and β obtained from the detection frames calculated for each region. The correction amounts α and β are set as values for a plot having the detection frame (R / G, B / G) as coordinates. These relationships are stored in an EEPROM (Electrically Erasable Programmable Read Only Memory) (not shown) of the system control unit 20, and correction amounts α and β corresponding to the use are read from the system control unit 20 and the WB gain unit via the control bus 86. 78 and 84, and the WB gain sections 78 and 84 adjust the gain. The operation of the gain adjustment will be described later.
[0030]
The spectral sensitivity correction unit 48 preferably includes at least one of the LMTX units 76 and 82 and the WB gain units 78 and 84 shown in FIG. 2 in the main photosensitive correction unit 70 and the secondary photosensitive correction unit 72.
[0031]
Returning to FIG. 1, the digital data 46 is supplied to the signal processing unit 18 as image signals to the image memories 66 and 68 via the data buses 88 and 90, respectively. The image memories 66 and 68 send temporarily stored digital data from the main photosensitive area and the secondary photosensitive area to the spectral sensitivity correction unit 48 to correct the spectral sensitivity of the digital data, and again the image memory 66. , 68. The spectral sensitivity correction unit 48 to the image reduction unit 64 in the signal processing unit 18 illustrated in FIG. 1 are controlled according to the control signal 102 supplied from the system control unit 20 via the control bus 86. A timing signal (not shown) is supplied to the signal processing unit 18 from the timing signal generator 24 shown in FIG. This timing signal includes a horizontal synchronization signal HD, a vertical synchronization signal VD, and operation clocks of respective units described later.
[0032]
Returning to FIG. 1, the image adder 50 is supplied with the digital data of the main photosensitive area and the digital data of the secondary photosensitive area, which have been subjected to spectral sensitivity correction, from the image memory 66 and the image memory 68, respectively. It has a function of widening image data obtained by adding digital data pixel by pixel. Widening dynamics is performed according to the scene determination signal 92 supplied from the histogram calculation unit 52. For example, the image addition unit 50 proceeds to the image addition processing in response to the supply of the scene determination signal 92 determined to include the highlight scene. In the image addition process, the main photosensitive area and the secondary photosensitive area corresponding to each pixel are added according to a control signal supplied from the system control unit 20 via the control bus 86. The image adding unit 50 stores the image data generated according to these processes in the image memory 66 via the data bus 88.
[0033]
The gamma conversion unit 54 has a lookup table for gamma correction, for example. The gamma correction unit 54 performs gamma correction on the image data supplied from the image memory 66 using the data in the lookup table. The gamma correction unit 54 stores the gamma corrected image data in the image memory 66.
[0034]
The image data after the gamma correction is also supplied to an evaluation value calculation unit (not shown). The evaluation value calculation unit includes an arithmetic circuit for calculating an aperture value / shutter speed, a white balance adjustment value, and a gradation correction value. In this arithmetic circuit, an appropriate parameter is calculated based on the supplied image data. The integrated value is calculated by In this case, the signal processing unit 18 shown in FIG. 3 supplies the calculated integrated value 94 to the system control unit 20 as a parameter. The evaluation value calculation unit may be arranged in the system control unit 20 without being limited to the arrangement in the signal processing unit 18. At this time, the signal processing unit 18 may supply the gamma-corrected image data to the system control unit 20.
[0035]
By the way, for example, since a single-plate primary color filter is used for the imaging unit 14, even if a light receiving element (actual pixel) is actually provided, it corresponds to a color other than the provided color filter segment. There is no pixel data. Returning to FIG. 1, the synchronization processing unit 56 has an arithmetic circuit that calculates a primary color that is not in the color filter segment for the target pixel by interpolation using surrounding pixel data. By this arithmetic circuit, the three primary colors for the target pixel can be aligned at the same time. This process is called synchronization.
[0036]
In addition, when the digital camera 10 is provided with a so-called honeycomb array solid-state imaging device in the imaging unit 14, a virtual pixel having no light receiving element is actually set. The synchronization processing unit 56 may generate new pixel data for the virtual pixel by making full use of surrounding real pixels and pixel data obtained by interpolation. The synchronization processing unit 56 may perform interpolation processing using the pixel data of the color G and the luminance data Y to widen the pixel data to be generated. The synchronized image data is supplied to the image memory 66.
[0037]
The correction unit 58 multiplies the synchronized image data of the three primary colors by a predetermined coefficient to perform color difference matrix processing. In addition, the correction unit 58 performs edge enhancement processing on the generated luminance data Y or generates the generated color data C _b , C _r Has a function of performing color enhancement processing. The correction unit 58 includes luminance data Y, color data C _b , C _r The color difference data is generated from the image data, and the image data thus obtained is supplied to the image memory 66. When RAW data is recorded, the processing of the correction unit 58 and the compression / decompression processing unit 60 is not performed.
[0038]
The compression / decompression processing unit 60 adds JPEG (Joint Photographic Coding Experts Group) or MPEG (Moving Picture Coding Experts Group)- 1, compression processing is performed according to standards such as MPEG-2. The compression / decompression processing unit 60 supplies the compressed image data to the card interface unit 62. The card interface unit 62 has a function of adjusting electrical characteristics and timing adjustment in writing / reading with the card recording medium of the storage 30, and outputs processed image data 96 to the storage 30. Yes. Further, the compression / decompression processing unit 60 reads the image data 96 recorded in the storage unit 30 and performs decompression processing via the card interface unit 62. This decompression process is the reverse process of the compression process.
[0039]
The image reduction unit 64 performs RGB conversion on the generated image data and image data (Y / C or color difference data) expanded with reproduction, and the pixel size that the monitor 28 can display the RGB converted image data. It has a function to make. As for the size in image display, an image without failure is generated by thinning-out processing. The image reduction unit 64 supplies the generated image data 98 to the monitor 28.
[0040]
Image data 46 is input to the image memories 66 and 68 and temporarily stored. The image memory 66 is a memory for storing pixel data obtained from the main photosensitive area among the light receiving elements. The image memory 68 is a memory for storing pixel data obtained from the secondary photosensitive region in the light receiving element. The digital camera 10 uses two memories to form one image. The image memories 66 and 68 are preferably non-volatile memories when repeatedly reading.
[0041]
In addition, the signal processing unit 18 operates a signal generation circuit (not shown) in response to the control signal. The signal generation circuit has a PLL (Phase Locked Loop) circuit capable of generating a plurality of frequencies. The signal generation circuit multiplies the oscillation frequency of the source as a reference clock to generate a plurality of types of clock signals, which are output to the system control unit 20 and the timing signal generator 24 (not shown).
[0042]
Returning to FIG. 3, the system control unit 20 is a microcomputer or CPU (Central Processing Unit) that controls a general-purpose part of the entire camera and a part that performs digital processing. Although not shown, the system control unit 20 includes an EEPROM for storing coefficients, a ROM (Read Only Memory) for storing instruction programs for operation procedures, and the like. The system control unit 20 sets the digital camera 10 to the still image shooting mode or the moving image shooting mode in accordance with the instruction signal 100 for instructing the mode or the operation trigger supplied from the operation unit 22 and picks up an image from a release shutter button (not shown). In response to the timing notification, control signals 102, 104, and 106 corresponding to the integrated value 94 are generated. The generated control signals 102, 104, and 106 are supplied to the signal processing unit 18, the timing signal generator 24, and the driver 26, respectively.
[0043]
The system control unit 20 generates a control signal 102 that also considers control for performing line interpolation and signal generation circuit in the signal processing unit 18 and signal processing, and performs read / write control by the control signal 108 in the storage 30. Is also going. Although not shown, the system control unit 20 also performs operation timing control in the preprocessing unit 16.
[0044]
Although not shown, the operation unit 22 includes a mode selection unit and a release shutter button. The mode selection unit selects one of the still image shooting mode and the moving image shooting mode. The mode selection unit outputs the selected mode as an instruction signal 100 to the system control unit 20. The release shutter button is a button having a two-stage stroke, and the trigger timing when the digital camera 10 is set to the preliminary imaging stage (S1) with the first stroke and the main imaging stage (S2) is set with the second stroke. Is output to the system control unit 20 as an instruction signal 100. In addition, the operation unit 22 may be provided with a zoom selection switch and a cross button, and may have a function of selecting conditions displayed on the liquid crystal display panel.
[0045]
The timing signal generator 24 generates a timing signal according to the control signal 104 supplied from the system control unit 20 based on a clock signal (not shown) supplied from the signal processing unit 18. The timing signal includes a vertical synchronization signal, a horizontal synchronization signal, a field shift pulse, a vertical transfer signal, a horizontal transfer signal, an electronic shutter pulse, and the like. The timing signal generator 24 also generates a CDS pulse 42 and a converted clock signal 44 and supplies them to the preprocessing unit 16. The timing signal generator 24 supplies the driver 26 with a timing signal 110 including the generated vertical synchronizing signal, horizontal synchronizing signal, field shift pulse, vertical transfer signal, horizontal transfer signal, and electronic shutter pulse.
[0046]
The driver 26 has a drive circuit that generates drive signals 32 to 38 based on the supplied timing signal 110 and control signal 106. The driver 26 supplies drive signals 32, 34, and 36 to the optical lens and the aperture adjustment mechanism of the optical system 12 based on the control signal 106, respectively, to perform AF adjustment and AE adjustment. The driver 26 outputs a drive signal 36 for opening and closing the mechanical shutter to the mechanical shutter in response to the main imaging timing supplied from the release shutter button of the operation unit 22. In addition, the driver 26 supplies a driving signal 38 generated based on the timing signal 110 to the solid-state imaging device of the imaging unit 14, and accumulates signal charges in the main photosensitive area and the secondary photosensitive area of each light receiving element during the exposure period. The stored signal charges are read out independently or simultaneously into the vertical transfer register by control according to the above-described conditions, transferred to the horizontal transfer register, and the analog voltage signal 40 is output through the horizontal transfer register and the output amplifier.
[0047]
The monitor 28 displays an image by operating image data 98 supplied from a display controller (not shown) on a display device. As the monitor 28, a liquid crystal monitor is generally used. The liquid crystal monitor is provided with a liquid crystal display controller. The liquid crystal controller performs switching control by arranging liquid crystal molecules and applying voltage based on the image data 98. By this control, the liquid crystal monitor displays an image. Needless to say, the monitor 28 is not limited to a liquid crystal monitor, and may be sufficiently used as long as it is a small display device that can confirm images and reduce power consumption.
[0048]
The storage 30 records image data 96 supplied from the signal processing unit 18 using a semiconductor memory or the like as a recording medium. As the recording medium, an optical disk, a magneto-optical disk, or the like may be used. The storage 30 writes / reads data using a recording / reproducing head by combining a pickup suitable for each recording medium, a pickup, and a magnetic head. Data writing / reading is performed under the control of the system control unit 20 although not shown.
[0049]
Next, FIG. 5 shows the potential of each line shown in FIG. 4 while paying attention to one light receiving element 112 of the solid-state imaging device arranged densely as a component of the imaging unit 14. The light receiving element 112 has a vertical transfer register 114 formed at an adjacent position. By forming the light receiving elements 112 densely, as a result, the vertical transfer register 114 bypasses each light receiving element 112 and is formed to meander.
[0050]
As shown in FIG. 4, the light receiving portion of the light receiving element 112 is an octagonal photosensitive region in the present embodiment, and this light receiving portion is divided into, for example, an L shape by a separating portion 116. In the divided photosensitive areas, a relatively wide photosensitive area is set as a main photosensitive area 118 and a narrow photosensitive area is set as a secondary photosensitive area 120. The light receiving element 112 is cut in a direction along cutting lines IV-IV, VV and VI-VI, and potentials at the cutting lines at this time are shown. The cutting line IV-IV is a trajectory obtained when the light receiving element 112 is cut at a predetermined depth perpendicular to the horizontal plane. The cutting lines VV and VI-VI are respectively a line cut at a predetermined depth perpendicular to the horizontal plane in the main photosensitive area and the secondary photosensitive area of the light receiving element 112, and a position where the line is located. It is a line showing the line which goes out to the substrate side.
[0051]
FIG. 5A sequentially shows the potentials of the transfer gate 122 that reads the signal charges accumulated in the main photosensitive region 118, the main photosensitive region 118, the separation unit 116, and the transfer gate 124 that reads the signal charges accumulated in the sub-photosensitive region 120. ing. FIG. 5B shows the potentials of the transfer gate 122, the main photosensitive region 118, and the vertical overflow drain. FIG. 5C shows the potentials of the transfer gate 124, the secondary photosensitive region 120, and the vertical overflow drain, respectively. It is.
[0052]
In FIG. 5A, the separation unit 116 separates the main photosensitive region 118 and the secondary photosensitive region 120 by forming a potential peak with a normal applied voltage. When an extremely high voltage is applied, the potential of the separation unit 116 forms a rectangular potential without forming a wide base in the potential peak. However, such a voltage is not actually applied because it is inefficient in view of energy. Therefore, the potential of the separation unit 116 is a mountain shape with a wide base. At this time, the range occupied by the base of the mountain is the main photosensitive area 118 and the secondary photosensitive area 120, and the opening 126 of the comparatively narrow secondary photosensitive area 120 is used as the secondary photosensitive area even if the base area is the same. The possible range is reduced and is affected at a greater rate than the opening 127 in the main photosensitive area 118. This influence means that the ratios of signal charge generation due to the areas of the colors R, G, B in the main photosensitive region 118 and the colors r, g, b in the secondary photosensitive region 120 do not match. Therefore, the color balance becomes the first cause of the collapse or mismatch between the main photosensitive area 118 and the secondary photosensitive area 120.
[0053]
Further, absorption of incident light is characterized in that it occurs spectrally in the order of color B, color G, and color R from the shallower side as viewed in the depth direction of the light receiving element 112. This tendency is not limited to the photosensitive areas of the main photosensitive area 118 and the secondary photosensitive area 120. This feature means that when incident light enters a spectrally deep region and signal charges are generated there, the signal charges generated on the substrate side are discarded. Considering these points, the spectral sensitivity on the long wavelength side, particularly the sensitivity of the color R, is remarkably lowered. This is the second cause. In consideration of the fact that the color R is insensitive, in the narrow secondary photosensitive region 120, as a practical measure, a high voltage is applied and a potential is formed by applying a normal voltage without forming a deep potential valley. Thus, the potential base of the photosensitive region 120 is set according to the level indicated by the broken line BL. Also, with this setting, the light receiving element 112 makes it easy to sweep out the signal charge in the secondary photosensitive region 120.
[0054]
In FIG. 5B and FIG. 5C, the peak level of the vertical overflow drain (OFD) represents the saturation level 128 of the main photosensitive region 118 and the secondary photosensitive region 120, respectively.
[0055]
As described above, the spectral sensitivity with respect to the wavelength is shown in FIG. 6 for each of the main photosensitive region 118 and the secondary photosensitive region 120 based on these causes. The spectral sensitivity characteristic of the main photosensitive region 118 is indicated by a solid line. The spectral sensitivity characteristic of the secondary photosensitive region 120 is indicated by a broken line. Comparing both spectral sensitivity characteristics, the peaks 130, 132, and 134 of the colors R, G, and B in the main photosensitive region are on the longer wavelength side than the peaks 136, 138, and 140 of the colors r, g, and b in the secondary photosensitive region. . In other words, it can be seen that the peak of each color in the secondary photosensitive region shifts to the short wavelength side.
[0056]
In addition, the spectral sensitivity characteristic of FIG. 6 has shown the characteristic when not considering IR (InfraRed) cutoff filter.
[0057]
In addition, as shown in the spectral sensitivity characteristics of FIG. 6, in the spectral sensitivity characteristics of each color, the end portion of the color G and the wing area overlap the wing areas of the colors R and B. In order to eliminate this overlap, the color reproducibility is improved by a process of reducing the amount corresponding to the wing area of the color G overlapping with the colors R and B. This process is performed by the LMTX units 76 and 82 shown in FIG. As described above, the pixel of color G used for correction is a pixel adjacent to or near the target pixel of colors R and B. In the equations (1) to (4), the coordinates are specified so that the adjacent pixels are used.
[0058]
The coefficients L_RG, L_rg, L_BG, and L_bg used for the colors R, r, B, and b in the equations (1) to (4) are in a relationship of L_rg> L_RG and L_bg <L_BG. This first relationship reduces the short wavelength component contained in the color R of the main photosensitive region 118 from the short wavelength component contained in the color r signal obtained from the secondary photosensitive region 120. The second relationship is to increase the long wavelength component contained in the color B of the main photosensitive region 118 from the long wavelength component contained in the color b signal obtained from the secondary photosensitive region 120. These coefficients used in the LMTX units 76 and 82 are preferably stored in advance in the EEPROM of the system control unit 20 and read out to the LMTX units 76 and 82 when the digital camera 10 is activated. As specific coefficients, L_RG = 16/256, L_BG = 8/256, L_rg = 32/256, L_bg = 4/256 may be used.
[0059]
By performing these arithmetic processes in the LMTX units 76 and 82, it is possible to reduce the shift of the spectral sensitivity to the short wavelength for the colors R and B obtained from the sub-photosensitive areas.
[0060]
The color balance adjustment is not limited to the calculation by the LMTX units 76 and 82, and can be performed using the WB gain units 78 and 84. This adjustment will be described below.
[0061]
In the WB gain units 78 and 84, correction for a predetermined color temperature is performed. The correction amount α is a red correction value, and the correction amount β is a blue correction value. These correction amounts α and β are obtained from the above-described equations (5) and (6), respectively. When the predetermined color temperature is set to 5000 K in the image quality adjustment process of camera manufacture, correction amounts α and β are calculated. Specific examples of the calculation include α (5000) = 1.4 and β (5000) = 1. The correction amounts α and β are stored in the EEPROM of the system control unit 20. Regardless of the color temperature, even if correction is performed with α (5000) and β (5000), a WB gain in which the original color remains can be performed. The original color described here means that red is strong in the low color temperature region and blue is strongly reproduced in the high color temperature region. Such an adjustment often gives a preferable WB adjustment, and a wide dynamic range process can be performed without giving a sense of incongruity.
[0062]
Incidentally, the correction amounts α and β have the relationship shown in FIG. This is because red is intensely reproduced in the low color temperature region and blue is strongly reproduced in the high color temperature region, so that the correction amount α can be small in the low color temperature region, and less redness is increased in the high color temperature region. It means to correct as follows. In addition, the correction amount β is increased so as to increase less bluishness in the low color temperature region, and since the bluishness is inherently strong in the high color temperature region, it means that a small correction amount is sufficient.
[0063]
As shown in FIG. 6, when the IR-blocking filter is not taken into consideration, the ratio of the same color of the main photosensitive area and the secondary photosensitive area in accordance with the definition of the correction amount is dependent on the color temperature as shown in FIG. A qualitative tendency is obtained. At a color temperature lower than 5000 K, the ratios R / r and B / b are both large and g / G tends to be small. Further, at a color temperature higher than 5000 K, both R / r and B / b tend to be small and g / G tends to be large.
[0064]
The above-described examination is a description of a case where no IR-cutoff filter is installed. Here, consider a digital camera 10 equipped with an IR-blocking filter as a more realistic situation. Considering this IR-blocking filter, the component of color r in the secondary photosensitive region 120 is already shaved from the incident light by the IR-blocking filter regardless of the spectral sensitivity characteristic. From this, the color temperature dependency does not change the ratio R / r regardless of the color temperature, as shown in FIG. Other ratios show the same tendency as in FIG. If this tendency is expressed by spectral sensitivity characteristics, as shown in FIG. 10, the peaks 130 and 136 of the colors R and r are located at the same wavelength. Since the sensitivity of the color r is smaller than that of the other colors g and b, it is desirable to perform correction with a correction amount α (5000) = 1.4. From the definition of the correction amount α, the correction amount α is governed by the color temperature dependency of the ratio g / G in green. Therefore, it is preferable to consider correction by the ratio g / G for further strict correction.
[0065]
On the other hand, when the correction amount β is considered, the color temperature dependency of the ratio B / b and the ratio g / G has a reverse tendency as described above. From this, it is difficult to say that the correction amount β for the color temperature dependency shown in FIG. 7 can be sufficiently satisfied as a qualitative one at this stage, but it is one of the phenomena. It is a certain fact that can be obtained as
[0066]
As apparent from FIG. 7, the color temperature dependency is small with respect to the correction amount α (= 1.4) in the color temperature region lower than the color temperature of 5000 K, and is large with respect to the correction amount β (= 1). The color temperature is higher than the correction amount α in the color temperature region higher than 5000 K, and smaller than the correction amount β. For this reason, when correcting the WB gain for the colors r and b in the sub-photosensitive region 120 using the correction amounts α and β in consideration of the color temperature dependency, the WB gain in the low color temperature region and the r_gain of the color r are correct. The b_gain of the color b is calculated to be smaller than the correct gain. Further, the WB gain in the high color temperature region and the r_gain of the color r are calculated to be smaller than the correct gain, and the b_gain of the color b is calculated to be larger than the correct gain.
[0067]
Taking this tendency into consideration, the WB gain unit 78 further uses a function for obtaining detection frames R / G and B / G used for light source discrimination for each block obtained by dividing the screen of the WB gain unit 78. FIG. The correction amounts α and β corresponding to the obtained plot positions are applied as shown in FIG. This application makes it possible to control the color temperature dependence of the correction amounts α and β. It is possible to perform a stable color balance process independent of luminance by correcting a color shift generated in the main photosensitive area 118 and the secondary photosensitive area 120.
[0068]
By configuring as described above, the color balance is adjusted using values obtained by changing the parameters in the LMTX processing of the main photosensitive area 118 and the secondary photosensitive area 120 in consideration of the spectral sensitivity characteristics. In the adjustment, a stable color balance can be obtained regardless of the luminance.
[0069]
In addition, by correcting the sub-photosensitive region 120 within a range that does not cause a sense of incongruity, a stable color balance can be obtained even if the color balance is simply adjusted. A range in which a sense of incongruity is not felt is selected for a predetermined color temperature.
[0070]
Further, the color balance is appropriately adjusted by using the WB gain and the colors r_gain and b_gain for the secondary photosensitive region set in advance in consideration of the color temperature dependency of the low color temperature region and the high color temperature region with respect to a predetermined color temperature. Therefore, it is possible to obtain a stable color balance regardless of luminance.
[0071]
【The invention's effect】
As described above, according to the solid-state imaging device of the present invention, the image signal sequentially read from each of the main photosensitive area and the secondary photosensitive area of the light receiving element is supplied to the signal processing means, and the sensitivity correction means provided in the signal processing means. By adjusting the color balance in the obtained image signal by correcting different spectral sensitivities in each of the primary photosensitive area and secondary photosensitive area, it is possible to achieve a stable color balance that does not depend on brightness, especially in the adjustment to the secondary photosensitive area. Can be obtained.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a schematic configuration of a signal processing unit in a digital camera to which a solid-state imaging device of the present invention is applied.
2 is a block diagram showing a schematic configuration of a main photosensitive correction unit and a secondary photosensitive correction unit in the spectral sensitivity correction unit of FIG. 1;
FIG. 3 is a block diagram showing a schematic configuration of a digital camera to which the solid-state imaging device of the present invention is applied.
4 is a diagram showing cutting directions IV-IV, VV, and VI-VI of the light receiving element with respect to one light receiving element of the solid-state imaging element disposed in the imaging unit of FIG. 3;
5 is a diagram illustrating a potential image obtained by a line cut in each direction of FIG. 4; FIG.
6 is a chart showing the spectral sensitivities of the main photosensitive region and the secondary photosensitive region with respect to the wavelength obtained by using the light receiving element of FIG. 4 without using an IR-blocking filter.
7 is a graph showing a relationship between correction amounts α and β that are WB gain correction coefficients with respect to color temperature in the WB gain section of FIG. 2;
8 is a diagram showing the color temperature dependence of the ratios R / r, B / b and g / G with respect to a color temperature of 5000 K without considering the IR-blocking filter in the digital camera of FIG. 3;
9 is a diagram showing the color temperature dependence of ratios R / r, B / b and g / G with respect to a color temperature of 5000 K in consideration of the IR-cutoff filter in the digital camera of FIG.
10 is a chart showing the spectral sensitivities of the main photosensitive region and the secondary photosensitive region with respect to the wavelength obtained in consideration of the IR-blocking filter in the digital camera of FIG. 3;
FIG. 11 is a diagram illustrating correction amounts α and β corresponding to a detection frame in consideration of color temperature dependency with respect to a predetermined color temperature.
[Explanation of symbols]
10 Digital camera
12 Optical system
14 Imaging unit
16 Pre-processing section
18 Signal processor
20 System controller
22 Operation unit
24 Timing signal generator
26 Driver
28 Monitor
30 storage
48 Spectral Sensitivity Correction
70 Main photosensitive correction part
72 Sub-photosensitive correction unit
76, 82 LMTX part
78, 84 WB gain section

Claims (9)

A plurality of light receiving elements including a main photosensitive region and a secondary photosensitive region having an area smaller than the main photosensitive region and converting incident light into an electrical signal; a solid-state imaging device arranged in a two-dimensional array;
Signal processing means for performing signal processing on the image signal read from the solid-state imaging device,
The signal processing means includes a sensitivity correction means for correcting a spectral sensitivity with respect to signals of the main photosensitive area and the auxiliary photosensitive area, respectively. 2. The solid-state imaging device according to claim 1, wherein the sensitivity correction means includes linear arithmetic means for performing a linear matrix operation on each of the signals of the main photosensitive area and the secondary photosensitive area. 3. The apparatus according to claim 2, wherein the linear computing means includes the target located in the vicinity of the signal from a signal for correcting the spectral sensitivity in each of the signals of the main photosensitive region and the secondary photosensitive region. A solid-state imaging device characterized by subtracting a value obtained by multiplying a green signal in a photosensitive region of the same type by a constant. 4. The apparatus according to claim 3, wherein the constant multiple is a value for the sub-photosensitive area for red that is larger than a value for the main photo-sensitive area for red and a value for the main photo-sensitive area for blue. A solid-state imaging device characterized in that the value for the sub-photosensitive region is made smaller. 2. The apparatus according to claim 1, wherein the sensitivity correction means sets a first ratio of red to green in the primary photosensitive area as a first ratio, a secondary ratio of red as green to the secondary photosensitive area, and a second ratio. The red gain in the spectral sensitivity based on the relationship of the first ratio is the first correction coefficient, the blue to green of the main photosensitive area is the third ratio, and the blue to green of the secondary photosensitive area is the fourth. And the second correction coefficient in the spectral sensitivity based on the relationship of the third ratio to the fourth ratio,
The red of the primary photosensitive area is multiplied by a first correction coefficient to correct the red of the secondary photosensitive area, and the blue of the primary photosensitive area is multiplied by a second correction coefficient to obtain the blue of the secondary photosensitive area. A solid-state imaging device characterized by correcting. 6. The solid-state imaging device according to claim 5, wherein the first and second correction coefficients are constants at a predetermined color temperature. The apparatus according to claim 6, wherein the first correction coefficient is set to a value lower than the first correction coefficient at the predetermined color temperature at a color temperature lower than the predetermined color temperature, and is higher than the predetermined color temperature. A solid-state imaging device having a color temperature that is higher than the first correction coefficient at the predetermined color temperature. 7. The apparatus according to claim 6, wherein the second correction coefficient is set to a value higher than the second correction coefficient at the predetermined color temperature at a color temperature lower than the predetermined color temperature, and is higher than the predetermined color temperature. A solid-state imaging device having a color temperature that is lower than a second correction coefficient at the predetermined color temperature. 6. The solid-state imaging device according to claim 2, wherein the sensitivity correction unit includes an offset unit that offsets a signal from the main photosensitive region and the sub photosensitive region.

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