JP2006237998A - Imaging device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To correctly unify an electric signal to a state derived from a linear conversion mode or a logarithm conversion mode. <P>SOLUTION: An imaging device 1 is provided with an imaging element 2 having a plurality of pixels G<SB>11</SB>to G<SB>mn</SB>switching the linear conversion mode at which incident light is linearly converted into the electric signal and the logarithm conversion mode at which the signal is logarithm-converted and with a signal processing part 3 which performs a signal processing on the electric signal. The signal processing part 3 is provided with a plurality of first to fourth conversion tables 36a to 36d performing characteristic conversion for converting the electric signal derived from the logarithm conversion mode into a state derived from the linear conversion mode in accordance with respective domains of respective driving conditions. Characteristic conversion is performed by the first to fourth conversion tables 36a to 36d corresponding to the driving conditions at the time of imaging among a plurality of the first to fourth conversion tables 36a to 36d. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an imaging apparatus having an imaging element that converts incident light into an electrical signal.

  2. Description of the Related Art Conventionally, an imaging device such as a digital camera is provided with an imaging element having a plurality of pixels that convert incident light into an electrical signal. These pixels are designed to switch the conversion mode to an electric signal based on the amount of incident light, and more specifically, a linear conversion mode for linearly converting incident light into an electric signal and a logarithmic conversion mode for logarithmic conversion. And are to be switched. Further, in the subsequent stage of the image sensor, the electrical signal derived from the logarithmic conversion mode is converted into a state derived from the linear conversion mode, or the characteristic conversion is performed to convert the electrical signal derived from the linear conversion mode into a state derived from the logarithmic conversion mode. A signal processing unit is provided to facilitate the processing of the electrical signal by unifying the entire electrical signal into a state derived from the linear conversion mode or the logarithmic conversion mode.

  According to such an image sensor, since the dynamic range of the electric signal is wide compared to an image sensor that performs only the linear conversion mode, even when a subject having a wide luminance range is imaged, It can be expressed as a signal.

By the way, the plurality of pixels described above have variations in input / output characteristics due to pixel differences. Therefore, as a method for eliminating such variation, there is a method of correcting the output from each pixel so as to match the reference output value (for example, see Patent Documents 1 and 2).
JP 11-298799 A JP-A-5-30350

  However, the correction method disclosed in the above-mentioned patent document corrects the deviation between the reference output value under the reference condition and the actual pixel output value when the input / output characteristics fluctuate due to driving conditions such as shooting conditions and environmental conditions. Can not do it. For this reason, it is impossible to accurately unify the entire electrical signal to a state derived from the linear conversion mode or the logarithmic conversion mode.

  The subject of this invention is providing the imaging device which can unify an electric signal correctly in the state derived from the linear transformation mode or the logarithmic transformation mode.

The invention according to claim 1 is an imaging apparatus,
An imaging device having a plurality of pixels that switch between a linear conversion mode for linearly converting incident light into an electrical signal and a logarithmic conversion mode for logarithmic conversion based on the amount of incident light;
A signal processing unit that performs signal processing on the electrical signal,
The signal processing unit
A plurality of characteristic conversion units that perform characteristic conversion for converting an electrical signal derived from one of the logarithmic conversion mode and the linear conversion mode into a state derived from the other conversion mode, corresponding to each domain of each driving condition In preparation,
Among the plurality of characteristic conversion units, the characteristic conversion is performed by the characteristic conversion unit corresponding to the driving condition at the time of imaging.

  Here, driving conditions for the image sensor include an external condition and an imaging condition. The external conditions include temperature, and the imaging conditions include pixel exposure time and control voltage.

According to the first aspect of the present invention, when the input / output characteristics of the image sensor fluctuate due to at least one drive condition of the image sensor, the characteristic conversion of the electric signal output from the image sensor is performed. Since it is performed by the characteristic conversion unit corresponding to the driving condition of time, the electric signal can be accurately unified to a state derived from the linear conversion mode or the logarithmic conversion mode.
Note that the drive condition region may include only one value.

The invention described in claim 2 is the imaging apparatus according to claim 1,
A plurality of the signal processing units are provided in association with each pixel.

  According to the second aspect of the present invention, since the signal processing unit is provided in association with each pixel, even if the conversion characteristics of photoelectric conversion and the fluctuation amount of the input / output characteristics are different for each pixel, the entire electric signal Can be accurately unified to a state derived from the linear transformation mode or the logarithmic transformation mode.

The invention described in claim 3 is the imaging apparatus according to claim 1 or 2,
An inflection signal deriving unit for deriving an inflection output signal value at a boundary where the linear transformation mode and the logarithmic transformation mode are switched;
The signal processing unit, when the output signal from the image sensor is an electric signal derived from the one conversion mode based on the magnitude of the signal value of the output signal from the image sensor and the inflection output signal value Only the signal processing is performed.

  According to the third aspect of the invention, the signal processing unit performs signal processing only when the output signal from the image sensor is an electrical signal derived from the one conversion mode, so that the output signal is the other conversion mode. If the electrical signal is derived from the other conversion mode, that is, it is not necessary to convert the electrical signal derived from the one conversion mode to a state derived from the other conversion mode, signal processing such as characteristic conversion and fluctuation correction is performed. I will not. Accordingly, it is possible to save time and effort for performing signal processing, and it is possible to speed up the processing.

According to a fourth aspect of the present invention, in the imaging apparatus according to the third aspect,
The inflection signal deriving unit derives the inflection output signal value based on the driving condition.

  According to the fourth aspect of the invention, since the inflection output signal value is derived based on the driving condition, the inflection output signal value can be accurately derived.

The invention according to claim 5 is the imaging apparatus according to claim 3 or 4,
The inflection signal deriving unit derives the inflection output signal value based on the driving condition and pixel information about the pixel.

Here, as the pixel information, unique information such as the ID number of the pixel, position information in the image sensor, or the like can be used.
According to the fifth aspect of the invention, since the inflection output signal value is derived based on the driving condition and the pixel information, the inflection output signal value can be accurately derived.

The invention described in claim 6 is the imaging apparatus according to claim 4 or 5,
The inflection signal deriving unit includes a lookup table for deriving the inflection output signal value based on at least the input of the driving condition.

  According to the sixth aspect of the invention, since the inflection output signal value is derived by the lookup table, the configuration of the inflection signal deriving unit is simplified and the derivation process is performed as compared with the case of deriving by calculation. The speed can be increased.

The invention according to claim 7 is the imaging apparatus according to claim 4 or 5,
The inflection signal deriving unit includes an arithmetic unit for deriving the inflection output signal value based on at least the input of the driving condition.

  According to the seventh aspect of the invention, the same effect as that of the fourth or fifth aspect of the invention can be obtained.

Invention of Claim 8 is an imaging device as described in any one of Claims 1-7,
The driving condition is at least one of a temperature during photographing, an exposure time of the pixel, and a control voltage for the pixel.

  According to the invention described in claim 8, it is possible to obtain the same effect as the invention described in any one of claims 1-7.

  According to the first aspect of the present invention, it is possible to accurately unify electrical signals into a state derived from the linear conversion mode or the logarithmic conversion mode.

  According to the second aspect of the invention, the same effect as that of the first aspect of the invention can be obtained, and the entire electrical signal is accurately unified to a state derived from the linear conversion mode or the logarithmic conversion mode. be able to.

According to the third aspect of the invention, the same effect as that of the first or second aspect of the invention can be obtained, and the processing can be speeded up.
According to the invention described in claim 4, the same effect as that of the invention described in claim 3 can be obtained, and the inflection output signal value can be accurately derived.

  According to the fifth aspect of the invention, the inflection output signal value can be accurately derived as well as the same effect as that of the third or fourth aspect of the invention.

  According to the invention described in claim 6, the same effect as that of the invention described in claim 4 or 5 can be obtained, and the configuration of the inflection signal derivation unit is simplified and the derivation process is performed at high speed. Can be

According to the seventh aspect of the invention, the same effect as that of the fourth or fifth aspect of the invention can be obtained.
According to the invention described in claim 8, it is possible to obtain the same effect as the invention described in any one of claims 1-7.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a block diagram showing a schematic configuration of an imaging apparatus 1 according to the present invention.

  As shown in FIG. 1, the imaging apparatus 1 includes an imaging element 2 that receives incident light through a lens group 10 and a diaphragm 11. As the lens group 10 and the diaphragm 11, conventionally known ones are used.

As shown in FIG. 2, the imaging element 2 has a plurality of pixels G _{11 to} G _mn (where n and m are integers of 1 or more) arranged in a matrix (matrix arrangement).
Each of the pixels G _{11 to} G _mn photoelectrically converts incident light and outputs an electrical signal. These pixels G _{11 to} G _mn switch the conversion mode to an electric signal based on the amount of incident light. In the present embodiment, as shown by the solid line in FIG. A linear conversion mode for linearly converting incident light is performed for the incident light amount, and a logarithmic conversion mode for logarithmically converting the incident light is performed for an incident light amount equal to or greater than the predetermined incident light amount th.

Here, the boundary at which the linear conversion mode and the logarithmic conversion mode are switched, the so-called inflection point, changes depending on the driving conditions of the pixels G _{11 to} G _mn in the image sensor 2, for example, the exposure time and control voltage at the time of photographing. It has become. Specifically, as shown in FIG. 4, as the exposure time becomes shorter in the order of “t ₁ ” to “t ₃ ”, the output signal value at the inflection point (hereinafter referred to as the inflection output signal value H) The predetermined incident light amount th increases in the order of “I” to “III”. Further, as shown in FIG. 5, as the control voltage decreases in the order of “V ₁ ” to “V ₃ ”, the inflection output signal value H of the pixels G _{11 to} G _mn increases in the order of “IV” to “VI”. Become. 4 and 5, “a ₁ ” to “a ₃ ”, “b” to “d”, “a”, and “d ₁ ” to “d ₃ ” are constants. Of these, the gradient a ₁ ~a ₃ input-output characteristic in the linear conversion mode in the driving conditions of the exposure time t ₁ ~t ₃ has a proportional relationship with respect to the exposure time t ₁ ~t ₃ . Also, sections d ₁ to d ₃ of input-output characteristics in the logarithmic conversion mode in the driving conditions of the control voltage V ₁ ~V ₃ has a proportional relationship with respect to the control voltage V ₁ ~V _3.

Filters (not shown) of any one of red, green, and blue are disposed on the lens group 10 side of the pixels G _{11 to} G _mn . Further, as shown in FIG. 2, the pixels G _{11 to} G _mn include a power supply line 20, signal application lines L _{A1 to} L _An , L _{B1 to} L _Bn , L _{C1 to} L _Cn , and signal readout lines L _{D1 to} L _{D Dm} is connected. Note that lines such as a clock line and a bias supply line are also connected to the pixels G _{11 to} G _mn , but these are not shown in FIG.

The signal application lines L _{A1 to} L _An , L _{B1 to} L _Bn , and L _{C1 to} L _Cn give signals φ _v and φ _VPS (see FIG. 8) to the pixels G _{11 to} G _mn . A vertical scanning circuit 21 is connected to these signal application lines L _{A1 to} L _An , L _{B1 to} L _Bn , and L _{C1 to} L _Cn . The vertical scanning circuit 21 applies signals to signal application lines L _{A1 to} L _An , L _{B1 to} L _Bn , and L _{C1 to} L _Cn based on signals from a signal generation unit 48 (see FIG. 1) described later. The signal application lines L _{A1 to} L _An , L _{B1 to} L _Bn , and L _{C1 to} L _Cn to which signals are applied are sequentially switched in the X direction.

The electric signals generated by the pixels G _{11 to} G _mn are derived from the signal readout lines L _{D1 to} L _Dm . Constant current sources D _{1 to} D _m and selection circuits S _{1 to} S _m are connected to these signal read lines L _{D1 to} L _Dm .
A DC voltage V _PS is applied to one end (lower end portion in the figure) of the constant current sources D _{1 to} D _m .

The selection circuits S _{1 to} S _m sample-hold the noise signals given from the pixels G _{11 to} G _mn through the signal readout lines L _{D1 to} L _Dm and the electrical signals at the time of imaging. A horizontal scanning circuit 22 and a correction circuit 23 are connected to these selection circuits S _{1 to} S _m . The horizontal scanning circuit 22 sequentially switches selection circuits S _{1 to} S _m that sample and hold an electric signal and transmit the signal to the correction circuit 23 in the Y direction. The correction circuit 23 removes the noise signal from the electrical signal based on the noise signal transmitted from the selection circuits S _{1 to} S _m and the electrical signal at the time of imaging.

As the selection circuits S _{1 to} S _m and the correction circuit 23, those disclosed in Japanese Patent Laid-Open No. 2001-223948 can be used. In the present embodiment, the description will be made assuming that only one correction circuit 23 is provided for the entire selection circuits S _{1 to} S _m , but the correction circuit 23 is provided for each of the selection circuits S _{1 to} S _m. It is good also as providing one by one.

  As shown in FIG. 1, the black reference setting unit 14 and the signal processing unit 3 are connected to the imaging element 2 in this order via an amplifier 12 and an AD converter 13.

The black reference setting unit 14 sets the minimum level of the digital signal.
The signal processing unit 3 performs signal processing on the electrical signal output from the image sensor 2 in the logarithmic conversion mode, and includes a linearization unit 36, a selector 35, and an output unit 31c as shown in FIG. ing. In FIG. 6, illustration of the AD converter 13, the control device 46, and the like is omitted.

The linearization unit 36 includes a plurality of first to fourth conversion tables 36a to 36d.
These first to fourth conversion tables 36a to 36d are characteristic conversion units according to the present invention. As indicated by an arrow Z in FIG. 3, among the electric signals output from the image sensor 2, the electric power derived from the logarithmic conversion mode is used. The signal is characteristically converted to a state derived from the linear conversion mode.

Further, the first through fourth conversion table 36a~36d are first to fourth driving condition variable area of each driving condition of the pixel G ₁₁ ~G _mn, in this embodiment as defined by the value of the driving conditions Is associated with. Specifically, the first conversion table 36a corresponds to the first driving condition in which the exposure time of the pixels G _{11 to} G _mn is t ₁ and the temperature is K ₁ . The second conversion table 36b, the exposure time is temperature t ₂ corresponds to the second driving condition of K _1. The third conversion table 36c corresponds to the third driving condition in which the exposure time is t ₁ and the temperature is K ₂ . The fourth conversion table 36d, the exposure time is temperature t ₂ corresponds to the fourth driving condition of K _2.

These first to conversion characteristics of the fourth conversion table 36a~36d is logarithmic conversion mode when the exposure time and temperature of the pixel G ₁₁ ~G _mn is the first to fourth driving condition from the pixel G ₁₁ ~G _mn Is set so that the electric signal output in the above is accurately derived from the linear conversion mode. Specifically, for example, the conversion characteristics of the first and second conversion tables 36a and 36b are as follows. As shown in FIGS. 7A and 7B, the exposure time of the pixels G _{11 to} G _mn at the time of imaging is t _1. , T ₂ , when the temperature is K ₁ , the electric signals output from the pixels G _{11 to} G _{mn in the} logarithmic conversion mode are set to be accurately derived from the linear conversion mode. Such conversion characteristics of the first to fourth conversion tables 36a to 36d can be obtained by experiments or theoretical calculations.

The selector 35 determines the magnitude of the electrical signal from the pixels G _{11 to} G _mn and the inflection output signal value H, and the electrical signal from the pixels G _{11 to} G _mn is less than or equal to the inflection output signal value H. The output signals from the pixels G _{11 to} G _mn are output to the output unit 31c. Further, the selector 35 is used when an electrical signal from the pixels G _{11 to} G _mn is larger than the inflection output signal value H, that is, when an electrical signal derived from the logarithmic conversion mode is output from the pixels G _{11 to} G _mn. Outputs the output signals from the pixels G _{11 to} G _mn to any one of the conversion tables 36 a to 36 d of the linearizer 36. Specifically, when the exposure time and temperature satisfy the first driving condition, the selector 35 stores output signals from the pixels G _{11 to} G _mn in the first conversion table 36a and satisfies the second driving condition. In the second conversion table 36b, the third conversion table 36c is output when the third drive condition is satisfied, and the fourth conversion table 36d is output when the fourth drive condition is satisfied. .

  The output unit 31c outputs an electrical signal input from the selector 35 or the first to fourth conversion tables 36a to 36d.

  As shown in FIG. 1, an inflection signal deriving unit 34 and an image processing unit 4 are connected to the signal processing unit 3, respectively.

The inflection signal deriving unit 34 derives the inflection output signal value H based on the exposure time information and temperature information of the pixels G _{11 to} G _mn and the pixel information. In the present embodiment, A lookup table 34a for deriving the inflection output signal value H by inputting such information is provided. The exposure time information of the pixels G _{11 to} G _mn is information about the exposure time, and the temperature information is information about the temperature. As pixel information, unique information such as ID numbers of the pixels G _{11 to} G _mn , position information in the image sensor, and the like are used.

The image processing unit 4 performs image processing on image data constituted by the entire electrical signals from the pixels G _{11 to} G _mn , and includes an AWB (Auto White Balance) processing unit 40, a color interpolation unit 41, a color A correction unit 42, a gradation conversion unit 43, and a color space conversion unit 44 are provided. The AWB processing unit 40, the color interpolation unit 41, the color correction unit 42, the gradation conversion unit 43, and the color space conversion unit 44 are connected to the signal processing unit 3 in this order.

The AWB processing unit 40 performs white balance processing on the image data, and the color interpolation unit 41 is based on electrical signals from a plurality of neighboring pixels provided with the same color filter, and between these neighboring pixels. For the pixel located, the electrical signal of this color is interpolated. The color correction unit 42 corrects the hue of the image data. More specifically, the color correction unit 42 corrects the electrical signal of each color for each of the pixels G _{11 to} G _mn based on the electrical signals of other colors. The gradation conversion unit 43 performs gradation conversion of image data, and the color space conversion unit 44 converts RGB signals into YCbCr signals.

Further, the evaluation value calculation unit 5 and the control device 46 are connected to the signal processing unit 3 in this order.
The evaluation value calculation unit 5 calculates an AWB evaluation value used for white balance processing (AWB processing) in the AWB processing unit 40 and an AE evaluation value used for exposure control processing (AE processing) in the exposure control processing unit 47. To do.

  The control device 46 controls each unit of the imaging device 1, and includes the amplifier 12, the black reference setting unit 14, the signal processing unit 3, the inflection signal derivation unit 34, the AWB processing unit 40, the color interpolation unit 41, and the like described above. The color correction unit 42, the gradation conversion unit 43, and the color space conversion unit 44 are connected. The control device 46 is connected to the diaphragm 11 via the exposure control processing unit 47 and is connected to the image sensor 2 and the AD converter 13 via the signal generation unit 48.

Next, the pixels G _{11 to} G _mn in this embodiment will be described.
As shown in FIG. 8, each of the pixels G _{11 to} G _mn includes a photodiode P and transistors T _{1 to} T ₃ . The transistors T _{1 to} T ₃ are N-channel MOS transistors whose back gates are grounded.

The light that has passed through the lens group 10 and the diaphragm 11 strikes the photodiode P. This is the cathode P _k of the photodiode P are DC voltage V _PD is applied, and the drain T _1D and gate T _1G of transistors T ₁ to the anode P _A, is connected to a gate T _2G of the transistor T ₂ Yes.

A signal application line L _C (corresponding to L _{C1 to} L _Cn in FIG. 2) is connected to the source T _1S of the transistor T ₁ , and the signal φ _VPS is input from the signal application line L _C. Yes. Here, the signal φ _VPS is a binary voltage signal, and more specifically, a voltage value VH for operating the transistor T ₁ in the subthreshold region when the amount of incident light exceeds a predetermined value, and the transistor T _1. The voltage value VL for setting the current to the conductive state is taken.

Further, the drain T _2D of the transistor T ₂ are are DC voltage V _PD is applied, is connected to the drain T _3D of the transistor T ₃ for source T _2S row selection transistor T _2.

_A signal application line L _A (corresponding to L _{A1 to} L _An in FIG. 2) is connected to the gate T _3G of the transistor T ₃ , and a signal φ _V is input from the signal application line L _A. ing. The source T _3S of the transistor T ₃ is connected to the signal readout line L _D (corresponding to L _{D1 to} L _Dm in FIG. 2).

As the pixels G _{11 to} G _mn as described above, those disclosed in JP-A-2002-77733 can be used.

Here, as shown in FIG. 4 described above, the proportion of the linear conversion mode increases as the exposure time decreases. The potential between the gate T _2G and the source T _2S of the transistor T ₂ decreases as the exposure time decreases. the difference becomes large, the proportion of subject brightness that transistor T ₂ is operated in a cut-off state, that is, the ratio of the object luminance linear conversion is increased. Although not shown in FIG. 4, subject luminance to be linearly converted even when the control voltage for the image sensor 2, that is, when the difference between the voltage values VL and VH of the signal φ _VPS is large or the temperature is low. The proportion of increases. Therefore, the dynamic range of the image signal, the predetermined incident light amount th at the inflection point, and the inflection output signal value H can be controlled by changing the control voltage, exposure time, temperature, and the like. Specifically, for example, when the luminance range of the subject is narrow, the voltage value VL is lowered to widen the luminance range for linear conversion, and when the subject luminance range is wide, the voltage value VL is increased to logarithmically. By widening the luminance range to be converted, the photoelectric conversion characteristics of the pixels G _{11 to} G _mn can be matched with the characteristics of the subject. Furthermore, the constantly state that linearly converting the pixel G ₁₁ ~G _mn when to minimize the voltage value VL, always be a state for logarithmically converting the pixel G ₁₁ ~G _mn is when the maximum voltage value VL.

Subsequently, an imaging operation of the imaging apparatus 1 will be described with reference to FIG.
First, the image sensor 2 photoelectrically converts incident light to the pixels G _{11 to} G _mn and outputs an electrical signal derived from the linear conversion mode or the logarithmic conversion mode as an analog signal. Specifically, when each of the pixels G _{11 to} G _mn outputs an electrical signal to the signal readout line L _D , the electrical signal is amplified by the constant current source D, and the selection circuit S sequentially samples and holds it. When the sampled and held electric signal is sent from the selection circuit S to the correction circuit 23, the correction circuit 23 removes noise and outputs the electric signal.

Next, this electric signal is transmitted to the selector 35 of the signal processing unit 3 via the amplifier 12, the AD converter 13, and the black reference setting unit 14. Further, the exposure time information and temperature information of the pixels G _{11 to} G _mn of the image sensor 2 and the pixel information are transmitted from the control device 46 to the selector 35 and the inflection signal deriving unit 34. Further, the inflection output signal value H derived by the lookup table 34a of the inflection signal deriving unit 34 based on the exposure time information, temperature information, and pixel information is transmitted to the selector 35 (step R1).

  Thus, since the lookup table 34a derives the inflection output signal value H based on the exposure time information, the temperature information, and the pixel information, the inflection output signal value H is accurately derived. In addition, since the inflection output signal value H is derived from the lookup table 34a, the configuration of the inflection signal deriving unit 34 is simplified and the derivation process is speeded up as compared with the case of deriving by calculation. .

Next, the selector 35 compares the inflection output signal value H with the signal value of the output signal from the pixels G _{11 to} G _mn (step R2), and the output signal from the pixels G _{11 to} G _mn changes. If it is less music output signal value H (step R2; Yes), the directly outputs the output signal from the pixel G ₁₁ ~G _mn via the output unit 31c (step R3).

When the output signal from the pixels G _{11 to} G _mn is larger than the inflection output signal value H in Step R 2 (Step R 2; No), the selector 35 determines that the exposure time and temperature of the pixels G _{11 to} G _mn are the same as those described above. It determines whether a first driving condition is satisfied (step R4), satisfies case (step R4; Yes) line characteristics converted into the first conversion table 36a for the output signals from the pixels G ₁₁ ~G _mn in (Step R5), the electrical signal after the characteristic conversion is output via the output unit 31c (Step R6).

When the exposure time and temperature do not satisfy the first drive condition in step R4 (step R4; No), the selector 35 determines whether or not the exposure time and temperature satisfy the second drive condition ( step R7), when the exposure time and temperature are the second driving condition is satisfied (step R7; the Yes), to perform the characteristic conversion in the second conversion table 36b with respect to the output signals from the pixels G ₁₁ ~G _mn After that (step R8), the electrical signal after the characteristic conversion is output via the output unit 31c (step R9).

If the exposure time and temperature do not satisfy the second drive condition in step R7 (step R7; No), the selector 35 determines whether or not the exposure time and temperature satisfy the third drive condition ( step R10), when the exposure time and temperature are the third drive condition is satisfied (step R10; the Yes), to perform the characteristic conversion in the third conversion table 36c for the output signal from the pixel G ₁₁ ~G _mn After that (step R11), the electrical signal after the characteristic conversion is output via the output unit 31c (step R12).

If the exposure time and temperature do not satisfy the third drive condition in step R10 (step R10; No), the selector 35 assumes that the exposure time and temperature satisfy the fourth drive condition, and the pixels G ₁₁ to G ₁₁ . After the fourth conversion table 36d performs characteristic conversion on the output signal from G _mn (step R13), the electric signal after characteristic conversion is output via the output unit 31c (step R14).

Next, the evaluation value calculation unit 5 calculates the AWB evaluation value and the AE evaluation value based on the electrical signal output from the signal processing unit 3.
Next, based on the calculated AE evaluation value, the control device 46 controls the exposure control processing unit 47 to adjust the exposure amount for the image sensor 2.
The control device 46 controls the AWB processing unit 40 based on the AWB evaluation value, the minimum level set by the black reference setting unit 14, etc., and the image data output from the signal processing unit 3 is white. Allow balance processing to be performed.

  The color interpolation unit 41, the color correction unit 42, the gradation conversion unit 43, and the color space conversion unit 44 perform image processing based on the image data output from the AWB processing unit 40, and then output the image data. .

According to the imaging apparatus 1 described above, even when the input-output characteristics of the pixel G ₁₁ ~G _mn by driving conditions, such as exposure time and temperature of the pixel G ₁₁ ~G _mn varies, the pixel G ₁₁ ~ Since the characteristic conversion of the electrical signal output from G _mn is performed by the first to fourth conversion tables 36a to 36d corresponding to the driving conditions at the time of imaging, the electrical signal is accurately unified to the state derived from the linear conversion mode. Can do.

Further, since the signal processing unit 3 performs characteristic conversion only when the output signals from the pixels G _{11 to} G _mn are electrical signals derived from the logarithmic conversion mode, the output signal is an electrical signal derived from the linear conversion mode. That is, when it is not necessary to convert the electrical signal derived from the logarithmic conversion mode to the state derived from the linear conversion mode, characteristic conversion is not performed. Accordingly, it is possible to save time and effort for performing signal processing, and it is possible to speed up the processing.

Further, since the signal processing section 3 for a plurality of pixels G ₁₁ ~G _mn comprises only one, as compared with the case where a plurality of signal processing unit 3 in association with each pixel G ₁₁ ~G _mn, imaging The configuration of the device 1 can be simplified.

In the above-described embodiment, it has been described that only one signal processing unit 3 is provided. However, a plurality of signal processing units 3 may be provided in association with the pixels G _{11 to} G _mn .
Moreover, although it has been described that the exposure time and the temperature are used as the driving conditions of the image sensor 2, a control voltage may be used.

Moreover, although it has been described that only one signal processing unit 3 is provided, a plurality of signal processing units 3 may be provided in association with each of the pixels G _{11 to} G _mn . In this case, even if the conversion characteristics of the photoelectric conversion are different for each of the pixels G _{11 to} G _mn , the entire electric signal can be accurately unified to a state derived from the linear conversion mode or the logarithmic conversion mode.

  Moreover, although the characteristic conversion part in this invention was demonstrated as the 1st-4th conversion tables 36a-36d which carry out characteristic conversion of the electric signal derived from logarithmic conversion mode to the state produced | generated by linear conversion, The signal may be subjected to characteristic conversion into a state derived from the logarithmic conversion mode.

  Further, although the inflection signal deriving unit 34 has been described as deriving the inflection output signal value H based on the driving condition and the pixel information, it may be derived based only on the driving condition. The inflection signal deriving unit 34 has been described as including the lookup table 34a for deriving the inflection output signal value H, but may include an arithmetic unit for deriving the inflection output signal value H.

  In addition, the signal processing unit 3 has been described as performing characteristic conversion using the first to fourth conversion tables 36a to 36d, but may be performed by calculation such as exponential conversion.

Further, the pixels G _{11 to} G _mn have been described as having the configuration as shown in FIG. 8. However, if the linear conversion mode and the logarithmic conversion mode can be switched, for example, the configuration as shown in Patent Document 1 described above. It is good also as having.

Furthermore, although it has been described that an RGB filter is provided for each of the pixels G _{11 to} G _mn , other color filters such as cyan, magenta, and yellow may be provided.

It is a block diagram which shows schematic structure of the imaging device which concerns on this invention. It is a block diagram which shows the structure of an image pick-up element. It is a figure for demonstrating operation | movement of a pixel and a linearization part. It is a figure which shows the relationship between exposure time and an inflection point. It is a figure which shows the relationship between a control voltage and an inflection point. It is a block diagram which shows a signal processing part. It is a figure which shows the 1st, 2nd conversion table. It is a circuit diagram which shows the structure of a pixel. It is a flowchart which shows the process of characteristic conversion.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Imaging device 2 Imaging element 3 Signal processing part 34 Inflection signal derivation | leading-out part 34a Look-up table 36a 1st conversion table (characteristic conversion part)
36b Second conversion table (characteristic conversion unit)
36c 3rd conversion table (characteristic conversion part)
36d Fourth conversion table (characteristic conversion unit)
G ₁₁ ~G _mn pixels

Claims (8)

An imaging device having a plurality of pixels that switch between a linear conversion mode for linearly converting incident light into an electrical signal and a logarithmic conversion mode for logarithmic conversion based on the amount of incident light;
A signal processing unit that performs signal processing on the electrical signal,
The signal processing unit
A plurality of characteristic conversion units that perform characteristic conversion for converting an electrical signal derived from one of the logarithmic conversion mode and the linear conversion mode into a state derived from the other conversion mode, corresponding to each domain of each driving condition In preparation,
An imaging apparatus characterized in that the characteristic conversion is performed by the characteristic conversion unit corresponding to the driving condition at the time of imaging among the plurality of characteristic conversion units. The imaging device according to claim 1,
An imaging apparatus comprising a plurality of the signal processing units in association with each pixel. The imaging apparatus according to claim 1 or 2,
An inflection signal deriving unit for deriving an inflection output signal value at a boundary where the linear transformation mode and the logarithmic transformation mode are switched;
The signal processing unit, when the output signal from the image sensor is an electric signal derived from the one conversion mode based on the magnitude of the signal value of the output signal from the image sensor and the inflection output signal value An image pickup apparatus that performs the signal processing only in The imaging device according to claim 3.
The inflection signal deriving unit derives the inflection output signal value based on the driving condition. The imaging device according to claim 3 or 4,
The inflection signal deriving unit derives the inflection output signal value based on the driving condition and pixel information about the pixel. The imaging device according to claim 4 or 5,
The imaging apparatus according to claim 1, wherein the inflection signal deriving unit includes a lookup table for deriving the inflection output signal value by at least input of the driving condition. The imaging device according to claim 4 or 5,
The inflection signal deriving unit includes an arithmetic unit that derives the inflection output signal value based on at least the input of the driving condition. In the imaging device according to any one of claims 1 to 7,
The image pickup apparatus, wherein the driving condition is at least one of a temperature at the time of photographing, an exposure time of the pixel, and a control voltage for the pixel.

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