JP2007116600A - Imaging apparatus and imaging method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an imaging apparatus and imaging method in which an electric signal can be accurately linearized by correction dispersion in input/output characteristics between pixels of an imaging element in simple apparatus configuration. <P>SOLUTION: An imaging apparatus comprises 1: an imaging element for outputting a saturation output signal value of an output signal linearly converted in each of pixels as an output signal value at a point of inflection at the time of set-up processing; a correction amount calculation unit 20 for calculating a difference between the output signal value at the point of inflection and a predetermined threshold incident light quantity value as a correction amount for each of the pixels; a correction amount storage unit 21 for storing the correction amount correspondingly to each of the pixels; a reference correction unit 22 for reading a correction amount from the correction amount storage unit 21, adding each of correction amounts and the predetermined threshold incident light quantity value and calculating a transformation reference value for each of the pixels; and a linear conversion unit 23 for linearly transforming, as a logarithmically transformed output signal, an output signal of the transformation reference value or more corresponding to each of the pixels among output signals of the pixels at the time of photographing. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an imaging apparatus and an imaging method, and more particularly, to an imaging apparatus and an imaging method having an imaging element capable of switching between a logarithmic conversion operation and a linear conversion operation.

  Conventionally, an imaging device such as a digital camera has been provided with an imaging element having a plurality of pixels that convert incident light into an electrical signal. In recent years, an image sensor (linear log conversion type sensor) that switches between a linear conversion operation for linearly converting incident light into an electrical signal and a logarithmic conversion operation for logarithmic conversion based on the amount of incident light has been proposed. According to this linear log conversion type sensor, the dynamic range of the electrical signal is wide compared to an image sensor that performs only a linear conversion operation. Therefore, even when a subject with a wide luminance range is photographed, all luminance information is represented by an electrical signal. can do.

  Such a linear log conversion type sensor has a problem that the arithmetic processing is complicated because the output signal includes an electrical signal logarithmically converted. Therefore, processing for facilitating computation is performed by converting the logarithmically converted electrical signal into a linearly transformed state and unifying the entire electrical signal into a linearly transformed state.

Here, the input / output characteristics of the linear log conversion type sensor vary from sensor to sensor due to changes in environmental temperature. Therefore, in order to correct the variation in input / output characteristics for each sensor, an imaging apparatus including various correction means has been proposed.

For example, Patent Literature 1 includes a temperature detector that detects the temperature of a linear log conversion sensor, and a gain control unit that sets a gain to be given to an output signal of the linear log conversion sensor according to the detected temperature. There has been proposed an imaging apparatus that corrects variations in input / output characteristics for each sensor due to changes in the sensor.
JP 2004-356866 A

  However, in the linear log conversion type sensor, there is not only a problem of variations in input / output characteristics in units of sensors, but also a problem of variations in input / output characteristics among pixels derived from the manufacturing process. When the input / output characteristics vary between the pixels in this way, the inflection point that is the boundary between the linear conversion operation and the logarithmic conversion operation varies, and the logarithmically converted electric signal is converted into a linearly converted state. There is a problem in that an error occurs between the pixels and the gradation is rough and a good captured image cannot be obtained.

  On the other hand, the inflection point can be changed by the user's operation at the time of shooting and may vary depending on the usage time of the sensor. Therefore, in order to correct the variation in input / output characteristics between each pixel, If the correction amount is stored in advance, a large amount of memory resources are used, resulting in high costs.

  SUMMARY OF THE INVENTION An object of the present invention is to correct an input / output characteristic variation between pixels of an image sensor with a simple device configuration, and to unify an electric signal into an accurately linearly converted state. It is to provide a method.

  In order to solve the above-described problem, the invention described in claim 1 is an imaging apparatus, wherein a plurality of linear conversion operations for linearly converting incident light into electrical signals and logarithmic conversion operations for logarithmic conversion can be switched according to the amount of incident light An image sensor that outputs a saturated output signal value of an output signal linearly converted in each of the pixels during the setup process, and the saturated output signal value as a conversion reference value for each of the pixels. A linear conversion unit that linearly converts an output signal equal to or higher than the conversion reference value.

  According to the first aspect of the present invention, when the integrated amount of the output signal exceeds the saturation point in the linear log conversion type sensor, each pixel starts a logarithmic conversion operation, so that the maximum amount of the output signal integrated is the output of the inflection point. Signal value. Therefore, by detecting the saturation output signal value specific to the pixel, it is possible to detect the variation of the inflection point of each pixel.

  Also, at the time of shooting, the saturation output signal value is used as a conversion reference value, and the output signal that is greater than or equal to the conversion reference value is linearly converted at each pixel, so that the logarithmically transformed output signal is linearly converted according to the inflection point of each pixel. It becomes possible to unify exactly to the state.

  The invention according to claim 2 is the imaging apparatus according to claim 1, wherein a difference between the saturated output signal value output from the imaging element and a predetermined threshold incident light amount value is calculated as a correction amount of each of the pixels. A correction amount calculation unit, a correction amount storage unit that stores the correction amount in association with each of the pixels, and the correction amount is read from the correction amount storage unit, and each correction amount and a predetermined threshold incident light amount value And a reference correction unit that calculates a conversion reference value for each of the pixels, and the linear conversion unit performs conversion based on the conversion reference value calculated by the reference correction unit. To do.

  According to the second aspect of the invention, the difference between the saturated output signal value and the predetermined threshold incident light amount value, that is, the deviation from the predetermined threshold incident light amount value is calculated as the correction amount, and this correction amount is stored. Thus, the memory capacity can be reduced as compared with the case where the saturated output signal value itself is stored.

  In addition, at the time of shooting, a predetermined threshold incident light amount value is added to the correction amount to obtain a conversion reference value for each pixel, and by linearly converting an output signal that is equal to or greater than the conversion reference value in each pixel, the saturated output signal value is converted into a conversion reference as it is. It is possible to obtain the same effect as when the value is used.

  A third aspect of the present invention is the imaging apparatus according to the first or second aspect, further comprising an exposure processing control unit that adjusts light that corresponds to a photosensitive portion of the imaging element, and the exposure processing control unit emits the light. The output signal linearly converted in each of the pixels is saturated at most.

  According to the invention described in claim 3, it is possible to detect the saturated output signal value of each pixel by saturating the linearly-converted output signal by increasing the light hitting the photosensitive portion of the image sensor.

  According to a fourth aspect of the present invention, in the imaging apparatus according to the third aspect, the exposure processing control unit blocks the light after the output signal linearly converted in each of the pixels is saturated. .

  According to the fourth aspect of the invention, since the saturated output signal value of each pixel is output from the image sensor by shielding the light after the linearly converted output signal is saturated, the inflection point of each pixel is output. It becomes possible to detect the output signal value.

  According to a fifth aspect of the present invention, there is provided the imaging apparatus according to the third or fourth aspect, further comprising an aperture, wherein the exposure processing control unit controls the aperture value of the aperture to adjust the light. And

  According to the fifth aspect of the present invention, if the aperture value is decreased, the aperture diameter is increased, and the light that hits the photosensitive portion of the image sensor can be increased.

  A sixth aspect of the present invention is the imaging apparatus according to the third or fourth aspect, further comprising a shutter, wherein the exposure processing control unit controls the opening and closing of the shutter to adjust the light. To do.

  According to the sixth aspect of the present invention, it is possible to block the light hitting the photosensitive portion of the image sensor by closing the shutter.

  A seventh aspect of the present invention is the imaging apparatus according to the third or fourth aspect of the present invention, comprising a light source that irradiates light to the photosensitive portion of the imaging element, and the exposure processing control portion turns on / off the light source. To control the light.

  According to the seventh aspect of the present invention, it is possible to increase the light hitting the photosensitive portion of the image pickup device by turning on the light source, and it is possible to block the light by turning off the light source. .

  The invention according to claim 8 is the imaging apparatus according to any one of claims 1 to 7, wherein the setup is performed when the imaging apparatus is turned on or when an inflection point is changed in each of the pixels. Processing is started.

  According to the eighth aspect of the present invention, the setup process can be performed at an appropriate time by performing the setup process when the imaging apparatus is turned on or when the inflection point is changed in each pixel.

  A ninth aspect of the present invention is the imaging apparatus according to any one of the first to seventh aspects, wherein the input / output characteristics vary between the pixels based on an output signal of the imaging element. And a control unit that determines whether the setup process is started when an instruction signal is received from the control unit.

  According to the ninth aspect of the present invention, the setup process can be performed at an appropriate time by performing the setup process in accordance with the instruction signal from the control unit.

  The invention according to claim 10 is an imaging method, comprising a plurality of pixels capable of switching between a linear conversion operation for linearly converting incident light into an electric signal and a logarithmic conversion operation for logarithmic conversion according to the amount of incident light, Using an imaging device that outputs a saturated output signal value of an output signal linearly converted in each of the pixels during the setup process, using the saturated output signal value as a conversion reference value for each of the pixels, A linear conversion step of linearly converting an output signal equal to or greater than the value is provided.

  According to the tenth aspect of the present invention, in the linear log conversion type sensor, when the integrated amount of the output signal exceeds the saturation point, each pixel starts a logarithmic conversion operation. Therefore, the maximum amount in which the output signal is integrated is the output of the inflection point. Signal value. Therefore, by detecting the saturation output signal value specific to the pixel, it is possible to detect the variation of the inflection point of each pixel.

  Also, at the time of shooting, the saturation output signal value is used as a conversion reference value, and the output signal that is greater than or equal to the conversion reference value is linearly converted at each pixel, so that the logarithmically transformed output signal is linearly converted according to the inflection point of each pixel. It becomes possible to unify exactly to the state.

  The invention according to claim 11 is the imaging method according to claim 10, wherein a difference between the saturated output signal value output from the image sensor and a predetermined threshold incident light amount value is calculated as a correction amount for each of the pixels. A correction amount calculating step, a correction amount storing step of storing the correction amount in association with each of the pixels, and adding each correction amount stored in the correction amount storing step and a predetermined threshold incident light amount value And a reference correction step for calculating a conversion reference value for each of the pixels, wherein the conversion is performed based on the conversion reference value calculated by the reference correction unit in the linear conversion step.

  According to the eleventh aspect of the invention, the difference between the saturated output signal value and the predetermined threshold incident light amount value, that is, the deviation from the predetermined threshold incident light amount value is calculated as the correction amount, and this correction amount is stored. Thus, the memory capacity can be reduced as compared with the case where the saturated output signal value itself is stored.

  In addition, at the time of shooting, a predetermined threshold incident light amount value is added to the correction amount to obtain a conversion reference value for each pixel, and by linearly converting an output signal that is equal to or greater than the conversion reference value in each pixel, the saturated output signal value is converted into a conversion reference as it is. It is possible to obtain the same effect as when the value is used.

  The invention according to claim 12 is the imaging method according to claim 10 or claim 11, wherein exposure is performed to saturate an output signal linearly converted in each of the pixels by increasing light that hits a photosensitive portion of the image sensor. It has a process control process.

  According to the twelfth aspect of the present invention, it is possible to detect the saturated output signal value of each pixel by saturating the linearly converted output signal by increasing the amount of light that hits the photosensitive portion of the image sensor.

  A thirteenth aspect of the present invention is the imaging method according to the twelfth aspect of the present invention, wherein in the exposure processing control step, the light is blocked after an output signal linearly converted in each of the pixels is saturated. .

  According to the thirteenth aspect of the invention, since the saturated output signal value of each pixel is output from the image sensor by shielding the light after the linearly converted output signal is saturated, the inflection point of each pixel is output. It becomes possible to detect the output signal value.

  The invention according to claim 14 is the imaging method according to claim 12 or claim 13, wherein an aperture is used, and the aperture value of the aperture is controlled in the exposure processing control step to adjust the light. Features.

  According to the fourteenth aspect of the present invention, if the aperture value is decreased, the aperture diameter is increased, and the light that hits the photosensitive portion of the image sensor can be increased.

  A fifteenth aspect of the present invention is the imaging method according to the twelfth or thirteenth aspect, wherein a shutter is used, and the light is adjusted by controlling opening and closing of the shutter in the exposure processing control step. And

  According to the fifteenth aspect of the present invention, it is possible to block light that hits the photosensitive portion of the image sensor by closing the shutter.

  A sixteenth aspect of the present invention is the imaging method according to the twelfth or thirteenth aspect of the present invention, wherein a light source that irradiates light to the photosensitive portion of the image sensor is used, and the light source is turned on / off in the exposure processing control step. The light is adjusted by controlling OFF.

  According to the sixteenth aspect of the present invention, it is possible to increase the light hitting the photosensitive portion of the image sensor by turning on the light source, and it is possible to block the light by turning off the light source. .

  The invention according to claim 17 is the imaging method according to any one of claims 10 to 16, wherein the setup is performed when the imaging device is turned on or when an inflection point is changed in each of the pixels. Processing is started.

  According to the seventeenth aspect of the present invention, the setup process can be performed at an appropriate time by performing the setup process when the imaging apparatus is turned on or when the inflection point is changed in each pixel.

  The invention according to claim 18 is the imaging method according to any one of claims 10 to 16, wherein there is variation in input / output characteristics between the pixels based on an output signal of the image sensor. And a control unit for determining whether the setup process is started when an instruction signal is received from the control unit.

  According to the eighteenth aspect, the setup process can be performed at an appropriate time by performing the setup process in accordance with the instruction signal from the control unit.

  According to the invention of claim 1 or claim 10, it is possible to correct the conversion reference value of the linear conversion with a simple device configuration, and to unify the output signal of each pixel into a state in which the linear conversion is accurately performed. .

  According to the second or eleventh aspect of the present invention, the memory capacity for storing the correction amount can be reduced.

  According to the invention of claim 3 or claim 12, it is possible to detect the saturation output signal value of each pixel of the image sensor.

  According to the invention of claim 4 or claim 13, it is possible to output the saturation output signal value of each pixel of the image sensor as the output signal value of the inflection point.

  According to the invention of claim 5 or claim 14, it is possible to saturate the linearly converted output signal of each pixel by controlling the diaphragm.

  According to the invention described in claim 6 or claim 15, it becomes possible to output the saturation output signal value of each pixel as the output signal value of the inflection point by controlling the shutter.

  According to the seventh or sixteenth aspect of the present invention, the output signal subjected to linear conversion of each pixel is saturated by controlling the light source, and the saturated output signal value of each pixel is output as the output signal value of the inflection point. It becomes possible to make it.

  According to invention of Claim 8 or Claim 17, it becomes possible to perform a setup process at an appropriate time.

  According to invention of Claim 9 or Claim 18, it becomes possible to perform a setup process at an appropriate time.

[First embodiment]
Hereinafter, a first embodiment of the present invention will be described with reference to FIGS.

  FIG. 1 shows a functional configuration of the imaging apparatus 1 according to the present embodiment. As shown in FIG. 1, the imaging apparatus 1 includes an imaging element 3 that receives incident light via an imaging adjustment unit 2. The imaging adjustment unit 2 includes, for example, a lens group 4, a shutter 5, and a diaphragm 6.

  The lens group 4 is configured by a conventionally known lens such as a focusing lens or a zoom lens. A known shutter mechanism can be used as the shutter 5. The diaphragm 6 is composed of a plurality of plates, and these plates are used to adjust the amount of light that corresponds to the photosensitive portion of the image sensor.

As shown in FIG. 2, the imaging device 3 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 pixel G ₁₁ ~G _mn is for outputting an electric signal incident light by photoelectric conversion. These pixels G _{11 to} G _mn switch the conversion operation to an electric signal based on the incident light amount, and linearly convert the incident light for an incident light amount less than a predetermined incident light amount as will be described later. In the linear conversion operation, a logarithmic conversion operation for logarithmically converting incident light is performed for an incident light amount equal to or greater than a predetermined incident light amount.

A filter (not shown) of any one of red, green, and blue is disposed on the lens group 4 side of each 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 7, 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 are adapted to give signals φ _v and φ _VPS (see FIG. 3) to the pixels G _{11 to} G _mn . A vertical scanning circuit 8 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 8 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 15 (see FIG. 1) described later. Yes, 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 9 and a correction circuit 10 are connected to these selection circuits S _{1 to} S _m . The horizontal scanning circuit 9 sequentially switches selection circuits S _{1 to} S _m that sample and hold an electric signal and transmit the signal to the correction circuit 10 in the Y direction. The correction circuit 10 removes a noise signal from the electric signal based on the noise signal transmitted from the selection circuits S _{1 to} S _m and the electric signal at the time of imaging.

As the selection circuits S _{1 to} S _m and the correction circuit 10, those disclosed in JP-A-2001-223948 can be used. In the present embodiment, the description will be made assuming that only one correction circuit 10 is provided for the entire selection circuits S _{1 to} S _m , but the correction circuit 10 is provided for each of the selection circuits S _{1 to} S _m. It is good also as providing one by one.

Next, the pixels G _{11 to} G _mn in this embodiment will be described.

As shown in FIG. 3, 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 4 and the diaphragm 6 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.

The imaging device 3 of the present embodiment performs logarithmic conversion of incident light with a natural logarithm by operating the transistor T ₁ of each pixel G _{m1 to} G _{mn in} the subthreshold region when the incident light quantity exceeds a predetermined threshold. It can be read as a voltage. Thereby, as shown in FIG. 4, the output signal of the image sensor 3 has a linear region and a logarithmic region that change continuously according to the amount of incident light.

Further, as shown in FIG. 3, 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 ing.

Further, 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.

In the imaging device 5 that operates in this way, the voltage value VL of the signal φ _VPS given to the pixels G _{11 to} G _mn is switched to switch the dynamic range, which is a boundary between the linear conversion operation and the logarithmic conversion operation. The inflection point can be changed. For example, by making the voltage value VL low and widening the luminance range for linear conversion, or increasing the voltage value VL and making the logarithmic conversion wide, the photoelectric conversion characteristics that match the characteristics of the subject are obtained. Can do. Note that it is possible to always perform linear conversion with the voltage value VL being minimized, or to constantly logarithmically convert the voltage value VH to be maximum.

Here, in each of the pixels G _{11 to} G _mn included in the image pickup device 3, variations in input / output characteristics of electric signals usually occur due to the manufacturing process. For example, as shown in FIG. 5, the curves (1) to (3) indicating the output signals of the pixels G _{11 to} G ₁₃ have the same linear region gradient, but the linear conversion operation and the logarithmic conversion operation are different. The output signal value (inflection output signal value H) at the switching boundary, so-called inflection point, is different.

The image pickup device 3 of the present embodiment outputs the saturation output signal value when the output signal linearly converted in each pixel G _{11 to} G _mn is in a saturated state during the setup process, and the inflection output of each pixel G _{11 to} G _mn. The signal values H _{11 to} H _mn are output to the correction amount calculation unit 20.

  As shown in FIG. 1, an exposure processing control unit 11 and a system control unit 12 are connected to the above imaging adjustment unit 2 and imaging device 3 in this order.

  The exposure processing control unit 11 is composed of a zoom control mechanism, a focus control mechanism, a shutter control mechanism, an aperture control mechanism, and the like, and receives a feedback such as a zoom position detection signal or a focus position detection signal according to a control signal from the system control unit 12. The imaging adjustment unit 2 is controlled.

  The system control unit 12 is composed of a CPU (Central Processing Unit), a RAM (Random Access Memory) composed of rewritable semiconductor elements, and a ROM (Read Only Memory) composed of nonvolatile semiconductor memory, Each component of the imaging device 1 is controlled.

  In addition, when the system control unit 12 determines that there is a variation in input / output characteristics between pixels based on the output signal of the image sensor 3, the system control unit 12 issues a setup processing instruction signal to the setup control unit 19. ing.

  As shown in FIG. 1, an amplifier 13 and an AD converter 14 are connected to the image sensor 3, and a signal generation unit 15 and a system control unit 12 are connected to the image sensor 3 and the AD converter 14 in this order. Has been.

  A conventionally known amplifier is used as the amplifier 13 and amplifies the signal photoelectrically converted by the image sensor 3.

  The AD converter 14 converts the electrical signal amplified by the amplifier 13 from an analog signal to a digital signal.

  The signal generator 15 controls the photographing operation of the image sensor 3. That is, a predetermined timing pulse (a pixel drive signal, a horizontal synchronization signal, a vertical synchronization signal, a horizontal scanning circuit drive signal, a vertical scanning circuit drive signal, etc.) is generated based on a control signal from the system control unit 12 and the image sensor 3. To output. The signal generator 15 also generates a timing signal for AD conversion.

  Further, the black reference setting unit 16 and the signal processing unit 17 are connected to the AD converter 14 in this order, and the image processing unit 18 and the system control unit 12 are connected to the signal processing unit 17.

  The black reference setting unit 16 sets the black reference value in the image signal based on the black reference value obtained from the optically shielded optical black pixel (optical black pixel) region provided in the image sensor 3. The setting, that is, the minimum level of the digital signal is set.

  The signal processing unit 17 performs signal processing on the electrical signal from each pixel of the image sensor 3, and includes a setup control unit 19, a correction amount calculation unit 20, a correction amount storage unit 21, a reference correction unit 22, and linear A conversion unit 23 is provided.

  The setup control unit 19 controls the exposure processing control unit 11, the correction amount calculation unit 20, the correction amount storage unit 21, and the reference correction unit 22 to correct variations in input / output characteristics between pixels in linear conversion. A setup process for calculating the conversion reference value and setting it in the linear conversion unit 23 is performed.

  Here, the setup control unit 19 starts the setup process when the user selects the setup mode on the function selection screen when the imaging apparatus 1 is turned on. The setup process may be automatically started when the power of the imaging apparatus 1 is turned on. Also, the setup control unit 19 starts the setup process when the inflection point is changed or when there is an instruction signal from the system control unit 12.

At the time of shooting in the setup process, the setup control unit 19 increases the aperture of the diaphragm 6 under the control of the exposure process control unit 11 so that the linearly converted output signal is saturated. This makes it possible to detect the saturation output signal values of the linearly converted output signals derived from the pixels G _{11 to} G _mn as the inflection output signal values H _{11 to} H _mn .

  Here, in normal imaging without opening the aperture 6, as shown in FIG. 6, the output signal of the image sensor 3 is linearly converted and logarithmically converted from the start of imaging to the end of imaging. It changes continuously in response.

On the other hand, when the aperture value is increased near the minimum value during shooting in the setup process, the amount of incident light increases, so that the linearly converted output signal is saturated as shown in FIG. When blocks the incident light by the shutter 5 after linearly converted output signal is saturated, linear transformed inflection output signal value H ₁₁ to H of the saturated output signal values i.e. the pixels G ₁₁ ~G _mn of the output signal _mn is output from the image sensor 3. Thus, the inflection output signal value H ₁₁ to H _mn of each pixel G ₁₁ ~G _mn is detected.

For example, in FIG. 7, the time from the start to the end of charge accumulation by photoelectric conversion of the image sensor 3 is t, the exposure time is t / 2, and the light shielding time is t / 2. In other words, when the aperture value of the aperture 6 is made close to the minimum value and the aperture is increased and the shutter 5 is opened at time t ₀ and exposure is started, the output signal linearly converted at time t ₁ is saturated. Then, after the elapse of t / 2 hours from the time t ₀ , the shutter 5 is closed to shield the light, and the exposure ends. Further, since the logarithmically converted electrical signal is escaped and the linearly converted output signal is derived, the charge accumulation is completed at time t ₂ after the elapse of t / 2 hours from the light shielding by the shutter 5, and the charge is read out. . Thereby, the saturation output signal value of the linearly transformed output signal derived from each of the pixels G _{11 to} G _mn can be detected as the inflection output signal value H _{11 to} H _mn .

  The exposure time is not limited to t / 2 as long as the linearly converted output signal can be saturated. Also, the light shielding time is not limited to t / 2 as long as the logarithmically converted electrical signal can be escaped and the linearly converted output signal can be derived.

Correction amount calculation unit 20, the image pickup element 3 outputs the inflection output signal value H ₁₁ to H _mn of each pixel G ₁₁ ~G _mn, taking the difference between the predetermined閾入Shako amount value H for these values Accordingly, the deviation amount from the predetermined threshold incident light amount value H is calculated as the correction amounts α _{11 to} α _mn . That is, the correction amounts α _{11 to} α _mn can be calculated by the following equation (1).

The correction amount storage unit 21 stores the correction amounts α _{11 to} α _{mn in association} with the pixels G _{11 to} G _mn . Thus, as compared with the case of storing the inflection output signal value H ₁₁ to H _mn of each pixel G ₁₁ ~G _mn, it is possible to reduce the memory capacity to be used. For example, when the inflection output signal values H _{11 to} H _mn are around 1200, a memory capacity of 11 bits × number of pixels is required, but when storing the correction amounts α _{11 to} α _mn , a predetermined threshold incident light quantity value If the deviation from H is within ± 20, a memory capacity of 5 bits × number of pixels is sufficient.

When the reference correction unit 22 reads out the correction amounts α _{11 to} α _mn corresponding to the pixels G _{11 to} G _mn from the correction amount storage unit 21, the reference correction unit 22 sets a predetermined threshold incident light amount value H to the correction amounts α _{11 to} α _mn. In addition, a conversion reference value is calculated for each of the pixels G _{11 to} G _{mn, and} each conversion reference value is set in the linear conversion unit 23. Thus, it is possible to obtain the same effect as if set to directly convert the reference value inflection output signal value H ₁₁ to H _mn saturated output signal value that is, each pixel G ₁₁ ~G _mn.

As indicated by an arrow Z in FIG. 4, the linear conversion unit 23 linearly converts an output signal that has been logarithmically converted from among the electrical signals output from the image sensor 3. Here, the linear conversion unit 23 of the present embodiment linearizes an output signal equal to or higher than the conversion reference value calculated by the reference correction unit 22 among the electrical signals derived from the pixels G _{11 to} G _mn. It has become. As a result, even if there is a variation in the inflection points between the pixels due to the manufacturing process, etc., this variation is adjusted by the correction amounts α _{11 to} α _{mn and} the error between the pixels in the linear conversion is corrected. Is done.

  The linear conversion in the linear conversion unit 23 may be performed using a lookup table, or may be performed by an operation such as exponential conversion.

  An evaluation value calculation unit 24 is connected to the linear conversion unit 23. The evaluation value calculation unit 24 calculates an AWB evaluation value used for white balance processing (AWB processing) and an AE evaluation value used for exposure control processing (AE processing).

  Next, the image processing unit 18 performs image processing on the electrical signal linearly converted by the linear conversion unit 23, and includes an AWB (Auto White Balance) processing unit 25, a color interpolation unit 26, and a color correction unit 27. , A tone correction unit 28 and a color space conversion unit 29 are provided. The AWB processing unit 25, the color interpolation unit 26, the color correction unit 27, the gradation correction unit 28, and the color space conversion unit 29 are connected to the signal processing unit 17 in this order.

  The AWB processing unit 25 performs white balance processing on the image data.

  The color interpolation unit 26 interpolates the electrical signals of this color for pixels located between the adjacent pixels based on the electrical signals from a plurality of adjacent pixels provided with the same color filter.

  The color correction unit 27 corrects the hue of the image data. More specifically, the color correction unit 27 corrects the electrical signal of each color for each pixel based on the electrical signals of other colors.

  The gradation correction unit 28 performs gradation correction of image data.

  The color space conversion unit 29 converts RGB signals into YCbCr signals.

  Further, the system control unit 12 includes an operation unit 30 for operating the imaging apparatus 1, a memory card I / F 32 for connecting a memory card 31 for storing captured image data, and captured image data. An LCD I / F 34 for connecting an LCD (Liquid Crystal Display) 33 to be displayed is connected.

In the operation unit 30, the inflection point at which the linear conversion operation is switched to the logarithmic conversion operation can be changed by switching the voltage value VL of the signal φ _VPS given to the pixels G _{11 to} G _mn of the image sensor 3. It is like that.

  Next, the imaging method of the present invention using the imaging apparatus 1 of the present embodiment will be described with reference to the flowchart of FIG.

  When the power of the imaging device 1 is turned on, the LCD 33 displays a setup mode selection screen (step S1). When the user selects the setup mode by operating the operation unit 30, the setup control unit 19 starts the setup process (steps S2 to S10).

  Note that the setup process may be automatically started when the power of the imaging apparatus 1 is turned on. Further, the setup process may be started when the inflection point is changed or when an instruction signal is received from the system control unit 12.

Next, when the setup mode is entered, the setup control unit 19 proceeds to the exposure process control step. First, the aperture value is set near the minimum value by the control of the exposure processing control unit 11, the aperture 6 is enlarged (step S2), and setup shooting is started (step S3). Subsequently, as shown in FIG. 7, when the exposure is started by opening the shutter 5 to the time t ₀ (step S4), and an output signal which is linearly converted to a time t ₁ is saturated. During this time, the dark closes the shutter 5 from the setup control unit 19 the time t ₀ has been determined whether the elapsed t / 2 hours (step S5), and after t / 2 hours from the time t _0, exposure Is finished (step S6). Subsequently, when the setup control unit 19 determines that t / 2 hours have elapsed since the light shielding by the shutter 5 (step S7), the integration of the charge is terminated assuming that the logarithmically converted electrical signal has been released, and linear conversion is performed. The charge is read by the operation (step S8). As a result, the saturated output signal values of the linearly converted output signals derived from the pixels G _{11 to} G _mn are detected as inflection output signal values H _{11 to} H _mn .

Subsequently, the process proceeds to a correction amount calculation process. When the correction amount calculation unit 20 detects the inflection output signal values H _{11 to} H _mn of the pixels G _{11 to} G _mn , these values and a predetermined threshold incident light amount value H are detected. Is calculated as correction amounts α _{11 to} α _mn (step S9). The correction amounts α _{11 to} α _mn can be calculated by the above equation (1).

Subsequently, the process proceeds to the correction amount storage step, and the correction amount storage unit 21 stores the correction amounts α _{11 to} α _{mn in association} with the pixels G _{11 to} G _mn (step S10). Thus, as compared with the case of storing the inflection output signal value H ₁₁ to H _mn of each pixel G ₁₁ ~G _mn, it is possible to reduce the memory capacity to be used.

Next, the process proceeds to the reference correction step. When the reference correction unit 22 reads the correction amounts α _{11 to} α _mn from the correction amount storage unit 21, a predetermined threshold incident light amount value H is set to the correction amounts α _{11 to} α _mn. Addition is performed to calculate a conversion reference value for each of the pixels G _{11 to} G _{mn, and} each conversion reference value is set in the linear conversion unit 23.

Subsequently, the process proceeds to a linear conversion step, and the linear conversion unit 23 linearly converts the logarithmically converted output signal among the electric signals output from the image sensor 3 as indicated by an arrow Z in FIG. At this time, among the electrical signals derived from the pixels G _{11 to} G _mn, an output signal equal to or higher than the conversion reference value calculated by the reference correction unit 22 is linearized. Thereby, the dispersion | variation in the input-output characteristic between each pixel in linear conversion is correct | amended.

On the other hand, when the setup mode is not selected on the selection screen of the LCD 33, the setup control unit 19 reads out the correction amounts α _{11 to} α _mn of the pixels G _{11 to} G _mn from the correction amount storage unit 21 and linear conversion unit 23. (Step S11), and the linear converter 23 linearizes an output signal equal to or greater than a value obtained by adding a predetermined threshold incident light quantity value H to the correction amounts α _{11 to} α _mn (step S12).

As described above, according to the imaging apparatus 1 and the imaging method of the present embodiment, in the linear log conversion type sensor, when the output signal integration amount exceeds the saturation point, the pixels G _{11 to} G _mn start logarithmic conversion operations. The maximum amount by which the output signal is integrated becomes the output signal value at the inflection point. Therefore, by detecting the saturation output signal value specific to the pixel, it is possible to detect the variation in the inflection points of the pixels G _{11 to} G _mn .
Further, the conversion reference value saturation output signal value at the time of shooting, by linearly converting the output signal of the above conversion reference value in each pixel G ₁₁ ~G _mn, depending on the inflection point of each of the pixels G ₁₁ ~G _mn It is possible to accurately unify the logarithmically transformed output signal into a linearly transformed state.

Further, the amount of deviation from the difference or the predetermined閾入Shako quantity value of the saturated output signal value and a predetermined閾入Shako amount value calculated as the correction amount alpha ₁₁ to? _Mn, and stores the correction amount alpha ₁₁ to? _Mn As a result, the memory capacity can be reduced as compared with the case where the saturated output signal value itself is stored.
Further, at the time of photographing correction alpha ₁₁ to? By adding a predetermined閾入Shako amount values _mn and conversion reference value of each pixel G ₁₁ ~G _mn, conversion reference value or more output signals in each pixel G ₁₁ ~G _mn Can be linearly converted to obtain the same effect as when the saturated output signal value is used as the conversion reference value as it is.

  Further, if the aperture value of the aperture 6 is reduced, the aperture diameter is increased, so that it is possible to increase the light hitting the photosensitive portion of the image sensor 3, and by closing the shutter 5, the light hitting the photosensitive portion of the image sensor 3 is blocked. It becomes possible to do.

  Further, by increasing the amount of light that hits the photosensitive portion of the image sensor 3, it is possible to saturate the linearly converted output signal and detect the saturated output signal value of each pixel.

Further, since the saturated output signal value of each pixel G _{11 to} G _mn is output from the image sensor 3 by shielding the light after the linearly converted output signal is saturated, the change of each pixel G _{11 to} G _mn is performed. It becomes possible to detect the output signal value of the music point.

  Further, the setup process can be performed at an appropriate time by performing the setup process when the imaging apparatus is turned on or when the inflection point is changed.

  Further, by performing the setup process according to the instruction signal from the control unit, the setup process can be performed at an appropriate time.

  In the present embodiment, the aperture 6 is enlarged by controlling the exposure processing control unit 11 to saturate the linearly converted output signal. However, the exposure time is increased by controlling the exposure processing control unit 11. Thus, the linearly transformed output signal may be saturated. In addition, a message may be displayed on the LCD 33 so that the user captures a sufficiently bright subject in the setup process.

[Second Embodiment]
Next, a second embodiment of the present invention will be described with reference to FIGS. In addition, the same code | symbol is attached | subjected to the component similar to the said embodiment, and the description is abbreviate | omitted.

  In the imaging apparatus 1 of the present embodiment, a light source 35 that irradiates light to the photosensitive portion of the imaging element 3 is incorporated.

  A setup control unit 19 is connected to the light source 35. When the setup control unit 19 turns on the light source 35 during shooting of the setup process, the light source 35 irradiates light to the photosensitive unit of the image sensor 3 and is linearly converted. The output signal is saturated.

  Next, the imaging method of the present invention using the imaging apparatus 1 of the present embodiment will be described with reference to the flowchart of FIG.

  Step S21 is the same as step S1 of the first embodiment.

  Next, in the setup mode, the setup control unit 19 turns on the light source 35 to irradiate the vicinity of the image sensor 3 (step S22), and starts setup imaging (step S23). Then, when the integrated value is saturated after a lapse of a predetermined time from the start of charge integration (step S24), the light source 35 is turned off (step S25). Further, when a predetermined time elapses after the light source 35 is turned off (step S26), the charge accumulation is terminated and the charge is read (step S27).

  Note that steps S28 to S31 are the same as steps S9 to S12 of the first embodiment.

  As described above, according to the imaging apparatus 1 and the imaging method of the present embodiment, the linearly converted output signal can be easily saturated by the control of the light source 35 incorporated in the imaging apparatus 1.

  As described above in detail, according to the imaging apparatus and imaging method of the present invention, the conversion reference value of linear conversion is corrected with a simple apparatus configuration, and the output signal of each pixel is unified into a state in which the linear conversion is accurately performed. It becomes possible to do.

  In addition, the memory capacity for storing the correction amount can be reduced.

  It is also possible to detect the saturation output signal value of each pixel of the image sensor.

  It is also possible to output the saturation output signal value of each pixel of the image sensor as the output signal value at the inflection point.

  Further, it becomes possible to saturate the linearly converted output signal of each pixel by controlling the aperture.

  In addition, the saturation output signal value of each pixel can be output as the inflection point output signal value by controlling the shutter.

  Further, it becomes possible to saturate the linearly converted output signal of each pixel by controlling the light source, and to output the saturated output signal value of each pixel as the output signal value of the inflection point.

  In addition, the setup process can be performed at an appropriate time.

1 is a block diagram illustrating a schematic configuration of an imaging apparatus according to a first embodiment. It is a block diagram which shows the structure of the image pick-up element which concerns on 1st Embodiment. FIG. 3 is a circuit diagram illustrating a configuration of a pixel according to the first embodiment. It is a graph which shows the output signal of the image sensor which concerns on 1st Embodiment. It is a graph which shows the output signal of each pixel of the image sensor concerning a 1st embodiment. It is a graph which shows the output signal at the time of performing normal imaging | photography. It is a graph which shows an output signal at the time of performing setup processing concerning a 1st embodiment. It is a flowchart which shows the imaging method which concerns on 1st Embodiment. It is a block diagram which shows schematic structure of the imaging device which concerns on 2nd Embodiment. It is a flowchart which shows the imaging method which concerns on 2nd Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Imaging device 2 Imaging adjustment means 3 Imaging element 4 Lens group 5 Shutter 6 Aperture 11 Exposure process control part 12 System control part 13 Amplifier 14 AD converter 15 Signal generation part 16 Black reference setting part 17 Signal processing part 18 Image processing part 19 Setup Control unit 20 Correction amount calculation unit 21 Correction amount storage unit 22 Reference correction unit 23 Linear conversion unit 24 Evaluation value calculation unit 25 AWB processing unit 26 Color interpolation unit 27 Color correction unit 28 Tone correction unit 29 Color space conversion unit 30 Operation unit 31 Memory card 32 Memory card I / F
33 LCD
34 LCD display I / F
35 Light source

Claims (18)

An output signal having a plurality of pixels capable of switching between linear conversion operation for linearly converting incident light into an electrical signal and logarithmic conversion operation for logarithmic conversion according to the amount of incident light, and linearly converted in each of the pixels during setup processing An image sensor that outputs a saturated output signal value of
The saturation output signal value is a conversion reference value for each of the pixels, and a linear conversion unit that linearly converts an output signal equal to or higher than the conversion reference value at the time of shooting,
An imaging apparatus comprising: A correction amount calculation unit that calculates a difference between the saturation output signal value output from the image sensor and a predetermined threshold incident light amount value as a correction amount of each of the pixels;
A correction amount storage unit that stores the correction amount in association with each of the pixels;
A reference correction unit that reads out the correction amount from the correction amount storage unit and adds each correction amount and a predetermined threshold incident light amount value to calculate a conversion reference value of each of the pixels;
The imaging apparatus according to claim 1, wherein the linear conversion unit performs conversion based on the conversion reference value calculated by the reference correction unit.   An exposure processing control unit that adjusts light that hits a photosensitive unit of the image sensor, wherein the exposure processing control unit increases the light to saturate an output signal linearly converted in each of the pixels. The imaging device according to claim 1 or 2.   The imaging apparatus according to claim 3, wherein the exposure processing control unit blocks the light after the output signal linearly converted in each of the pixels is saturated.   The imaging apparatus according to claim 3, further comprising an aperture, wherein the exposure processing control unit adjusts the light by controlling an aperture value of the aperture.   The imaging apparatus according to claim 3, further comprising a shutter, wherein the exposure processing control unit controls the opening and closing of the shutter to adjust the light.   The light source which irradiates light to the photosensitive part of the said image pick-up element is provided, The said exposure process control part controls ON / OFF of the said light source, and adjusts the said light, The said light is adjusted. Imaging device.   The imaging apparatus according to claim 1, wherein the setup process is started when the imaging apparatus is turned on or when an inflection point is changed in each of the pixels.   A control unit that determines whether or not input / output characteristics vary among the pixels based on an output signal of the image sensor, and the setup process is started when an instruction signal is received from the control unit; The imaging device according to any one of claims 1 to 7. An output signal having a plurality of pixels capable of switching between linear conversion operation for linearly converting incident light into an electrical signal and logarithmic conversion operation for logarithmic conversion according to the amount of incident light, and linearly converted in each of the pixels during setup processing Using an image sensor that outputs a saturated output signal value of
An imaging method comprising: a linear conversion step of linearly converting an output signal equal to or higher than the conversion reference value at the time of photographing using the saturated output signal value as a conversion reference value for each of the pixels. A correction amount calculating step of calculating a difference between the saturated output signal value output from the image sensor and a predetermined threshold incident light amount value as a correction amount of each of the pixels;
A correction amount storing step of storing the correction amount in association with each of the pixels;
A reference correction step of calculating each conversion reference value of the pixel by adding each correction amount stored in the correction amount storage step and a predetermined threshold incident light amount value;
The imaging method according to claim 10, wherein in the linear conversion step, conversion is performed based on the conversion reference value calculated by the reference correction unit.   The imaging method according to claim 10, further comprising an exposure processing control step of saturating an output signal linearly converted in each of the pixels by increasing light hitting a photosensitive portion of the imaging element.   13. The imaging method according to claim 12, wherein, in the exposure processing control step, the light is shielded after an output signal linearly converted in each of the pixels is saturated.   14. The imaging method according to claim 12, wherein an aperture is used and the light is adjusted by controlling an aperture value of the aperture in the exposure processing control step.   14. The imaging method according to claim 12, wherein a shutter is used and the light is adjusted by controlling opening and closing of the shutter in the exposure processing control step.   14. The light source for irradiating light to the photosensitive part of the image sensor is used, and the light is adjusted by controlling ON / OFF of the light source in the exposure processing control step. Imaging method.   The imaging method according to any one of claims 10 to 16, wherein the setup process is started when the imaging apparatus is turned on or when an inflection point is changed in each of the pixels.   Using a control unit that determines whether or not input / output characteristics vary among the pixels based on the output signal of the image sensor, and starting the setup process when there is an instruction signal from the control unit The imaging method according to any one of claims 10 to 16, wherein the imaging method is characterized.

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