JP2006279714A - Imaging apparatus and imaging method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To photograph an image in which luminance saturation is reduced in comparison with the prior art. <P>SOLUTION: An imaging apparatus 1 comprises an imaging element 2 including a plurality of pixels G<SB>11</SB>-G<SB>mn</SB>for switching between a linear conversion mode for linearly converting light into an electric signal, and a logarithmic transformation mode for logarithmic transformation based on the quantity of incident light, and a control device 46 for controlling the imaging element 2. The control device 46 causes the imaging element 2 to perform consecutive photographing by shifting a point of inflection Q as a boundary between the linear conversion mode and the logarithmic transformation mode. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an imaging device having an imaging device that converts incident light into an electrical signal, and an imaging method using the imaging device.

  2. Description of the Related Art Conventionally, an image pickup apparatus that takes a digital image using an image pickup element that converts incident light into an electrical signal has a function of taking a plurality of images with different image pickup conditions such as an exposure amount by a single release operation, a so-called auto bracket. A function is added (see, for example, Patent Documents 1 to 3). According to such an imaging apparatus, as shown in FIG. 15, the user can select a desired image from a plurality of captured images (see (a) to (c) in the figure), such as whiteout or blackout. An image with low luminance saturation (see (b) in the figure) can be selected.

By the way, in recent years, the image pickup device switches the conversion mode to an electric signal based on the amount of incident light. More specifically, the imaging element performs logarithmic conversion with a linear conversion mode for linearly converting incident light into an electric signal. The logarithmic conversion mode is switched (see, for example, Patent Documents 4 and 5). According to such an image sensor, luminance information in a wide luminance range can be expressed by an electric signal because the dynamic range of the electric signal is wide compared to an image sensor that performs only the linear conversion mode. Images with even less saturation can be taken.
JP 2003-110923 A JP 2004-229073 A JP 2003-224812 A JP 2002-77733 A JP 2004-88312 A

  However, since the auto bracket function is not yet added to the image pickup apparatus having the image pickup element as in Patent Documents 4 and 5, when shooting using this image pickup apparatus, depending on the luminance range of the subject, There are cases where an image with low luminance saturation cannot be taken.

  The subject of this invention is providing the imaging device and imaging method which can image | photograph an image with little brightness saturation compared with the past.

The invention according to claim 1 is an imaging device,
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 control device for controlling the image sensor;
The control device shifts an inflection point that is a boundary between the linear conversion mode and the logarithmic conversion mode, and causes the image sensor to perform continuous shooting.

  According to the first aspect of the present invention, since the pixels of the image sensor switch between the linear conversion mode and the logarithmic conversion mode based on the amount of incident light, the electric signal in the image data is compared with the case where only the linear conversion mode is performed. As the dynamic range becomes wider, luminance information in a wider luminance range can be expressed by an electric signal, that is, an image with less luminance saturation can be taken. In addition, the inflection point that is the boundary between the linear conversion mode and the logarithmic conversion mode is shifted, and the image sensor performs continuous shooting. As a result, the dynamic range of the electrical signal changes between each imaging operation. As a part of the image, an image with less luminance saturation can be obtained. Therefore, unlike the conventional case of imaging without using the auto bracket function, an image with less luminance saturation can be taken.

Note that in continuous shooting, imaging conditions other than the inflection point, such as the exposure amount of the imaging element, may be shifted.
The amount of incident light corresponds to the luminance of the subject.

The invention described in claim 2 is the imaging apparatus according to claim 1,
A storage unit for storing a plurality of image data is provided.

  According to the second aspect of the present invention, since the storage unit that stores a plurality of image data is provided, a plurality of captured images can be collectively stored in the storage unit. Therefore, it is possible to reliably store an image with little luminance saturation.

The invention described in claim 3 is the imaging apparatus according to claim 2,
An input device for inputting operation instructions is provided.
The storage unit stores image data based on an operation instruction input to the input device.

  According to the third aspect of the present invention, since the storage unit stores the image data based on the operation instruction input to the input device, an image with less luminance saturation can be more reliably saved.

According to a fourth aspect of the present invention, in the imaging apparatus according to the second aspect,
The storage unit stores all image data shot by one continuous shooting.

  According to the fourth aspect of the present invention, since the storage unit stores all image data captured by one continuous shooting, an image with less luminance saturation can be stored more reliably.

Invention of Claim 5 is an imaging device as described in any one of Claims 1-4,
A display unit that displays a plurality of images is provided.

  According to the fifth aspect of the present invention, since the display unit that displays a plurality of images is provided, the operator can check the plurality of captured images at a time. Therefore, it can be easily confirmed that an image with little luminance saturation has been taken.

The invention described in claim 6 is the imaging apparatus according to claim 5,
The display unit displays all images taken by one continuous shooting.

  According to the sixth aspect of the invention, since the display unit displays all images taken by one continuous shooting, the operator can more easily confirm that an image with low luminance saturation has been shot. it can.

Invention of Claim 7 is an imaging device as described in any one of Claims 1-6,
The control device shifts the inflection point to the side where the incident light amount corresponding to the inflection point increases, and causes the image sensor to perform continuous photographing.

  According to the invention of the seventh aspect, the same effect as that of the invention according to any one of the first to sixth aspects can be obtained.

Invention of Claim 8 is an imaging device as described in any one of Claims 1-6,
The control device shifts the inflection point to the side where the incident light amount corresponding to the inflection point decreases, and causes the image sensor to perform continuous photographing.

  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 1-6.

The invention according to claim 9 is an imaging method,
A plurality of pixels that photoelectrically convert incident light to each pixel into an electrical signal by an imaging device having a plurality of pixels that switch between a linear conversion mode that linearly converts incident light into an electrical signal and a logarithmic conversion mode that performs logarithmic conversion based on the amount of incident light A photoelectric conversion step;
A control step of causing the image sensor to perform continuous shooting by controlling the image sensor so that an inflection point that is a boundary between the linear conversion mode and the logarithmic conversion mode is shifted between the photoelectric conversion steps. It is characterized by providing.

  According to the ninth aspect of the present invention, imaging is performed by an imaging device having pixels that perform only the linear conversion mode by performing imaging by using an imaging device having pixels that switch between the linear conversion mode and the logarithmic conversion mode based on the amount of incident light. Compared with the case of performing the image processing, the dynamic range of the electrical signal in the image data is widened, so that the luminance information in a wide luminance range can be expressed by the electrical signal, that is, it is possible to take an image with less luminance saturation. it can. In addition, by shifting the inflection point that is the boundary between the linear conversion mode and the logarithmic conversion mode and causing the image sensor to perform continuous shooting, the dynamic range of the electric signal changes between each photoelectric conversion step, resulting in multiple As part of the captured image, an image with little luminance saturation can be obtained. Therefore, unlike the conventional case of imaging without using the auto bracket function, an image with less luminance saturation can be taken.

The invention according to claim 10 is the imaging method according to claim 9,
A storage step of storing a plurality of image data is provided.

  According to the tenth aspect of the present invention, a plurality of photographed images are stored together by storing a plurality of image data. Therefore, it is possible to reliably store an image with little luminance saturation.

The invention described in claim 11 is the imaging method according to claim 10,
Using an input device to input operation instructions,
In the storing step, image data is stored based on an operation instruction input to the input device.

  According to the eleventh aspect of the invention, by storing the image data based on the operation instruction input to the input device, an image with less luminance saturation can be stored more reliably.

The invention according to claim 12 is the imaging method according to claim 10,
In the storing step, all image data photographed by one continuous photographing is stored.

  According to the twelfth aspect of the present invention, it is possible to store an image with less luminance saturation more reliably by storing all the image data taken by one continuous photographing.

Invention of Claim 13 in the imaging method as described in any one of Claims 9-12,
A display step for displaying a plurality of images is provided.

  According to the invention of claim 13, by displaying a plurality of images, the operator can confirm the plurality of captured images at a time. Therefore, it can be easily confirmed that an image with little luminance saturation has been taken.

The invention according to claim 14 is the imaging method according to claim 13,
In the display step, all images taken by one continuous shooting are displayed.

  According to the invention of the fourteenth aspect, by displaying all the images taken by one continuous shooting, the operator can more easily confirm that an image with little luminance saturation has been shot.

The invention according to claim 15 is the imaging method according to any one of claims 9 to 14,
In the control step, the inflection point is shifted to the side where the amount of incident light corresponding to the inflection point increases, and the image sensor is continuously photographed.

  According to the invention of the fifteenth aspect, the same effect as that of the invention according to any one of the ninth to fourteenth aspects can be obtained.

The invention according to claim 16 is the imaging method according to any one of claims 9 to 14,
In the control step, the inflection point is shifted to the side where the amount of incident light corresponding to the inflection point becomes smaller, and the image sensor is continuously photographed.

  According to the invention described in claim 16, the same effect as that of any one of claims 9-14 can be obtained.

  According to the first and ninth aspects of the invention, an image with little luminance saturation can be taken.

  According to the second and tenth aspects of the invention, the same effect as the first and ninth aspects of the invention can be obtained, and an image with less luminance saturation can be reliably stored.

  According to the third, fourth, eleventh and twelfth aspects of the invention, the same effect as that of the second and tenth aspects of the invention can be obtained, and an image with less luminance saturation can be stored more reliably. be able to.

  According to the fifth and thirteenth inventions, it is possible to obtain the same effect as that of any one of the first to fourth and ninth to twelfth inventions. It can be easily confirmed that the image has been photographed.

  According to the sixth and fourteenth aspects of the invention, it is possible to obtain the same effect as that of the fifth and thirteenth aspects of the invention. It can be easily confirmed.

  According to the invention of Claims 7, 8, 15, and 16, the same effect as that of any one of Claims 1 to 6 and 9 to 14 can be obtained.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the present embodiment, the imaging device according to the present invention will be described as a compact digital camera.

FIG. 1A is a diagram illustrating an appearance of an imaging apparatus 1 according to the present invention.
As shown in this figure, a lens unit 11 is disposed in the center of the front surface of a housing 10 provided in the imaging apparatus 1.

  The lens unit 11 collects light from the subject at a predetermined focal point, and includes a lens group 11a and a diaphragm 11b as shown in FIG. Conventionally known lenses are used as the lens group 11a and the diaphragm 11b. An exposure control processing unit 47 is connected to the stop 11b so as to adjust the amount of light collected by the lens group 11a.

As shown in FIG. 1A, an irradiation device 12 and a light control sensor 13 are disposed on the upper portion of the lens unit 11.
The irradiating device 12 is an auxiliary light source that emits instantaneous light at the time of shooting. When the brightness of the surrounding environment is insufficient at the time of shooting of the subject, the irradiation device 12 irradiates the subject with light at a predetermined light emission timing and light emission amount. Yes. As such an irradiation device 12, a strobe or a high-intensity LED can be used. The irradiation device 12 may be externally attached to the housing 10.
The light control sensor 13 detects the light emission amount of the irradiation device 12.

  A USB terminal 14 is provided on the side surface of the housing 10. A USB cable can be connected to the USB terminal 14, whereby the imaging device 1 can be connected to an external device (not shown) such as a personal computer.

  A power switch 15 and a release switch 16 are disposed on the upper surface of the housing 10. The power switch 15 is a switch for turning on (starting) or turning off (starting and stopping) the power supply of the imaging apparatus 1, and the release switch 16 is a switch for performing shutter release. In the present embodiment, the release switch 16 causes each part of the imaging apparatus 1 to start a shooting preparation operation by “half-pressing”, and starts a shooting operation by “full-pressing”. The shooting preparation operation includes an operation for acquiring parameters necessary for shooting, and specifically includes photometry and distance measurement of a subject.

  Further, as shown in FIG. 1B, a monitor 17 as a display unit in the present invention is provided on the back surface of the housing 10. The monitor 17 is configured by an LCD (Liquid Crystal Display), a CRT (Cathode Ray Tube), or the like, and displays a menu screen for a user to select a function in addition to a subject preview screen and a captured image. It has become.

A plurality of operation keys 18,... And an optical finder 19 are disposed in the vicinity of the monitor 17.
The operation key 18 is an input device according to the present invention, and various operation instructions are input from the operator. The optical viewfinder 19 is used to make the operator confirm the subject from the back side of the housing 10.

Next, the internal configuration of the imaging device 1 will be described.
As shown in FIGS. 1 and 2, the imaging device 1 includes an imaging element 2 that receives incident light via a lens unit 11 inside the housing 10.

As shown in FIG. 3, 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, and more specifically, as shown in FIG. The conversion mode and the logarithmic conversion mode for logarithmic conversion are switched using the inflection point Q as a boundary. In the present embodiment, each of the pixels G _{11 to} G _mn changes the linear conversion mode for an incident light amount less than th corresponding to the inflection point Q (hereinafter referred to as an inflection incident light amount) th. A logarithmic conversion mode is performed for an incident light quantity equal to or greater than the curved incident light quantity th. Here, in the present embodiment, linear conversion or logarithmic conversion of incident light into an electric signal means that a time integral value of light quantity is converted into an electric signal having a linear change mode, or a logarithmic change mode. It is to convert it into an electrical signal. Further, the inflection point Q serving as the boundary between the linear conversion mode and the logarithmic conversion mode varies 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, and the inflection point As the point Q changes and the inflection incident light amount th increases, the proportion of the linear conversion mode performed increases. Specifically, FIG.
As the control voltage (the difference between voltage values VL and VH of a signal φ _VPS described later) increases in the order of “V ₁ ” to “V ₃ ”, the output signal value corresponding to the inflection point Q (hereinafter, The inflection output signal value H) and the inflection incident light quantity th increase in the order of “VI” to “IV”, and the rate at which the linear conversion mode is performed increases. In FIG. 5, “a” to “d” and “d ₁ ” to “d ₃ ” are constants. Of these, 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 .

The lens unit 11a side of the pixel G ₁₁ ~G _mn, Red respectively (Red), green one color filter of the (Green), and blue (Blue) (not shown) is disposed. Further, as shown in FIG. 3, 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 , φ _VD and φ _VPS to the pixels G _{11 to} G _mn (see FIGS. 6 and 7). It has become. 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. 2) 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. Further, the output signal value output from the image sensor 2 in association with each of the pixels G _{11 to} G _mn takes a value in the range of 0 to 256.

  As shown in FIG. 2, a black reference correction unit 32 and a signal processing unit 33 are connected to the imaging device 2 in this order via an amplifier 30 and an AD converter 31.

  The black reference correction unit 32 corrects the black level that is the lowest luminance value to the reference value. As a result, even if the black level varies depending on the dynamic range of the image pickup device 2, the signal level that becomes the black level is subtracted from the signal level of each of the RGB signals output from the A / D converter 31, thereby correcting the black reference. To be done.

The signal processing unit 33 performs linear conversion on the electrical signal output in the logarithmic conversion mode from each of the pixels G _{11 to} G _mn of the image sensor 2, thereby converting the output signal from the image sensor 2 from the linear conversion mode. It is designed to be unified with the state. The signal processing unit 33 may perform conversion using a look-up table, or may perform conversion by calculation such as exponential conversion.

The signal processing unit 33 is connected to the image processing unit 4.
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 33 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 pixel 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.

  The monitor 17 and the storage unit 60 are connected to the image processing unit 4. The storage unit 60 is a recording memory and has an image data recording area for recording image data input from the signal processing unit 33. The storage unit 60 may be configured to be a built-in type such as a flash memory or a hard disk, or may be configured to be detachable using a memory card, a memory stick, a floppy disk, or the like.

Further, the evaluation value calculation unit 5 and the control device 46 are connected to the signal processing unit 33 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. Is. Note that the AE evaluation value calculated here includes information about the width of the luminance distribution of the subject (see, for example, FIG. 9C).

  The control device 46 controls each part of the imaging device 1, and includes the amplifier 30, the black reference correction unit 32, the image processing unit 4, the irradiation device 12, the operation keys 18,..., The monitor 17, the storage unit 60, and the like. Connected with. The control device 46 is connected to the diaphragm 11 b via the exposure control processing unit 47 and is connected to the image sensor 2 and the AD converter 31 via the signal generation unit 48. Further, the control device 46 is connected to the power supply unit 61.

The signal generator 48 generates predetermined timing pulses (pixel drive signal, horizontal synchronization signal, vertical synchronization signal, horizontal scanning circuit drive signal, vertical scanning circuit drive signal, etc.) based on the imaging control signal from the control device 46. Are output to the image sensor 2. The signal generator 48 also generates an A / D conversion clock used in the A / D converter 31.
The power supply unit 61 supplies power to the control device 46 and the like.

Next, the pixels G _{11 to} G _mn in this embodiment will be described.
Each pixel G _{11 to} G _mn includes a photodiode P, transistors T _{1 to} T _6, and a capacitor C as shown in FIG. The transistors T _{1 to} T ₆ are P-channel MOS transistors.

The light passing through the lens group 11a and the aperture stop 11b strikes the photodiode P. A DC voltage V _PD is applied to the cathode P _{k of the} photodiode P, and the drain T _1D of the transistor T ₁ is connected to the anode P _A.

The signal φ _S is inputted to the gate T _1G of the transistor T ₁ , and the gate T _2G and the drain T _2D of the transistor T ₂ are connected to the source T _1S .

A signal application line L _C (corresponding to L _{C1 to} L _Cn in FIG. 3) is connected to the source T _2S of the transistor T ₂ , and the signal φ _VPS is input from the signal application line L _C. ing. Here, as shown in FIG. 7, the signal φ _VPS is a binary voltage signal, and more specifically, the transistor T ₂ is operated in the subthreshold region when the incident light quantity exceeds the inflection incident light quantity th. The voltage value VL for this purpose and the voltage value VH for bringing the transistor T ₂ into a conductive state are taken.

Also, gate T _3G of the transistor T ₃ is connected to a source T _1S of the transistor T _1.
A DC voltage V _PD is applied to the drain T _3D of the transistor T ₃ . Further, the source T _3S of the transistor T ₃ has one end of a capacitor C, a drain T _5D of the transistor T _5, and the gate T _4G of the transistor T ₄ is connected.

A signal application line L _B (corresponding to L _{B1 to} L _Bn in FIG. 3) is connected to the other end of the capacitor C, and a signal φ _VD is given from this signal application line L _B. Here, as shown in FIG. 7, the signal φ _VD is a ternary voltage signal. More specifically, the voltage value Vh when the capacitor C is integrated and the voltage when the photoelectrically converted electric signal is read out. The value Vm and the voltage value Vl at the time of noise signal reading are taken as three values.

A DC voltage V _RG is input to the source T _5S of the transistor T ₅ , and a signal φ _RS is input to the gate T _5G .

The DC voltage V _PD is applied to the drain T _4D of the transistor T _{4 in} the same manner as the drain T _3D of the transistor T ₃ , and the drain T _6D of the transistor T ₆ is connected to the source T _4S. ing.

A signal readout line L _D (corresponding to L _{D1 to} L _Dm in FIG. 3) is connected to the source T _6S of the transistor T ₆ , and a signal application line L _A (L in FIG. 3) is connected to the gate T _6G . _A signal φ _V is input from _{A1 to} L _An ).

Next, operations of the pixels G _{11 to} G _mn and the vertical scanning circuit 21 will be described.
First, as shown in FIG. 7, the vertical scanning circuit 21 performs a reset operation of the pixels G _{11 to} G _mn .
Specifically, from the state in which the signal φ _S is Low, the signal φ _V is Hi, the signal φ _VPS is VL, the signal φ _RS is Hi, and the signal φ _VD is Vh, the vertical scanning circuit 21 generates the pulse signal φ and _V, after outputted an electric signal by applying a pulse signal phi _VD of the voltage value Vm in the pixel G ₁₁ ~G _mn to the signal reading line L _D, the transistors T ₁ to signal phi _S as Hi to OFF.

Next, the vertical scanning circuit 21 to the signal phi _VPS and VH, the gate T _2G and drain T _2D of the transistor T _2, and quickly recombine negative charges accumulated in the gate T _3G of the transistor T ₃ Let Further, the vertical scanning circuit 21 sets the signal φ _RS to Low and turns on the transistor T ₅ to initialize the voltage at the connection node between the capacitor C and the gate T _4G of the transistor T ₄ .

Next, after the vertical scanning circuit 21 sets the signal φ _VPS to VL to return the potential state of the transistor T _{2 to} the original state, the signal φ _{RS is set} to Hi and the transistor T ₅ is turned OFF. Next, the capacitor C performs an integration operation. As a result, the voltage at the connection node between the capacitor C and the gate T _4G of the transistor T ₄ becomes in accordance with the reset gate voltage of the transistor T ₂ .

Then, by giving the vertical scanning circuit 21 is a pulse signal phi _V to the gate T _6G of the transistor T ₆ together with the transistor T ₆ to ON, a pulse signal is applied phi _VD voltage value Vl to the capacitor C. At this time, since the transistor T ₄ operates as MOS transistor of a source follower type, the noise signals on the signal reading line L _D appears as a voltage signal.

After the vertical scanning circuit 21 applies the pulse signal φ _RS to the gate T _5G of the transistor T ₅ to reset the voltage at the connection node between the capacitor C and the gate T _4G of the transistor T ₄ , the signal φ _{S is set} to Low. to turn oN the transistor T _1. As a result, the reset operation is completed, and the pixels G _{11 to} G _mn are ready for imaging.

Next, the pixels G _{11 to} G _mn perform an imaging operation.
Specifically, the light charge corresponding to the amount of incident light from the photodiode P has the flow into the transistor T _2, the optical charges are accumulated in the gate T _2G of the transistor T _2.

Here, when the luminance of the subject is low and the amount of incident light on the photodiode P is smaller than the inflection incident amount of light th, the transistor T ₂ is in the cut-off state, so that it is stored in the gate T _2G of the transistor T _2. A voltage corresponding to the amount of photocharge appears at the gate T _2G . Therefore, a voltage obtained by linearly converting incident light appears at the gate T _3G of the transistor T ₃ .
On the other hand, the luminance of the subject is high and the amount of incident light with respect to the photodiode P is greater than the inflection incident light quantity th, the transistor T ₂ performs the operation in the sub-threshold region. Therefore, a voltage obtained by logarithmically converting incident light with a natural logarithm appears at the gate T _3G of the transistor T ₃ .
In the present embodiment, the predetermined value is the same among the pixels G _{11 to} G _mn .

When the voltage on the gate T _3G of the transistor T ₃ appears, the current flowing from the capacitor C to the drain T _3D of the transistor T ₃ in accordance with the amount of voltage is amplified. Therefore, a voltage obtained by linearly converting or logarithmically converting the incident light of the photodiode P appears at the gate T _4G of the transistor T ₄ .

Next, the vertical scanning circuit 21 _sets the voltage value of the signal φ _VD to Vm and sets the signal φ _V to Low. As a result, a source current corresponding to the gate voltage of the transistor T ₄ flows to the signal read line L _D via the transistor T ₆ . At this time, since the transistor T ₄ operates as MOS transistor of a source follower type, the signal reading line L _D appear electrical signals at the time of imaging as a voltage signal. Here, since the signal value of the electric signal output through the transistors T ₄ and T ₆ is a value proportional to the gate voltage of the transistor T ₄ , the signal value is linearly converted or logarithmized from the incident light of the photodiode P. It becomes the converted value.

The vertical scanning circuit 21 _sets the voltage value of the signal φ _VD to Vh and sets the signal φ _V to Hi, thereby completing the imaging operation.

Here, as shown in FIG. 5 described above, as the control voltage for the image sensor 2 increases, that is, as the voltage value VL during imaging of the signal φ _VPS decreases and the difference from the voltage value VH during reset increases. The inflection incident light amount th increases and the ratio of the linear conversion mode increases. As the control voltage increases, the potential difference between the gate T _2G and the source T _2S of the transistor T ₂ increases. This is because the ratio of the subject brightness that operates in the cutoff state T ₂ , that is, the ratio of the subject brightness that undergoes linear conversion increases. Although not shown in FIG. 5, the ratio of subject luminance to be linearly converted also increases when the exposure time of the image sensor 2 is shortened or when the temperature is low. Therefore, the inflection point Q is shifted by changing these control voltage, exposure time, temperature, etc. As a result, the dynamic range of the image signal, the inflection incident light quantity th at the inflection point Q, the inflection point, and the like. The output signal value H can be controlled. Specifically, for example, when the luminance range of the subject is narrow, the voltage value VL is lowered and the inflection incident light quantity th at the inflection point Q is increased to widen the luminance range for linear conversion, while the luminance of the subject is increased. When the range is wide, the voltage value VL is increased and the inflection incident light quantity th at the inflection point Q is decreased to widen the luminance range for logarithmic conversion, so that the photoelectric conversion characteristics of the pixels G _{11 to} G _mn Can be adapted to the characteristics of 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.

Next, the imaging operation of the imaging device 1 when shooting one image will be described.
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, each pixel G ₁₁ ~G _mn as described above and outputs an electrical signal to the signal reading line L _D, the electric signal is amplified by the constant current source D, selection circuit S is sequentially sample and hold. 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, the amplifier 30 amplifies the analog signal output from the image sensor 2, and the AD converter 31 converts it into a digital signal. Next, after the black reference correction unit 32 performs the black reference correction, the signal processing unit 33 unifies the digital signal into a state derived from the linear conversion mode. In this way, by taking an image with the image pickup device 2 having the pixels G _{11 to} G _mn that switches between the linear conversion mode and the logarithmic conversion mode based on the amount of incident light, the image pickup is performed with the image pickup device having pixels that perform only the linear conversion mode. Compared with the case of performing the luminance information, the luminance information in a wide luminance range is expressed by the electric signal as the dynamic range of the electric signal in the image data becomes wider.

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 33. 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.
Further, the control device 46 controls the AWB processing unit 40 based on the AWB evaluation value, the minimum level set by the black reference correction unit 32, etc., and the image data output from the signal processing unit 33 is white. Allow balance processing to be performed.

  Then, after 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, the image data is monitored on the monitor 17. In this case, the image capturing operation is terminated by displaying the image or storing it in the storage unit 60.

  Subsequently, an imaging operation of the imaging apparatus 1 when images are continuously shot, that is, an imaging method according to the present invention will be described. In the following description, the imaging apparatus 1 will be described as continuously capturing three images.

First, as shown in FIG. 8, when the user depresses the release switch 16 (step S1), as shown in FIG. 9A, the control device 46 sets the inflection point Q of the image sensor 2 to a predetermined point Q _a. (Step S2), the imaging apparatus 1 is caused to take a first image (step S3 (photoelectric conversion process)).

As a result, an image composed of output signals as shown in FIGS. 9B and 9C is taken by the image sensor 2. Here, as shown in FIG. _9B , the output signal values from the pixels G _{11 to} G _mn are all the maximum values 256 in the regions R _a and R _b in the image sensor 2, and are caused by whiteout. The subject cannot be identified.

Next, the control device 46 shifts the inflection point Q _a of the image sensor 2 by _a predetermined amount to inflection points Q _b and Q _c (steps S4 and S6 (control process)), and the second image is input to the imaging device 1. , The third image is taken (steps S5 and S7 (photoelectric conversion process)).

In this way, by shifting the inflection point Q and causing the image sensor 2 to perform continuous photographing, the dynamic range of the electric signal changes between the respective image capturing operations. As a result, as shown in FIGS. region R _a, variations occur according to the object luminance in the output signal values in the region in the order of R _b, luminance information of a wide luminance range is subject are represented by the electric signal becomes distinguishable. As a method of shifting the inflection point Q, as described above, there is a method of changing the control voltage, exposure time, and temperature of the pixels G _{11 to} G _mn . In this embodiment, the control voltage is changed. The method is used. Further, the direction in which the inflection point Q is shifted may be on the side where the inflection incident light quantity th increases or on the side where it decreases, but in this embodiment, FIG. 9 (a) to FIG. 11 (a). As shown in FIG. 5, the inflection incident light quantity th is reduced, that is, the ratio of the logarithmic conversion mode is increased. Further, an arbitrary amount can be set as the shift amount of the inflection point Q, that is, the predetermined amount, but in the present embodiment, as the first shift amount, the over-exposed region _Ra , An amount for eliminating whiteout is set on one side of R _b , and an amount for eliminating _whiteout in both regions R _a and R _b is set as the second shift amount.

  Then, the monitor 17 displays the three consecutively photographed images side by side (step S8 (display process)), and the storage unit 60 stores each image data (recording process), and the imaging operation is terminated.

According to the above imaging method, imaging is performed by the imaging element 2 having the pixels G _{11 to} G _mn for switching between the linear conversion mode and the logarithmic conversion mode, so that imaging is performed by the imaging element having pixels that perform only the linear conversion mode. Compared with the case where it is performed, luminance information in a wide luminance range can be expressed by an electric signal, so that an image with less luminance saturation can be taken. In addition, by shifting the inflection point Q and causing the image sensor 2 to perform continuous shooting, an image with less luminance saturation can be obtained as part of a plurality of captured images. As described above, it is possible to capture an image with less luminance saturation than in the past.

  Further, by displaying all the images taken by one continuous shooting side by side on the monitor 17, it can be easily confirmed that an image with less luminance saturation has been shot.

  Further, by storing all the image data taken by one continuous shooting in the storage unit 60, it is possible to reliably save an image with less luminance saturation.

  In the above embodiment, the imaging apparatus according to the present invention has been described as a compact digital camera. However, a single-lens reflex digital camera may be used, and a photographing function such as a camera-equipped mobile phone or an in-vehicle camera may be provided. An electronic device may be used, or a camera unit or the like incorporated in an electronic device such as a mobile phone or a vehicle-mounted camera.

In addition, the inflection point Q is shifted by the change of the control voltage of the pixels G _{11 to} G _mn and continuous shooting is performed. However, as shown in this order in FIGS. It is also possible to shift the exposure amount of the pixels G _{11 to} G _mn and perform continuous shooting as so-called bracket shooting. Here, as a method of shifting the exposure amount, a method of adjusting the aperture amount by the aperture 11b, a method of adjusting the sensitivity of the image sensor 2, a method of adjusting the light emission amount of the irradiation device 12, and a method of adjusting the shutter time. and so on. By performing such bracket shooting, region R _a, while eliminating overexposure of R _b, it can be eliminated collapse black region R _c.

  Further, the inflection point Q has been described as being shifted by a predetermined amount. However, the inflection point Q may be shifted by an amount based on an operation instruction input to the operation key 18, or the first shooting in continuous shooting or continuous shooting may be performed. It may be shifted by an amount based on an evaluation result such as an AE evaluation value of image data obtained by preliminary shooting performed before shooting. Here, when the inflection point is shifted by an amount based on the AE evaluation value, the variation amount of the inflection incident light amount th is increased when the luminance range of the subject is wide, and the variation amount is increased when the luminance range is narrow. It is preferable to make it small.

In addition, although it has been described that the monitor 17 displays all three images photographed by bracketing side by side, only one or two images are displayed based on an operation instruction from the operator input to the operation key 18. It can also be displayed.
Further, although it has been described that the storage unit 60 stores each of the three images captured by bracketing, only one or two images are stored based on an operation instruction from the operator input to the operation key 18. It may be memorized.

Further, the pixels G _{11 to} G _mn have been described as having the configuration shown in FIG. 6. However, as long as the linear conversion mode and the logarithmic conversion mode can be switched, for example, as described in Patent Documents 4 and 5 described above. It is good also as having a structure.

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 figure which shows the external appearance of the imaging device which concerns on this invention, (a) is a perspective view from the front side, (b) is a perspective view from the back side. 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 signal processing part. It is a figure which shows the relationship between a control voltage and an inflection point. It is a circuit diagram which shows the structure of a pixel. 6 is a timing chart illustrating a pixel reset operation. It is a figure which shows the imaging operation of the imaging device which concerns on this invention. It is a schematic diagram which shows the 1st imaging | photography result in the continuous imaging | photography which shifted the inflection point. It is a schematic diagram which shows the imaging | photography result of the 2nd time in the continuous imaging | photography which shifted the inflection point. It is a schematic diagram which shows the 3rd imaging | photography result in the continuous imaging | photography which shifted the inflection point. It is a schematic diagram which shows the 1st imaging | photography result in the continuous imaging | photography which shifted the inflexion point and the exposure amount. It is a schematic diagram which shows the 2nd imaging | photography result in the continuous imaging | photography which shifted the inflexion point and the exposure amount. It is a schematic diagram which shows the 3rd imaging | photography result in the continuous imaging | photography which shifted the inflexion point and the exposure amount. It is a figure which shows a picked-up image, (a) is an image in which whiteout occurs in a round part, (b) is an image without luminance saturation, (c) is an image in which black crushing occurs in a triangular part and a square part. .

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Imaging device 2 Imaging element 46 Control device 18 Operation key (input device)
17 Monitor (display unit)
G _{11 to} G _mn Pixel Q Inflection point

Claims (16)

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 control device for controlling the image sensor;
The control apparatus shifts an inflection point that is a boundary between the linear conversion mode and the logarithmic conversion mode, and causes the image sensor to perform continuous shooting. The imaging device according to claim 1,
An imaging apparatus comprising a storage unit that stores a plurality of image data. The imaging apparatus according to claim 2, wherein
An input device for inputting operation instructions is provided.
The imaging device, wherein the storage unit stores image data based on an operation instruction input to the input device. The imaging apparatus according to claim 2, wherein
The storage device stores all image data taken by one continuous shooting. In the imaging device according to any one of claims 1 to 4,
An imaging apparatus comprising a display unit that displays a plurality of images. The imaging device according to claim 5.
The display unit displays all images taken by one continuous shooting. In the imaging device according to any one of claims 1 to 6,
The control device shifts the inflection point to the side where the amount of incident light corresponding to the inflection point increases, and causes the image sensor to perform continuous photographing. In the imaging device according to any one of claims 1 to 6,
The control apparatus shifts the inflection point to the side where the incident light amount corresponding to the inflection point becomes smaller, and causes the image sensor to perform continuous photographing. A plurality of pixels that photoelectrically convert incident light to each pixel into an electrical signal by an imaging device having a plurality of pixels that switch between a linear conversion mode that linearly converts incident light into an electrical signal and a logarithmic conversion mode that performs logarithmic conversion based on the amount of incident light A photoelectric conversion step;
A control step of causing the image sensor to perform continuous shooting by controlling the image sensor so that an inflection point that is a boundary between the linear conversion mode and the logarithmic conversion mode is shifted between the photoelectric conversion steps. An imaging method characterized by comprising: The imaging method according to claim 9.
An imaging method comprising a storage step of storing a plurality of image data. The imaging method according to claim 10.
Using an input device to input operation instructions,
In the storing step, image data is stored based on an operation instruction input to the input device. The imaging method according to claim 10.
In the storage step, all the image data photographed by one continuous photographing is stored. In the imaging method as described in any one of Claims 9-12,
An imaging method comprising a display step of displaying a plurality of images. The imaging method according to claim 13.
In the display step, the whole image photographed by one continuous photographing is displayed. In the imaging method as described in any one of Claims 9-14,
In the control step, the inflection point is shifted to the side where the amount of incident light corresponding to the inflection point becomes larger, and the image pickup device performs continuous photographing. In the imaging method as described in any one of Claims 9-14,
In the control step, the inflection point is shifted to the side where the amount of incident light corresponding to the inflection point becomes smaller, and the image pickup device performs continuous photographing.

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