JP2007067491A - Imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an imaging apparatus which can favorably reproduce an object for various object conditions without requiring a time for determining a point of inflection becoming the boundary of a linear conversion region and a logarithmic conversion region in an electric signal outputted from an image sensor while offering a favorable operational feeling to a user. <P>SOLUTION: The imaging apparatus comprises an image sensor having a plurality of pixels capable of outputting an electric signal converted linearly for the amount of incident light and an electric signal converted logarithmically, a means performing the alteration control of a point of inflection becoming the boundary of a linear conversion region and a logarithmic conversion region, a means for detecting the luminance of an object, and a means for storing the position of a point of inflection preset in correspondence with the luminance of an object. Based on the luminance of an object detected by the means for detecting the luminance, the means for controlling the point of inflection performs the alteration control of a point of inflection stored in the storage means. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image pickup apparatus having an image pickup device capable of outputting an electric signal linearly converted with respect to an incident light amount and an electric signal converted logarithmically with respect to the incident light amount.

  2. Description of the Related Art Conventionally, an imaging device that photoelectrically converts subject light is used in an imaging device such as a digital camera, an in-vehicle camera, or a camera module built in a portable terminal. As this imaging device, there is a solid-state imaging device such as a CCD (Charge Coupled Device) type image sensor or a CMOS (Complementary Metal-Oxide Semiconductor) type image sensor. Further, these image pickup devices generally output an electrical signal that is linearly converted with respect to the amount of incident light.

  The image pickup device that outputs the linearly converted electric signal has a drawback that a dynamic range that can be reproduced is narrow because a signal proportional to the amount of generated photocharge is output.

On the other hand, in order to eliminate this drawback, an image sensor (also referred to as a linear log sensor) capable of outputting an electric signal linearly converted with respect to the incident light amount and an electric signal converted logarithmically with respect to the incident light amount. Have been proposed). There has been disclosed an imaging apparatus that attempts to reproduce a subject satisfactorily for various subject conditions by eliminating the occurrence of overexposure by adapting the dynamic range of the imaging element to the subject luminance width (for example, Patent Documents). 1).
JP 2004-88312 A

  The imaging device described in Patent Document 1 can obtain a subject image without saturating a high-luminance portion with respect to a subject condition in which a luminance difference between each portion of the subject is large. However, a processing time is required to determine an inflection point that becomes a boundary between the linear transformation region and the logarithmic transformation region in the electric signal output from the image sensor prior to photographing. In other words, it takes a predetermined time to capture the subject image before shooting, calculate the luminance width of the subject from the obtained image, and determine the inflection point according to the luminance width. There is a problem that the user's operation feeling is slightly impaired.

  In view of the above problems, the present invention does not require time for determining an inflection point that is a boundary between a linear transformation region and a logarithmic transformation region in an electrical signal output from an image sensor, and is a good operation for the user An object of the present invention is to obtain an imaging apparatus that can reproduce a subject satisfactorily for various subject conditions.

  The above problem is solved by the following configuration.

  1) An image pickup device having a plurality of pixels capable of outputting an electric signal linearly converted with respect to an incident light amount and an electric signal logarithmically converted with respect to the incident light amount, and an electric signal output from the image pickup device An inflection point control means for changing and controlling an inflection point that is a boundary between the linear transformation area and the logarithmic transformation area, a luminance detection means for detecting the subject brightness, and a preset variable corresponding to the subject brightness. Storage means storing the inflection point position, and based on the subject brightness detected by the brightness detection means, the inflection point control means converts the inflection point to the inflection point position stored in the storage means. An image pickup apparatus characterized in that change control is performed.

  2) The imaging apparatus according to 1), further including an incident light amount control unit that controls an incident light amount incident on the imaging element, wherein the inflection point is changed and controlled when the incident light amount control unit has an excessive exposure amount.

  3) The imaging device according to 1) or 2), wherein the storage unit stores in advance a control value of the incident light amount control unit corresponding to subject luminance.

  4) An image sensor having a plurality of pixels capable of outputting an electric signal linearly converted with respect to the incident light amount and an electric signal logarithmically converted with respect to the incident light amount, and an electric signal output from the image sensor An inflection point control means for changing and controlling an inflection point that is a boundary between the linear transformation area and the logarithmic transformation area, a luminance detection means for detecting subject luminance, and a sensitivity changing means for changing the sensitivity of the image sensor. Incident light quantity control means for controlling the incident light quantity incident on the imaging device, and based on the subject brightness detected by the brightness detection means, the incident light quantity control means, the sensitivity change means, An inflection point control means is selectively used to perform exposure control on the image sensor.

  According to the present invention, it is possible to obtain an imaging apparatus that can reproduce a subject satisfactorily with respect to various subject conditions and has a good operational feeling for a user.

  Hereinafter, the present invention will be described in detail with reference to embodiments, but the present invention is not limited thereto.

  FIG. 1 is an external perspective view of an imaging apparatus 1 according to the present embodiment. The image pickup apparatus 1 shown in FIG. 1 is a digital camera. FIG. 1A shows the front side of the camera, and FIG. 1B shows the back side of the camera.

  As shown in FIG. 2A, a lens unit 3 that forms an image of subject light at a predetermined focal position is disposed in the vicinity of the center of the front surface of the housing 2 included in the imaging device 1. The shaft is provided so as to be orthogonal to the front surface of the housing 2. An imaging element (not shown) that photoelectrically converts the reflected light of the subject incident through the lens unit 3 into an electric signal is provided inside the housing 2 and behind the lens unit 3.

  In addition, a flash light emitting unit 5 that irradiates light as auxiliary light at the time of photographing is provided in the vicinity of the front upper end portion of the housing 2. The flash light emitting unit 5 according to the present embodiment is configured by an electric flash built in the imaging apparatus 1. A light control sensor 6 is provided near the upper portion of the lens unit 3 on the front surface of the housing 2 to receive the reflected light from the subject of the light emitted from the flash light emitting unit 5. Reference numeral 14a denotes an entrance window on the objective side of the optical viewfinder.

  A release switch 16 for performing shutter release is provided on the upper surface. The release switch 16 can be operated in a “half-pressed state” in which it is pressed halfway and in a “fully pressed state” in which it is further pressed. On the side surface, a USB terminal 18 for connecting a USB cable for connecting the imaging device 1 to a personal computer or the like is provided.

  Furthermore, a circuit board including circuits such as a system control unit and a signal processing unit (not shown) is provided inside the housing 2 included in the imaging apparatus 1.

  Further, as shown in FIG. 2B, an image display monitor 11 is provided on the back surface of the housing 2. The monitor 11 includes an LCD (Liquid Crystal Display), an organic EL display, and the like, and can display a subject preview screen and a captured image.

  Zoom buttons 12 and 13 for adjusting the zoom are provided in the vicinity of the upper rear portion of the imaging apparatus 1. When the zoom button 12 is turned on, zooming is performed in the wide direction, and when the zoom button 13 is turned on, zooming is performed in the tele direction. Further, an optical viewfinder eyepiece 14b for confirming the subject is disposed on the back surface of the imaging apparatus 1.

  Further, on the rear surface of the image pickup apparatus 1, a selection cross key 15a including a cursor displayed on the screen of the monitor 11, a window, or a cross key for changing a designated range of the window is provided. . Next to the selection cross key 15a, a confirmation key 15b for confirming the contents designated by the cursor or window is provided.

  Although not shown in the figure, a recording unit such as a battery and a memory card is loaded inside the housing 2.

  Although described with a compact camera type digital camera, the imaging device of the present invention includes a single-lens reflex digital camera, a mobile phone with a camera, an electronic device having a photographing function such as an in-vehicle camera, a mobile phone, A camera unit incorporated in an electronic device such as an in-vehicle camera is also included.

  FIG. 2 is a block diagram illustrating a functional configuration of the imaging apparatus 1 according to the present embodiment.

  As described above, the imaging apparatus 1 includes the system control unit 7 on the circuit board inside the housing 2. The system control unit 7 includes a CPU (Central Processing Unit), a RAM (Random Access Memory) composed of rewritable semiconductor elements, and a ROM (Read Only Memory) composed of a nonvolatile semiconductor memory.

  Further, each component of the imaging device 1 is connected to the system control unit 7, and the system control unit 7 develops a processing program recorded in the ROM on the RAM and executes the processing program by the CPU. These components are driven and controlled.

  As shown in the figure, the system control unit 7 includes a lens unit 3, an aperture / shutter control unit 19, an image sensor 4, a signal processing unit 8, a timing generation unit 20, a recording unit 10, a flash light emitting unit 5, and dimming. The sensor 6, the monitor 11, the operation unit 21, and the inflection point changing unit 22 are connected.

  The lens unit 3 includes a plurality of lenses that form a subject light image on the imaging surface of the image sensor 4 and a diaphragm / shutter unit that adjusts the amount of light collected by the lenses.

  The aperture / shutter control unit 19 controls the drive of an aperture / shutter unit that is an incident light amount control unit that adjusts the amount of light collected by the lens in the lens unit 3. That is, the aperture / shutter control unit 19 sets the aperture value based on the control value input from the system control unit 7 and moves the shutter unit opened during the imaging operation of the image sensor 4 to a predetermined exposure time. The incident light quantity is controlled by closing after the passage.

  The image sensor 4 captures the incident light of each color component of R, G, and B, which is a subject light image, by photoelectrically converting it into an electrical signal.

  FIG. 3 is a block diagram illustrating a configuration of the image sensor according to the present embodiment.

As shown in the figure, the image pickup device 4 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 can switch the conversion operation of the electric signal according to the amount of incident light. More specifically, the pixel G _{11 to} G _mn perform a logarithmic conversion and a linear conversion operation for linearly converting incident light into an electric signal. The logarithmic conversion operation is switched. In the present embodiment, linear conversion or logarithmic conversion of incident light into an electric signal means conversion into an electric signal that linearly changes the time integral value of the light amount, or electric conversion that changes logarithmically. Logarithmic conversion to a signal.

A filter (not shown) of any one of red (Red), green (Green), and blue (Blue) is disposed on the lens unit 3 side of each of the pixels G _{11 to} G _mn . The pixels G _{11 to} G _mn have power supply lines 23, 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 N as shown in FIG. _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 the figure.

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. 4 and 5). It has become. A vertical scanning circuit 24 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 24 applies signals to the signal application lines L _{A1 to} L _An , L _{B1 to} L _Bn , and L _{C1 to} L _Cn based on signals from the timing generator 20 (see FIG. 2). 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 . Further, 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 25 and a correction circuit 26 are connected to these selection circuits S _{1 to} S _m . The horizontal scanning circuit 25 sequentially switches selection circuits S _{1 to} S _m that sample and hold an electric signal and transmit the electric signal to the correction circuit 26 in the Y direction. The correction circuit 26 removes the 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 26, those disclosed in Japanese Patent Laid-Open No. 2001-223948 can be used. In the present embodiment, it is assumed that only one correction circuit 26 is provided for the entire selection circuits S _{1 to} S _m , but the correction circuit 26 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 included} in the image sensor 4 will be described.

  FIG. 4 is a circuit diagram illustrating a configuration of a pixel included in the image sensor according to the present embodiment.

As shown in the figure, each of the pixels G _{11 to} G _mn includes a photodiode P, transistors T _{1 to} T _6, and a capacitor C. The transistors T _{1 to} T ₆ are P-channel MOS transistors.

The light passing through the lens unit 3 hits 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, the signal φ _VPS is a voltage signal, and more specifically, a voltage value VL for operating the transistor T ₂ in the subthreshold region when the incident light amount exceeds the predetermined incident light amount th, and the transistor T ₂ are The voltage value VH to be in a conductive state is 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, the signal φ _VD is a ternary voltage signal. More specifically, the voltage value Vh when the capacitor C is integrated, the voltage value Vm at the time of reading out the photoelectrically converted electric signal, and the noise signal reading out. It takes three values with the hourly voltage value Vl.

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 ).

By adopting such a circuit configuration, each of the pixels G _{11 to} G _mn performs the following reset operation.

  FIG. 5 is a diagram illustrating a timing chart of the operation of the pixels provided in the image sensor according to the present embodiment.

As shown in the figure, the vertical scanning circuit 24 performs a reset operation of the pixels G _{11 to} G _mn . Specifically, from the state where 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 24 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, to the transistors T ₁ and OFF signals phi _S as Hi It has become.

Next, the vertical scanning circuit 24 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 It is supposed to let you. Further, the vertical scanning circuit 24 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, the vertical scanning circuit 24 sets the signal φ _VPS to VL to return the potential state of the transistor T _{2 to} the original state, and then sets the signal φ _RS to Hi and turns off the transistor T ₅ . 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 .

Next, the vertical scanning circuit 24 is turned ON transistor T ₆ by giving a pulse signal phi _V to the gate T _6G of the transistor T _6, is a pulse signal phi _VD voltage value Vl to be applied to the capacitor C ing. 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.

The vertical scanning circuit 24 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 , and then sets the signal φ _S to Low. It is adapted to the transistor T ₁ and oN. As a result, the reset operation is completed, and the pixels G _{11 to} G _mn are ready for imaging.

Each of the pixels G _{11 to} G _mn performs the following imaging operation.

When light charges corresponding to the amount of incident light from the photodiode P flows into the transistor T _2, photocharge is adapted to be accumulated in the gate T _2G of the transistor T _2.

Here, when the luminance of the subject is low and the amount of light incident on the photodiode P is smaller than the predetermined amount of incident light th, the transistor T ₂ is in the cut-off state, so that it is accumulated in the gate T _2G of the transistor T ₂ . A voltage corresponding to the amount of photocharge appears at the gate _T2G . 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 larger than the predetermined amount of incident light th, the transistor T ₂ is adapted to perform 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 adapted to be amplified. Therefore, a voltage obtained by linear conversion or logarithmic conversion of incident light from the photodiode P appears at the gate T _4G of the transistor T ₄ .

Next, the vertical scanning circuit 24 _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 so that the electrical signal at the time of imaging appears 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 24 _sets the voltage value of the signal φ _VD to Vh and sets the signal φ _V to Hi, thereby completing the imaging operation.

When operating as described above, the potential value between the gate and the source of the transistor T ₂ increases as the voltage value VL of the signal φ _VPS during imaging decreases and the difference from the voltage value VH of the signal φ _VPS during reset increases. difference therebetween increases, the proportion of subject brightness that transistor T ₂ is operated in a cut-off state is increased. Therefore, as shown in FIG. 6 below, the lower the voltage value VL, the larger the ratio of subject luminance to be linearly converted. As described above, the output signal of the image sensor 4 according to the present embodiment has a linear region and a logarithmic region that change continuously according to the amount of incident light. That is, the region for linear conversion increases by lowering the voltage value VL, and the desired photoelectric conversion characteristics can be obtained by increasing the region for logarithmic conversion by increasing the voltage value VL.

As described above, the dynamic range can be switched by switching the voltage value VL of the signal φ _VPS given to the pixels G _{11 to} G _mn of the image sensor 4. That is, the system control unit 7 switches the value of the voltage value VL of the signal φ _VPS to the image sensor 4 via the inflection point changing unit 22 to change from the linear conversion operation of the pixels G _{11 to} G _mn to the logarithmic conversion operation. The inflection point to be switched can be changed.

FIG. 6 is a graph showing the output with respect to the amount of light received by the pixel according to the present embodiment. As described above, when the system control unit 7 switches the voltage value VL, the inflection point at which the linear conversion operation of the pixels G _{11 to} G _mn is switched to the logarithmic conversion operation can be changed. Yes.

  The graph of A shown in the figure shows the output when the linear conversion operation is performed on the received light amount, B shows the output when the logarithmic conversion operation is performed on the received light amount, and C shows the linear conversion operation and the logarithmic conversion operation desired. The output state when changed at the inflection point and used together is shown.

  Note that the image pickup device 4 according to the present embodiment may be any device that automatically switches between linear conversion operation and logarithmic conversion operation in each pixel, and is an image pickup device 4 including pixels having a configuration different from that shown in FIG. Also good.

In the present embodiment, the linear conversion operation and the logarithmic conversion operation are switched by changing the voltage value VL of the signal φ _VPS at the time of imaging. However, the voltage value VH of the signal φ _VPS at the time of reset is changed. Thus, the inflection point between the linear conversion operation and the logarithmic conversion operation may be changed. Further, the inflection point between the linear conversion operation and the logarithmic conversion operation may be changed by changing the reset time.

  In addition, although the image pickup device 4 of the present embodiment is provided with an RGB filter in each pixel, it may be provided with other color filters such as cyan, magenta, and yellow.

  Returning to FIG. 2, the signal processing unit 8 includes an amplifier 27, an A / D converter 28, a black reference correction unit 29, an AE evaluation value calculation unit 30, a WB processing unit 31, a color interpolation unit 32, a color correction unit 33, and tone conversion. Part 34 and a color space conversion part 35.

  Among these, the amplifier 27 amplifies the electrical signal output from the image sensor 4 to a predetermined specified level to compensate for a lack of level in the captured image. The A / D converter 28 (ADC) converts the electrical signal amplified by the amplifier 27 from an analog signal to a digital signal.

  The black reference correction unit 29 corrects the black level that is the lowest luminance value to the reference value. That is, since the black level varies depending on the dynamic range of the image sensor 4, the black reference correction is performed by subtracting the signal level that becomes the black level from the signal level of each RGB signal output from the A / D converter 28. It has come to be.

  The AE evaluation value calculation unit 30 has the following functions for AE (automatic exposure) from the electric signal after black reference correction. By performing a predetermined calculation on the electric signal level composed of each primary color component of RGB, the average value of the luminance in a predetermined range of the image sensor 4 is calculated, and the system control unit 7 sets the incident light quantity as an AE evaluation value. It has a function to output. That is, in this example, the AE evaluation value calculation unit 30 is a luminance detection unit that detects the subject luminance.

  On the other hand, the ROM in the system control unit 7 has a storage area in which the inflection point position set in advance corresponding to the subject brightness, that is, the voltage value VL corresponding to the subject brightness is stored. ing. When the system control unit 7 serving as the inflection point control unit obtains the subject luminance information from the AE evaluation value calculation unit 30 serving as the luminance detection unit, the inflection point position stored in the ROM associated with the subject luminance value. Thus, the inflection point of the image sensor 4 is controlled via the inflection point changing unit 22.

  The WB processing unit 31 adjusts the level ratio (R / G, B / G) of each of the R, G, and B color components of the captured image by calculating a correction coefficient from the electric signal after the black reference correction, thereby generating a white color. Is displayed correctly. The color interpolation unit 32 can obtain R, G, and B color component values for each pixel when the signals obtained at the pixels of the image sensor 4 are only one or two of the primary colors. Color interpolation processing for interpolating missing color components for each pixel is performed. The color correction unit 33 corrects the color component value for each pixel of the image data input from the color interpolation unit 32, and generates an image in which the hue of each pixel is emphasized. In order to reproduce the image faithfully, the gradation conversion unit 34 sets the response characteristic of the image gradation to the image pickup apparatus 1 in order to realize the ideal gradation reproduction characteristic with gamma being 1 from the input of the image to the final output. A gamma correction process is performed to correct the curve according to the gamma value.

  The color space conversion unit 35 converts the color space from RGB to YUV. YUV is a management method for expressing a color with two chromaticities: a luminance (Y) signal, a blue color difference (U, Cb), and a red color difference (V, Cr), and converting the color space to YUV. This facilitates data compression of only the color difference signal.

  The timing generation unit 20 controls the photographing operation (charge accumulation based on exposure, reading of accumulated charge, etc.) by the image sensor 4. That is, a predetermined timing pulse (a pixel driving signal, a horizontal synchronizing signal, a vertical synchronizing signal, a horizontal scanning circuit driving signal, a vertical scanning circuit driving signal, etc.) is generated on the basis of a photographing control signal from the system control unit 7 and an image pickup device. 4 is output. The timing generation unit 20 also generates an A / D conversion clock used in the A / D converter 28.

  The recording unit 10 is a recording memory composed of a semiconductor memory or the like, and has an image data recording area for recording image data input from the signal processing unit 8. The recording unit 10 may be a built-in memory such as a flash memory, a removable memory card, or a magnetic recording medium such as a hard disk.

  The flash light emitting unit 5 emits light at a predetermined light emission timing under the control of the system control unit 7 when the brightness of the surrounding environment detected at the time of photographing the subject is insufficient. The light control sensor 6 receives the reflected light of the flash light reflected from the subject side in order to control the light emission amount, and outputs the light reception result to the system control unit 7.

The monitor 11 functions as a display unit, displays a preview image of a subject, displays a photographed image that has been subjected to image processing by the signal processing unit 8 based on control of the system control unit 7, and allows the user to A text screen such as a menu screen for selecting a function is displayed. That is, the monitor 11 displays a shooting mode selection screen for selecting a still image shooting mode or a moving image shooting mode, a strobe mode selection screen for selecting any one of an auto mode, an off mode, and an on mode. .
The operation unit 21 includes a zoom button 12, a zoom button 13, a selection cross key 15a, a release switch 16, a power switch 17, and the like. When the user operates the operation unit 21, the function of each button or switch is set. Is transmitted to the system control unit 7, and each component of the imaging device 1 is driven and controlled in accordance with the instruction signal.

  Of these, the selection cross key 15a functions to move a cursor or window on the screen of the monitor 11 when the cross key is pressed, and also functions to confirm the selection contents by the cursor or window when the enter key 15b is pressed. Yes. That is, by pressing the cross key of the selection cross key 15a, the cursor displayed on the monitor 11 is moved to open the shooting mode selection screen from the menu screen, and the desired shooting mode is displayed on the shooting mode selection screen. When the cursor is moved to the button and the enter key 15b is pressed, the shooting mode can be determined.

  The release switch 16 starts shooting preparation operation when pressed halfway (hereinafter referred to as ON of the switch S1) in the still image shooting mode, and is also applied to the image sensor 4 when pressed fully (hereinafter referred to as ON of the switch S2). A series of photographing operations is performed in which exposure is given, electrical signals obtained by the exposure are subjected to predetermined signal processing and recorded in the recording unit 10. When the main switch 17 is pressed, the imaging apparatus 1 is turned on and off sequentially.

  The above is the schematic configuration of the imaging device 4 according to the present embodiment and the imaging device 1 including the imaging device 4. Below, operation | movement of the imaging device 1 is demonstrated.

  The imaging apparatus 1 has a still image shooting mode, a moving image shooting mode, a playback mode, a setup mode, and the like. However, the present invention relates to a still image or moving image shooting mode. A case will be described as an example in which an image is shot with a so-called program AE in which exposure is performed in advance by a combination of an aperture value and a shutter speed in accordance with subject brightness.

  FIG. 7 is a flowchart showing an outline of the operation of the imaging apparatus 1 according to this embodiment in the still image shooting mode. Hereinafter, description will be given according to the flow shown in FIG.

  In the figure, when the still image shooting mode is entered, driving of the image pickup unit such as an image pickup device, an amplifier, and an A / D converter is started (step S150), and live view display is performed on a monitor which is an image display unit (step S151). ). The live view display here is performed based on the image sensor output that is linearly converted with respect to the incident light amount.

  Here, it is determined whether the main switch is ON (step S152). When the main switch is turned off (step S152; No), the live view display is stopped (step S180), the driving of the imaging unit is stopped (step S185), and the process is terminated.

  If the main switch is ON (step S152; Yes), it is determined again whether the still image shooting mode is set (step S153). When the mode is switched to a mode other than the still image shooting mode (step S153; No), the mode is switched to another switched mode (step S170).

  If it is the still image shooting mode (step S153; Yes), it is next determined whether or not the switch S1 is turned on (step S155). If the switch S1 is not turned on (step S155; No), the process returns to step S152.

  When the switch S1 is turned on (step S155; Yes), an AF operation and an AE preparation operation (step S156) are performed. For example, the AF operation repeatedly moves and stops the focusing lens in the lens unit in small increments, captures an image at each stop position, evaluates each image, and indicates that the highest frequency component exists and is in focus. This is done by positioning the focusing lens at the position where the evaluated image is obtained. The AE preparation operation is as follows.

  FIG. 8 is a flowchart showing an outline of the AE preparation operation in step S156 shown in FIG.

  In the AE preparation operation, for example, an inflection point is set so that the image sensor output is logarithmically converted for all luminances, and a subject image is captured with a predetermined exposure time and aperture value (step S201). Next, using the obtained image data of the subject, an average luminance value of an area in a predetermined range is obtained by calculation (step S202).

  Next, the average luminance value obtained in step S202 is output from the AE evaluation value calculation unit 30 to the system control unit 7 (see FIG. 2), and the system control unit 7 is stored in advance in the ROM in the system control unit 7. The setting of the inflection point at the time of photographing is read out from the table of the subject brightness and the inflection point position and determined (step S203). Thereafter, the process proceeds to step S157 shown in FIG.

  After this AE preparation operation, live view display is performed by the image sensor output at the inflection point position determined in step S203. This live view display is performed until the switch S1 in step S157 is turned off or the switch S2 in step S158 is turned on. By doing so, it is possible to assume an image after shooting, and to prevent flickering of the screen.

  That is, in this embodiment, the setting of the inflection point at the time of shooting is determined in advance corresponding to the subject brightness and stored in the storage means. After obtaining the subject brightness, the inflection point setting corresponding to the subject brightness is stored from the storage means. The setting position of the inflection point is read out and shooting is performed with the setting.

  Table 1 shows an example of a correspondence table of subject brightness, shooting conditions, and inflection point settings stored in the storage means.

  FIG. 9 is a diagram showing the relationship between the amount of light received by the pixel and the output according to the present embodiment. FIG. 4A is a graph showing pixel output when the image sensor is used only for linear conversion, and FIGS. 2B and 2C use the image sensor in combination with a linear conversion area and a logarithmic conversion area. FIG. 6B is a graph showing the pixel output in the case where the inflection points in the linear transformation area and the logarithmic transformation area are different. This will be described in more detail with reference to Table 1 and FIG.

  As shown in Table 1, the ROM in the system control unit, which is a storage unit, is a bright value value (BV value) representing subject luminance and an incident light amount control unit at the time of shooting corresponding to each BV value. The aperture value, shutter speed, ISO sensitivity corresponding to the gain of the image sensor, and whether the conversion of the received light amount of the pixel and the output is linear or logarithm are stored in advance.

  As shown in the table, when the BV value is 4 to 9, the pixel output is set so that only linear conversion is used, and exposure is performed by selectively changing the aperture value, shutter speed, and ISO sensitivity. It is decided to be made. At this time, it is determined and stored so as to obtain a pixel output like the graph shown in FIG.

  When the BV value is 10, the linear output area and the logarithmic conversion area are used together for the pixel output, and the aperture value, shutter speed, and ISO sensitivity are exposed using the exposure conditions when the BV value is 9. Is done. At this time, in the graph shown in FIG. 9B, that is, out of the output range of the pixel output, the inflection point is determined so that the linear transformation region: log transformation region is 4: 1, It is remembered.

  When the BV value is 11, the linear output area and the logarithmic conversion area are used together for the pixel output, and the aperture value, shutter speed, and ISO sensitivity are exposed using the exposure conditions when the BV value is 9. Is done. At this time, in the graph shown in FIG. 9C, that is, out of the output range of the pixel output, the inflection point is determined so that the linear transformation region: log transformation region is 3: 2. It is remembered.

  After step S203 in FIG. 8, the process returns to FIG. 7 to confirm again whether the switch S1 is turned on (step S157). If the switch S1 is not turned on (step S157; No), the process returns to step S152. When the switch S1 is turned on (step S157; Yes), it waits for the switch S2 to be turned on (step S158). If the switch S2 is not turned on (step S158; No), the process returns to step S157.

  When the switch S2 is turned on (step S158; Yes), shooting is performed under the exposure conditions and pixel output conditions shown in Table 1 above, which are determined in advance according to the subject brightness and stored in the storage means ( Step S160). Next, the photographed image data is recorded on the memory card (step S161), and the photographed image is displayed on the image display unit after view for a predetermined time (step S162), and then the display returns to the live view display in step S151.

  The above is the outline of the operation of the imaging apparatus according to the present embodiment.

  In the above description, the program AE has been described as an example, but the same can be applied to the aperture priority AE and shutter speed priority AE.

  Table 2 shows an example of a correspondence table of subject brightness, shooting conditions, and inflection point settings stored in the storage means in the case of aperture priority AE. The table shows the case where the aperture value is F2.8.

  As shown in the table, when the BV value is 4 to 7, the pixel output is set so that only linear conversion is used, and exposure is performed by selectively changing the shutter speed and ISO sensitivity. It is decided to. At this time, it is determined to obtain a pixel output as shown in the graph of FIG. 9A and is stored in the storage means in advance.

  When the BV value is 8, the linear output region and the logarithmic conversion region are used together for the pixel output, and exposure is performed using the exposure conditions when the shutter speed and the ISO sensitivity are 7 for the BV value. At this time, in the graph shown in FIG. 9B, that is, out of the output range of the pixel output, the inflection point is determined so that the linear transformation region: log transformation region is 4: 1, It is remembered.

  When the BV value is 9, the linear output area and the logarithmic conversion area are used together for the pixel output, and the aperture value, shutter speed, and ISO sensitivity are exposed using the exposure conditions when the BV value is 7. . At this time, in the graph shown in FIG. 9C, that is, out of the output range of the pixel output, the inflection point is determined so that the linear transformation region: log transformation region is 3: 2. It is remembered.

  When the BV value is 10, the linear output region and the logarithmic conversion region are used together for the pixel output, and exposure is performed using the exposure conditions when the shutter speed and the ISO sensitivity are 7 for the BV value. At this time, although not shown, the inflection point is determined and stored so that the linear transformation region: log transformation region becomes 2: 3 in the output range of the pixel output.

  When the BV value is 11, the linear output region and the logarithmic conversion region are used together for the pixel output, and exposure is performed using the exposure conditions when the shutter speed and the ISO sensitivity are 7 for the BV value. At this time, although not shown, the inflection point is determined and stored so that the linear transformation area: log transformation area is 1: 4 in the output range of the pixel output.

  Table 3 shows an example of a correspondence table of subject brightness, shooting conditions, and inflection point settings stored in the storage means in the case of shutter speed priority AE. The table shows the case where the shutter speed is 1/128 seconds.

  As shown in the table, when the BV value is 4 to 7, the pixel output is set so that only linear conversion is used, and exposure is performed by selectively changing the aperture value and the ISO sensitivity. It is decided to. At this time, it is determined to obtain a pixel output as shown in the graph of FIG. 9A and is stored in the storage means in advance.

  When the BV value is 8, the linear output area and the logarithmic conversion area are used together for the pixel output, and exposure is performed using the exposure condition when the aperture value and the ISO sensitivity are 7 for the BV value. At this time, in the graph shown in FIG. 9B, that is, out of the output range of the pixel output, the inflection point is determined so that the linear transformation region: log transformation region is 4: 1, It is remembered.

  When the BV value is 9, the linear output area and the logarithmic conversion area are used together for the pixel output, and exposure is performed using the exposure condition when the aperture value and the ISO sensitivity are BV values of 7. At this time, in the graph shown in FIG. 9C, that is, out of the output range of the pixel output, the inflection point is determined so that the linear transformation region: log transformation region is 3: 2. It is remembered.

  When the BV value is 10, the linear output region and the logarithmic conversion region are used together for the pixel output, and exposure is performed using the exposure condition when the aperture value and ISO sensitivity are BV value 7. At this time, although not shown, the inflection point is determined and stored so that the linear transformation region: log transformation region becomes 2: 3 in the output range of the pixel output.

  When the BV value is 11, the linear output area and the logarithmic conversion area are used together for the pixel output, and exposure is performed using the exposure condition when the aperture value and the ISO sensitivity are 7 for the BV value. At this time, although not shown, the inflection point is determined and stored so that the linear transformation area: log transformation area is 1: 4 in the output range of the pixel output.

  As described above, the subject brightness is detected, the inflection point position is read from the storage means storing the inflection point position set in advance corresponding to the subject brightness, and the inflection point is changed and controlled. It is possible to obtain an imaging apparatus that can shorten the time for determining the time inflection point and can reproduce the subject satisfactorily with respect to various subject conditions having a good operational feeling for the user.

  Further, the brightness of the subject is detected, and the aperture value, the shutter speed, the sensitivity, and the control of the inflection point, which are preset incident light amount control means corresponding to the subject brightness, are selectively used to the image sensor. In particular, the pixel output using both linear conversion and logarithmic conversion on the high-luminance side allows the subject to be captured even for subject conditions with a wide subject brightness range that occur frequently when the subject brightness is high. It is possible to obtain an imaging device that can be reproduced well.

  In the above description, in the case of each of the program AE, the aperture priority AE, and the shutter speed priority AE, the subject brightness ranges from BV4 to BV11. However, the present invention is not limited to this, and a wider range is stored in advance. It is preferable to keep it. Of course, the aperture priority AE is stored in advance for each aperture value used, and the shutter speed priority AE is stored in advance for each shutter speed used. .

It is an external appearance perspective view of the imaging device concerning this embodiment. It is a block diagram which shows the functional structure of the imaging device which concerns on this Embodiment. It is a block diagram which shows the structure of the image pick-up element which concerns on this Embodiment. It is a circuit diagram which shows the structure of the pixel with which the image pick-up element which concerns on this Embodiment is provided. It is a figure which shows the timing chart of operation | movement of the pixel with which the image pick-up element which concerns on this Embodiment is provided. It is the graph which showed the output with respect to the light reception amount of the pixel which concerns on this Embodiment. 6 is a flowchart illustrating an outline of an operation in a still image shooting mode of the imaging apparatus according to the present embodiment. It is a flowchart which shows the outline of AE preparation operation | movement of step S156 shown in FIG. It is a figure which shows the relationship between the light reception amount of the pixel which concerns on this Embodiment, and an output.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Imaging device 2 Case 3 Lens unit 4 Image pick-up element 5 Flash light emission part 6 Light control sensor 7 System control part 8 Signal processing part 11 Monitor 12 Zoom button W
13 Zoom button T
DESCRIPTION OF SYMBOLS 14 Optical finder 15 Selection cross key 16 Release switch 17 Power switch 18 USB terminal 22 Inflection point change part 27 Amplifier 28 A / D converter 29 Black reference correction part 30 AE evaluation value calculation part 31 WB process part 32 Color interpolation part 33 Color correction unit 34 Gradation conversion unit 35 Color space conversion unit

Claims (4)

An image sensor having a plurality of pixels capable of outputting an electric signal linearly converted with respect to the incident light amount and an electric signal logarithmically converted with respect to the incident light amount, and linear in the electric signal output from the image sensor An inflection point control means for changing and controlling an inflection point that is a boundary between the transformation area and the logarithmic transformation area, a luminance detection means for detecting the subject brightness, and an inflection point set in advance corresponding to the subject brightness Storage means for storing the position,
The imaging apparatus according to claim 1, wherein the inflection point control means controls to change the inflection point to the inflection point position stored in the storage means based on the subject brightness detected by the brightness detection means. 2. An incident light amount control unit that controls an incident light amount incident on the image sensor, wherein the inflection point is changed and controlled when the incident light amount control unit has an excessive exposure amount. The imaging device described in 1. The imaging apparatus according to claim 1, wherein the storage unit stores in advance a control value of the incident light amount control unit corresponding to subject brightness. An image sensor having a plurality of pixels capable of outputting an electric signal linearly converted with respect to the incident light amount and an electric signal logarithmically converted with respect to the incident light amount, and linear in the electric signal output from the image sensor An inflection point control means for changing and controlling an inflection point as a boundary between the transformation area and the logarithmic transformation area, a luminance detection means for detecting subject luminance, a sensitivity changing means for changing the sensitivity of the image sensor, and An incident light amount control means for controlling the incident light amount incident on the image sensor,
Based on the subject brightness detected by the brightness detection means, exposure control to the image sensor is performed by selectively using the incident light quantity control means, the sensitivity changing means, and the inflection point control means. An imaging apparatus characterized by that.

Images