JP2008118293A - Imaging apparatus and method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an imaging method by which an image of high quality can be photographed even under severe photographic conditions wherein the image is apt to be affected. <P>SOLUTION: The imaging method is provided which includes: an imaging step of generating image data through photoelectric conversion of an imaging element; a correction step (S512) of correcting vertical shading of the image data; and a dark current difference detection step (S506) of detecting a dark current difference of an imaging device generated according to a position difference in the imaging device, wherein the correction step is characterized in that the vertical shading correction is performed according to the detected dark current difference. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an imaging apparatus and method using an imaging element.

  In recent years, in an imaging apparatus such as a digital camera or a video camera, a CCD or a CMOS type image sensor (hereinafter referred to as a CMOS sensor) is generally used as an imaging element.

  Among the imaging devices, the CMOS sensor accumulates photocarriers generated by a photodiode (hereinafter referred to as PD) in the gate electrode (floating diffusion = FD) of the MOS transistor. The CMOS sensor amplifies and outputs the potential change to the output unit in accordance with the drive timing from the scanning circuit. A MOS type fixed imaging device (CMOS sensor) realized by a CMOS process, including the CMOS sensor portion that is a light converting portion and its peripheral circuit portion, has attracted particular attention.

  A general image sensor such as the CMOS sensor will be described with reference to FIGS. FIG. 8 is an equivalent circuit diagram of a CMOS sensor which is the image sensor.

  In the figure, S 11 is a pixel, and a plurality of pixels (S 21... Sm 1) having the same structure as the pixel S 11 are connected to the vertical output line 13. In the pixel, a photodiode (PD) 1, a transfer switch (TX) 2, a reset switch (TRES) 3, an amplification transistor 10 that is a source follower (SF) constituting the pixel amplifier, a load current source 7, and a first A switch 8 is provided. Since the load current source 7 and the first switch 8 are common to a plurality of pixels connected to the vertical output line 13, the amplification transistor 10 will be referred to as a source follower (SF) 10 for convenience of explanation.

  Further, a row selection switch (TSEL) 6 is provided, the gate of the transfer switch (TX) 2 is connected to the signal ΦTX, the gate of the reset switch 3 is connected to the signal ΦRES, and the gate of the row selection switch 6 is connected to the signal ΦSEL. It is connected.

  A plurality of columns (pixels S1 to Smn, vertical output lines 13 to 13n, etc.) are arranged in the circuit configuration.

  Photoelectric conversion is performed by the photodiode 1, and the transfer switch 2 is in an off state (ΦTX = high level) during a light amount charge accumulation period, and the photodiode 1 is connected to the gate of the source follower 10 constituting the pixel amplifier. The photoelectrically converted charge is not transferred. The floating diffusion region (FD) 11 at the gate of the source follower 10 constituting the pixel amplifier is initialized to an appropriate voltage by turning on the reset switch 3 (ΦRES = low level) before starting the accumulation. That is, this is a dark level. Next or simultaneously, when the row selection switch 6 is turned on (ΦSEL = low level), the load current source 7, the switch 8, and the source follower 10 constituting the pixel amplifier are activated. Here, by turning on the transfer switch 2 (ΦTX = low level), the charge accumulated in the photodiode 1 is transferred to the floating diffusion region 11 which is the gate of the source follower 10 constituting the pixel amplifier. . Here, 4 is a reset power source, and 5 is a power source for driving the source follower 10.

  Here, the output of the selected row is generated on the vertical output line 13. This output is stored in the signal storage unit 16 through the transfer gates 15a and 15b. The output temporarily stored in the signal storage unit 16 is sequentially read out to the output amplifier unit by a horizontal scanning circuit (not shown).

  FIG. 9 is a schematic timing chart of the imaging operation of the image sensor (CMOS sensor), and FIG. 10 is a timing chart illustrating the operation of FIG. 9 in more detail.

  In FIG. 9, (a) shows an imaging timing chart in a global exposure mode (collective reset mode) in which charges are sequentially stored after performing an accumulation operation at the same timing as in a CCD. (B) shows an imaging timing chart in a rolling exposure mode in which accumulation, readout, and reset are sequentially repeated for each scanning row.

  (A) Resets all scanning rows at the same timing (T1), similarly stores (T2) at the same timing, and sequentially transfers and reads out each scanning row (T3). The exposure is completed by blocking the exposure light by shading with a mechanical shutter or the like. However, in terms of electrical circuit, the accumulation operation is performed between T1 and T3. There is a difference in the accumulation time from the bottom to the transfer / readout after the exposure.

  (B) repeats reset (T1) / accumulation (T2) / transfer / readout (T3) for each scanning row, and reset / accumulation / transfer / readout at the same time with different timings depending on the scanning row. In the rolling exposure mode, the accumulation start timing is sequentially designated for each scanning row. For this reason, when recording as a still image, there is a drawback that distortion due to the difference in the accumulation time above and below the image, but there is no difference between scanning lines in the transfer / readout time. It is considered valid. In the rolling exposure mode, in consideration of a frame rate (repetition time) in moving image imaging (continuous imaging), it is general that light shielding such as a mechanical shutter is not performed while imaging is repeated.

  FIG. 10 is a detailed timing chart of the imaging operation of the CMOS sensor of FIG. 8, and shows the global exposure operation described in FIG.

  At the timing of the all-pixel reset period T1, the signals ΦTX1 to ΦTXm become active, and the charges of the photodiodes 1 of all the pixels are transferred to the gates of the source followers 10 via the transfer switches 2, and the photodiodes 1 Is reset. By activating the signals ΦRES1 to ΦRESm at the same timing (T1 period), the potential of the gate (FD) 11 of the source follower 10 (= potential of the capacitor C) becomes almost the same level as that of the reset power supply 4. The situation is reset.

  In this state, the cathode charge of the photodiode 1 is shifted to the gate (floating diffusion region) 11 of the source follower 10 and averaged. Here, by increasing the capacitance component of the capacitor of the gate of the source follower 10, the level becomes the same as the level at which the cathode of the photodiode 1 is reset.

  Simultaneously with the end of T1, accumulation in the photodiode 1 is performed. At this time, a mechanical shutter (not shown) that guides the amount of light of the target image is open, and at the end of time T1, accumulation starts for all pixels simultaneously. The mechanical shutter remains open for a period T2, and this period becomes the accumulation period of the photodiode 1. However, as the subsequent operation, operations such as charge transfer to the readout circuit in the subsequent stage are performed for each scanning row. Therefore, the electrical accumulation in the photodiode 1 in each row is continuously performed until the transfer is performed. Has been done. For example, the accumulation operation is performed with the mechanical shutter closed until T2 'and the light from the subject is blocked.

  When the accumulation time T2 ends, the accumulation of photocharges in the photodiode 1 ends. In this state, charges are accumulated in the photodiode 1.

  Next, reading starts for each line. That is, after reading the first row, the second row is read.

  During the period of time T3, the signal ΦSEL1 becomes active, the row selection switch 6 is turned on, and the source follower 10 composed of the pixel amplifiers of all the pixels connected to the first row is in an operating state.

  Here, in the floating diffusion region 11 which is the gate of the source follower 10 constituted by the pixel amplifier, the signal ΦRES1 becomes active during the period T4, and the reset switch 3 is turned on. As a result, the gate (floating diffusion region) 11 of the source follower 10 is reset. That is, this dark level signal is output to the vertical output line 13.

  Next, the signal ΦTN becomes active, and the transfer gate 15 b is turned on during the period T 4 ′ and held in the signal storage unit 16. This operation is executed in parallel for all the pixels connected to the first row.

  A period from T4 to T4 'when the dark level signal output is held in the signal storage unit 16 is referred to as "N reading" (noise component reading).

  Next, after turning off the signal ΦTN, the signal ΦTX1 is activated during the period T5, and the charge accumulated in the photodiode 1 is transferred to the vertical output line 13 via the floating diffusion region 11 and the source follower 10, An optical signal level signal is output.

  Subsequently, the transfer gate 15 b is turned on during the period T 5 ′ and held in the signal storage unit 16. This operation is executed in parallel for all the pixels connected to the first row.

  Here, the signal ΦTS becomes active only during the period T 5 ′, the transfer gate 15 a is turned on, and the signal level is held in the signal storage unit 16. This operation is executed in parallel for all the pixels connected to the first row.

  A period from T5 to T5 'in which the signal output of the signal level is held in the signal storage unit 16 is referred to as "S reading" (signal component reading).

  When the operation is finished, the signal storage unit 16 holds the dark level and the signal level of all the pixels connected to the first row. By taking the difference between the signal level and dark level between each pixel, fixed pattern noise (FPN) due to threshold voltage (threshold voltage) Vth variation of the source follower 10 and KTC noise generated when the reset switch 3 is reset Cancel. Thereby, a signal from which a noise component having a high S / N is removed is obtained.

  That is, the signal accumulating unit 16 includes difference means for subtracting the noise component from the signal component.

  This signal is horizontally scanned by a horizontal scanning circuit (not shown), and the difference signal between the dark level and the signal level stored in the signal storage unit 16 is output in time series. This completes the output of M lines. Similarly, by driving ΦSEL2 to m, ΦRES2 to m, ΦTX2 to m, ΦTN, and ΦTS in the same manner as the first row as shown in FIG. 10, the signals of the 2nd to mth rows can be read out.

  In the image pickup apparatus using the image pickup element such as the CMOS sensor described above, the dark level changes according to shooting conditions such as storage time, ISO sensitivity setting, and temperature. Particularly noticeable is high-temperature and long-time exposure, which generates a lot of dark current, and dark current greatly changes the dark level from normal shooting (room temperature and short-time exposure), and it compresses the dynamic range. .

  For this reason, in the imaging apparatus as described above, it is necessary to always make the dark level constant by correcting the dark level and to secure a dynamic range.

  As a method for correcting the dark level, a clamp circuit using an integration circuit using a capacitor (see Patent Document 1), or a clamp circuit that directly feeds back with an output of a D / A converter (see Patent Document 2). Etc. have been proposed. In recent years, a configuration having an analog front end (AFE) having both an OB clamp function and an A / D conversion function for clamping an OB (optical black) level by such a clamp circuit is generally used. It has become.

  An outline of the clamping operation using the AFE will be described with reference to FIGS. FIG. 13 shows signals for each horizontal line in FIG. FIG. 13A corresponds to the drive signals for the lines 1 to 8 in FIG. FIG. 13B corresponds to line drive signals after Line 9. In readout of each line, first, an imaging signal is transferred to a horizontal readout line in the imaging device 114 by various drive pulses supplied to the imaging device 114 by the timing generation circuit 118 of FIG. Next, pixel signals for one line are sequentially read by a horizontal shift register drive pulse in the horizontal scanning period. In this horizontal scanning period, the timing generation circuit 118 generates an OB clamp pulse for the AFE 116 to prompt an OB clamp process. When the OB clamp pulse is input, the AFE 116 samples pixel signals for a predetermined number of pixels from that time, and feeds back the difference between the average value and a desired dark output value to the offset adjustment circuit.

  Examples of the offset adjustment circuit include a type using an integrating circuit using a capacitor and a type that feeds back the output of the D / A converter as it is, but FIG. 11 shows an AFE 116 using the latter type. The example of a structure is shown.

  Reference numeral 801 denotes an image signal input terminal to which an analog signal from the image sensor 114 is input. This analog signal is supplied to the non-inverting input terminal (+) of the amplifier circuit 802, multiplied by a predetermined gain, converted to a digital signal by the A / D conversion circuit 803, and then subjected to subsequent signal processing from the output terminal 804. Output to the system. Here, when the OB clamp pulse is input to the AFE 116 in accordance with the input of the OB pixel signal, the average value of the pixel signals for a predetermined number of pixels is calculated by the averaging circuit 805 from that point. Next, the subtracter 806 subtracts the clamp target value from the average value, and the calculation unit 807 calculates the correction value from the result and sets it in the D / A converter 808. Offset adjustment is performed by feeding back the output of the D / A converter 808 to the inverting input terminal (−) of the amplifier circuit 802, and the dark level is adjusted to the clamp target value.

  That is, the AFE 116 performs an optical black clamp process for adjusting the offset of the pixel signal of the image sensor 114 based on the signal of the OB pixel and a process for converting the pixel signal of the image sensor 114 from analog to digital.

  Note that an imaging apparatus provided with such a clamp circuit increases the time constant of the OB clamp in order to avoid degradation of image quality due to clamp noise due to the influence of pixel signal noise. Thereby, the change of the dark level before and after one OB clamping operation is prevented from becoming large.

  In addition, the imaging device using the imaging element such as the CMOS sensor described above has a slight potential difference and dark current difference due to the influence of the wiring length of the electric circuit and the peripheral circuit. Shading which is uneven output occurs.

  For this reason, an image pickup apparatus using the image pickup device is provided with horizontal and vertical shading correction data in advance so as to correct the shading in the horizontal direction and the vertical direction under general photographing conditions. Then, each shading correction is performed by performing arithmetic processing such as subtraction on the shading correction data from the output at the time of shooting.

JP-A-5-153428 JP 2000-224440 A Japanese Patent Laid-Open No. 2-48864

  By the way, in recent years, due to the widespread use of imaging devices and technological improvements, the usage conditions of imaging devices have expanded. For example, exposure operations of several hours are performed for astronomical photography, etc. In some cases, the continuous shooting operation is performed.

  In photographing as described above, since an electric circuit / image sensor is energized for a long time, heat generated inside the image pickup apparatus may affect the image.

  For example, the dark current of the image sensor due to heat generation increases, and even if correction is performed with shading correction data acquired under general shooting conditions, correction is not possible, and unevenness remains in the surface, causing problems as an image There is concern about getting out.

  Basically, the conventional shading correction corresponds to the shading correction due to the increase of the dark current, and it appears that there is almost no in-plane dark current unevenness even when shooting for a long time. Corrections have been made.

  As a part of the shading correction, a correction for a local dark current increase (mainly at the periphery of the imaging area) generated by heat generated by a general operation of a circuit unit arranged in the imaging element is also provided. It is included.

  However, in recent imaging apparatuses such as digital single-lens reflex cameras, as described above, as a basic imaging operation, the accumulation operation starts at the same timing for all images, and transfer / readout to the subsequent amplification circuit, etc. This is sequentially performed in the vertical direction, that is, for each scanning line from the top. Therefore, since the waiting time (= accumulation time) becomes longer until reading as it goes to the lower part, the influence of shading in the vertical direction becomes large when the dark current is large.

  Generally, the shading difference due to the vertical difference of the dark current and the local shading during normal operation hardly occur under the shooting conditions at normal temperature, so the normal shading correction value corrects the shading vertical difference. There is nothing.

  In particular, the difference caused by the minute dark current due to the optical black clamping operation is canceled out by drawing it to the target value, and thus has no effect.

  Further, even in long-second shooting with a long storage time, the ratio of the readout time to the entire storage time is small, and therefore the influence of the dark current difference between the upper and lower sides is small and hardly causes a problem as an image.

  However, when shooting with a short exposure time is performed in a state in which heat is generated by performing long-time shooting or continuous operation, there is a problem that a difference in the vertical direction of dark current appears in the image.

  For example, the dark current difference that is originally desired to be pulled to the target value by the OB clamp cannot be sufficiently pulled because the time constant of the OB clamp is large as described above, and the image is affected as the rest of the clamp. End up.

  This problem may occur remarkably immediately after a moving image shooting operation that repeats shooting for a long time with a short accumulation time or in the latter half of continuous shooting.

  As shown in FIG. 14, normal correction is possible with (a) vertical shading correction data and (b) local shading correction data (peripheral correction data). The actual shading after operation is affected by the difference in readout time in the vertical direction. For this reason, after the shading correction of (d), a correction remainder (up / down difference) occurs.

  As a proposal regarding a correction means for dark current of the image sensor, there is a method that includes a means for detecting (external) temperature and corrects shading according to the result of temperature detection (see Patent Document 3). ).

  However, since external temperature detection is fundamental, it is difficult to actually detect the temperature change of the image sensor, and fine correction such as the vertical difference of the dark current due to the operation described above is performed. It is difficult.

  An object of the present invention is to provide an imaging apparatus and method capable of capturing a high-quality image even under severe imaging conditions that easily affect the image.

  The image pickup apparatus of the present invention includes an image pickup device that generates image data by photoelectric conversion, a correction unit that corrects shading in a vertical direction with respect to the image data, and the image pickup that occurs according to a positional difference in the image pickup device. A dark current difference detecting means for detecting a dark current difference between elements, wherein the correcting means performs the shading correction in the vertical direction according to the detected dark current difference.

  Further, the imaging method of the present invention corresponds to an imaging step of generating image data by photoelectric conversion of the imaging device, a correction step of correcting shading in the vertical direction with respect to the image data, and a positional difference in the imaging device. A dark current difference detecting step of detecting a dark current difference of the image sensor generated by the correction, wherein the correcting step performs the shading correction in the vertical direction according to the detected dark current difference. And

  High-quality images can be taken even under harsh shooting conditions that tend to affect the images.

  FIG. 1 is a block diagram illustrating a configuration of an electronic camera that is an imaging apparatus according to an embodiment of the present invention. In the figure, reference numeral 111 denotes a photographing lens. A shutter 112 controls the exposure amount of the image sensor 114 such as a CMOS sensor. Reference numeral 114 denotes an image sensor that converts an optical image into an electrical signal. In the present embodiment, a CMOS sensor is used as the image sensor 114.

  The image sensor 114 has a micro lens ML for transmitting and condensing light for each pixel and a color filter CF having a different Bayer array and having different spectral transmittances on the upper surface of a semiconductor portion that performs photoelectric conversion. . The image sensor 114 generates image data by photoelectric conversion. The image sensor 114 has the configuration of the CMOS area sensor of FIG. 8, and the description thereof is the same as described above.

  Note that a low-pass filter LPF for cutting an extra wavelength of light transmitted through the photographing lens 111 (an unnecessary wavelength that affects color reproduction) is arranged between the photographing lens 111 and the imaging element 114. You may set up.

  Reference numeral 116 denotes an analog front end circuit (hereinafter referred to as AFE) including an A / D converter that converts an analog signal output from the image sensor 114 into a digital signal, a clamp circuit (offset adjustment circuit), and a D / A converter. Called). A timing generation circuit 118 supplies a clock signal and a control signal to the image sensor 114 and the AFE 116, and is controlled by the memory control circuit 122 and the system control circuit 150.

  An image processing circuit 120 performs predetermined pixel interpolation processing and color conversion processing on the data from the AFE 116 or the data from the memory control circuit 122. The image processing circuit 120 performs a predetermined calculation process using imaged image data as necessary.

  The distance measurement control unit 142 and the photometry control unit 146 perform AF (autofocus) processing and AE (automatic exposure) processing by the system control circuit 150.

  A memory control circuit 122 controls the AFE 116, the timing generation circuit 118, the image processing circuit 120, the image display memory 124, and the memory 130.

  Data from the AFE 116 is written to the image display memory 124 or the memory 130 via the image processing circuit 120 and the memory control circuit 122 or directly via the memory control circuit 122.

  The image processing circuit 120 corrects the charge signal output from the image sensor 114 based on shading correction data stored in a memory 152 to be described later, and forms an image. The image processing circuit 120 Include image correction means.

  Reference numeral 124 denotes an image display memory. Reference numeral 128 denotes an image display unit composed of a TFT LCD.

  Reference numeral 130 denotes a memory for storing captured still images and moving images, and has a storage capacity sufficient to store a predetermined number of still images and moving images for a predetermined time.

  A shutter control unit 140 controls the shutter 112. A distance measurement control unit 142 is a distance measurement unit for performing AF (autofocus) processing. Reference numeral 144 denotes a thermometer which is a temperature detection means for measuring the ambient temperature in the photographing environment and the temperature inside the camera (such as the periphery of the image sensor). A photometry control unit 146 is a photometry unit for performing AE (automatic exposure) processing.

  The photometry control unit 146 also has a flash photographing function in cooperation with the flash unit 148.

  Reference numeral 148 denotes a flash unit used for shooting in the dark, which also serves as a function of projecting AF auxiliary light.

  A system control circuit 150 controls the entire image processing apparatus and incorporates a CPU and the like.

  A memory 152 is a storage unit that stores constants, variables, programs, and the like for operation of the system control circuit 150. Preset shading correction data and the like are stored in the memory 152. The shading correction coefficient and the like after the continuous operation in this embodiment are also stored in the memory 152.

  The image display unit 128 displays an operation state, a message, and the like according to the execution of the program in the system control circuit 150.

  Reference numeral 156 denotes a nonvolatile memory which is a storage means such as an electrically erasable / recordable EEPROM in which a program described later is stored.

  Reference numeral 160 denotes an operation unit including a main switch (start switch) for inputting various operation instructions of the system control circuit 150, a shutter switch, a mode setting dial for switching a photographing mode, and the like. The operation unit 160 includes a shutter switch that is turned on in steps by turning on the two switches (SW1, SW2). In the first stage (SW1 ON), operations such as AF (autofocus) processing, AE (automatic exposure) processing, AWB (auto white balance) processing, and EF (flash dimming) processing are performed. The shutter 112 and the like are controlled in the second stage (SW2 on). An exposure process for writing the signal read from the image sensor 114 to the memory 130 via the AFE 116 and the memory control circuit 122 is performed. Next, a development process using operations in the image processing circuit 120 and the memory control circuit 122, a recording process for reading the image data from the memory 130, compressing the image data, and writing the image data on the recording medium 1200 are performed. The shutter switch instructs the operation start of the series of processes. In addition, the operation unit 160 has a mode setting dial which is a shooting mode setting unit for switching various shooting modes. The above shooting modes include an automatic shooting mode, a program shooting mode, a shutter speed priority shooting mode, an aperture priority shooting mode, a manual shooting mode, a night scene shooting mode, an astronomical shooting mode, a portrait shooting mode, and the like. The operation unit 160 also provides a single / continuous shooting switch for switching between single shooting / continuous shooting, a still image / moving image mode switching switch, an ISO sensitivity setting switch for setting shooting sensitivity (ISO sensitivity), and power supply to various systems. Power switch and the like.

  In the embodiment of the present invention, the term “moving image capturing mode” is used. However, the moving image capturing is not limited to moving image recording, and display moving image capturing for displaying an image on a viewfinder or the like in almost real time is also possible. It is included.

  182 is a power supply control unit composed of a battery detection circuit, a DC-DC converter, and the like. 186 is a primary battery such as an alkaline battery and a lithium battery, a secondary battery such as a NiCd battery, a NiMH battery, and a Li battery, and an AC adapter. It is a power supply unit. 1200 is a detachable recording medium such as a memory card or a hard disk.

  Next, the operation of the imaging apparatus according to the embodiment of the present invention will be described in detail with reference to FIGS.

  In step S101, the system control circuit 150 initializes flags, control variables, and the like by turning on the power supply such as battery replacement, and performs necessary initial settings for each part of the image processing area.

  In step S102, the system control unit 150 determines the setting position of the main (power) switch in the operation unit 160, and determines whether or not the main switch is set to OFF. When the main switch is set to ON, the process proceeds to step S104, and when the main switch is set to OFF, the process proceeds to step S103.

  In step S103, when the main switch is set to OFF, the display of each display unit is changed to the end state, and necessary parameters, setting values, and setting modes including flags and control variables are recorded in the nonvolatile memory 156. To do. Thereafter, the power control unit 182 performs a predetermined end process such as shutting off unnecessary power in each part of the image processing area including the image display unit 128, and then returns to the process of step S102.

  In step S104, the system control circuit 150 reads setting information such as ISO sensitivity that has already been set. Next, in step S105, if the main switch is set to ON in step S102, the system control circuit 150 causes the power control unit 182 to determine the remaining capacity and operation status of the power source 186 such as a battery in the operation of the image processing area. It is determined whether or not there is. If it is determined that there is a problem, the process proceeds to step S106. If it is determined that there is no problem, the process proceeds to step S107.

  In step S106, the system control circuit 150 gives a predetermined warning to the image display unit 128 or a display unit / sound generator (not shown) by displaying an image or outputting a sound, and then returns to the process of step S102.

  In step S107, the system control circuit 150 determines the setting position of the mode setting dial switch in the operation unit 160. If the mode setting dial switch is set to another mode (for example, ISO sensitivity setting mode), the process proceeds to step S108. If the mode setting dial switch is set to the shooting mode, the process proceeds to step S109.

  In step S108, the system control circuit 150 executes processing (for example, ISO sensitivity setting) according to the selected mode, and returns to the processing of step S102 after execution.

  In step S <b> 109, the system control circuit 150 determines whether or not the recording medium 1200 is loaded, and acquires management information of image data recorded on the recording medium 1200. Then, it is determined whether or not the operation state of the recording medium 1200 has a problem in the image processing operation, particularly the recording / reproducing operation of the image data on the recording medium. If it is determined that there is a problem, the process proceeds to step S106 that has already been described, and if it is determined that there is no problem, the process proceeds to step S110.

  In step S110, the system control circuit 150 checks the selection state of the single / continuous shooting switch for selecting single shooting / continuous shooting in the operation unit 160.

  In step S110, if single shooting is selected, the process proceeds to step S111. If continuous shooting is selected, the process proceeds to step S112.

  In step S111, the system control circuit 150 sets the single / continuous shooting flag to “single”. In step S112, the system control circuit 150 sets the single / continuous shooting flag to “continuous shooting”. The setting state of the single / continuous shooting flag in steps S111 to S112 is stored in the internal memory of the system control circuit 150 or the memory 152.

  When the single / continuous shooting flag stored in steps S111 to S112 is stored in the memory, various data (single / continuous shooting mode, astronomical shooting / general shooting mode, exposure time, shooting date and time) at the time of the previous shooting are stored. Etc.) is also stored in a predetermined area of the internal memory or the memory 152.

  In step S113, the system control circuit 150 displays various setting states of the image processing area by displaying an image or outputting sound on the image display unit 128 or a display unit / sound generation unit (not shown). Here, when the image display switch of the image display unit 128 is on, various setting states of the image processing area may be displayed using the image display unit 128 by an image or sound.

  In step S114, the system control circuit 150 determines whether or not the shutter switch SW1 is pressed. If the shutter switch SW1 is not pressed, the process returns to step S102. If the shutter switch SW1 is pressed, the process proceeds to step S115.

  In step S115, the system control circuit 150 performs distance measurement processing to focus the photographing lens 110 on the subject, perform light measurement processing, and perform distance measurement / photometry processing to determine an aperture value and a shutter speed. In the photometric process, the flash is set if necessary.

  In step S115, the system control circuit 150 measures the temperature with the thermometer 144 and stores it in a predetermined area of the memory 152.

  In step S <b> 116, the system control circuit 150 reads out one-dimensional correction data used for horizontal and vertical shading correction stored in advance from the nonvolatile memory 156 and expands it in a predetermined area of the memory 130. After the development of the correction data is completed, the process proceeds to step S117.

  In step S117, the system control circuit 150 determines whether or not the shutter switch SW2 is pressed. If the shutter switch SW2 is not pressed, the process proceeds to step S118. If the shutter switch SW2 is pressed, the process proceeds to step S119.

  In step S118, the system control circuit 150 determines whether or not the shutter switch SW1 has been released. If the shutter switch SW1 has not been released, the process returns to step S117, and if the shutter switch SW1 has been released, the process proceeds to step S102.

  In step S119, the system control circuit 150 determines whether or not the memory 130 has an image storage buffer area capable of storing captured image data. If it is determined that there is no area capable of storing new image data in the image storage buffer area of the memory 130, the process proceeds to step S120. If it is determined that there is an area capable of storing new image data, the process proceeds to step S121. Transition.

  In step S120, the system control circuit 150 gives a predetermined warning to the image display unit 128 or a display unit / sound generator (not shown) by displaying an image or outputting a sound, and then returns to the process of step S102.

  For example, immediately after performing the maximum number of continuous shots that can be stored in the image storage buffer area of the memory 130, the first image to be read from the memory 130 and written to the storage medium 1200 is not yet recorded in the storage medium 1200. State. That is, there is a case where one empty area cannot be secured in the image storage buffer area of the memory 130 yet.

  When the captured image data is compressed and stored in the image storage buffer area of the memory 130, it is considered that the amount of image data after compression varies depending on the compression mode setting. That is, it is determined in the process of step S120 whether or not the storable area is on the image storage buffer area of the memory 130.

  In step S <b> 121, the system control circuit 150 reads an image signal that has been captured and accumulated for a predetermined time from the image sensor 114. Then, a photographing process for writing image data photographed in a predetermined area of the memory 130 via the AFE 116, the image processing circuit 120 and the memory control circuit 122, or directly from the AFE 116 via the memory control circuit 122 is executed.

  It should be noted that during the photographing process in step S121, the optical black (OB) region clamping operation by the AFE 116 which has already been described with reference to FIGS. 11 to 13 is performed. At that time, the drawing target charge amount (≈dark current amount) is set in the D / A converter 808 by the clamping operation obtained by the calculation unit 807 for each row of the image sensor 114 and simultaneously stored in the memory. Then, the clamp pull-in target charge amount data is added to a part of the image file (for example, at the end of each horizontal line of the image data) (see FIG. 7). That is, the AFE operation in step S121 performs dark current detection.

  In step S122, the system control circuit 150 reads a part of the image data written in a predetermined area of the memory 130 through the memory control circuit 122 and performs a development process by performing a WB (white balance) integration calculation process. I do. The system control circuit 150 performs OB (optical black) integration calculation processing, and stores the calculation result in the internal memory of the system control circuit 150 or the memory 152. The system control circuit 150 reads captured image data written in a predetermined area of the memory 130 using the memory control circuit 122 and, if necessary, the image processing circuit 120. Then, using the calculation result stored in the internal memory of the system control circuit 150 or the memory 152, various development processes including an AWB (auto white balance) process, a gamma conversion process, and a color conversion process are performed.

  In the development process in step S122, correction values are obtained for the horizontal and vertical shading correction data developed in step S116 in the memory 152, and a subtraction process is performed. The correction value is a correction value that takes into account the local shading correction coefficient (for example, the peripheral portion) associated with the temperature measurement result measured in step S115 and the vertical shading data correction coefficient (up / down difference) associated with the previous imaging mode or the like. Details thereof will be described in detail with reference to FIG. Further, correction calculation processing for canceling fixed pattern noise and scratches of the image sensor 114 is also performed.

  In step S123, the system control circuit 150 reads the image data written in the predetermined area of the memory 130, and performs image compression processing according to the set mode using a compression / decompression circuit (not shown). Then, image data that has been shot and finished a series of processing is written in the empty image portion of the image storage buffer area of the memory 130.

  In step S124, the system control circuit 150 reads out the image data stored in the image storage buffer area of the memory 130, and starts a recording process for writing the image data to the recording medium 1200 such as a memory card or a compact flash (registered trademark) card. To do.

  This recording start process is performed on the image data every time new image data that has been shot and finished a series of processes is newly written in the empty image portion of the image storage buffer area of the memory 130.

  In order to indicate that the writing operation is being performed while the image data is being written to the recording medium 1200, a recording medium writing operation display such as blinking a display unit (LED or the like) not shown is performed.

  In step S125, the system control circuit 150 stores data such as the mode at the time of the main shooting process in the memory 152, the non-volatile memory 156, etc., for example, single shooting / continuous shooting mode, astronomical shooting / general shooting mode, exposure time, shooting. The date and time (by a date function (not shown)) is stored.

  In step S126, the system control circuit 150 determines whether or not the shutter switch SW1 is pressed. If the shutter switch SW1 is released, the process returns to step S102, and if the shutter switch SW1 is pressed, the process proceeds to step S127.

  In step S127, the system control circuit 150 determines the state of the single / continuous shooting flag stored in the internal memory or the memory 152. If single shooting is set, the process returns to the processing of step S126, and the shutter switch SW1. The current process is repeated until is released. On the other hand, if continuous shooting (high-speed continuous shooting and low-speed continuous shooting) has been set, the process returns to step S117 to prepare for the next shooting. As a result, a series of processing relating to photographing is completed.

  FIG. 4 is a flowchart showing details of the photographing processing procedure in step S121 in FIG.

  In step S301, the system control circuit 150 drives a mirror (not shown) and moves it to the mirror up position.

  In step S302, the system control circuit 150 drives an aperture (not shown) to a predetermined aperture value according to the photometric data stored in the internal memory or the memory 152.

  In step S303, the system control circuit 150 performs a charge clear operation of the image sensor 114. In steps S <b> 304 to S <b> 306, the system control circuit 150 starts charge accumulation in the image sensor 114, opens the shutter 112 by the shutter control unit 140, and starts exposure of the image sensor 114.

  In steps S307 to S308, the system control circuit 150 determines whether or not the flash unit 148 is necessary based on the flash flag, and if necessary, causes the flash unit 148 to emit light.

  In steps S309 to S310, the system control circuit 150 waits for the exposure of the image sensor 114 to end in accordance with the photometric data. When the exposure ends, the shutter control unit 140 closes the shutter 112 and ends the exposure of the image sensor 114.

  In steps S311 to S312, the system control circuit 150 drives a diaphragm (not shown) to an open diaphragm value, and moves a mirror (not shown) to the mirror down position.

In steps S313 to S315, the system control circuit 150 determines whether or not the set charge accumulation time has elapsed. When the set charge accumulation time has elapsed, the system control circuit 150 reads the charge signal from the image sensor 114 after completing the charge accumulation of the image sensor 114. The system control circuit 150 writes the photographed image data in a predetermined area of the memory 130 via the AFE 16, the image processing circuit 120, the memory control circuit 122, or directly from the AFE 16 via the memory control circuit 122.
When the series of processes is completed, the present process is terminated and the process returns to the main process.

  FIG. 5 is a flowchart showing details of the development processing procedure in step S122 in FIG.

  In step S501, the system control circuit 150 reads the image data written in the predetermined area in step S121 of FIG. 3 into the development area in the image processing circuit 120.

  In step S502, the system control circuit 150 confirms the shooting date and time from various information at the time of previous shooting stored in a predetermined area of the internal memory or the memory 152, and compares it with the current date and time. Thereby, the elapsed time from the previous photographing is confirmed, and it is confirmed whether or not a predetermined time (for example, 15 minutes) has elapsed. If the predetermined time has elapsed, the process proceeds to step S507. If the predetermined time has not elapsed, the process proceeds to step S503.

  In step S503, the system control circuit 150 checks whether or not the previous shooting was continuous shooting from various information at the time of the previous shooting stored in a predetermined area of the internal memory or the memory 152. If it is continuous shooting, the process proceeds to step S505. If it is not continuous shooting, the process proceeds to step S504.

  In step S504, the system control circuit 150 checks whether or not the previous shooting was in the astronomical shooting mode from various information at the previous shooting stored in a predetermined area of the internal memory or the memory 152. If it is the astronomical mode, the process proceeds to step S505, and if it is not the astronomical mode, the process proceeds to step S507.

  In step S505, the system control circuit 150 determines that there is an influence due to the previous photographing, and confirms the data of the clamp pull-in amount recorded at the end of each line of the image data.

  In step S506, the system control circuit 150 calculates a vertical difference correction coefficient for the vertical shading correction value stored in advance from the clamp pull-in amount confirmed in step S505.

  That is, the dark current amount detected by the operation of the AFE 116 in step S121 is detected as a vertical difference in steps S505 to S506. That is, the AFE 116 and the image processing circuit 120 performing the calculation process are combined to form a dark current difference detection unit. The dark current difference detection means detects a dark current difference of the image sensor 114 that occurs according to the vertical position difference in the image sensor 114.

  In step S507, the system control circuit 150 checks the temperature measured in step S115 of FIG. 3 and determines whether or not the temperature is within a predetermined temperature. If it is outside the predetermined temperature, the process proceeds to step S508, and if it is within the predetermined temperature, the process proceeds to step S510.

  In step S508, the system control circuit 150 checks the dark current amount. As an example of the method, the output value before clamping of the uppermost row OB portion of the image data is compared with the output value at normal temperature stored in advance, and the dark current amount is confirmed from the difference.

  In step S509, the system control circuit 150 calculates a coefficient for performing local shading correction (for example, peripheral correction) from the dark current amount confirmed in step S508.

  In step S510, the system control circuit 150 calculates a horizontal shading correction value in which the local correction coefficient obtained in step S509 is added to the horizontal shading correction value stored in advance.

  In step S511, the system control circuit 150 calculates a vertical shading correction value obtained by adding the vertical difference correction coefficient obtained in step S506 and the local correction coefficient obtained in step S509 to the previously stored vertical shading correction value. When the local correction is also up and down, the vertical correction may be added to the local correction coefficient, and the vertical difference correction may be performed after the correction.

  In step S512, the system control circuit 150 performs shading correction in the horizontal and vertical directions on the image data generated by the image sensor 144 using the horizontal and vertical shading correction values obtained in steps S510 to S511.

  In step S513, the system control circuit 150 corrects pixel defects stored in advance in consideration of shooting conditions and the like. In step S514, the system control circuit 150 performs OB integration correction to compensate for a slight optical black output shift or the like.

  In step S515, the system control circuit 150 performs white balance correction on the image data after performing various corrections.

  In step S516, the system control circuit 150 performs gamma processing for performing color conversion on the image data. In step S517, the system control circuit 150 performs color conversion processing on the image data for which gamma processing has been completed, and returns to step S123 in FIG.

FIG. 6 is an example of vertical shading corrected by the sequence of FIGS.
(O) is a projection in the vertical direction of the original data before shading correction, and is a normal in-plane unevenness, local shading that occurs only in the peripheral part (only the upper and lower parts for projection), and dark current due to the influence of the readout time This is a state where all the top and bottom differences remain.
(A) is normal vertical shading data stored in advance.
(B) is local correction data (upper and lower correction data) obtained by calculation by adding the dark current amount to the local shading data stored in advance.
(C) is dark current up-and-down difference correction data obtained by calculating the inclination with respect to the dark current amount of each row obtained by the OB clamping operation at the time of image capturing and further calculating the correction amount.
(D) is a shading correction result (corrected vertical shading) obtained by subtracting the obtained shading correction value from (o) in consideration of the shading data of (a) to (c).

  As described above, by correcting the dark current up-and-down difference under conditions that easily affect an image, an imaging device that can capture high-quality images even under severe imaging conditions can be realized.

  In the embodiment of the present invention, the dark current amount data is obtained from the target charge amount of each OB clamp line, but the present invention is not specialized to that. For example, there is no problem if pixels that do not perform the clamping operation are provided above and below, the normal output values of the pixels are stored in advance, and the dark current and the vertical difference are obtained by comparison with the output values at the time of photographing.

  Furthermore, in the embodiment of the present invention, switching of whether to correct the dark current up / down difference correction only by the mode setting of the previous shooting (continuous shooting / astrophotography) is described to reduce the calculation time. However, the gist of the present invention is that, regardless of the mode or the like, the level of the dark current up / down difference is detected, and if it is larger than a predetermined value, the dark current up / down difference correction is performed.

  It is also possible to observe the dark current by observing the amount of defects in an area not affected by light, such as a predetermined OB area, and changing the output value or the number of defects due to the dark current.

  The defect may be a defect generated in manufacturing, but there is no problem in a pixel whose output change due to a dark current intentionally generated by specifying an address or the like is large.

  Furthermore, when the local shading described in the present embodiment is in the peripheral part of the image, pay attention to the upper and lower parts or the vertical direction of the peripheral part, and the output value or shape of the part Therefore, it is no problem to predict the dark current.

  In addition, in the embodiment of the present invention, the case where the image pickup device is a CMOS sensor has been described as an example. However, the present invention is not specialized thereto, and the same problem occurs even when the image pickup device is a CCD, for example. Can be effective.

  According to the present embodiment, it is possible to provide an imaging apparatus that can capture a high-quality image even under severe imaging conditions that are likely to affect the image, and to expand the scene that can be captured.

  The above-described embodiments are merely examples of implementation in carrying out the present invention, and the technical scope of the present invention should not be construed in a limited manner. That is, the present invention can be implemented in various forms without departing from the technical idea or the main features thereof.

It is a block diagram which shows the structural example of the imaging device (electronic camera) in embodiment of this invention. It is a flowchart which shows the operation | movement sequence (main 1) in embodiment of this invention. It is a flowchart which shows the operation | movement sequence (main 2) in embodiment of this invention. It is a flowchart which shows the operation | movement sequence (imaging | photography) in embodiment of this invention. It is a flowchart which shows the operation | movement sequence (development) in embodiment of this invention. It is a figure which shows the example of correction | amendment of the vertical shading in embodiment of this invention. It is a figure which shows the example of an output of the image data in embodiment of this invention. It is a circuit diagram which shows the pixel part of the CMOS type area sensor in embodiment of this invention. It is an operation timing chart (conceptual diagram) of a conventional CMOS sensor. It is an operation | movement timing chart (detail drawing) of the conventional CMOS sensor. It is a figure which shows the structural example of the clamp circuit inside AFE in embodiment of this invention. 4 is a drive timing chart (schematic diagram) of an image sensor and an AFE according to an embodiment of the present invention. It is a drive timing chart (detail drawing) of the image sensor and AFE in the embodiment of the present invention. It is a figure which shows the example of a correction | amendment of the conventional vertical shading.

Explanation of symbols

111 Shooting Lens 112 Shutter 114 Image Sensor (CMOS Sensor)
116 AFE
118 Timing Generation Circuit 120 Image Processing Circuit 122 Memory Control Circuit 150 System Control Circuit 160 Operation Unit

Claims (8)

An image sensor that generates image data by photoelectric conversion;
Correction means for correcting shading in the vertical direction with respect to the image data;
Dark current difference detection means for detecting the dark current difference of the image sensor generated according to the position difference in the image sensor;
The image pickup apparatus, wherein the correction unit performs the shading correction in the vertical direction according to the detected dark current difference.   The dark current difference detection means detects a charge draw amount in a clamping operation of an optical black region of the image pickup device, and detects a dark current difference of the image pickup device according to the draw amount. The imaging apparatus according to 1.   The imaging apparatus according to claim 1, wherein the dark current difference detection unit adds data on the amount of optical black area drawing after the image data of each row of the imaging device.   The correction means performs the vertical shading correction according to the dark current difference according to the elapsed time from the previous shooting, or performs the vertical shading correction regardless of the dark current difference. The imaging apparatus according to any one of claims 1 to 3, wherein the imaging apparatus is characterized in that Furthermore, it has temperature detection means for detecting temperature,
The correction unit performs the shading correction in the vertical direction according to the dark current difference according to the detected temperature, or performs the shading correction in the vertical direction regardless of the dark current difference. The imaging device according to any one of claims 1 to 4. Furthermore, it has a shooting mode switching means for switching the imaging mode,
The correction unit performs the shading correction in the vertical direction according to the dark current difference according to the previous shooting mode, or performs the shading correction in the vertical direction regardless of the dark current difference. The imaging device according to any one of claims 1 to 5.   The imaging apparatus according to claim 6, wherein the correction unit performs the shading correction in the vertical direction according to the dark current difference when the previous shooting mode is the continuous shooting mode. An imaging step of generating image data by photoelectric conversion of the imaging element;
A correction step of correcting shading in the vertical direction with respect to the image data;
A dark current difference detection step for detecting a dark current difference of the image sensor generated according to a position difference in the image sensor;
In the imaging method, the correcting step performs the shading correction in the vertical direction according to the detected dark current difference.

Images