JP3984045B2 - Imaging apparatus and control method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an imaging apparatus and a control method therefor, for example, an imaging apparatus suitable for application to a digital camera having a wide dynamic range, more specifically, a video camera, an electronic still camera, an image input apparatus, and the like. It relates to a control method.
[0002]
[Prior art]
Conventionally, various methods have been proposed as methods for widening the dynamic range of an image sensor or a captured image. For example, Japanese Patent Laid-Open No. 5-145857 discloses a camera in which pixels provided with microlenses and pixels without microlenses are arranged in a checkered pattern, and pixels having a large amount of incident light and pixels having a small amount of incident light are provided. It is disclosed. The dynamic range is widened by combining data from pixels with a large amount of incident light and data from pixels with a small amount of incident light.
[0003]
In addition, JP 2000-224467, JP 2000-209492, JP 2000-92378, JP 2000-50151, and JP 10-327357 disclose a plurality of exposures with different exposure amounts. A technique is disclosed in which a plurality of images with different exposure amounts are obtained, and a dynamic range is widened by adding these images.
[0004]
[Problems to be solved by the invention]
However, in the method using the microlens, pixels having microlenses and pixels having no microlens are alternately present, so that pixels having a large amount of incident light and pixels having a small amount of incident light are alternately present. For pixels with a large amount of incident light, data with a small amount of incident light is interpolated from data for pixels with a small amount of incident light. For pixels with a small amount of incident light, data with a large amount of incident light is interpolated from data for pixels with a large amount of incident light. For this reason, the resolution is lowered. In particular, the reduction becomes significant in the case of still images.
[0005]
In addition, the method of shooting multiple times with different exposure amounts has a problem with moving subjects because the exposure timing is different.
[0006]
SUMMARY OF THE INVENTION It is an object of the present invention to provide an image pickup apparatus that eliminates the drawbacks of the prior art and has a wide dynamic range and prevents a reduction in resolution, and a control method therefor. Another object of the present invention is to provide an imaging apparatus that has a wide dynamic range and can obtain an appropriate image even for a moving subject, and a control method thereof.
[0007]
[Means for Solving the Problems]
In order to solve the above-described problems, the present invention provides a plurality of light receiving elements that convert incident light from a subject field into signal charges, and a plurality of light receiving elements that are provided corresponding to the light receiving elements and read out signal charges from the corresponding light receiving elements. In an imaging apparatus including a signal reading unit and a signal processing unit that receives the read signal charge and processes it as an image signal, the signal reading unit accumulates smear during the exposure period, and the accumulated smear is signal processing unit The signal processing unit generates an image signal including smear as a part of the image signal.
[0008]
The image pickup apparatus of the present invention has a wide dynamic range and can prevent a reduction in resolution by using a smear component mixed at a certain ratio in a signal reading unit provided corresponding to the light receiving element. Since the smear component is mixed in the signal reading unit at a constant rate, it is proportional to the amount of incident light. By using the smear component corresponding to the light receiving element, the dynamic range can be widened without reducing the resolution.
[0009]
In the present invention, the signal readout unit accumulates smear when the light receiving element accumulates the signal charge, and outputs the accumulated smear to the signal processing unit, and then reads out the signal charge accumulated by the light receiving element. It is preferable to output to the signal processing unit. In this case, since smear is accumulated in the same period as the period in which the light receiving element is exposed, images having different exposure amounts can be obtained in the same time period. Since the exposure timing is the same, there is no problem even with a moving subject.
[0010]
The apparatus of the present invention includes smear discharging means for discharging smear, which is an error component already accumulated in the signal reading unit, before the signal reading unit accumulates the smear. The accumulation of smear may be started after a certain smear is discharged. As a result, smear can be measured with high accuracy.
[0011]
In addition, in order to reduce the influence of smear that is an error component, the signal processing unit obtains and accumulates the amount of smear that is already accumulated in the signal reading unit before the signal reading unit accumulates the smear. The amount of smear may be corrected by the amount of smear that is an error component.
[0012]
Furthermore, in the apparatus of the present invention, images having different exposure amounts are obtained using smear, but in order to adjust the exposure amount, smear control means for controlling the amount of smear accumulated in the signal reading unit is included. Can do.
[0013]
In order to solve the above-described problems, the present invention provides a method for controlling an imaging apparatus according to the present invention, wherein incident light from an object field is converted into a signal charge by a plurality of light receiving elements, and is provided corresponding to the light receiving elements. In the control method of the imaging apparatus in which the plurality of signal readout units read out the signal charges from the corresponding light receiving elements, and the read signal charges are input to the signal processing unit and processed as image signals, smearing is performed during the exposure period. Is included in the signal reading unit, and the accumulated smear is output to the signal processing unit, and the second step of generating an image signal including the smear as part of the image signal in the signal processing unit. It is characterized by.
[0014]
In the method of the present invention, in the first step, smear is accumulated when the light receiving element is accumulating signal charges, and the signal charges accumulated by the light receiving element are output after the accumulated smear is output to the signal processing unit. May be read out and output to the signal processing unit.
[0015]
Further, in the above method, in the first step, before the signal reading unit accumulates the smear, the smear that is the error component already accumulated in the signal reading unit is discharged, and the smear that is the error component is discharged. Later, the signal reading unit can start smear accumulation.
[0016]
Further, in the above method, in the first step, before the signal reading unit accumulates the smear, an amount of smear that is an error component already accumulated in the signal reading unit is obtained, and the accumulated amount of smear is calculated as follows: Correction can also be made with the amount of smear that is an error component.
[0017]
Note that the method according to any one of the above may include a third step of controlling the amount of smear accumulated in the signal reading unit.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Next, an embodiment of an imaging apparatus according to the present invention will be described in detail with reference to the accompanying drawings.
[0019]
In this embodiment, the image pickup apparatus of the present invention is applied to a digital camera 10, particularly an electronic still camera 10. The illustration and description of parts not directly related to the present invention are omitted. Here, the reference number of the signal is represented by the reference number of the connecting line that appears.
[0020]
Digital camera 10 1 Optical lens system 12, mechanical shutter 14, imaging unit (CCD unit) 16, shutter pulse driver 18, vertical transfer path and horizontal transfer path drive pulse driver 20, CDS / GCA 42, A / D conversion A unit 22, a signal processing unit 24, a recording unit 26, a display unit 28, a system control unit 30, a timing signal generation unit 32, and an operation unit 34 are provided.
[0021]
The optical lens system 12 is configured by combining a plurality of optical lenses, for example, and causes the imaging unit 16 to focus an incident light beam via an iris formed by a diaphragm mechanism (not shown) and a mechanical shutter 14. The optical lens system 12 obtains the distance between the subject and the camera 10 by preliminary imaging before the main imaging, and adjusts the focus according to the obtained distance, and an AF (Automatic Focus) adjustment mechanism and incident light quantity AE (Automatic Exposure) adjustment mechanism that adjusts These adjusting mechanisms respond to the iris and lens driving signal 32a supplied from the timing signal generator 32. The mechanical shutter 14 responds to the shutter driving signal 32b supplied from the timing signal generator 32.
[0022]
The imaging unit 16 includes a color filter and a solid-state imaging device. The color filter may be either a color filter for the three primary colors RGB or a complementary color filter.
[0023]
The solid-state imaging device uses a CCD (Charge Coupled Device) type. The solid-state imaging device photoelectrically converts incident light that has passed through the optical lens system 12 and the shutter 14 to generate signal charges. As shown in FIG. 2, the solid-state image sensor includes a light receiving element 36, a transfer gate 38, and a vertical transfer CCD 40. The solid-state imaging device in FIG. 2 is an IT (Interline Transfer) -CCD. FIG. 2 is a pixel block diagram of the all-pixel readout system CCD, and shows two pixels among the pixels constituting the image sensor. The present embodiment is a three-phase drive system. FIG. 3 shows a potential profile in the vertical transfer path 40 region of each pixel in FIG. FIG. 3 shows a state where a deep potential is formed at the position (V1) where the transfer gate 38 is located.
[0024]
The present embodiment is an all-pixel readout system, but the present invention can also be applied to a field readout system and can be applied to other than IT-CCD. Furthermore, the present invention can be applied to drive systems other than the three-phase drive system.
[0025]
The light receiving element 36 is a photosensitive portion arranged in an array and has a function of converting incident light into signal charges. For the light receiving element 36, for example, a photodiode is used. The light receiving element 36 converts to signal charges according to the intensity of incident light, and accumulates the signal charges with time.
[0026]
The transfer gate 38 is closed and shielded so that the signal charge of the light receiving element 36 does not leak to the vertical transfer path 40, and when the signal charge is read to the vertical transfer path 40, the gate is opened to transfer the signal charge vertically. This is a gate having a function of moving to the path 40. That is, the transfer gate 38 opens the gate when a transfer gate pulse (TG) is applied from the driver 20 so as to turn on the gate, and closes the gate at other times.
[0027]
Three vertical CCDs are formed adjacent to one light receiving element 36 in the vertical transfer path 40. Each CCD has an electrode (not shown). The vertical transfer paths 40 in FIG. 2 are denoted by reference numerals of electrodes in order to facilitate the correspondence of what drive signals are supplied. Vertical drive signals V1a, V2a, V3a are supplied to the electrodes V1, V2, V3, respectively. The vertical transfer path 40 is supplied with three-phase drive signals having three types of phase shifts from the driver 20.
[0028]
The present embodiment is intended to widen the dynamic range of the image sensor by using a smear component mixed in the vertical transfer path 40 at a constant rate. Conventionally, the smear component has been considered only as noise. In the present embodiment, the smear component mixed in the vertical transfer path 40 is proportional to the amount of incident light as shown in FIG. A smear component is accumulated in the adjacent electrode (V1).
[0029]
FIG. 4 is a graph showing the relationship between the amount of incident light and the smear level. The horizontal axis indicates the intensity of the incident light amount. In order to indicate the intensity of the incident light quantity, the shutter speed at the same light quantity is used as a scale. The vertical axis represents the smear level as a ratio (%) to the signal charge. As can be seen from this figure, the smear component is proportional to the amount of incident light.
[0030]
In the present embodiment, the transfer of charges in the vertical transfer path 40 is stopped immediately before starting the main exposure after the pre-exposure, and an electronic shutter voltage higher than usual is applied to the substrate of the imaging unit 16 to thereby receive the light receiving element 36. Both unnecessary charges accumulated at that time in the vertical transfer path 40 are discharged to the substrate. Thereafter, signal charges are accumulated in the light receiving element 36, and at the same time, a smear component is accumulated under the electrode (V1) of the vertical transfer path 40.
[0031]
During the main exposure, the vertical transfer path 40 forms a charge storage potential only under the electrode (V1) next to the transfer gate 38. A certain amount of smear is mixed under the electrode (V1) during the main exposure period. After the main exposure is completed, the transfer of the vertical transfer path 40 is resumed with the mechanical shutter 14 closed, and the smear component is first read out. The smear component is sent to the signal processing unit 24 via the CDS / GCA 42 and the AD conversion unit 22.
[0032]
After reading the smear component, the transfer gate 38 is opened, the signal charge accumulated in the light receiving element 36 is read to the vertical transfer path 40, and the signal charge is transferred by the vertical transfer path 40. The signal charge is also sent to the signal processing unit 24 in the same manner as the smear component. In this way, two images with different exposure amounts are obtained.
[0033]
There are various methods for using the two images. For example, as shown in FIG. 5, there is a method of simply adding two images by the signal processing unit 24. In FIG. 5, the horizontal axis represents the amount of incident light, the vertical axis represents the amount of charge accumulated by the light receiving element 36, and the amount of charge due to the smear component accumulated at the position of the electrode V1, and the signal charge graph 44 and the smear component graph. 46 is shown. A graph 48 represents a simple addition of the signal charge 44 and the smear component 46. The graphs 50 to 56 will be described later. As another method of using images having different exposure amounts, there is a method of adding the signal charge 44 and the smear component 46 only for pixels whose luminance in the image is higher than a predetermined value.
[0034]
In this embodiment, the amount of smear components to be mixed is also controlled. This corresponds to exposure control in a normal camera. As a smear component control method, for example, there are a method of variably controlling the voltage of the electronic shutter pulse and a method of variably controlling the voltage of the transfer gate. When controlling the voltage of the electronic shutter pulse, the mixing amount increases as the voltage decreases. When the voltage of the transfer gate is variably controlled, the barrier between the light receiving element 36 and the vertical transfer path 40 becomes lower as the gate voltage becomes higher.
[0035]
This will be described with reference to FIG. FIG. 6 is a cross-sectional view of the light receiving element 36, the transfer gate 38, the vertical transfer path 40, and the periphery thereof. There are three causes of smear. Charges generated by the first incident light 58 are generated in the deep part of the substrate, enter the vertical transfer path 40 by diffusion, and generate smear. When the voltage of the electronic shutter pulse is variably controlled, this generation amount is controlled. When the DC voltage 64 is increased, smear is easily absorbed by the substrate 66, and when the voltage 64 is decreased, a part of the charge flows into the vertical transfer path 40. This relationship is illustrated in FIG. In FIG. 7, the horizontal axis represents the electronic shutter pulse voltage (OFD voltage) 64, and the vertical axis represents the smear amount. A curve 76 indicates a smear amount corresponding to the electronic shutter pulse voltage 64. During the main exposure, the smear amount is controlled by applying a constant voltage 64 to a terminal for applying an electronic shutter pulse.
[0036]
In the second incident light 60, the light reaching the element surface passes through the gate 38 and enters the vertical transfer path 40. The higher the voltage applied to the transfer gate 38, the easier it is for smear to enter. FIG. 8 shows a change in the state of smear mixing when the applied voltage is changed. FIG. 8A shows a case where the applied voltage is low, and FIG. 8B shows a case where the applied voltage is high. Since the potential of the light shielding film 68 near the gate 38 changes, the amount of smear mixed changes. Returning to FIG. 6, the third incident light 62 passes through the light shielding film 68 and the electrode 70 of the vertical transfer path 40 and enters the vertical transfer path 40.
[0037]
In smear control, the absolute value of smear mixed in the vertical transfer path 40 is controlled, and when the amount of contamination is expected to be small, control is performed to increase the amount of contamination. The case where the mixing amount is small is, for example, a case where the subject is dark. When the mixing amount is small, it is uncertain whether the obtained smear amount is due to noise or valid information. Therefore, the amount of smear is increased to increase the measurement accuracy.
[0038]
Whether or not the subject is dark, that is, whether or not to increase the amount of smear is determined by, for example, the shutter speed. If the aperture is the same, the subject is considered dark when the shutter speed is slow, and the subject is bright when the shutter speed is fast. Since the amount of smear mixed is proportional to the product of the exposure time and the subject brightness, the amount of smear is small when it is dark (when the shutter speed is slow), and it is large when it is bright (when the shutter speed is fast).
[0039]
Since the shutter speed is determined at the time of preliminary exposure, after the shutter speed is determined, the luminance of the subject is predicted, and it is determined whether to perform smear control from the prediction result. When it is determined that the subject is very bright and the smear information accuracy is high, the smear control is set to the default state. When the subject is dark and the smear information accuracy is low, the electronic shutter pulse voltage and transfer The gate pulse voltage is changed to increase the amount of contamination.
[0040]
Graphs 50 and 52 in FIG. 5 are graphs of smear components when the amount of smear is increased in this way. Graphs 54 and 56 are graphs of signal charge graph 44 and smear component graphs 50 and 52, respectively. It is simply an addition.
[0041]
By the way, in this embodiment, immediately before starting the main exposure after the pre-exposure, the transfer of the charge in the vertical transfer path 40 is stopped, and an electronic shutter pulse (OFD) voltage higher than usual is applied to the substrate of the imaging unit 16. Thus, both unnecessary charges accumulated in the light receiving element 36 and the vertical transfer path 40 at that time are discharged to the substrate. Hereinafter, this is referred to as “VCCD reset”. This discharging method will be described with reference to FIG.
[0042]
FIGS. 9 (a) and 9 (b) show the operation of a conventional electronic shutter pulse, which is accumulated in the light receiving element 36 by applying the electronic shutter pulse shown in FIG. 9 (a) to the substrate. Charge is discharged to the substrate as indicated by arrow 80. The magnitude of the pulse voltage at this time is indicated by an arrow 78.
[0043]
FIGS. 9 (c), (d), and (e) show the operation of the electronic shutter pulse and transfer gate pulse at the time of VCCD reset. As shown in FIG. 9 (c), the electronic shutter pulse voltage 84 at this time is larger than the pulse voltage 78 of FIG. 9 (a) by the voltage indicated by the arrow 82. FIG. 9D shows a potential state when the electronic shutter pulse is applied. The electric charge is discharged from the light receiving element 36 as indicated by an arrow 86. When VCCD is reset, the transfer gate pulse is applied at the same time as the electronic shutter pulse is applied. FIG. 9 (e) shows a case where an electronic shutter pulse and a transfer gate pulse are applied. As shown in FIG. 9 (e), the potential of the vertical transfer path 40 is raised as indicated by the arrow 92 and moved closer to the surface, and the potential of the transfer gate 38 is lowered as indicated by the arrow 90 to charge from the VCCD 40. Is discharged as shown by arrow 88.
[0044]
Returning to FIG. 1, the signal charge is sent from the vertical transfer path 40 in the imaging unit 16 to a horizontal transfer path (not shown) in the imaging unit 16. For example, a two-phase horizontal transfer drive signal 20a is supplied from the driver 20 to the horizontal transfer path. As a result, the horizontal transfer path transfers the signal charges toward an output amplifier (not shown) in the imaging unit 16. In FIG. 1, the signal 20a includes vertical drive signal lines V1, V2, V3 and a horizontal transfer drive signal, but is shown by one line in the figure.
[0045]
The imaging unit 16 outputs a signal charge as an imaging signal 16a from the output amplifier. The imaging signal 16a is an analog signal obtained by converting the signal charge (Q) into the voltage signal (V) in the output amplifier. The imaging unit 16 outputs the obtained imaging signal 16a to the CDS / GCA 42.
[0046]
A CDS (Correlated Double Sampling) removes a low-frequency noise component included in the supplied imaging signal 16a. The signal from which noise has been removed is subjected to waveform shaping by amplifying with a GCA (Gain Control Amplifier), and is sent to the A / D converter 22. The A / D conversion unit 22 converts the supplied analog signal into a digital signal 22 a and outputs the digital signal 22 a to the signal processing unit 24. The CDS / GCA 42 and the A / D converter operate according to various timing signals 32g and 32h supplied from the timing signal generator 32.
[0047]
The driver 18 generates a drive signal 18a based on the OFD pulse 32d from the timing signal generator 32 and the applied voltage control signal 32c. At the time of VCCD reset, the driver 18 increases the voltage value of the OFD pulse and outputs it according to the applied voltage control signal 32c as described above.
[0048]
In the main exposure following VCCD reset, when the above-mentioned smear amount control is performed (other than the default setting), a predetermined OFD pulse 18a is applied during the main exposure to increase the amount of smear mixed into VCCD40. Apply according to voltage control signal 32d.
[0049]
The applied voltage control signal 32d is used to output a normal electronic shutter pulse, when VCCD is reset, and when the amount of smear is controlled, for example, the magnitude of the voltage of the applied voltage control signal 32d is, for example, 0V, 3V The driver 18 is instructed by changing it to 6V. When controlling the smear amount, changing the OFD voltage in several steps and changing the smear amount, the magnitude of the voltage of the applied voltage control signal may be changed to 6V, 9V, 12V, for example.
[0050]
The driver 20 receives the vertical drive signals V1a, V2a, V3a, and the horizontal drive signals based on the horizontal pulse (not shown) and the vertical pulse 32e from the timing signal generator 32 and the transfer gate voltage control signal 32f. Is supplied to the solid-state imaging device 14c via the signal line 20a. The vertical drive signal V1a also serves as a transfer gate pulse. The driver 20 drives the vertical CCD 40 in three phases with the vertical drive signals V1a, V2a, V3a, and drives the horizontal CCD in two phases with the horizontal drive signal.
[0051]
At the time of VCCD reset, the driver 20 increases the voltage value of the transfer gate pulse as described above according to the transfer gate voltage control signal 32f and outputs it. In the main exposure following the VCCD reset, when the smear amount control described above is performed (other than the default setting), the transfer gate voltage 32f is set to the transfer gate during the main exposure to increase the amount of smear mixed into the VCCD40. The voltage is applied according to the voltage control signal 32f.
[0052]
The transfer gate voltage control signal 32f includes the case where the normal transfer gate pulse (readout pulse) is output, the time when the VCCD is reset, and the case where the smear amount is controlled, for example, the magnitude of the voltage of the transfer gate voltage control signal 32f Is changed to 0V, 3V, 6V, for example, to instruct the driver 20. When controlling the amount of smear, if the transfer gate voltage is changed to several steps and the smear amount is changed to several steps, the magnitude of the voltage of the transfer gate voltage control signal 32f is changed to, for example, 6V, 9V, 12V. You can do it.
[0053]
The applied voltage control signal 32d and the transfer gate voltage control signal 32f described above, when controlling the smear amount, promptly output a predetermined OFD voltage and transfer gate voltage from the drivers 18 and 20 when controlling the smear amount after the start of the main exposure. In order to be able to do so, an applied voltage control signal 32d and a transfer gate voltage control signal 32f of 6V, 9V, and 12V indicating that the smear amount is controlled are output to the drivers 18 and 20 immediately before the start of the main exposure. Then, immediately after the start of the main exposure, 6V, 9V, and 12V may be output again to start the smear amount control. In this embodiment, the applied voltage control signal 32d and the transfer gate voltage control signal 32f are output according to this method.
[0054]
The signal processing unit 24 is an image signal processing unit, and is composed of, for example, a RISC (Reduced Instruction Set Computer) chip. This chip includes a signal generation circuit, a memory, a gamma correction circuit, an evaluation value calculation unit, a pixel interpolation processing circuit, a color difference matrix processing circuit, and a compression / decompression processing circuit (not shown). The signal processor 24 receives the timing signal 32i from the timing signal generator 32 in order to perform these processes.
[0055]
The memory receives the image data 22a converted into digital data, temporarily stores it, and outputs it as image data to the gamma correction circuit. The gamma correction circuit includes a lookup table for gamma correction, for example. The gamma correction circuit performs gamma correction on the supplied image data using table data as one of the pre-processes in the image processing. The gamma correction circuit supplies the gamma corrected image data to the evaluation value calculation unit and the pixel interpolation processing circuit, respectively.
[0056]
The evaluation value calculation unit includes an arithmetic circuit that calculates an aperture value / shutter speed, a white balance (hereinafter referred to as WB) adjustment value, and a gradation correction value. The evaluation value calculation unit calculates appropriate parameters by calculation processing based on the supplied image data in the above-described circuit. These calculation results are supplied as parameters to the system control unit 30 via the signal line 30b.
[0057]
The pixel interpolation processing circuit has a function of calculating and interpolating pixel data. Since the imaging unit 16 uses the single-plate color filter 14b, colors other than the colors of the actual color filter segment cannot be obtained from the imaging device. Therefore, the pixel interpolation processing circuit generates pixel data of the color that cannot be obtained by interpolation. The pixel interpolation processing circuit supplies plain image data to the color difference matrix processing circuit.
[0058]
The color difference matrix processing circuit generates luminance data Y and color data Cb, Cr using the image data supplied from the pixel interpolation processing circuit and predetermined coefficients. The generated image data is supplied to a compression / decompression processing circuit.
[0059]
The compression / decompression processing circuit performs compression processing on image data (Y / C) supplied in a still image or moving image (movie) mode according to a standard such as JPEG (Joint Photographic coding Experts Group). The compression / decompression processing circuit sends the compressed image data 24a to the storage unit 26 for recording. The compression / decompression processing unit reads the image data 24a recorded in the storage unit 26, and performs decompression processing. This decompression process is the reverse process of the compression process.
[0060]
In addition, the signal processing unit 24 performs RGB conversion on the generated image data and image data (Y / C) 24a expanded with reproduction, and converts the RGB converted image data into an analog signal. The signal processing unit 24 outputs the image signal 24b converted into an analog signal to the monitor 28. The signal processing unit 24 may include an external I / F circuit (not shown) when inputting / outputting image data to / from an external device.
[0061]
The system control unit 30 is a microcomputer or CPU (Central Processing Unit) that controls a general-purpose part of the entire camera and a part that performs digital processing. The system control unit 30 receives a signal or the like indicating that the release shutter button has been half-pressed (S1) or fully pressed (S2), supplied from the key operation unit.
[0062]
The system control unit 30 controls the signal processing unit 24, the recording unit 26, and the timing signal generation unit 32. In imaging, the system control unit 30 receives a control signal from the signal processing unit 24 via the signal line 30b in response to the release shutter button (not shown) being half-pressed (S1) or fully pressed (S2) in the imaging mode. Supply.
[0063]
The system control unit 30 is supplied with a clock signal from the timing signal generation unit 32 via a signal line 30a. The parameter information obtained by the signal processing unit 24 is also supplied to the system control unit 30. The system control unit 30 generates a control signal corresponding to the parameter based on the clock signal, and supplies the control signal to the timing signal generation unit 32 and the signal processing unit 24, respectively.
[0064]
The timing signal generation unit 32 generates a timing signal according to a control signal supplied from the system control unit 30 based on the clock signal. The timing signal includes a vertical synchronization signal, a horizontal synchronization signal, a field shift pulse, a vertical transfer signal, a horizontal transfer signal, and the like. Further, drive signals 32a and 32b are generated and supplied to the optical lens system 12 and the mechanical shutter 14 described above.
[0065]
Signals supplied by the timing signal generator 32 and the drivers 18 and 20 will be described with reference to the timing chart of FIG. FIG. 10 (a) shows a timing chart in the prior art for comparison. In this figure, VD is a vertical synchronizing signal output from the timing signal generator 32 to the signal processor. V is a vertical transfer signal 18a. In this figure, the vertical transfer signal is schematically shown, and includes a transfer gate pulse 96 and a vertical transfer pulse 98. FIGS. 10 (a) (v), (b) (v) show the operation modes of the camera, respectively.
[0066]
In the conventional operation mode, the preliminary operation 108, the main exposure 110, the vertical transfer path sweep 116, and the signal readout 118 are processed in this order. In this embodiment, the preliminary operation 108, the main exposure 110, the smear read 112, and the signal read 114 are processed in this order.
[0067]
Conventionally, the vertical transfer signal has a sweep pulse 94 as shown in FIGS. 10 (a) and 10 (ii), but this is not used in this embodiment. Instead, a VCCD reset is performed, and the transfer gate pulse 102 and the OFD pulse 100 which are part of the vertical transfer signal are used for the VCCD reset. Thereafter, the main exposure is performed. During the main exposure (period 106 in FIGS. 10 (b) and (ii)), the vertical transfer signal is stopped to accumulate smear.
[0068]
As shown in FIGS. 10 (a), (iv), (b), and (iv), the mechanical shutter 14 is “open” and then “closed” until the end of the main exposure.
[0069]
When increasing the amount of smear for smear control, in period 106, voltage 104 is applied only to vertical transfer electrode V1 in order to adjust the transfer gate voltage. When the OFD voltage is controlled for smear control, the OFD voltage is applied during this period 106.
[0070]
Returning to FIG. 1, the storage unit 26 records the supplied image data 24c using a semiconductor memory or the like as a recording medium. Data writing / reading is performed according to a control signal 30c of the system control unit 30. The monitor 28 displays the image signal 24d supplied from the signal processing unit 24. As the monitor 28, a liquid crystal monitor is generally used.
[0071]
Next, the operation of the digital camera 10 will be described with reference to FIG. When information indicating that a release shutter (not shown) included in the operation unit 34 is half-pressed is sent from the operation unit 34 to the system control unit 30, the mechanical shutter 14 is opened and preliminary photometry is started (step S10). The image signal obtained by the preliminary photometry is sent from the CCD 16 to the signal processing unit 24 through the CDS / GCA 42 and the AD conversion unit 22, and the signal processing unit 24 determines the shutter speed and the aperture. The determined information is sent to the system control unit 30 via the signal line 30b.
[0072]
The system control unit 30 determines whether to perform smear value control from the shutter speed (step S12). Then, when it is determined that the luminance of the subject is lower than the predetermined value (in the case of YES), smear value control is performed when the operation unit detects that the camera user has fully pressed the release shutter (step S14). . In the present embodiment, only the read gate voltage is controlled as smear value control.
[0073]
However, in the present invention, the electronic shutter voltage can be controlled as smear value control. Further, as the smear value control, it is possible to control both the read gate voltage and the electronic shutter voltage.
[0074]
In step S14, as a preparatory stage for smear value control, the system control unit 30 immediately before the start of the main exposure so that the driver 20 can quickly output a signal 18a having a predetermined magnitude at the start of smear amount control immediately after the start of the main exposure. The timing signal generator 32 is instructed to output a signal 32f having a predetermined voltage to the driver 20 as a transfer gate (read gate) voltage control signal 32f. Upon receiving this voltage control signal 32f, the driver 20 turns on the power supply voltage of a circuit (not shown) that generates a transfer gate signal at the time of smear value control inside the driver 20. Even when the electronic shutter voltage is controlled as smear value control, in step S14, similar processing is performed on the electronic shutter voltage using the applied voltage control signal 32d.
[0075]
If it is determined in step S12 that the luminance of the subject is higher than the predetermined value (NO), the process proceeds to step S16 without performing smear value control when the release button is fully pressed.
[0076]
In step S16, the timing signal generator 32 receives an instruction to start the main exposure operation from the system control 30. Receiving the instruction, the timing signal generator 32 stops driving the VCCD by stopping the vertical transfer signal 32e. Next, in order to reset VCCD, a high voltage electronic shutter pulse 18a and a high voltage transfer gate voltage 20a are applied to the CCD 16 (step S18).
[0077]
After discharging the charge accumulated in the light receiving element 36 and the vertical transfer path 40 by resetting VCCD, the voltage of the electronic shutter pulse 18a is set to 0 V, and the potential is applied only to the electrode V1 among the electrodes V1, V2, and V3 of the vertical transfer path. A voltage is applied to the electrode V1 so that is formed.
[0078]
Next, in step S20, the system control unit 30 determines whether to perform transfer gate voltage control for smear value control. If it is determined that the luminance of the subject is lower than the predetermined value (YES), smear value control is performed (step S22). In the present embodiment, only the read gate voltage is controlled as smear value control.
[0079]
However, in the present invention, the electronic shutter voltage can be controlled as smear value control. Further, as the smear value control, it is possible to control both the read gate voltage and the electronic shutter voltage.
[0080]
In step S22, as a smear value control, the system control unit 30 sends a transfer gate voltage control signal 32f to the timing signal generation unit 32 as a transfer gate voltage control signal 32f to the driver 20 with a transfer gate having a voltage lower than the transfer gate voltage during normal reading. Instructs to output voltage. Upon receiving this voltage control signal 32f, the driver 20 generates a signal 104 (DC voltage) in FIG. 10 (b) (ii) from a circuit (not shown) that generates a transfer gate signal at the time of smear value control inside the driver 20. Is output. Even when the electronic shutter voltage is controlled as smear value control, in step S22, similar processing is performed on the electronic shutter voltage using the applied voltage control signal 32d.
[0081]
If it is determined in step S20 that the luminance of the subject is higher than the predetermined value (NO), the process proceeds to step S24 without performing smear value control.
[0082]
In step S24, signal charges are accumulated in the light receiving element 36 and smear is accumulated at the electrode V1 of the vertical transfer path as an exposure operation. In step S26, the system control unit 30 determines whether or not the predetermined exposure time has expired. If it is determined that the predetermined time has not elapsed (NO), the exposure is continued. If it is determined that the predetermined time has elapsed (in the case of YES), it is determined that the exposure is completed, and the process proceeds to step S28.
[0083]
In step S28, the timing signal generator 32 “closes” the mechanical shutter 14 with the signal 32b, and the driver 20 stops outputting the signal 104 in FIG. 10 (b) (ii) that was output to the signal line 20a. . Thereafter, transfer in the vertical transfer path 40 is started in step S30, and the accumulated smear is read and sent to the signal processing unit 24.
[0084]
After smear reading is completed, in step S32, by applying a transfer gate pulse, the signal charge is read from the light receiving element 36 to the electrode V1 of the vertical transfer path, and this signal charge is transferred in the vertical transfer path 40. To the signal processing unit 24. The signal processing unit 24 obtains two images with different exposure amounts in this way and stores them in the recording unit 26, respectively.
[0085]
According to the present embodiment, it is possible to provide an image pickup apparatus having a wide dynamic range and preventing a reduction in resolution and a control method thereof. In addition, it is possible to provide an imaging apparatus capable of obtaining an appropriate image even for a moving subject having a wide dynamic range and a control method thereof.
[0086]
Next, another embodiment of the present invention will be described. In this embodiment, instead of performing the above-described VCCD reset, the amount of charge (offset charge) accumulated in the electrode V1 at the start of the main exposure is obtained. In the case of VCCD reset, the charge (offset charge) accumulated in the electrode V1 at the start of the main exposure is discharged to the substrate at the start of the main exposure. In this embodiment, the main exposure is performed without discharging the offset charge, the amount of the offset charge is obtained, the smear including the offset charge is read, and then the net smear is obtained by subtracting the offset charge from the smear. It is what you want.
[0087]
The principle of the method for obtaining the offset charge will be described with reference to FIG. FIG. 12 shows a vertical transfer path to a horizontal transfer path when the signal charge 126 is read from the light receiving element without performing the sweep 94 of FIG. 10 (a) (ii) in the conventional method of FIG. The signal charge (the sum of signal 126 and smear 120) sequentially swept out is shown. In this case, as shown in FIG. 10 (a) (ii), the vertical transfer path is driven several times before and during the main exposure at regular intervals. The same amount of smear 120 is mixed in. This mixing amount 120 can be known by reading a signal of OB (Optical Black) 122 at the lower end of the image sensor.
[0088]
Therefore, in the present embodiment, the vertical transfer path 40 is driven at a constant cycle at least twice (period 130 in FIG. 13 (ii)) before the main exposure start time (time 128 in FIG. 13 (ii)). The same offset charge is accumulated in the vertical transfer path 40. Thereafter, as shown in FIGS. 13 (ii) and (iii), the main exposure 110 is performed without performing the VCCD reset. Next, smear reading 112 is performed after the mechanical shutter is closed. At the beginning of smear reading 112, the signal charge of OB 122 in FIG. 12 is read. Since the smear for smear reading includes the signal charge of OB 122 as an offset, the signal processing unit subtracts the offset to obtain a net smear. In the case of the present embodiment, smear control can be performed in the same manner as the above-described embodiments.
[0089]
Also according to the present embodiment, it is possible to provide an image pickup apparatus having a wide dynamic range and preventing a reduction in resolution and a control method thereof. In addition, it is possible to provide an imaging apparatus capable of obtaining an appropriate image even for a moving subject having a wide dynamic range and a control method thereof.
[0090]
【The invention's effect】
As described above, according to the imaging apparatus and the control method thereof of the present invention, it is possible to prevent a reduction in resolution while having a wide dynamic range. In addition, an appropriate image can be obtained even for a subject having a wide dynamic range and moving.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a configuration of a digital camera to which an imaging apparatus of the present invention is applied.
FIG. 2 is a pixel unit configuration diagram of an all-pixel readout type CCD.
3 is an explanatory diagram when a potential is formed on an electrode V1 of the pixel portion of FIG. 2;
FIG. 4 is a diagram illustrating a relationship between an incident light amount and a smear level.
FIG. 5 is a diagram illustrating a relationship between smear and signal charge with respect to an incident light amount;
FIG. 6 is a diagram for explaining a cause of occurrence of smear.
FIG. 7 is a diagram showing a relationship between OFD voltage and smear.
FIG. 8 is an explanatory diagram of a principle of controlling smear by controlling a transfer gate voltage.
FIG. 9 is an explanatory diagram of the principle of VCCD reset.
10 is a timing chart illustrating a timing relationship between a timing signal and a driving signal supplied from the drivers 18 and 20 of FIG. 1 to the solid-state imaging device.
FIG. 11 is a flowchart showing an operation procedure of the digital camera of FIG. 1;
FIG. 12 is an explanatory diagram of a method for obtaining an offset charge of VCCD.
FIG. 13 is a timing chart of a digital camera using a method for obtaining an offset charge of VCCD.
[Explanation of symbols]
10 Digital camera
12 Optical lens system
14 Mechanical shutter
16 CCD section
18, 20 drivers
30 System controller
32 Timing signal generator
36 Photo detector
38 Transfer gate
40 vertical transfer path
V1, V2, V3 electrode

Claims (3)

A plurality of light receiving elements for converting incident light from the object field into signal charges; a read gate provided corresponding to the light receiving elements for reading the signal charges from the corresponding light receiving elements; In an image pickup apparatus including a CCD type vertical transfer path for transferring signal charges and a signal processing unit for inputting the read signal charges and processing them as image signals.
The CCD vertical transfer path accumulates smear during an exposure period, and outputs the accumulated smear to the signal processing unit.
The image processing apparatus, wherein the signal processing unit generates an image signal from the smear and the signal charge converted in the light receiving element . 2. The apparatus according to claim 1, wherein the CCD vertical transfer path accumulates the smear when the light receiving element accumulates the signal charge, and outputs the accumulated smear to the signal processing unit. An image pickup apparatus that reads out a signal charge accumulated in the light receiving element and outputs the signal charge to the signal processing unit. The apparatus according to claim 1 or 2, the device, before the CCD-type vertical transfer channel accumulates the smear, to discharge the smear is an error component which has already been accumulated in the CCD-type vertical transfer channel An image pickup apparatus comprising smear discharging means, wherein the CCD vertical transfer path starts smear accumulation after smear as an error component is discharged.

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