JP2009049981A - Image sensing apparatus and method of controlling the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To do gain setting delicately according to a change in the object brightness during moving image shooting and to improve the S/N. <P>SOLUTION: An image sensing apparatus has: an image sensor (103) which converts an optical image of an object into an electrical signal; a signal amplifier circuit (105) which amplifies the electrical signal by a first gain; a digital amplifier (121) which further amplifies the amplified electrical signal by a second gain that is changeable in finer steps than the first gain; and a system control unit (118) which obtains a third gain based on a quantity of incident light to the image sensor and adjusts the first and second gains so that a sum of the first and second gains equals the third gain. The system control unit adjusts a gain component of the third gain, which can not be adjusted by the first gain, using the second gain, and ensures the third gain by adjusting only the second gain, without adjusting the first gain, when a brightness change more than the preset brightness difference does not continue for not less than a preset time. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an imaging apparatus and a control method therefor, and more particularly to sensitivity control of an imaging apparatus when capturing a moving image.

  2. Description of the Related Art Conventionally, an imaging apparatus such as an electronic camera that records and reproduces a still image or a moving image captured by an imaging element such as a CCD or CMOS on a recording medium of a memory card having a memory element is commercially available.

  Many of these electronic cameras have a shooting mode that automatically changes the sensitivity according to the brightness of the shooting scene. Shooting in this shooting mode enables shooting under appropriate shooting conditions. Yes. Especially in an imaging device that captures and records moving images, such as an electronic video camera, the sensitivity is automatically controlled by the photographer with little or no manual adjustment of the sensitivity according to changes in the brightness of the shooting scene. ing.

  By the way, as exposure control in an electronic camera, first, control of the optical incident light quantity to the image sensor by a diaphragm or the like, and control of temporal incident light quantity by a mechanical shutter or an electronic shutter are performed. However, when high sensitivity settings are required, such as when the brightness of the subject is low and sufficient signal amount cannot be obtained by optical and temporal exposure control alone, it is generated by the photoelectric conversion unit of the image sensor. Electrical control for amplifying the electrical signal is performed.

  There are several means for amplifying electrical signals in electronic cameras. FIG. 7 is a block diagram illustrating an example of an electric signal flow and an amplifier in an imaging apparatus such as a conventional electronic camera.

  In the imaging element 201, a plurality of pixels 202 each including a photoelectric conversion unit are arranged. The electrical signal generated in the photoelectric conversion unit passes through the vertical output line and is input to the column amplifier 203 provided in each column of the plurality of pixels 202. The gain of the column amplifier 203 can be changed. However, because of restrictions on the layout in the image sensor 201 and restrictions on the number of control signal lines to the image sensor 201, the gain is a discrete set value such as 1, 2 times, 4 times, 8 times, etc. Often have.

  The electric signal amplified by the column amplifier 203 is input to the output amplifier 204 through the horizontal shift register. The gain of the output amplifier 204 can also be changed. However, as with the column amplifier 203, there are many discrete set values due to restrictions on the layout in the image sensor 201. However, compared with the column amplifiers 203 that need to be provided in the number corresponding to the number of columns, the output amplifiers 204 need only be provided in the number corresponding to the number of output terminals.

  The electric signal amplified by the output amplifier 204 is output from the image sensor 201 and input to an analog signal processing circuit (Analog Front End: AFE) 205. The electrical signal input to the analog signal processing circuit 205 is subjected to some analog signal processing by a correlated double sampling circuit (CDS) 206 or the like, and then input to an analog signal amplifier (PGA) 207. Although the gain of the analog signal amplifier 207 is also variable, it is possible to set a more continuous gain than the column amplifier 203 and the output amplifier 204 arranged inside the image sensor 201.

  The electric signal amplified by the analog signal amplifier 207 is converted from an analog signal to a digital signal by the A / D converter 208 and then output from the analog signal processing circuit 205. Then, it is input to a digital signal processing circuit (Digital Front End: DFE / video engine) 209.

  In the digital signal processing circuit 209, digital amplification processing is performed along with various correction processing and development processing. Also in this digital amplification processing, the gain is variable, and the gain setting can be made finer and continuous than the gain setting in the analog signal amplifier 207.

  The electrical signal output from the digital signal processing circuit 209 is stored in a memory and used for display on a display device and recording on a recording medium.

  By the way, considering the image quality of the obtained image, the final amount of noise differs depending on which amplification processing is applied with gain. That is, when gain is applied by the column amplifier 203, the noise amplified is only noise generated in the pixel and the vertical output line before being input to the column amplifier 203. Therefore, noise generated in the analog signal processing circuit 205, the digital signal processing circuit 209, and the wiring connecting them after the horizontal shift register in the image sensor 201 is not amplified.

  On the other hand, when gain is applied by the digital signal processing circuit 209, noise generated in the path before being input to the digital signal processing circuit 209 is amplified by the same amount as the signal gain. Therefore, when gain is applied by the digital signal processing circuit 209, the final amount of noise is larger than when gain is applied by the column amplifier 203.

  In this way, a higher quality image with less noise can be obtained by applying gain with the amplifier in the previous stage.

  Next, the adjustment of the gain when the incident light amount changes during moving image shooting will be considered. When gain is applied by the digital signal processing circuit 209, sensitivity, image noise, image characteristics such as shading, and the like change according to the gain applied to the signal. However, since the gain setting is fine and continuous, it is difficult to understand that the gain has been adjusted.

  On the other hand, when gain is applied using the column amplifier 203, shading, sensitivity, etc. may not necessarily be proportional to the gain depending on the performance of the image sensor. In addition, since the gain setting is coarse and discrete, a change in image characteristics such as noise is increased, and the user may know that the gain has been adjusted. As a result, under a situation where the subject brightness frequently changes and the gain adjustment frequently occurs, the image may flicker and may be disturbed.

  Thus, in order to perform fine and smooth sensitivity setting according to the amount of incident light, it is necessary to apply gain by the digital signal processing circuit 209 capable of more continuous gain setting.

  As described above, the sensitivity setting in the electronic camera has the above-described characteristics depending on at which stage the gain is changed. For this reason, in a still camera in which still image shooting where importance is placed on image quality is the main application, a process of applying gain in the previous stage using an amplifier arranged inside the image sensor is suitable. On the other hand, in a video camera centering on moving image shooting in which connection for each frame is important, a process of applying continuous gain using an amplifier in an analog signal processing IC or a video engine is suitable.

JP-A-2005-217771

  More specifically, for example, a surveillance camera or the like is required to have a capability of recognizing a human face or the like even in a low illumination environment. Therefore, it is necessary to have a performance that can obtain a high-sensitivity and high-quality moving image and can adjust sensitivity in response to changes in the shooting environment. However, as described above, when an amplifier gain is applied in an analog signal processing IC or a video engine, noise generated so far is also amplified, resulting in poor image quality. On the other hand, when gain is applied by an amplifier arranged inside the image sensor, the settable gain values are discrete, so when viewed as a moving image, the image flickers, resulting in poor image quality. There was a case.

  As a specific example, when a person or an object crosses in front of the camera in a bright environment, the amount of light incident on the image pickup device once decreases rapidly and immediately returns to the original amount of light. In this way, if sensitivity adjustment according to a rapid change in luminance is performed with discrete gain using an amplifier arranged inside the image sensor, the continuity of the image deteriorates and obstructive flickering occurs. There was a fear.

  The present invention has been made in view of the above problems, and an object of the present invention is to perform gain setting sensitively to changes in luminance of a subject and improve the S / N ratio during moving image shooting.

  In order to achieve the above object, an imaging apparatus according to the present invention includes an imaging device that converts an optical image of a subject into an electrical signal, first amplification means that amplifies the electrical signal with a first gain, and the first A second amplifying unit that amplifies the electric signal amplified by the amplifying unit with a second gain that can be changed with a step size finer than the first gain, and a second amount based on the amount of light incident on the image sensor. And a control means for adjusting the first gain and the second gain so that a sum of the first gain and the second gain becomes the third gain. The control means adjusts, by the second gain, a gain that cannot be adjusted by the first gain among the third gain, and changes in the luminance of the subject exceeding a preset luminance difference And there is a state in which the luminance has changed. If you do not continue because the set time or more, so that the said third gain by adjusting the second gain without adjusting the first gain.

  According to another aspect of the present invention, there is provided a method of controlling an image pickup apparatus including an image pickup device that converts an object image into an electric signal. The method includes a step of amplifying the electric signal with a first gain; A step of amplifying with a second gain that can be changed with a smaller step size than the first gain, a step of setting a third gain based on the amount of light incident on the image sensor, and the first gain And a control step of adjusting the first gain and the second gain so that the sum of the second gains becomes the third gain. In the control step, the third gain Among these, the amount of gain that cannot be adjusted by the first gain is adjusted by the second gain, the luminance of the subject exceeds the preset luminance difference, and the luminance has changed Is more than the preset time If not continue to make it so that the third gain by adjusting the second gain without adjusting the first gain.

  According to the present invention, at the time of moving image shooting, it is possible to perform gain setting that responds sensitively to a change in luminance of a subject and improve the S / N ratio.

  The best mode for carrying out the present invention will be described below in detail with reference to the accompanying drawings.

<First Embodiment>
FIG. 1 is a block diagram showing a configuration of an imaging apparatus according to a preferred embodiment of the present invention.

  Reference numeral 101 denotes an optical system including a lens and a diaphragm, 102 denotes a mechanical shutter, and 103 denotes an image sensor that converts an optical image of a subject into an electrical signal and outputs the electrical signal. Reference numeral 104 denotes a photoelectric conversion unit that converts incident light into an electrical signal (image data) inside the image sensor 103, and reference numeral 105 denotes a signal amplification circuit that amplifies the electrical signal photoelectrically converted by the photoelectric converter 104 inside the image sensor 103. It is. The image sensor 103 outputs the electrical signal amplified by the signal amplifier circuit 105. An analog signal processing circuit 106 performs analog signal processing on the electrical signal output from the image sensor 103. Reference numeral 107 denotes a CDS circuit that performs correlated double sampling on the electrical signal output from the image sensor 103. Reference numeral 108 denotes a programmable gain amplifier (PGA) that is an analog amplifier that amplifies an electric signal output from the CDS circuit 107 that is an analog signal inside the analog signal processing circuit 106. Reference numeral 109 denotes an A / D converter that converts an electric signal, which is an analog signal amplified inside the analog signal processing circuit 106, into a digital signal.

  Reference numeral 110 denotes a timing signal generation circuit that generates signals for operating the image sensor 103 and the analog signal processing circuit 106, and 111 denotes a drive circuit for the optical system 101 and the mechanical shutter 102. Reference numeral 112 denotes a digital signal processing circuit that performs digital signal processing necessary for captured image data, and includes a digital amplifier 121 and an image processing circuit 122.

  Reference numeral 113 denotes an image memory for storing signal processed image data, 114 denotes a recording medium removable from the imaging apparatus, and 115 denotes a recording circuit for recording the signal processed image data on the recording medium 114. Reference numeral 116 denotes an image display device that displays image data subjected to signal processing, 117 denotes a display circuit that displays an image on the image display device 116, and 118 denotes a system control unit that controls the entire imaging device. Reference numeral 119 denotes a program describing a control method executed by the system control unit 118, control data such as parameters and tables used when executing the program, and correction data such as a scratch address and the like. ). Reference numeral 120 denotes a volatile memory (RAM) that is used to transfer and store a program, control data, and correction data stored in the nonvolatile memory 119 and used when the system control unit 118 controls the imaging apparatus.

  Hereinafter, a photographing operation in the imaging apparatus configured as described above will be described. Prior to the shooting operation, necessary programs, control data, and correction data are transferred from the nonvolatile memory 119 to the volatile memory 120 and stored at the start of the operation of the system control unit 118 such as when the imaging apparatus is turned on. Shall. These programs and data are used when the system control unit 118 controls the imaging apparatus, and additional programs and data are transferred from the nonvolatile memory 119 to the volatile memory 120 as necessary. Alternatively, it is assumed that the system control unit 118 directly reads out and uses data in the nonvolatile memory 119.

  First, the drive circuit 111 drives the aperture and lens of the optical system 101 by a control signal from the system control unit 118 to form a subject image on the image sensor 103 on which a plurality of pixels are arranged. The mechanical shutter 102 is driven to shield the image sensor 103 in accordance with the operation of the image sensor 103 so that a necessary exposure time is reached by a control signal from the system control unit 118 during still image shooting. At this time, when the image sensor 103 has an electronic shutter function, it may be used together with the mechanical shutter 102 to ensure a necessary exposure time. Further, the mechanical shutter 102 is maintained in an open state at the time of moving image shooting so that the image sensor 103 is always exposed during shooting by a control signal from the system control unit 118.

  The image sensor 103 is driven by a drive pulse based on an operation pulse generated by the timing signal generation circuit 110 controlled by the system control unit 118, and the photoelectric conversion unit 104 converts the subject image into an electrical signal by photoelectric conversion. . The signal amplifying circuit 105 (first amplifying means) applies a first gain to the electric signal and outputs it as analog image data. The image data output from the image sensor 103 is processed in the CDS circuit 107 by the operation pulse generated by the timing signal generation circuit 110 controlled by the system control unit 118, and the clock synchronization noise is removed. The programmable gain amplifier 108 applies a gain set in accordance with the amount of incident light (subject luminance), and the A / D converter 109 converts the gain into digital image data.

  Next, in the digital amplifier 121 (second amplification unit) of the digital signal processing circuit 112 controlled by the system control unit 118, a second gain set according to the incident light amount is applied to the digital image data. The image processing circuit 122 performs image processing such as color conversion, white balance, and gamma correction, resolution conversion processing, and image compression processing on the digital image data. The image memory 113 is used to temporarily store digital image data during signal processing or to store digital image data subjected to signal processing.

  The image data signal-processed by the digital signal processing circuit 112 and the image data stored in the image memory 113 are converted by the recording circuit 115 into data suitable for the recording medium 114 (for example, file system data having a hierarchical structure). Recorded on the recording medium 114. Alternatively, after the resolution conversion process is performed by the digital signal processing circuit 112, the display circuit 117 converts the signal into a signal suitable for the image display device 116 (for example, an NTSC analog signal) and displays it on the image display device 116. Is done.

  Note that the digital signal processing circuit 112 may output the image data as it is to the image memory 113 or the recording circuit 115 without performing signal processing in accordance with a control signal from the system control unit 118. Further, when requested by the system control unit 118, the digital signal processing circuit 112 outputs image data information generated in the signal processing process to the system control unit 118. Such information includes, for example, information such as the spatial frequency of the image, the average value (luminance information, etc.) of the image data in the designated area, the data amount of the compressed image, and information extracted from them. Furthermore, when requested by the system control unit 118, the recording circuit 115 outputs information such as the type and free capacity of the recording medium 114 to the system control unit 118. The system control unit 118 also sets a third gain according to the amount of incident light, and the first gain and the second gain so that the sum of the first gain and the second gain becomes the third gain. A function to adjust the gain is provided. Note that the amount of incident light can be obtained based on luminance information obtained from the digital signal processing circuit 112, for example. In addition, the first gain applied in the image sensor 103, the gain applied by the programmable gain amplifier 108, and the second gain applied by the digital amplifier 121 are also considered, and the third gain of the next frame is determined. The

  Next, a reproduction operation when image data is recorded on the recording medium 114 will be described. The recording circuit 115 reads image data from the recording medium 114 in accordance with a control signal from the system control unit 118. Then, when the image data is a compressed image, the digital signal processing circuit 112 performs an image expansion process according to a control signal from the system control unit 118 and stores it in the image memory 113. The image data stored in the image memory 113 is subjected to resolution conversion processing in the digital signal processing circuit 112, converted into a signal suitable for the image display device 116 in the display circuit 117, and displayed on the image display device 116. The

  Next, an example of gain setting according to the amount of incident light will be described with reference to FIG.

  In the graph of FIG. 2, the horizontal axis represents the amount of incident light. In the graph of FIG. 2, the lower the illumination is on the right side, the higher gain is set. In the graph of FIG. 2, the vertical axis represents the decibel value (dB) of the gain of each amplifier. In FIG. 2, in the signal amplification circuit 105 of the image sensor 103, for example, a first gain that can be changed in units of 6 dB is applied. Next, the gain is set so that the digital amplifier 121 of the digital signal processing circuit 112 applies a second gain that can be changed with a finer step size. Further, the sum of the first gain and the second gain is adjusted to be a third gain that is set according to a change in the luminance of the subject image. In this way, the amount of gain that cannot be adjusted by the first gain in the third gain is adjusted by the second gain.

  For example, when the third gain is set to 9 dB according to the change in the luminance of the subject image, the first gain is set to 6 dB and the second gain is set to 3 dB. However, as will be described later, during the preset time after the luminance of the subject decreases, the gain adjustment corresponding to the luminance change is performed only by the second gain without changing the first gain. Then, after a predetermined time has passed with the changed luminance level after the luminance of the subject has changed, the first gain is also changed, and as shown in the graph of FIG. The second gain is set to be the third gain.

  Specifically, for example, immediately after the luminance of the subject decreases, the second gain is set to 9 dB, for example, and after the luminance of the subject is stabilized, for example, the first gain is 6 dB and the second gain is 3 dB. Set to. As shown in FIG. 2, for example, when a gain of 6 dB is applied, the second gain is set to 6 dB immediately after the luminance change of the subject, and after the luminance of the subject is stabilized, the first gain is set. Set the gain to 6 dB. With such a configuration, a high-quality image with less noise can be obtained by using amplification in the signal amplification circuit 105 in a shooting environment where high sensitivity setting is required at low illuminance. On the other hand, the gain change accompanying a minute change in the amount of incident light can suppress flicker caused by the gain change during moving image shooting by using amplification by a digital signal amplifier.

  FIG. 4 is an example of a flowchart relating to the control method of the imaging apparatus according to the first embodiment of the present invention. Each step of this flowchart is executed by the system control unit 118 of FIG. 1 unless otherwise specified.

  In FIG. 4, when shooting is started, first, the luminance of the subject is measured (step S101). Next, it is determined whether or not the luminance has changed compared to the value at the previous measurement (step S102). Whether or not the luminance has changed is determined based on whether or not the difference between the luminance at the previous measurement and the luminance measured this time is within a predetermined luminance difference range. The predetermined range is, for example, x (n− when the third gain set when it is determined that the “brightness has changed” most recently is xn (x is a reference dB value). The range of change in luminance is required to be changed to a gain between 1) and x (n + 1). In step S102, if it exceeds this range, it is determined that the subject brightness has changed, and if within this range, it is determined that the subject brightness has not changed.

  If the subject brightness has changed (“Yes” in step S102), the second gain of the digital amplifier 121 is changed according to the brightness change amount (step S103), and the process proceeds to step S107. . In step S103, the gain adjustment using the signal amplification circuit 105 as described in FIG. 2 is not performed, and the adjustment is performed only by the second gain of the digital amplifier 121.

  On the other hand, if the subject brightness has not changed (“No” in step S102), it is determined whether or not a predetermined time has elapsed since the most recent “brightness change” was determined (step S104). . Note that the predetermined time may be set as appropriate, for example, for each shooting mode, each imaging device, or the like according to the purpose of shooting, the characteristics of the imaging device, the user's preference, and the like.

  If the predetermined time has elapsed (“Yes” in step S104), the first and the first amplifiers of the signal amplifier circuit 105 and the digital amplifier 121 are set so as to have a predetermined desired setting as described above in FIG. The distribution of the second gain is adjusted (step S105). Then, the process proceeds to step S107.

  In the time determination in step S104, if it is determined that the predetermined time has not elapsed (that is, the luminance change has not continued for a predetermined time or more) ("No" in step S104), the process proceeds to step S106. Then, based on the measured luminance of the subject, the second gain of the digital amplifier 121 is adjusted as necessary, and the process proceeds to step S107.

  In step S107, it is determined whether or not to terminate the main photographing. If the photographing is not finished (“No” in step S107), the process returns to step S101, the subject brightness is measured again, and the above process is repeated. When the shooting is to be ended (“Yes” in step S107), the shooting is ended as it is. As described above, gain control is performed.

  Next, the effect when the gain control described in FIG. 4 is used will be described with reference to FIGS.

  FIG. 5 is a diagram for explaining the progress of gain control when the luminance of the subject decreases from a bright state to a dark state. Note that the imaging apparatus described with reference to FIG. 5 is an imaging apparatus that adjusts sensitivity using the gains of the two amplifiers of the signal amplifier circuit 105 and the digital amplifier 121 of the imaging element 103 as described with reference to FIG. To do.

  FIG. 5A shows a state in which a bright room into which sunlight is inserted is photographed. The gain in this case is set to “0 dB” for both the first gain of the signal amplifier circuit 105 and the second gain of the digital amplifier 121.

  FIG. 5B shows a state in which the day is shaded from the state of FIG. In this case, sensitivity adjustment is performed so that the output is appropriate, and the second gain is set to, for example, “7 dB”.

  FIG. 5C shows a state where a predetermined time has passed while the brightness state of FIG. 5B is maintained. In this case, the first gain is adjusted to “6 dB” and the second gain is adjusted to “1 dB” so that the gain distribution shown in FIG. 2 is obtained.

  For a shooting environment in which one stable luminance state transitions to another stable luminance state as in the series of luminance changes in FIG. 5, the imaging apparatus eventually uses the first gain as the main gain. To adjust sensitivity. Therefore, it is possible to obtain a high-quality image with little noise even under a situation where high sensitivity setting is necessary.

  FIG. 6 is a diagram illustrating the progress of gain control when a person crosses the front of the imaging apparatus in a somewhat bright shooting environment. Note that the imaging apparatus described with reference to FIG. 6 is also an imaging apparatus that performs sensitivity adjustment using the gains of the two amplifiers of the signal amplifier circuit 105 and the digital amplifier 121 of the imaging element 103, as in the imaging apparatus of FIG. .

  FIG. 6A shows a state in which a bright room is being photographed as in FIG. The gain in this case is set to “0 dB” for both the first gain and the second gain.

  FIG. 6B shows a state where the amount of incident light temporarily decreases when a person crosses in the shooting environment of FIG. 6A, and sensitivity adjustment is necessary as in FIG. 5B. Also in this case, sensitivity adjustment is performed so that the output is appropriate, and the second gain is set to, for example, “7 dB”.

  FIG. 6C shows a state where the person shown in FIG. 6B passes and returns to the state of FIG. Again, since the shooting environment has become brighter, the second gain is returned to “0 dB”.

  As described above, the imaging apparatus performs sensitivity adjustment using only the second gain for a shooting environment in which the brightness temporarily changes, such as the series of brightness changes in FIG. Therefore, it is possible to obtain a smooth moving image that is not concerned with flickering when changing the gain.

  As described above with reference to FIGS. 5 and 6, the imaging apparatus according to the preferred embodiment of the present invention suppresses S / N degradation at high sensitivity and is sensitive to changes in the surrounding environment of the subject. It is possible to perform appropriate automatic sensitivity setting.

  The image pickup apparatus according to the preferred embodiment of the present invention has been described above with reference to FIGS. 1, 2, and 4 to 6, but the present invention is not limited to this and takes various forms. It is possible.

  For example, regarding the adjustment of the gain distribution with respect to the luminance change described with reference to FIG. 5, in the above description, the first gain is changed from “0 dB” to “6 dB”, and the second gain is changed from “7 dB” to “1 dB”. To change to "". However, for example, the second gain may be changed in stages, such as changing from “0 dB” to “6 dB” via “3 dB”. Similarly, other gains such as the first gain can be changed in stages.

  In the first embodiment, the gain used in the signal amplifier circuit 105 is the first gain, and the gain used in the digital amplifier 121 is the second gain. However, the amplifier that performs gain adjustment is not limited to these. Absent. For example, the gain of the programmable gain amplifier 108 can be changed. In that case, the gain of the programmable gain amplifier 108 may be set as the second gain. In addition, the gain of the programmable gain amplifier 108 can be set to the first gain.

<Second Embodiment>
Next, a second embodiment of the present invention will be described.

  In the first embodiment described above, as described with reference to FIGS. 5 and 6, the first gain and the second gain as described with reference to FIG. The form which used two types together was demonstrated. In the second embodiment, as shown in FIG. 3, if there is a programmable gain amplifier 108 of the analog signal processing circuit 106 or any other provided amplifier, three or more amplifiers may be used in combination. .

  Another example of gain setting according to the amount of incident light will be described with reference to FIG. In the second embodiment, as the signal amplifier circuit 105 configured in the image sensor 103, as in the image sensor 201 shown in FIG. 7, a column amplifier (first amplifier) and a column amplifier are provided. And an output amplifier (second amplifying means) arranged in a subsequent stage. In the second embodiment, the column amplifier and the output amplifier are referred to by the same reference numbers as in FIG.

  In FIG. 3, the gain setting (first gain) in units of 12 dB in the column amplifier 203 and the gain setting (second gain) in units of 3 dB in the output amplifier 204 are used. Further, the gain setting (third gain) in 1 dB units in the programmable gain amplifier 108 (third amplification means) inside the analog signal processing circuit 106 is used. Further, a finer gain setting (fourth gain) of 0.2 dB in the digital amplifier 121 (fourth amplification means) inside the digital signal processing circuit 112 is also used.

  For example, when a gain of 16.2 dB is applied, the first gain is set to 12 dB, the second gain is set to 3 dB, the third gain is set to 1 dB, and the fourth gain is set to 0.2 dB. Here, as in the case of the first embodiment described above and FIG. 2, immediately after the luminance change of the subject, the fourth gain is set to 16.2 dB, for example, and the luminance of the subject is stabilized. Adjust the gain of each amplifier according to the above distribution. With such a configuration, as with the gain setting described with reference to FIG. 2, in addition to obtaining a high-quality and non-flickering image, the number of gain stages of the column amplifier 203 is reduced. It is possible to reduce the circuit scale. Further, by using the programmable gain amplifier 108, the maximum value of the gain of the digital amplifier 121 can be kept low, and the amount of noise at the time of fine gain setting can be reduced.

  In the first and second embodiments, two examples of gain setting according to the amount of incident light have been described with reference to FIGS. 2 and 3, but the present invention is not limited to these. The gains of the column amplifier 203, the output amplifier 204 of the image sensor 103, the programmable gain amplifier 108 of the analog signal processing circuit 106, and the digital amplifier 121 of the digital signal processing circuit 112 can be set in accordance with the characteristics of the mounted imaging device. is there. The gain values shown in FIGS. 2 and 3 are exemplary, and the present invention is not limited to these, and each gain value can be changed as appropriate.

It is a block diagram which shows the structure of the imaging device which concerns on suitable embodiment of this invention. It is a figure explaining an example of the gain setting according to the incident light quantity in the 1st Embodiment of this invention. It is a figure explaining an example of the gain setting according to the incident light quantity in the 2nd Embodiment of this invention. 3 is a flowchart relating to a control method of the imaging apparatus according to the first embodiment of the present invention. It is a figure explaining the operation example of the imaging device which concerns on the 1st Embodiment of this invention. It is a figure explaining another example of operation of the imaging device concerning a 1st embodiment of the present invention. It is a block diagram explaining an example of the flow of control of an electric signal and an amplifier in a conventional imaging device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 103 Image pick-up element 104 Photoelectric conversion part 105 Signal amplifier circuit 106 Analog signal processing circuit 107 CDS circuit 108 Programmable gain amplifier (PGA)
109 A / D converter 112 Digital signal processing circuit 118 System control unit 121 Digital amplifier 122 Image processing circuit 203 Column amplifier 204 Output amplifier

Claims (7)

An image sensor that converts an optical image of a subject into an electrical signal;
First amplification means for amplifying the electrical signal with a first gain;
A second amplifying means for amplifying the electric signal amplified by the first amplifying means with a second gain that can be changed with a step size finer than the first gain;
A third gain is obtained based on the amount of light incident on the image sensor, and the first gain and the second gain are set such that a sum of the first gain and the second gain becomes the third gain. Control means for adjusting the gain of
The control means adjusts, by the second gain, a gain that cannot be adjusted by the first gain in the third gain, and changes in luminance of the subject exceeding a preset luminance difference. If the brightness change state does not continue for a preset time, the third gain is obtained by adjusting the second gain without adjusting the first gain. An imaging apparatus characterized by that. The image sensor has a plurality of pixels,
The imaging apparatus according to claim 1, wherein the first amplifying unit includes a column amplifier disposed in each column of the plurality of pixels.   The image pickup apparatus according to claim 1, wherein the first amplifying unit includes an output amplifier arranged inside the image pickup device.   The imaging apparatus according to claim 1, wherein the first amplifying unit includes an analog amplifier disposed at a subsequent stage of the imaging element.   The imaging apparatus according to claim 1, wherein the second amplifying unit includes an analog amplifier disposed at a subsequent stage of the imaging element.   The imaging apparatus according to claim 1, wherein the second amplifying unit includes a digital amplifier disposed at a subsequent stage of the imaging element. A method for controlling an imaging apparatus including an imaging element that converts a subject image into an electrical signal,
Amplifying the electrical signal with a first gain;
Amplifying the electrical signal amplified with the first gain with a second gain that can be changed with a step size finer than the first gain;
Setting a third gain based on the amount of light incident on the image sensor;
A control step of adjusting the first gain and the second gain so that a sum of the first gain and the second gain becomes the third gain;
In the control step, a part of the third gain that cannot be adjusted by the first gain is adjusted by the second gain, and a change in luminance of the subject exceeding a preset luminance difference occurs. If the brightness change state does not continue for a preset time, the third gain is obtained by adjusting the second gain without adjusting the first gain. A method for controlling an imaging apparatus, comprising:

Images