Patent Application
20130076946
This application claims priority under 35 USC 119 from Japanese Patent Application No. 2011-209538 filed on Sep. 26, 2011, the disclosure of which is incorporated by reference herein.
1. Field of the Invention
The present invention relates to an imaging apparatus, a computer readable medium storing an imaging program, and an imaging method.
2. Description of the Related Art
Heretofore, among imaging apparatuses that use imaging devices such as CCDs and the like, a variety of imaging apparatuses have been proposed that may perform imaging with improved sensitivity by pixel addition.
For example, Japanese Patent Application Laid-Open (JP-A) No. 2007-166600 discloses a technology that sets the gain of an amplifier in an addition mode, with two-pixel addition or the like, to half the gain in a non-addition mode, and thus realizes a dynamic range in the addition mode that is the same as the dynamic range in the non-addition mode.
JP-A No. 2002-10140 discloses a technology that, when 2×2 horizontal and vertical pixel addition—addition at a horizontal transfer path and at a floating diffusion amplifier—is performed, prevents image degradation by halving a light exposure amount and setting the size of a reference voltage of an analog-to-digital converter to twice that in an ordinary mode.
JP-A No. 2004-172845 discloses a technology that, during electronic zooming, halts addition of vertical lines, implements non-added readouts, and doubles the amplification ratio of a gain control amplifier.
JP-A No. 9-107505 discloses a technology that controls the potential of a semiconductor support portion in a field mode (a pixel addition mode) such that a ratio between an amount that is half of a saturation charge amount of optoelectronic conversion elements in a frame mode (a non-pixel addition mode) and a maximum charge transfer amount of a vertical transfer path is approximately 1:1.
In cases in which pixels of an imaging device are added by a pixel addition function, saturation charge amounts of the imaging device change. However, in the related art technologies mentioned above, no consideration is given to changes in the saturation charge amounts of the imaging devices when pixel addition is performed, and the dynamic range may be impaired.
The present invention has been made in view of the above circumstances and provides an imaging apparatus, a computer readable storage medium storing an imaging program and an imaging method.
According to an aspect of the invention, there is provided an imaging apparatus including: an imaging device that images an imaging subject; a setting unit that, on the basis of a saturation charge amount of the imaging device which changes in accordance with a pixel addition number according to a pixel addition function of the imaging device, sets a gain of imaging signals in accordance with a specified pixel addition number; and a gain control unit that controls the gain of the imaging signals in accordance with the gain set by the setting unit.
According to another aspect of the invention, there is provided a non-transitory computer readable medium storing a program causing a computer to execute image processing, the image processing including: setting a gain of imaging signals in accordance with a specified pixel addition number on the basis of a saturation charge amount of an imaging device that images an imaging subject, which saturation amount changes in accordance with a pixel addition number according to a pixel addition function of the imaging device; and controlling the gain of the imaging signals in accordance with the set gain.
According to another aspect of the invention, there is provided an imaging method including: setting a gain of imaging signals in accordance with a specified pixel addition number on the basis of a saturation charge amount of an imaging device that images an imaging subject, which saturation amount changes in accordance with a pixel addition number according to a pixel addition function of the imaging device; and controlling the gain of the imaging signals in accordance with the set gain.
Preferred embodiments of the present invention will be described in detail based on the following figures, wherein:
Herebelow, an exemplary embodiment of the present invention is described with reference to the attached drawings.
The imaging apparatus 10 images the imaging subject and outputs the acquired image data of the imaging subject to the image processing device 100. The image processing device 100 applies predetermined image processing to the received image data in accordance with requirements, and displays the image data at a display section 202.
The casing 20 includes a cavity portion 21 formed in a substantially cuboid shape, and includes thereinside the imaging subject arrangement portion 40 on which the imaging subject PS is disposed. The lid 22 shown in
The imaging section 30 is fixed to an upper face 20a of the casing 20 and is described in detail below. The imaging section 30 includes, for example, an imaging device such as a CCD or the like. A cooling device is mounted at the imaging device and cools the imaging device. Thus, the inclusion of a noise component due to dark currents in captured image information is prevented.
A lens unit 31 is mounted at the imaging section 30. The lens unit 31 is provided to be movable in the direction of arrow Z, for focusing on the imaging subject PS.
The epi-illumination light sources 50 illuminate excitation light towards the imaging subject PS disposed on the imaging subject arrangement portion 40. The transmission light source 60 illuminates imaging light from below the imaging subject PS. If a fluorescent material is being imaged, excitation light is illuminated at the imaging subject from one or both of the epi-illumination light sources 50 and the transmission light source 60, depending on the imaging subject.
The main controller 70 is structured with a CPU (central processing unit) 70A, a ROM (read-only memory) 70B, a RAM (random access memory) 70C, A non-volatile memory 70D and an input/output interface (I/O) 70E that are connected to one another via a bus 70F.
The display section 202, an operation section 72, a hard disk 74 and a communications interface (I/F) 76 are connected to the I/O 70E. The main controller 70 performs overall control of these functional units.
The display section 202 is constituted with, for example, a cathode ray tube, a liquid crystal display device or the like. The display section 202 displays images captured by the imaging apparatus 10, and displays screens for applying various specifications and instructions to the imaging apparatus 10 and so forth.
The operation section 72 is constituted with a mouse and keyboard or the like. The operation section 72 is for a user to give various instructions to the imaging apparatus 10 by operating the operation section 72.
The hard disk 74 stores image data of captured images that have been imaged by the imaging apparatus 10, a control program that is described below, various data that are required for control, and so forth.
The communications interface 76 is connected with the imaging section 30, epi-illumination light sources 50 and transmission light source 60 of the imaging apparatus 10. The CPU 70A instructs the imaging section 30, via the communications interface 76, to capture images under imaging conditions according to types of imaging subject. In a case in which excitation light is to be illuminated at an imaging subject, the CPU 70A instructs the illumination of excitation light from one or both of the epi-illumination light sources 50 and the transmission light source 60, receives imaging data of a captured image that is imaged by the imaging section 30, and carries out image processing and the like.
When an imaging instruction is received from the image processing device 100 via the communications interface 84, the control section 80 controls the respective sections in accordance with details of the instruction and images the imaging subject PS disposed on the imaging subject arrangement portion 40. The control section 80 transmits the image data of the captured image to the image processing device 100 via the communications interface 84.
The control section 80 is connected to the lens unit 31, a timing generator 86, a cooling device 90 that cools an imaging device 88, and a temperature sensor 91 that detects a temperature of the imaging device 88.
The control section 80 is constituted by a computer that includes, for example, a CPU, RAM, ROM, non-volatile ROM and the like, which are not shown in the drawings. The non-volatile ROM stores a control program that controls the respective sections. The respective sections connected to the control section 80 are controlled by this program being read out and executed by the CPU.
Although not shown in the drawings, the lens unit 31 includes, for example, a lens group formed of plural optical lenses, an aperture adjustment mechanism, a zoom mechanism, an automatic focus control mechanism and the like. The lens group is provided to be movable in the direction of arrow Z in
Light from the imaging subject PS passes through the lens unit 31 and is focused on the imaging device 88 as an image of the imaging subject.
As described in detail below, the imaging device 88 includes light detection portions corresponding with a plural number of pixels, a horizontal transfer path, vertical transfer paths and so forth. The imaging device 88 features a function of optoelectronically converting the imaging subject image that has been imaged at the imaging surface to electronic signals. For example, an image sensor such as a charge coupled device (CCD), a metal oxide semiconductor (MOS) sensor or the like is employed. In the present exemplary embodiment, a CCD is used as the imaging device 88.
The imaging device 88 is controlled by timing signals from the timing generator 86, and optoelectronically converts incident light from the imaging subject PS at the light detection portions.
The signal charges to which the light is optoelectronically converted by the imaging device 88 are voltage-converted by a charge-voltage conversion amplifier (a floating diffusion amplifier) 92 to analog signals, and are outputted to a signal processing section 94.
The timing generator 86 includes an oscillator that generates a basic clock signal (a system clock) that operates the imaging section 30. This basic clock is, for example, supplied to the respective sections and divided to generate various timing signals. For example, timing signals representing a vertical synchronization signal, a horizontal synchronization signal, electronic shutter pulses and the like are generated and supplied to the imaging device 88. Further timing signals—sampling pulses for correlated double sampling, a conversion clock for analog-to-digital conversion, and the like—are generated and supplied to the signal processing section 94.
As described in detail below, the signal processing section 94 includes an amplification circuit 94A, a correlated double sampling (CDS) circuit, an analog-to-digital (A/D) converter and the like. The amplification circuit 94A amplifies the image signals in accordance with a gain set in accordance with pixel addition numbers. The CDS circuit is controlled by timing signals from the timing generator 86 and applies correlated double sampling processing to the inputted analog signals. The A/D converter converts the analog signals to which the correlated double sampling processing has been applied to digital signals. The signal processing section 94 further includes a processing section that performs A/D sampling of feed-through portions and signal portions and that performs processing to calculate difference data between digital values of the feed-through portions and signal portions.
An object of the correlated double sampling processing is to reduce noise and the like included in the output signals of the imaging device 88. The correlated double sampling processing obtains pixel data by finding differences between levels of the feed-through portion and levels of the signal portion corresponding to an image portion, which are included in the output signals of each pixel of the imaging device 88.
The digital signals after the correlated double sampling processing are outputted to a memory 96 and temporarily stored. The image data temporarily stored in the memory 96 is sent to the image processing device 100 via the communications interface 84.
The cooling device 90 is constituted by, for example, a Peltier device or the like, and a cooling temperature thereof is controlled by the control section 80. If the imaging subject PS is a chemoluminescent material, the image is captured by image exposure being performed for a relatively long time without excitation light being illuminated. Correspondingly, the temperature of the imaging device 88 may rise and image quality may be adversely affected by an increase in dark currents and the like. Therefore, in the control section 80, the temperature of the imaging device 88 is maintained at a cooling temperature instructed by the image processing device 100. While the temperature of the imaging device 88 detected by the temperature sensor 91 is monitored, the cooling device 90 is controlled by pulse width modulation (PWM) to cool the imaging device 88.
Charges to which light detected by the light detection portions 88A have been optoelectronically converted are outputted to the vertical transfer path 88B in each column. The charges outputted to the vertical transfer path 88B in each column are respectively transferred to the horizontal transfer path 88C, and the charges respectively outputted to the horizontal transfer path 88C are sequentially transferred to the charge-voltage conversion amplifier 92.
The imaging device 88 is equipped with a pixel addition function. Pixel addition in the vertical direction is implemented at the horizontal transfer path 88C, and pixel addition in the horizontal direction is implemented at the charge-voltage conversion amplifier 92. In a case of a structure in which a summing gate is provided at an output stage of the horizontal transfer path 88C, the horizontal direction pixel addition may be implemented by the summing gate. In the present exemplary embodiment, however, a case in which pixel addition in the horizontal direction is implemented by the charge-voltage conversion amplifier 92 is described.
The light detection portions 88A, the horizontal transfer path 88C and the charge-voltage conversion amplifier 92 each have particular saturation charge amounts.
In the present exemplary embodiment, as an example, a case is described in which the saturation charge amount of each light detection portion 88A is 10 ke−, the saturation charge amount of the horizontal transfer path 88C is 25 ke−, and the saturation charge amount of the charge-voltage conversion amplifier 92 is 55 ke−. Furthermore, in the described case, gradation of an image is 16 bits, that is, 65,536 (=216) gradations.
Here, in a case in which 1 pixel is added in the vertical direction and 1 pixel is added in the horizontal direction for (1×1) pixel addition, that is, a case with no pixel addition, the charge amounts of charges outputted from the imaging device 88 are limited by the saturation charge amounts of the light detection portions 88A. Therefore, the maximum value of charge amounts of the charges outputted from the imaging device 88 is 10 ke−. Therefore, if the gain is set such that a pixel value is at the maximum value of 65,535 in a case in which the charge amount is 10 ke−, the dynamic range may be utilized to the maximum extent.
In a case in which 2 pixels are added in the vertical direction and 2 pixels are added in the horizontal direction for (2×2) pixel addition, the maximum value of charge amounts of the charges outputted from the imaging device 88 is 40 ke−(=2×2×10 ke−). Therefore, if the gain is set such that a pixel value is at the maximum value in a case in which the charge amount is 40 ke−, the dynamic range may be utilized to the maximum extent.
In a case in which 3 pixels are added in the vertical direction and 1 pixel is added in the horizontal direction for (3×1) pixel addition, the maximum value of charge amounts of the charges outputted from the imaging device 88 is 25 ke−. When three pixels are added in the vertical direction at the horizontal transfer path 88C, the maximum value of the charge amount is 30 ke−, but the saturation charge amount of the horizontal transfer path 88C is 25 ke− and there may be saturation, so 25 ke− is the maximum value. Therefore, if the gain is set such that a pixel value is at the maximum value in a case in which the charge amount is 25 ke−, the dynamic range may be utilized to the maximum extent.
In a case in which 3 pixels are added in the vertical direction and 2 pixels are added in the horizontal direction for (3×2) pixel addition, the maximum value of charge amounts of the charges outputted from the imaging device 88 is (the saturation charge amount of the horizontal transfer path 88C)×(the pixel addition number in the horizontal direction), which specifically is 50 ke−(=25 ke−×2). Therefore, if the gain is set such that a pixel value is at the maximum value in a case in which the charge amount is 50 ke−, the dynamic range may be utilized to the maximum extent.
In a case in which 3 pixels are added in the vertical direction and 3 pixels are added in the horizontal direction for (3×3) pixel addition, the maximum value of charge amounts of the charges outputted from the imaging device 88 is 55 ke−. The maximum value of charge amounts of pixel charges when three pixels in the vertical direction are added at the horizontal transfer path 88C is 25 ke−. If three of these are added in the horizontal direction by the charge-voltage conversion amplifier 92, the maximum value of charge amounts is 75 ke−(=25 ke−×3). However, the saturation charge amount of the charge-voltage conversion amplifier 92 is 55 ke− and there may be saturation, so 55 ke− is the maximum value. Therefore, if the gain is set such that a pixel value is at the maximum value in a case in which the charge amount is 55 ke−, the dynamic range may be utilized to the maximum extent.
Thus, because saturation charge amounts of the imaging device 88 differ depending on pixel addition numbers, if the gain is fixed regardless of saturation charge amounts, the dynamic range may be impaired. Accordingly, in the present exemplary embodiment, impairment of the dynamic range is avoided by the gain being set in accordance with pixel addition numbers.
Specifically, the gain is set in accordance with the pixel addition numbers, using data in a table of gains as illustrated in
Each value in the table data of gains shown in
The table data of gains shown in
Next, as operation of the present exemplary embodiment, processing that is executed by the CPU 70A of the image processing device 100 is described with reference to the flowchart shown in
The flowchart shown in
In step 100, imaging conditions are specified. At this time, for example, an imaging condition specification screen is displayed at the display section 202 and various imaging conditions are specified by the user. The imaging conditions include, for example, a color mode specifying color imaging or monochrome imaging, an exposure duration, an imaging mode and the like. The user specifies imaging conditions and then instructs the start of imaging.
In step 102, a determination is made as to whether the start of imaging has been instructed. If the start of imaging has been instructed, the processing proceeds to step 104. If the start of imaging has not been instructed, the processing waits.
In step 104, the pixel addition numbers are specified. The pixel addition numbers are specified in accordance with, for example, the imaging mode specified by the user (resolution, sensitivity and the like). Specifically, for example, table data in which correspondences between imaging modes and pixel addition numbers are pre-specified is memorized in advance in the hard disk 74, and the pixel addition numbers corresponding to the imaging mode are specified using this table data. However, the pixel addition numbers may be specified among the imaging conditions by the user.
In step 106, a gain corresponding to the specified pixel addition numbers is found from the table data of gains illustrated in
In step 108, the imaging section 30 is instructed to execute imaging. Hence, the imaging section 30 executes imaging of the imaging subject PS with the specified exposure duration and pixel addition numbers. At the imaging device 88, the imaging signals are subjected to pixel addition in the specified pixel addition numbers and outputted. The imaging signals outputted from the imaging device 88 are amplified by the set gain at the amplification circuit 94A of the signal processing section 94, and outputted to subsequent circuits. For example, if the pixel addition numbers are 2×2, then the gain is 1.64 as shown in
Thus, in the present exemplary embodiment, table data of gains is specified on the basis of saturation charge amounts of the imaging device 88, which change in accordance with the pixel addition numbers, and, from this table data, the gain is set and imaging signals are amplified in accordance with pixel addition numbers that are specified in accordance with an imaging mode. Therefore, compared with a case in which the gain has a fixed value regardless of saturation charge amounts, impairment of the dynamic range may be avoided.
The table data of gains illustrated in
In the present exemplary embodiment, a case is described in which the saturation charge amount of each light detection portion 88A is 10 ke−, the saturation charge amount of the horizontal transfer path 88C is 25 ke−, and the saturation charge amount of the charge-voltage conversion amplifier 92 is 55 ke−. However, even among the same kind of imaging device, saturation charge amounts of the components may be slightly different depending on individual differences. Accordingly, the table data of saturation charge amounts illustrated in
Further, in the present exemplary embodiment a case is described in which control of the gain is implemented at the amplification circuit 94A of the signal processing section 94. However, the gain may be controlled by multiplying pixel values by the gain after the imaging signals have been converted to digital image data.
The constitution of the imaging system 1 described in the present exemplary embodiment (see
The flow of processing of the control program described in the present exemplary embodiment (see
According to a first aspect of the invention, there is provided an imaging apparatus including: an imaging device that images an imaging subject; a setting unit that, on the basis of a saturation charge amount of the imaging device which changes in accordance with a pixel addition number according to a pixel addition function of the imaging device, sets a gain of imaging signals in accordance with a specified pixel addition number; and a gain control unit that controls the gain of the imaging signals in accordance with the gain set by the setting unit.
According to this invention, the gain of the imaging signals captured by the imaging device is set on the basis of the specified pixel addition number and the saturation charge amount that changes in accordance with the pixel addition number, which is the saturation charge amount of a location relating to the pixel addition function of the imaging device that images an imaging subject, and the gain of the imaging signals is controlled in accordance with the set gain. Therefore, even in a case in which pixel addition is performed and the saturation charge amount of the imaging device changes, impairment of the dynamic range may be avoided.
In a second aspect of the present invention, in the first aspect, the saturation charge amount of the imaging device may be determined on the basis of pixel addition numbers in a vertical direction and a horizontal direction, and at least one of a saturation charge amount of a light detection element of the imaging device, a saturation charge amount of a horizontal transfer path of the imaging device, or a saturation charge amount of an amplifier that amplifies imaging signals outputted from the horizontal transfer path.
In a third aspect of the present invention, in the first or second aspect, the setting unit may set, as the gain, a value for which a pre-specified number of gradations is divided by the saturation charge amount according to the specified pixel addition number.
In a fourth aspect of the present invention, in any one of the first to third aspects, the imaging apparatus may further include a storage unit that stores table data of gains that are values for which a pre-specified number of gradations is respectively divided by saturation charge amounts of respective pixel addition numbers, and the setting unit may set the gain in accordance with the specified pixel addition number on the basis of the table data.
In a fifth aspect of the present invention, in the fourth aspect, the imaging apparatus may further include a correction unit that corrects the table data for each of the pixel addition numbers, a new gain being a value for which the pre-specified number of gradations is divided by an output value of the imaging device if the imaging device is exposed and saturated.
In a sixth aspect of the present invention, in any one of the first to fifth aspects, the setting unit may specify the pixel addition number in accordance with an imaging mode.
According to a seventh aspect of the invention, there is provided a non-transitory computer readable storage medium storing a program causing a computer to function as each of the units which configure the imaging apparatus according to any one of the first to sixth aspect
According to an eighth aspect of the invention, there is provided an imaging method including: setting a gain of imaging signals in accordance with a specified pixel addition number on the basis of a saturation charge amount of an imaging device that images an imaging subject, which saturation amount changes in accordance with a pixel addition number according to a pixel addition function of the imaging device; and controlling the gain of the imaging signals in accordance with the set gain.
According to the present invention, impairment of the dynamic range may be avoided even in cases in which pixel addition is performed.
Embodiments of the present invention are described above, but the present invention is not limited to the embodiments as will be clear to those skilled in the art.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2011-209538 | Sep 2011 | JP | national |
