JP2014236429A - Imaging system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To acquire an image signal converged into a target luminance value by instantaneously setting an exposure time even when a rapid luminance change occurs.SOLUTION: The imaging system includes: imaging means for acquiring image data by imaging a sample S in a set exposure time; evaluation value calculation means for calculating an evaluation value on the basis of the signal level of an arbitrary region in the image data; storage means for storing a first threshold as a reference value for determining that an amount of light incident to the imaging means is increased; determination means for determining whether or not the evaluation value is equal to or more than a first threshold, and for determining whether or not the exposure time is longer than the period of the vertical synchronous signal of the imaging means; and exposure time calculation means for, when the evaluation value is equal to or more than the first threshold, and the exposure time is longer than the period of the vertical synchronous signal as the result of determination by the determination means, calculating a new exposure time which is equal to or less than the period of the vertical synchronous signal.

Description

  The present invention relates to an imaging system, and more particularly to an imaging system that is applied to a microscope and captures an observation image by the microscope.

2. Description of the Related Art Conventionally, in a microscope system in which an imaging device is attached to a microscope apparatus and acquires an image to be observed, a function for automatically setting an exposure time so as to converge to a target luminance value with respect to a luminance change (hereinafter referred to as “AE”). ”).
In such a microscope system, when performing various operations such as switching of an objective lens for changing the observation magnification, switching of an optical path for photographing an observation target, insertion of an ND filter or a polarizing filter on the optical path, The amount of light incident on the imaging device changes suddenly. If such a sudden change in the amount of incident light occurs while the AE is being driven, it may take a long time to converge to the target luminance value.

That is, for example, when the objective lens is switched, when the revolver is rotated, the light incidents on the image sensor again after the incident on the image sensor temporarily enters a light-shielding state close to zero. At this time, on the basis of the time when the image sensor is in a light-shielded state, processing is performed so that the exposure time becomes longer when the AE operation is performed so as to converge to the target luminance value. When the image sensor is again incident from the state set to the long exposure, the signal data of the acquired image signal is saturated, so-called whiteout image.
For this reason, Patent Document 1 discloses an exposure in a state in which light immediately before switching starts when it is detected that switching has started from a state in which light is incident on an image sensor. It is disclosed that the AE control is performed based on the held exposure time after the time is detected and it is detected that the light is not incident on the image sensor and switched to the incident state.

Japanese Patent No. 4367203

  However, in Patent Document 1 described above, when the held exposure time is not appropriate exposure, it may take time for the convergence of the exposure time if AE control is performed based on the held exposure time. Further, when the held exposure time is a long exposure time, it may take time for the exposure time to converge when the amount of incident light increases. Furthermore, since a configuration for storing the detection of the switching and the state immediately before the switching is required, the apparatus is increased in size.

  The present invention has been made in view of the above-described circumstances, and even when a sudden change in luminance occurs, an image signal that is immediately set to an appropriate exposure time and converges to a target luminance value. The purpose is to acquire.

In order to achieve the above object, the present invention provides the following means.
One aspect of the present invention is an imaging unit that captures a sample with a set exposure time to acquire image data, and an evaluation value calculation unit that calculates an evaluation value based on a signal level of an arbitrary region in the image data. A storage unit that stores a first threshold value that is a reference value for determining that the amount of incident light on the imaging unit has increased; and whether or not the evaluation value is greater than or equal to the first threshold value, and A determination unit that determines whether an exposure time is longer than a cycle of a vertical synchronization signal of the imaging unit; as a result of determination by the determination unit, the evaluation value is equal to or greater than the first threshold value; and the exposure When the time is longer than the period of the vertical synchronization signal, an imaging system is provided that includes an exposure time calculation unit that calculates a new exposure time equal to or less than the period of the vertical synchronization signal.

  According to this aspect, the evaluation value is calculated based on the image data of the specimen imaged at the set exposure time, and the evaluation value is compared with the first threshold value. By comparing the evaluation value with the first threshold value, it is determined whether the signal level of the image data is higher than the target signal level, that is, whether the set exposure time is excessively long. Can do. Therefore, if the evaluation value is equal to or greater than the first threshold as a result of the determination, it is considered that the exposure time is long and image data with the target luminance value cannot be acquired. Therefore, the determination means also determines whether or not the set exposure time is longer than the period of the vertical synchronization signal. If the set exposure time is longer than the period of the vertical synchronization signal, the vertical synchronization is performed. A new exposure time equal to or shorter than the signal period is calculated. In this way, even when the amount of incident light on the imaging means has increased rapidly, a new exposure time can be calculated and set so that the next time the image data is acquired, It is possible to obtain preferable image data converged to the luminance value.

  In the aspect described above, the storage unit stores a second threshold value that is a reference value for determining that the amount of incident light on the imaging unit has decreased, and the determination unit determines that the evaluation value is the second value. It is determined whether or not the exposure time is longer than a period of a vertical synchronization signal of the imaging means, and the exposure time calculation means is determined by the determination means as a result of the evaluation. When the value is equal to or less than the second threshold value and the exposure time is shorter than the period of the vertical synchronization signal, it is preferable to calculate the period of the vertical synchronization signal as a new exposure time.

  By comparing the evaluation value with the second threshold value, it is determined whether the signal level of the image data is lower than the target signal level, that is, whether the set exposure time is excessively short. Can do. Therefore, when the evaluation value is equal to or smaller than the second threshold as a result of the determination, it is considered that the exposure time is short and the image data of the target luminance value cannot be acquired. Therefore, the determination means also determines whether or not the set exposure time is longer than the period of the vertical synchronization signal. If the set exposure time is shorter than the period of the vertical synchronization signal, the vertical synchronization is performed. The period of the signal is calculated as a new exposure time. In this way, even when the amount of incident light on the image pickup unit is drastically reduced, a new exposure time can be calculated and set so that the next time the image data is acquired, It is possible to obtain preferable image data converged to the luminance value.

  According to the present invention, it is possible to obtain an image signal converged to a target luminance value by setting an exposure time immediately even when a sudden luminance change occurs.

1 is a block diagram illustrating a schematic configuration of an imaging system according to a first embodiment of the present invention. It is a figure which shows the linearity of the image pick-up element applied to the imaging system which concerns on 1st Example of this invention. It is a flowchart which shows the effect | action in the case of calculating exposure time in the imaging system which concerns on the 1st Embodiment of this invention. 5 is a timing chart illustrating the operation of the image sensor during short-time exposure in the imaging system according to the first embodiment of the present invention. 4 is a timing chart illustrating the operation of the image sensor during long exposure in the imaging system according to the first embodiment of the present invention. It is the figure which represented typically the time required when calculating the exposure time in the imaging system concerning a 1st embodiment of the present invention. It is a flowchart which shows the effect | action in the case of calculating exposure time in the imaging system which concerns on the 2nd Embodiment of this invention.

(First embodiment)
The imaging system according to the first embodiment of the present invention will be described below with reference to the drawings.
As shown in FIG. 1, the imaging system includes a microscope main body 1, a camera 2, a controller 3, and a display unit 4.

The microscope main body 1 includes at least an objective lens 11, a revolver 12, and a trinocular tube 13 in order to observe a specimen S that is a subject.
The revolver 12 holds a plurality of objective lenses 11 having different magnifications. By rotating the revolver 12, the objective lens 11 having a desired magnification can be inserted into the observation optical path. Here, the plurality of objective lenses 11 may have the same magnification. Light from the specimen S is incident on the objective lens arranged on the observation optical path a1 and can be observed by the magnification of the objective lens.

  When the objective lens 11 is changed in order to change the observation magnification, the portion of the revolver 12 where the objective lens is not attached is positioned on the observation optical path a1 and the light enters the objective lens 11 when the objective lens 11 is changed. Since the state which does not occur arises, the state by which the light to the observation optical path a1 mentioned later is interrupted | blocked will generate | occur | produce.

  The trinocular tube 13 has a prism for switching the optical path so that the observation image can be led out of the microscope main body 1 along the observation optical path a1, and the user can insert the prism into the observation optical path. The observation image of the specimen S can be visually observed through the eyepiece 14. When this prism is inserted, a state occurs in which light to the observation optical path a1 is temporarily blocked.

The camera 2 is arranged at a position where an observation image from the microscope main body 1 is projected on the observation optical path a1 outside the microscope main body 1. The camera 2 includes an image sensor 21, a preprocessing unit 22, an amplification unit 23, and an A / D conversion unit 24.
A CCD, CMOS, or the like can be applied to the image pickup device 21. The image pickup device 21 is controlled by an exposure time according to a signal from the controller 3, photoelectrically converts the observation image, and inputs an output signal to the preprocessing unit 22.

The pre-processing unit 22 samples the signal output from the image sensor 21 by performing a correlated double sampling (CDS) process and outputs the sample to the amplification unit 23.
The amplification unit 23 amplifies the image signal input via the pre-processing unit 22 and outputs the amplified image signal to the A / D conversion unit 24.
The A / D conversion unit 24 quantizes the image signal amplified by the amplification unit 23 to generate quantized data, and outputs the quantized data to an image processing unit 40 described later.

The controller 3 generates and outputs various signals for controlling the camera 2, and an evaluation value calculation unit 31, a storage unit 32, a determination unit 33, and an exposure time calculation unit 34 that are driven by control of a CPU (not shown). And an image processing unit 40. Further, the controller 3 sets the cycle T _VD of the vertical synchronization signal VD, which is the shortest time required to acquire one frame, in the camera 2, or sets the exposure time (imaging condition) or exposure stored in the storage unit 32. The image sensor 21 is controlled based on the exposure time calculated by the time calculation unit 34.

  The evaluation value calculation unit 31 calculates an evaluation value based on the signal level of an arbitrary area in the image data captured by the camera 2. That is, the evaluation value calculation unit 31 calculates an average value of signal levels in an arbitrary region of the image data output from the A / D conversion unit 24, and outputs this to the determination unit 32 as an evaluation value S1.

The evaluation value S1 is an average value of signal levels in an arbitrary region, but the maximum value, mode value, or median value of signal levels in an arbitrary region may be used as the evaluation value S1.
Further, the image data may be YC converted from R, Gr, Gb, and B, and the Y data may be used as the evaluation value S1, or the G signal may be used as the evaluation value S1 without YC conversion. In the case of a monochrome image sensor, a signal in an arbitrary region of the image signal data output from the A / D converter 24 may be used as the evaluation value S1.

The storage unit 32 includes a signal level SH1, which is a first threshold value for determining that the amount of incident light from the microscope body 1 to the camera 2 has increased, and a reference value for determining that the amount of incident light has decreased. A signal level SL1 which is a certain second threshold value is stored. The storage unit 32 also stores a signal level SH0 having a signal level lower than the signal level SH1 and a signal level SL0 having a signal level lower than the signal level SH0. The relationship among SL0, SL1, SH0, and SH1 is as shown in the following formula (1).
SL1 <SL0 <SH0 <SH1 (1)
The relationship between SL0, SL1, SH0, SH1 and exposure time is shown in FIG.

Note that the values of the signal levels SL0, SL1, SH0, and SH1 can be arbitrarily determined.
The storage unit 32 also stores the target signal level S0 and the loop count N for the acquired image data, in addition to the imaging conditions set in the imaging element 21 and the parameters when the image processing unit 40 performs image processing. .

The determination unit 33 determines whether or not the evaluation value S1 is equal to or higher than the signal level SH1, and the exposure time when the image data related to the evaluation value S1 is acquired is shorter than the cycle T _VD of the vertical synchronization signal of the camera 2. Determine whether it is long or not. Further, it is determined whether or not the evaluation value S1 is equal to or less than the signal level SL1, and whether or not the exposure time when the image data related to the evaluation value S1 is acquired is longer than the cycle T _VD of the vertical synchronization signal of the camera 2. Determine whether.
That is, the determination unit 33 compares the evaluation value S1 output from the evaluation value calculation unit 31 with the signal levels SL0, SL1, SH0, and SH1 stored in the storage unit 32, and compares the comparison results with the exposure time calculation unit. 34.

In the exposure time calculation 34, the evaluation value S1 is equal to or higher than the signal level SH1 as a result of determination by the determination unit 33, and the exposure time when the image data related to the evaluation value S1 is acquired is the vertical synchronization signal of the camera 2. If longer than the period T _VD of calculates a new exposure time of less than period T _VD. As a result of the determination by the determination unit 33, the evaluation value S1 is equal to or less than the signal level SL1, and the exposure time when the image data related to the evaluation value S1 is acquired is the period T _VD of the vertical synchronization signal of the camera 2. If it is shorter, the period _TVD is calculated as a new exposure time.
The controller 3 outputs an electronic shutter pulse φSUB that is input to the image sensor 21 based on the exposure time output from the exposure time calculation unit 34.

  The image processing unit 40 performs image processing such as demosaicing processing, color matrix conversion processing, contrast processing, and sharpening processing on the image data, and outputs the image data after these various types of image processing to the display unit 4. The display unit 4 displays the image data after various image processing as an observation image.

Hereinafter, the operation when the exposure time is calculated in the imaging system configured as described above will be described with reference to the flowchart of FIG.
In step S101, it is determined whether exposure control of the imaging system is automatic exposure control (AE control). If the exposure control of the imaging system is automatic exposure, the number of loops N stored in the storage unit 32 by the controller 3 is reset to 0, stored in the storage unit 32, and the process proceeds to the next step S102. If the exposure control is not AE control, the exposure time calculation process ends.

  In step S102, the evaluation value S1 is acquired from the image data acquired at the exposure time T1 stored in the storage unit 32. That is, the evaluation value calculation unit 31 calculates an average value of signal levels in an arbitrary area of the image data acquired at the exposure time T1 output from the A / D conversion unit 24, and evaluates the calculated average value. It outputs to the determination part 33 as value S1.

In the next step S103, it is determined whether the exposure time is appropriate based on the evaluation value S1 calculated in step S102. That is, the determination unit 33 compares the evaluation value S1 with the signal levels SL0 and SH0. Arbitrary signal levels SL0 and SH0 define the upper and lower limits of the tolerance of the target signal level S0. If the evaluation value S1 falls within this tolerance, that is, whether SL0 ≦ S1 ≦ SH0 is satisfied. When it is satisfied, it is determined that the image data of the target signal level has been acquired, the loop count N stored in the storage unit 32 is set to 0, and the exposure time calculation process is terminated.
If SL0 ≦ S1 ≦ SH0 is not satisfied, it is determined that the image data of the target signal level has not been acquired, and the process proceeds to the next step S104.

  In step S104, the amount of deviation from the target signal level is determined based on the determination that image data of the target signal level S0 has not been acquired in step S103, and an appropriate exposure time is calculated. That is, the determination unit 33 compares the evaluation value S1 with the signal levels SL1 and SH1.

  The signal level SL1 stipulates that the signal level of the image data output from the A / D converter 24 is insufficient, and when the evaluation value S1 is less than or equal to this value, that is, S1 ≦ SL1. In this case, it is determined that the amount of incident light from the optical path a1 to the image pickup device 21 has rapidly decreased.

  On the other hand, the signal level threshold value SH1 defines that the signal level of the image data output from the A / D converter 24 is saturated, and when the evaluation value S1 is equal to or higher than this value, that is, S1. When ≧ SH1, it is determined that the amount of light incident on the image sensor 21 from the optical path a1 has increased rapidly.

For this reason, when SL1 <S1 <SH1, the process proceeds to step S105. In step S105, since the signal level and the exposure time are in a proportional relationship, the exposure time calculation unit 34 calculates a new exposure time T that achieves the target signal level S0 from the following equation (2).
T0 = S0 / S1 × T1 (2)
The controller 3 generates an electronic shutter pulse φSUB based on the exposure time T 0 calculated by the exposure time calculation unit 34 and sets it in the image sensor 21.

  FIG. 4 shows a timing chart showing the operation of the image sensor during short exposure, and FIG. 5 shows a timing chart showing the operation of the image sensor during long exposure. As shown in FIGS. 4 and 5, the exposure time T0 set for the image sensor 21 is from the falling edge of the electronic shutter pulse φSUB to the rising edge of the readout pulse SG, and exposure is performed with the exposure time T0. The image data photoelectrically converted by the image sensor 21 is output from the A / D conversion unit 24 via the preprocessing unit 22 and the amplification unit 23. Within the processing time, the processing from the evaluation value calculation unit 31 to the exposure time calculation unit 34 is performed, and the exposure time T0 is calculated from the above equation (2). While the exposure time is set, the number of electronic shutter pulses φSUB input from the controller 3 to the image sensor 21 is set.

  If SL1 <S1 <SH1, it is determined that the amount of light incident on the image sensor 21 has changed significantly due to switching of the objective lens 11, switching of the observation optical path of the trinocular tube 13, or the like. Then, the controller 3 increments the loop count N, holds it in the storage unit 32, and proceeds to step S107.

  In step S107, it is determined whether the amount of light incident on the image sensor 21 has changed greatly and the signal level of the image data is saturated or insufficient. Therefore, first, the determination unit 33 compares the evaluation value S1 with the signal level SH1. When S1 ≧ SH1, that is, when S1 ≦ SL1, it is determined that the signal level is insufficient due to a sudden decrease in the amount of light incident on the image sensor 21, and the process proceeds to step S108. When S1 ≧ SH1, it is determined that the signal level is saturated due to a sudden increase in the amount of light incident on the image sensor 21, and the process proceeds to step S109.

In step S108, the exposure time is calculated by the exposure time calculator 34 based on the determination that the signal level is insufficient due to the sudden decrease in the amount of light incident on the image sensor 21 in step S107.
For this purpose, the determination unit 33 first compares the currently set exposure time T1 with the cycle T _VD of the vertical synchronization signal VD, and determines whether the exposure time T1 is longer than the cycle T _VD of the vertical synchronization signal VD. Thus, it is determined whether or not it is appropriate to set the newly calculated exposure time T0 as the cycle T _VD of the vertical synchronization signal VD. That is, the determination unit 33 compares the exposure time T1 with the cycle T _VD of the vertical synchronization signal VD set by the controller 3, and determines whether or not the following equation (3) is satisfied.

T _VD > S0 / S1 × T1 (3)
When the expression (3) is satisfied, the process proceeds to step S110, the exposure time T0 is calculated from the following expression (4), and the cycle T _VD of the vertical synchronization signal VD is set as a new exposure time.
T0 = 2 ^(N−1) × T _VD (4)

If the expression (3) is not satisfied, the process proceeds to step S111, and the exposure time T0 is calculated from the following expression (5) instead of setting the cycle _TVD as a new exposure time.
T0 = 2 ^(N−1) × T1 (5)
In the above equations (4) and (5), T0 is the new exposure time, N is the number of loops, and _TVD is the period of the vertical synchronizing signal of the imaging means.

In step S109, the exposure time calculation unit 34 calculates a new exposure time based on the determination that the signal level is saturated due to the sudden increase in the amount of light incident on the image sensor 21 in step S107.
For this purpose, the determination unit 33 first compares the currently set exposure time T1 with the cycle T _VD of the vertical synchronization signal VD, and determines whether the exposure time T1 is longer than the cycle T _VD of the vertical synchronization signal VD. Thus, it is determined whether or not it is appropriate to set the new exposure time T to be equal to or shorter than the cycle T _VD of the vertical synchronization signal VD.
That is, the determination unit 33 compares the exposure time T1 with the cycle T _VD of the vertical synchronization signal VD set by the controller 3, and determines whether or not the following equation (6) is satisfied.
T _VD <S0 / S1 × T1 (6)

As a result of the determination, if the expression (6) is satisfied, the process proceeds to step S112, and a new exposure time T0 is calculated based on the following expression (7).
T0 = 1 / (2 ^(N−1) ) × T _VD (7)
If the above equation (6) is not satisfied, the process proceeds to step S113, and a new exposure time T0 is calculated from the following equation (8).
T0 = 1 / (2 ^(N−1) ) × T1 (8)
Then, the new exposure time T0 calculated in step S105, step S110, step S111, step S112, and step S113 is replaced with the exposure time T1, and in step S102, the evaluation value S1 is obtained from the image data acquired at the exposure time T1. get.

More specifically, for example, in the case of switching from the objective lens A to the objective lens B, a flow until calculation of an appropriate exposure time will be described (see FIG. 6).
The appropriate exposure time when the objective lens A is inserted in the optical path is T1 (T1 ≦ T _VD ), and the image data is 8-bit gradation, the target signal level S0, the signal levels SL1, SL0, SH0, Assume that SH1 is S0 = 128, SL1 = 25, SL0 = 121, SH0 = 135, and SH1 = 230, respectively.

At the start of AE exposure control, the objective lens A is inserted in the optical path, and the exposure time during which image data of the target signal level can be acquired is T1 (T1 = 1/60 × T _VD ). Since the light is temporarily blocked when the objective lens is switched, the evaluation value S1 at this time is extremely small, and the new exposure time T is a long exposure time from the new exposure time T0 = (S0 / S1) × T1. It becomes. Here, T0 = 30 × T _VD .

Then, the new exposure time T0 is replaced with the exposure time T1, and exposure is started at the exposure time T1 = 30 × T _VD . The objective lens is switched and the objective lens B is inserted into the optical path. Since the amount of light incident on the image sensor has increased, the signal level of the image data captured at this time is saturated. As a result of calculating the evaluation value S1 from the image data, S1 = 255.
Since S1 ≧ SH1, it is determined that the amount of light incident on the image pickup device 21 increases rapidly and the signal level is saturated. Furthermore, when comparing the exposure time T1 and _{T VD} which image data is _acquired, since a T VD <(S0 / S1) × T1, equal to or less than _{T VD} new exposure time T0, T0 = (1 / 2 ^ (N−1)) × T _VD As a result of the calculation, T0 = _TVD .

Exposure is started at an exposure time T = T _VD , and image data is captured. As a result of calculating the evaluation value S1 from the image data, S1 = 128. It is determined that SL0 ≦ S1 ≦ SH0, and the exposure time calculation process is completed.
As described above, in the case of the present embodiment, when switching from the objective lens A to the objective lens B, it is necessary to obtain an appropriate exposure only by requiring 4 frames from the insertion of the objective lens B into the optical path until the calculation of an appropriate exposure time. Can do.

For reference, unlike the present embodiment, when a new exposure time is calculated without considering the relationship between the exposure time and the period of the vertical synchronization signal, the following is performed.
The appropriate exposure time when the objective lens A is inserted in the optical path is T1 (T1 ≦ T _VD ), and the image data is 8-bit gradation, the target signal level S0, the signal levels SL1, SL0, SH0, Assume that SH1 is S0 = 128, SL1 = 25, SL0 = 121, SH0 = 135, and SH1 = 230, respectively.

At the start of AE exposure control, the objective lens A is inserted in the optical path, and the exposure time during which image data of the target signal level can be acquired is T1 (T1 = 1/60 × T _VD ). Since the light is temporarily blocked when the objective lens is switched, the evaluation value S1 at this time is extremely small, and the new exposure time T is longer than the new exposure time T0 = (S0 / S1) × T1. It becomes. Here, T0 = 30 × T _VD .

Then, the new exposure time T0 is replaced with the exposure time T1, and exposure is started at the exposure time T1 = 30 × T _VD . The objective lens is switched and the objective lens B is inserted into the optical path. Since the amount of light incident on the image sensor has increased, the signal level of the image data captured at this time is saturated. For this reason, as a result of calculating the evaluation value S1 from the image data, S1 = 255. In this case, it is determined that SL0 ≦ S1 ≦ SH0 is not satisfied, T0 = 15 × T _VD is calculated as a new exposure time T0, the new exposure time T0 is replaced with the exposure time T1, and exposure starts at this exposure time T1. Is done.

As a result of calculating the evaluation value S1 from the image data captured with the exposure time T1 = 15 × T _VD , S1 = 255. As a result of calculating SH0 <S1 and calculating a new exposure time T0, T0 = 7.5 × T _VD is calculated, the new exposure time T0 is replaced with the exposure time T1, and the exposure time T1 = 7.5 × T Exposure starts with _VD .
As a result of calculating the evaluation value S1 from the captured image data, S1 = 255, and it is determined that SL0 ≦ S1 ≦ SH0 is not satisfied, and a new exposure time T0 = 3.75 × T _VD is calculated. The new exposure time T0 is replaced with the exposure time T1, exposure is started at the exposure time T1 = 3.75 × T _VD , and image data is acquired.

As a result of calculating the evaluation value S1, S1 = 255, and it is determined that SL0 ≦ S1 ≦ SH0 is not satisfied, a new exposure time T0 = 1.875 × T _VD is calculated, and exposure is started at this exposure time, and image data To get. The evaluation value S1 is calculated as S1 = 240, it is determined that SL0 ≦ S1 ≦ SH0 is not satisfied, T0 = T _VD is calculated, and exposure is started.
As a result of calculating the evaluation value S1 from the image data, S1 = 128, and it is determined that SL0 ≦ S1 ≦ SH0, and the exposure time calculation process is completed.
Thus, when switching from the objective lens A to the objective lens B, it takes 35 frames from the insertion of the objective lens B into the optical path to the calculation of an appropriate exposure time.

  As described above, according to the present embodiment, it is also determined whether or not the set exposure time is longer than the period of the vertical synchronization signal, and the new exposure time is set in consideration of the determination result. calculate. In this way, even when the amount of incident light on the camera (imaging device) suddenly decreases, an appropriate exposure time can be newly calculated and set, and the next time image data is acquired In addition, it is possible to obtain preferable image data converged to the target luminance value.

(Second Embodiment)
Hereinafter, a second embodiment of the present invention will be described.
In the present embodiment, in addition to the configuration in the first embodiment described above, the controller 3 includes a cumulative exposure time evaluation value calculation unit. The exposure time evaluation value calculation unit causes the storage unit 32 to store the exposure time calculated by the exposure time calculation unit 34 and set for each frame by the controller 3 in the past a predetermined number of times, for example, 50 exposure time information. . Further, the average value of the exposure time of a plurality of past times, the calculated average value and past exposure time T _P.
As past exposure time T _P, addition of the average value of the exposure time of a plurality of past times, the mode and the predetermined number of times in the past, may calculate the median value.

Hereinafter, the operation when the exposure time is calculated in the imaging system configured as described above will be described with reference to the flowchart of FIG. In the following description, it is assumed that the accumulated exposure time is set to the past 50 times.
In step S201, the accumulated exposure time evaluation value calculating unit detects for each frame, to store the exposure time of the last 50 times the storage unit, the past exposure time T _P by calculating the average value thereof, the storage unit And proceed to the next step S202.

In step S202, image data is acquired at the currently set exposure time T1, and an evaluation value S1 is acquired from the acquired image data. Note that the method for calculating the evaluation value S1 is the same as that in the first embodiment described above, and a description thereof will be omitted.
In the next step S203, it is determined whether the exposure time T1 is an appropriate exposure time based on the evaluation value S1 calculated in step S202. That is, the evaluation value S1 is compared with the signal levels SL0 and SH0 stored in the storage unit.

  If the result of determination in step S203 is SL0 ≦ S1 ≦ SH0, the exposure time calculation process is terminated. If SL0 ≦ S1 ≦ SH0 is not satisfied, it is determined that image data of the target signal level has not been acquired, and step The process proceeds to S204.

In step S204, the amount of deviation from the appropriate exposure time is determined, and the appropriate exposure time is calculated. That is, the evaluation value S1 is compared with the signal levels SL1 and SH1. When SL1 <S1 <SH1, since the signal level and the exposure time are in a proportional relationship, the process proceeds to step S205, and the exposure time calculation unit 34 sets a new exposure time T0 so as to achieve the target signal level S0. Calculated from the above equation (2).
On the other hand, if SL1 <S1 <SH1, it is determined that the amount of incident light on the image sensor 21 has changed significantly due to switching of the objective lens 11 or switching of the observation optical path of the trinocular tube 106, and the process proceeds to step S206.

In step S206, it is determined whether the amount of light incident on the image sensor 21 has changed greatly and the signal level of the image data is saturated or insufficient. The signal level comparison unit 302 compares the evaluation value S1 with an arbitrary signal level SH1.
When S1 ≧ SH1, that is, when S1 ≦ SL1, the process proceeds to step S207, where it is determined that the signal level is insufficient because the amount of incident light on the image sensor 21 has changed abruptly, and the exposure time is calculated. The unit 34 calculates a new exposure time T from the following equation (9).
_{T0 = S0 / S1 × T P} ··· (9)

On the other hand, when S1 ≧ SH1, it is determined that the signal level is saturated because the amount of light incident on the image sensor 21 has changed abruptly, and the process proceeds to step S208, where the exposure time calculation unit 34 performs a new exposure. exposure time T0 is calculated such that the time T0 = the last exposure time T _P.
In this way, even when the amount of incident light on the imaging means changes suddenly, an appropriate exposure time can be newly calculated and set, and the next time the image data is acquired, It is possible to obtain preferable image data converged to the luminance value.

DESCRIPTION OF SYMBOLS 1 Microscope main body 2 Camera 3 Controller 4 Display part 11 Objective lens 12 Revolver 13 Trinoculars 14 Eyepiece 21 Image pick-up element 22 Preprocessing part 23 Amplification part 24 A / D conversion part 31 Evaluation value calculation part 33 Determination part 34 Exposure time Calculation unit 40 Image processing unit

Claims (2)

An imaging means for capturing the image data by capturing the sample with a set exposure time;
Evaluation value calculation means for calculating an evaluation value based on a signal level of an arbitrary region in the image data;
Storage means for storing a first threshold value that is a reference value for determining that the amount of light incident on the imaging means has increased;
Determining means for determining whether the evaluation value is equal to or greater than the first threshold, and determining whether the exposure time is longer than a period of a vertical synchronization signal of the imaging means;
If the evaluation value is equal to or greater than the first threshold and the exposure time is longer than the period of the vertical synchronization signal as a result of the determination by the determination means, a new value equal to or less than the period of the vertical synchronization signal is obtained. An imaging system comprising exposure time calculating means for calculating an exposure time. The storage means stores a second threshold value which is a reference value for determining that the amount of incident light on the imaging means has decreased;
The determination unit determines whether the evaluation value is equal to or less than the second threshold, and determines whether the exposure time is longer than a period of a vertical synchronization signal of the imaging unit,
If the evaluation value is equal to or less than the second threshold value and the exposure time is shorter than the period of the vertical synchronization signal, the exposure time calculation means determines the vertical synchronization. The imaging system according to claim 1, wherein the period of the signal is calculated as a new exposure time.

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