JP4314724B2 - Imaging apparatus and exposure control management method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an imaging apparatus and an exposure control management method.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, in an imaging apparatus using an imaging element such as a CCD, exposure control for automatically controlling exposure at the time of imaging according to the brightness of a subject is generally performed. In addition, when controlling the exposure time (charge accumulation time) of the CCD by the CPU during exposure control, the vertical synchronization signal of the imaging signal is used as a trigger signal for the end of one screen frame exposure or image data transfer. Control is performed by calculating the exposure time of the next frame at the timing. A specific example is shown in FIG. In this example, the CPU performs exposure time control using the falling edge of the vertical synchronizing signal as a trigger. The CPU receives the falling edge of the vertical synchronizing signal, and at the timing, the next result from the imaging result of the n-1 frame. The exposure time of n frames is calculated and set in the driving means of the image sensor. For example, when the exposure result at n−1 is recognized as “too dark”, the driving unit sets the exposure time for the next n frames to be longer. This makes it possible to perform exposure control according to the brightness of the subject.
[0003]
[Problems to be solved by the invention]
However, when a vertical synchronization signal or the like is used as a trigger signal for control timing as described above, an appropriate process is possible if the CPU that performs exposure control can perform processing at the timing when the trigger signal is received. When the CPU is controlling an imaging device on a system that is incorporated in a multifunctional system such as a personal computer, or when the CPU is controlling an imaging device incorporated in a portable information device, Problems arise.
[0004]
For example, as shown in FIG. 5, when the CPU is notified of the falling edge of the vertical synchronization signal and is required to perform exposure control, when another task with higher priority than such control is being executed. The next exposure time cannot be set before the rising edge of the n-frame vertical synchronization signal when the imaging device (imaging device) starts exposure of the next n frames, and the exposure result is “too dark” in n−1 frames. Even if it is determined, the timing at which the next exposure time is reflected is n + 1 frames. In other words, depending on the load status of the CPU, it may not always be possible to actually control the exposure time or the like at the timing of the trigger signal, and as a result, inconsistency occurs between the actual captured image and the exposure control. Of course, in order to avoid the occurrence of such a situation, for example, a large margin for the period of the imaging control by the CPU may be taken, but in that case, the responsiveness of the imaging control deteriorates. Therefore, it is difficult to ensure both controllability and responsiveness.
[0005]
The present invention has been made in view of such a conventional problem, and it is possible to ensure the controllability and responsiveness of exposure control at the same time even when the imaging apparatus constitutes a system with another apparatus. An object of the present invention is to provide an imaging device and an exposure control management method that can be used.
[0006]
[Means for Solving the Problems]
In order to solve the above problem, in the imaging apparatus according to claim 1, an imaging unit that images a subject, an exposure control unit that performs exposure control according to the brightness of the subject, and a previous time by the exposure control unit Timing supply means for supplying execution timing of next exposure control to the exposure control means at a predetermined time when the exposure control result is reflected in the image taken by the imaging means, and the exposure control means includes the When the exposure control is started based on the execution timing supplied by the timing supply means and the exposure time is set in the imaging means, if the imaging means is under exposure, a new exposure time is set after the end of the exposure. It was supposed to be set .
[0008]
In the image pickup apparatus according to claim 2, the timing supply unit supplies the execution timing of the next exposure control to the exposure control unit on the basis of the time when the previous exposure control is executed by the exposure control unit. It was supposed to be.
[0009]
In the image pickup apparatus according to the third aspect, the predetermined time is a time when the transfer of the picked-up image reflecting the previous exposure control result ends.
[0010]
The exposure control management method according to claim 4 is a method for managing exposure control in an imaging apparatus, wherein the imaging apparatus is under exposure when setting an exposure time according to the brightness of a subject. In some cases, exposure control is performed so that a new exposure time is set after the exposure is completed , and the next exposure control is performed at a time when the previous exposure control result is reflected in the captured image.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing an imaging apparatus according to the present invention.
[0013]
That is, the imaging lens 1 forms an optical image of the subject on the photosensitive surface of the CCD 2. The formed optical image is photoelectrically converted by the CCD 2 and output as an analog imaging signal. The output imaging signal is digitally converted by the A / D converter 3, processed by the color processor 4, and transferred to the memory 5. The CCD 2 is supplied with various clock signals including a vertical drive signal from the timing generator 6, and is controlled in charge accumulation time, that is, exposure time, and readout of signal charges. The timing generator 6 includes a register for storing an exposure time control parameter sent from the CPU 7, and changes the exposure time based on the control parameter. In accordance with the control program stored in the ROM 8, the CPU 7 controls each unit described above using the RAM 9 as a working memory, calculates the exposure time based on the luminance information included in the captured image data transferred to the memory 5, and accordingly Exposure control is performed by setting a control parameter in the register of the timing generator 6.
[0014]
The timing generator 6 is configured to send an exposure control request signal to the CPU 7 at a predetermined time corresponding to the time when the register control parameters are rewritten by the CPU 7. That is, in the present embodiment, when the control parameter is rewritten at a time when the next vertical drive signal is not yet in the rising state, the second vertical drive signal rising after that time is written. When the exposure control request signal is sent at the time of falling and the time when the control parameter is rewritten is the time when the next vertical driving signal is already in the rising state, the third vertical driving signal after that time The exposure control request signal is set to be sent at the falling edge (see FIG. 3).
[0015]
FIG. 2 is a flowchart showing the operation related to the exposure control of the CPU 7 in the above configuration. The CPU 7 sets a preprogrammed control parameter in the register of the timing generator 6 at the beginning of the control (step). S1). Thereafter, an exposure control request signal is waited for from the timing generator 6 (step S2). When the exposure control request signal is sent (YES in step S3), the luminance information sent from the color processor 4 is added to the luminance information. Based on the calculation of an exposure time for obtaining an appropriate exposure based on the calculation result, a control parameter necessary for imaging the next frame is calculated according to the result (step S4), and the calculated control parameter is sent to the register of the timing generator 6 The setting contents are rewritten (step A5). Thereafter, the above operation is repeated to perform exposure control according to the brightness of the subject.
[0016]
On the other hand, FIG. 3 shows a case where the above-described imaging device is incorporated in a multifunctional system such as a personal computer, and when the CPU 7 controls such a system, or the imaging device is incorporated in a portable information device. It is the figure which showed the execution timing of exposure control in the case where is controlled. In this case, the waiting operation of the exposure control request signal in step S2 (FIG. 2) of the CPU 7 is performed by an interrupt process set with a higher priority than other tasks other than the exposure control. To do.
[0017]
In FIG. 3, the control parameter required for the exposure control is set by the CPU 7 at a certain time (timing (1)), and the control result based on the control parameter is reflected in the n-2 frame immediately after that. The time for transferring the image data of the n-2 frame to the color processor 4 is a period until the next n-1 frame is exposed, that is, 2 of the vertical drive signal after the previous control parameter is set. This is the period up to the time of falling for the second time (the timing of (2)). Therefore, the CPU 7 receives the exposure control request signal from the timing generator 6 when the transfer of the image data of the n-2 frame is completed, and shifts to the calculation of the exposure time of the next frame and the control parameter setting operation. It becomes. However, the timing for such an operation varies depending on the status of other tasks undertaken by the CPU 7.
[0018]
In the example shown in the figure, when an exposure control request is generated at the time of the fall of the vertical drive signal described above (the timing of (2)), the CPU 7 is executing another task, and the task is finished and actually This is a case where the timing for starting the exposure control process is delayed until the time point when the imaging of the next n frames is already started (timing (3)). In this case, the newly set exposure time is not reflected in the n frame already being imaged, but is reflected in the next n + 1 frame. Accordingly, the three frames from the n-2 frame to the n frame are imaged with the same exposure time (exposure state).
[0019]
On the other hand, the setting operation of the control parameter related to the exposure control reflected in the (n + 1) th frame is the time when the imaging of the nth frame is already started, that is, the time when the vertical drive signal is already in the rising state. The timing when the exposure control request signal 6 is issued is the time when the vertical drive signal falls for the third time (timing (4)) after the time when the above control parameter setting operation is performed (timing (3)). Become. That is, it is the time when the transfer of the image data of n + 1 frame is completed, and the time when the exposure of n + 2 frame is completed. Here, as shown in the figure, when the CPU 7 is in an idle state, the CPU 7 immediately reacts to the sent exposure control request signal, and the time point before the exposure of n + 3 frames is started (timing (5)). Then, the process proceeds to the calculation of the exposure time and the setting operation of the control parameter, and it can be completed. For this reason, imaging with the same exposure time (exposure state) is performed for the n + 1 frame and the n + 2 frame, and the result of the exposure control based on the newly set control parameter is reflected in the n + 3 frame. It will be. After that, when the exposure of n + 4 frames is completed, an exposure control request signal is sent from the timing generator 6 to the CPU 7.
[0020]
As described above, in the image pickup apparatus according to the present embodiment, even if the time from when the CPU 7 receives the exposure control request signal until when the exposure control is actually executed varies depending on the load state of the CPU 7, the timing generator Since the time when the exposure control request signal 6 is sent is the time when the result of the previous exposure control is reflected in the image data, the next exposure control is always performed based on the correct information reflecting the previous control content. Is possible. Therefore, it is possible to ensure matching between the actual captured image and the exposure control. Moreover, the exposure control interval is the shortest time according to the load state of the CPU 7 at that time. Therefore, both controllability and responsiveness can be ensured.
[0021]
In the present embodiment, the timing generator 6 is the timing supply means of the present invention, and the time when the control parameter of the register is rewritten by the CPU 7 is used as a reference, and the result of the previous exposure control is reflected. In this example, the exposure control request signal is sent to the CPU 7 at the time when the transfer of the image data is completed. However, in addition to this, when the result of the previous exposure control by the CPU 7 is reflected in the captured image. If an exposure control request signal can be sent to the CPU 7 at a corresponding predetermined time, other timing supply means may be provided.
[0022]
In this embodiment, the CPU 7 controls only the exposure time (charge accumulation time of the CCD 2). However, the CPU 7 controls the aperture value and gain control of the output signal of the CCD 2 in addition to this. Even when exposure control including the above is performed, the execution timing of the next exposure control is supplied as described above at a predetermined time corresponding to the time when these settings are reflected in the captured image. The same effect as the form can be obtained.
[0023]
In addition, mainly the case where the imaging device constitutes a multifunctional system such as a personal computer, or the case where the CPU 7 is incorporated in another device such as a portable information device and the CPU 7 controls such a system or device has been described. However, in addition to this, the image pickup apparatus is provided with a number of additional functions, and the same effect can be obtained even when the CPU 7 needs to execute a task having priority over exposure control.
[0024]
【The invention's effect】
As described above, in the present invention, even when there is a delay in exposure control, it is possible to always perform exposure control based on correct information that reflects the immediately preceding control content. And alignment can be ensured between exposure control. Moreover, the exposure control interval is set to the shortest time according to the state at that time. Therefore, even when the imaging apparatus constitutes a system with another apparatus, it is possible to ensure both controllability and responsiveness of exposure control of the imaging apparatus.
[Brief description of the drawings]
FIG. 1 is a block diagram of an imaging apparatus showing an embodiment of the present invention.
FIG. 2 is a flowchart showing an operation related to exposure control of a CPU.
FIG. 3 is a timing diagram of exposure control when the imaging apparatus is incorporated in another system.
FIG. 4 is a timing diagram of exposure control showing the prior art.
FIG. 5 is a timing diagram of exposure control showing the problems of the prior art.
[Explanation of symbols]
2 CCD
4 color processor 6 Timing generator 7 CPU
8 ROM

Claims (4)

Imaging means for imaging a subject;
Exposure control means for performing exposure control according to the brightness of the subject;
Timing supply means for supplying the exposure control means with the next exposure control execution timing at a predetermined time when the previous exposure control result by the exposure control means is reflected in the image captured by the imaging means ;
The exposure control means starts exposure control based on the execution timing supplied by the timing supply means, and sets the exposure time for the imaging means when the imaging means is under exposure. An imaging apparatus , wherein a new exposure time is set after completion .   2. The imaging apparatus according to claim 1, wherein the timing supply means supplies the next exposure control execution timing to the exposure control means based on a time point when the previous exposure control is executed by the exposure control means.   3. The imaging apparatus according to claim 1, wherein the predetermined time is a time when transfer of a captured image reflecting a previous exposure control result is finished. A method for managing exposure control in an imaging device, wherein when setting the exposure time according to the brightness of a subject, if the imaging device is under exposure, a new exposure time is set after the exposure is completed. An exposure control management method characterized in that the next exposure control is performed at a time when the exposure control is performed and the previous exposure control result is reflected in the captured image.

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