JPH11146251A - Photographing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate the deficiency of exposure and also to obtain a photographic image uniform in brightness independently of the acceleration of illumination switching speed by providing a light source which radiates a subject with illumination light and performing on-off control the light source synchronously with an image pickup operation of an image pickup device. SOLUTION: The on-off of charge storage and light emission of a CCD are performed while line transfer is not performed in a drive stop period of a mirror. The storage period of the CCD is a period from the point of time of time up of a timer 0 to the on of the next line transfer signal ϕSG. Start time of the light generation is defined by a time 1, and end time is defined by a timer 2. The timer 1 is set so that time may be up after line transfer is finished and also before time of the timer 9 is up, and the light emission is turned on before the storage period starts. The timer 2 is set so that the time may be up just before the on of the next line transfer signal γSG, and the light emission is turned off just before the storage period is finished.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for photographing a subject by an imaging device represented by a CCD image sensor.

[0002]

2. Description of the Related Art In recent years, handheld digital cameras have been commercialized as easy image input means for personal use. Generally a two-dimensional imaging device (area sensor)
Many digital cameras of this type have a flash photography function similar to a silver halide camera.
On the other hand, a combination of a one-dimensional imaging device (line sensor) and a sub-scanning mechanism such as a mirror rotating mechanism is called a line sensor camera. The line sensor camera can capture a higher resolution image than a popular digital camera using an area sensor. For example, an entire document of about A4 size can be photographed so that characters of normal size can be read.

[0003]

However, line-sequential scanning requires a long shooting time for one frame. Therefore, the effect of camera shake is large in handheld shooting. If the speed of the sub-scanning is increased, the influence of camera shake is reduced, but the imaging time per line is shortened, so that the image quality (S / N ratio) is reduced due to insufficient exposure when the illuminance of the object surface is low. In particular, in indoor photography, the illuminance on the object surface is low. In addition, the influence of so-called flicker such as density unevenness and color unevenness due to an illumination light source represented by a fluorescent lamp also occurs.

As a countermeasure against such a problem, it is conceivable to provide a line sensor camera with a flash light source to compensate for the lack of illuminance. 1/1 required for scanning one frame
In order to maintain the illumination for about 0 seconds, a well-known flat light emitting technique for switching the power supply to the light source is suitable. If the switching is performed at a sufficiently high speed with respect to the line scanning cycle, it is possible to obtain a good captured image with no variation in brightness between lines. However, ultra-high-speed switching elements are expensive, and it is difficult to ensure the accuracy of switching control.

According to the present invention, in a case where line-sequential photographing is performed by intermittently driving a sub-scanning mechanism, an insufficient exposure is eliminated, and a photographed image having uniform brightness is obtained without increasing the speed of illumination switching. The purpose is to get.

[0006]

According to the present invention, the switching of the illumination is synchronized with the repetition of the photographing operation in line units or frame units. As a result, variations in brightness between lines or between frames are reduced. By making the brightness of the illumination variable, it becomes easy to optimize the exposure state. Further, if the amount of light emission is adjusted by measuring the brightness of the subject, the change in external light including flicker can be canceled, and the brightness of the subject during the shooting period can be stabilized.

According to a first aspect of the present invention, there is provided a photographing apparatus for photographing a subject line-sequentially by an image pickup device and an intermittent drive type sub-scanning mechanism. Illumination control means for performing on / off control of the light source in synchronization with the imaging operation.

According to a second aspect of the present invention, there is provided a photographing device, wherein the photometric means is provided, and the illumination control means turns off the light source when the light intensity reaches a set value after the light source is turned on.

In the photographing apparatus according to the third aspect of the present invention, the illumination control means causes the light source to emit light during a driving stop period of the sub-scanning mechanism.

[0010]

FIG. 1 is a diagram showing the configuration of a line sensor camera 1 to which the present invention is applied. The line sensor camera 1 is a handy type digital image input unit. A window 10a for guiding subject light inside is provided on the front surface of the housing 10, and a mirror 14 for sub-scanning is disposed behind the window 10a. Subject light is mirror 14
And is incident on the line sensor 11 through the lens unit 17 for image formation. By arranging the mirror 14 on the front side (subject side) of the imaging lens system in this manner,
The dimension of the housing 10 in the front-rear direction can be reduced.

The line sensor 11 is a color image pickup device composed of a CCD array, and converts a projected subject image into three colors of R, G, and B and converts it into an electric signal. Each pixel of the line sensor 11 is vertically arranged. As the line sensor 11, another imaging device (for example, a MOS imaging device) can be used instead of the CCD sensor.

The mirror 14 is attached to a rotation axis of a scan motor 15 which is a stepping motor, and this rotation axis is parallel to the pixel array direction (main scanning direction) of the line sensor 11. With the intermittent rotation of the mirror 14, the subject image is scanned in a sub-scanning direction orthogonal to the main scanning direction,
The light is projected onto the light receiving surface of the line sensor 11 one line at a time. That is, the mirror 14 and the scan motor 15 constitute the rotating mirror mechanism 13 as a sub-scanning unit. The shooting range (angle of view) in the sub-scanning direction is
4 depends on the rotation angle (the amount of rotation movement). The format of the sub-scan is not limited to the example, and a linear scanning format in which the line sensor 11 is moved in parallel with respect to the projection image can be adopted.

The lens unit 17 is of an in-focus type, and a part of the incident light is used for AF (auto focusing). An actuator 18 for electric zooming is attached to the lens unit 17. The actuator 18 has a built-in encoder that indicates the position of the movable lens. The finder 19 of the line sensor camera 1 is of an optical type.

A photometric sensor 51, a distance measuring sensor 54, and a light source (xenon lamp) 91 for illumination are mounted on an upper portion on the front side of the housing 10, and a release switch 63 and a mode switch 68 are disposed on the upper surface. .
The mode switch 68 is used for switching between a photographing mode including a document mode and a landscape mode.

FIG. 2 is a functional block diagram of a main part of the line sensor camera 1. As described above, the line sensor camera 1 mainly includes an imaging system 60 for scanning a subject image in a line-sequential manner, a signal processing system 80 for outputting photographing data of a predetermined format, and a CPU 71 having a microprocessor. And a lighting system 90 for optimizing the brightness of the subject.

The imaging system 60 includes a line sensor 11, a scan motor 15, a motor driving circuit 150, a lens driving circuit 180, and an imaging control circuit 120. The imaging control circuit 120 gives various signals (φCLK, φSG, etc.) to be described later to the line sensor 11.

The signal processing system 80 includes an analog processing circuit 81 for amplifying an input signal, an A / D converter 83 for sampling and holding the amplified photoelectric conversion signal and converting the amplified photoelectric conversion signal into photographing data of a predetermined number of bits (for example, 8 bits). , A digital processing circuit 85 for performing image correction, etc., and an interface 8 for transferring the processed photographing data D20 to an external device.
Consists of six. The external device includes an image editing device represented by a computer system, a storage medium including an IC card, and an image output device such as a printer display. It should be noted that a storage medium may be built in and the line sensor camera 1 may store shooting information. In this case, the stored information is transferred to the external device by data communication or transfer of the recording medium as appropriate.

The illumination system 90 includes a xenon lamp (discharge tube) 91 as a light source of the present invention, a lighting circuit 92, and a light emission control circuit 190. Light emission control circuit 190
In addition, the CPU 71 notifies the CPU 71 of a light emission amount suitable for the mode (zero if no illumination is required), and receives a line transfer signal φSG from the imaging control circuit 120 to synchronize switching of the light source with line-sequential imaging. Can be

FIG. 3 is a diagram showing a circuit configuration of the illumination system 90. The lighting circuit 92 includes a capacitor 93 for storing discharge energy, a trigger circuit 94 for inducing the discharge of the xenon lamp 91, and an IGBT (Insulated Gate Bipolar Transistor) 95 as a switching element for opening and closing the discharge path.
It is composed of The light emission control circuit 190 includes a controller 191, a switching driver 192, a comparator 193, and a photometry circuit 194.

The outline of the operation of the illumination system 90 is as follows. In response to the input of the light emission request signal S191 from the CPU 71, the controller 191 causes the comparator 193 to output a light emission control signal (switching signal) Ssw of a predetermined level.
And the IGBT 95 is turned on, and the trigger circuit 9
4 is instructed to start discharging. Xenon lamp 91
Starts emitting light, a part of the emitted light enters the photosensor 96 for light source photometry, and a detection signal S96 corresponding to the illumination intensity is input to the controller 191 via the photometry circuit 194. When the illumination intensity reaches the upper limit set according to the light emission amount DL notified from the CPU 71, the controller 191 sets the switching signal Ssw to non-active. As a result, the output of the comparator 193 is inverted, and the switching driver 192 turns off the IGBT 95. When light emission is repeated during the imaging of one line, the switching signal Ssw is activated when the illumination intensity decreases to the lower limit, and thereafter, the switching of the IGBT 95 is performed so that the illumination intensity becomes a value within the set range. Control is performed. In the case of “external light photometric format” in which the illumination intensity is adjusted according to a change in external light amount, instead of “light source photometric format” in which the illumination intensity is made constant, the photosensor 96 and the photometric circuit 194 can be omitted. Instead of the detection signal S96, a signal corresponding to the output of the photometric sensor 51 for measuring the subject luminance (sum of the illumination intensity and the external light intensity) is input to the controller 191.

FIG. 4 is a flowchart showing the general operation of the CPU 71 of the control system 70. When the battery is mounted and the control power is turned on, the CPU 71 performs initialization (# 1) of various control registers and the like and initial adjustment (# 2) of a control target, and waits for a switch operation.

When the user operates the main switch 61, if the main switch 61 is in the ON state and the apparatus is being started, an OFF operation process for cutting off the supply of the drive current to the control object is performed. An ON operation process for supplying a drive current is performed (# 3 to # 6). When the mode switch 68 is operated during the startup, the mode setting is switched in a circulating manner (# 7, # 8). In this embodiment,
A document mode suitable for recording character information and a landscape mode suitable for recording a natural image are provided. Then, when the user operates the release switch 63 to instruct the start of shooting, a release operation is performed (# 9, # 10).

FIG. 5 is a flowchart of the release operation subroutine of FIG. The outputs of the photometric sensor 51 and the distance measuring sensor 54 are taken in, and the brightness (illuminance) of the object and the distance between the objects in the light-off state are measured (# 51), and the mode is checked (# 52). Since the effect of camera shake is more serious in document shooting than in landscape shooting, the document mode in which high-speed sub-scanning is performed is suitable. In the case of the document mode, the illumination is always performed to increase the S / N ratio. Then, based on the results of the photometry and the distance measurement, the light emission amount DL is calculated so that the exposure of the line sensor 11 is not excessive or insufficient, and the calculated value is notified to the controller 191 of the illumination system 90. On the other hand, in the case of the landscape mode, the light emission amount DL is calculated when the brightness of the subject is equal to or less than a certain value and the distance between the objects is equal to or less than a certain value, that is, when illumination is required and effective illumination is possible. (#
53- # 55). When lighting is performed in either of the modes, the controller 191 notifies the user of the light emission amount DL.
To start light emission (# 56), and the motor drive circuit 150
Then, it instructs the imaging control circuit 120 to start the imaging operation (# 57).

Subsequently, an accumulation period timer (hereinafter, referred to as a timer 0) for setting an effective integration time of the CCD in a photographing period for one line (line cycle 1H) is set (# 5).
8), charge accumulation is started when the timer 0 times out (# 59). After that, the CCD integration is terminated after the scanning start timing of the next line (on-edge of the line transfer signal φSG) arrives (# 60, # 61), and the line for reading one line of photoelectric conversion information from the line sensor 11 The transfer is controlled (# 62). Such line sequential scanning control is repeated (# 63), and when the photographing of a predetermined number of lines is completed, the drive of the line sensor 11 and the scan motor 15 is stopped (# 64), and thereafter, the light emission stop is instructed to the controller 191. (# 65).

In the line sensor camera 1 having the above configuration, in order to obtain a photographed image without uneven brightness, the IGB
Light emission control unique to the present invention, which synchronizes the switching of T95 with the operation of the line sensor 11, is performed. Hereinafter, an operation of the line sensor 11 and an example of light emission control will be described.

FIG. 6 is a configuration diagram of the line sensor 11, and FIG. 7 is a time chart showing the basic operation of the line sensor 11. As shown in FIG. 6, the line sensor 11 has an overflow drain 111, a shutter gate 112, a charge storage unit 113, a shift gate 114, an analog shift register 115, a clock pulse generator 116, and an output amplifier 117.

The shutter gate 112 is provided for discharging unnecessary accumulated charges to the overflow drain 111 so as to make the actual integration time variable, and is controlled by a shutter signal SHUT. The photoelectric conversion during the accumulation period from the off edge of the shutter signal SHUT to the on edge of the line transfer signal φSG that defines the line cycle (1H) is effective. When the line transfer signal φSG is input to the shift gate 114, the charges of the respective pixels charged in the charge storage unit 113 are simultaneously transferred to the analog shift register 115. The charge is the pixel transfer clock φC
The data is transferred to the output amplifier 117 in the order of pixel arrangement in synchronization with LK, and output to the signal processing system 80 as a photoelectric conversion signal.
As shown in FIG. 7, the reading of the charges accumulated in response to a certain line transfer signal φSG (line transfer) is started in response to the next line transfer signal φSG.

FIGS. 8 and 9 are time charts showing examples of light emission control. In these examples, the mirror 14 is intermittently rotated (step-driven) by a predetermined angle in synchronization with the line transfer signal φSG, and at the same time, a signal is read from the line sensor 11 (line transfer). C
The charge accumulation on the CD is performed while the mirror 14 is stopped. Then, the IGBT 95 is turned on during a blanking period of the line transfer in the drive stop period of the mirror 14 (that is, a period during which the line transfer is not performed). This is because if the IGBT 95 is switched during the line transfer, the line transfer synchronized with the high-frequency clock may be disturbed by the switching noise generated particularly when the IGBT 95 is turned on, and the image quality may be degraded.

In this embodiment, the accumulation period of the CCD is a period from the time when the timer 0 times up to the time when the next line transfer signal φSG is turned on. The start time of light emission is defined by the timer 1, and the end time is defined by the timer 2. Each of these timers 0, 1 and 2 starts counting from the on-edge of the line transfer signal φSG.

In the example of FIG. 8, the timer 1 is set to expire after the end of the line transfer and before the timer 0 expires, and the light emission is turned on before the start of the accumulation period. The timer 2 is set to time-up immediately before the next line transfer signal φSG is turned on, and light emission is turned off immediately before the end of the accumulation period.

In the example of FIG. 9, the timer 1 is set so as to time up after the end of the line transfer and before the time up of the timer 0, and the light emission is turned on before the start of the accumulation period. The timer 1 is set to be short so as to emit light earlier when the required light emission amount is large, and set to be long so as to delay light emission when the required light emission amount is small. Timer 2 is set to expire before timer 0 expires, and light emission is turned off before the accumulation period starts. In other words, imaging is performed under illumination of gradually attenuating afterglow.

The use of the control in FIG. 8 and the control in FIG.
It is determined by various conditions such as the light emission waveform characteristics, the required light emission amount, and the length of the accumulation period. For example, if the accumulation period is long,
Since the light quantity becomes excessive in the control of FIG. 8, the control of FIG. 9 is more suitable.

FIG. 10 shows a controller 191 of the illumination system 90.
9 is a flowchart of light emission control corresponding to FIG. In response to a light emission start request from the CPU 71, the light amount setting (# 301), the IGBT 95 is turned on (# 303), and the light emission trigger is turned on (# 303). Thereafter, the control of starting light emission by the timer 1 and stopping the light emission after the illumination intensity reaches the upper limit value and the timer 2 times out is repeated in synchronization with the line transfer signal φSG (# 304 to # 311). ). When the light emission stop is instructed from the CPU 71, the IGBT 95 is turned off and stands by (# 31).
2, # 313).

FIG. 11 is a flowchart of light emission control corresponding to FIG. In response to the light emission start request from the CPU 71, the IGBT 95 is turned on (# 401) and the light emission trigger is turned on (# 402). Thereafter, the control of starting light emission by the timer 1 and stopping light emission by the timer 2 is repeated in synchronization with the line transfer signal φSG (# 40).
3 to # 408). When the light emission stop is instructed from the CPU 71, the IGBT 95 is turned off and stands by (# 409, # 4).
10).

FIG. 12 is a diagram for explaining the relationship between the light emission waveform and the aperture shape. The physical aperture (imaging window) AP0 of each pixel of the line sensor 11 is substantially rectangular. In the case of the step drive in which the scan motor 15 is intermittently rotated, assuming that the subject brightness is constant over one line cycle, the aperture AP1 taking into account the relative position change with the subject in one line cycle becomes a triangle. The substantial aperture AP2 is a rectangle having the same width as the aperture AP0, though the height is lower than the aperture AP0 because the emission waveform is not rectangular. If the waveform is controlled so that the light emission amount becomes uniform, the area of the aperture (aperture ratio) increases.

According to the above-described embodiment, when the illuminance of the object surface is low, the shortage of the exposure can be solved without extending the photographing time, and high-quality imaging with a good SN ratio can be realized regardless of the illuminance of the object surface. it can. Illumination can be performed only when needed to prevent unnecessary power consumption and overexposure.
Irrespective of the presence or absence of a change in external light during photographing, it is possible to obtain a photographed image without uneven brightness. By synchronizing the line-by-line imaging and the switching light emission, the light emission waveforms of the respective lines during the charge accumulation period can be made uniform, and uneven light quantity between the lines can be prevented. By performing light emission control using the same type of signal (clock) as line sensor control, it is possible to reduce the effect of electromagnetic noise of switching light emission on image quality,
The timing control circuit can be simplified. If light emission is stopped during periods other than the accumulation period, energy for light emission can be effectively used.

In the above embodiment, a linear scanning mechanism for moving the line sensor 11 in parallel may be used as the sub-scanning means. In addition, camera structure, electric circuit configuration,
The operation sequence and the like can be appropriately changed according to the gist of the present invention.

[0038]

According to the first to third aspects of the present invention,
In the case where line-sequential photographing is performed by intermittently driving the sub-scanning mechanism, insufficient exposure can be eliminated, and a photographed image with uniform brightness can be obtained without increasing the speed of illumination switching.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a line sensor camera to which the present invention is applied.

FIG. 2 is a functional block diagram of a main part of the line sensor camera.

FIG. 3 is a diagram illustrating a circuit configuration of an illumination system.

FIG. 4 is a flowchart illustrating a schematic operation of a CPU of a control system.

FIG. 5 is a flowchart of a release operation subroutine of FIG. 4;

FIG. 6 is a configuration diagram of a line sensor.

FIG. 7 is a time chart illustrating a basic operation of the line sensor.

FIG. 8 is a time chart illustrating an example of light emission control.

FIG. 9 is a time chart illustrating an example of light emission control.

FIG. 10 is a flowchart of light emission control corresponding to FIG. 8 executed by a controller of the illumination system.

FIG. 11 is a flowchart of light emission control corresponding to FIG.

FIG. 12 is a diagram for explaining a relationship between a light emission waveform and an aperture shape.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 line sensor camera (photographing device) 11 line sensor (one-dimensional imaging device) 13 rotating mirror mechanism (sub-scanning mechanism) 51 photometric sensor (photometric means for detecting brightness of subject) 91 xenon lamp (light source) 96 photosensor ( Light metering means for detecting the brightness of the light source) 120 Imaging control circuit (Imaging control means) 191 Controller (Illumination control means) 1H Line cycle (Imaging cycle of one line) Lu Upper limit value (Set value) φSG Line transfer signal (Imaging cycle) Signal that specifies

Claims (3)

[Claims] An imaging apparatus for sequentially photographing a subject by an imaging device and an intermittent drive type sub-scanning mechanism, wherein the light source irradiates the subject with illumination light, and an imaging operation of the imaging device is synchronized. A photographing apparatus, comprising: an illumination control unit that performs on / off control of the light source. 2. The photographing apparatus according to claim 1, further comprising photometric means, wherein the illumination control means turns off the light source when the light intensity reaches a set value after the light source is turned on. 3. The photographing apparatus according to claim 1, wherein said illumination control means causes said light source to emit light during a driving stop period of said sub-scanning mechanism.