JPH0888796A - Photographing device - Google Patents

Abstract

PURPOSE: To prevent uneven exposure by setting a frequency of an AC power supply driving a light source for photography to a prescribed ratio with respect to a frequency driving an image pickup element. CONSTITUTION: A lighting light source 10 driven by an AC lamp power supply 11 lights an image film 12 being an object. An image pickup element 15 comprising a CCD converts an optical image formed via an image pickup lens 13 into an electric signal and provides an output of an image pickup signal via an image pickup circuit 16. A timing circuit (TG) 17 controls a drive timing of the image pickup element 15 and simultaneously controls a drive phase of the lamp power supply 11 via a synchronization changeover circuit 18a. When an exposure time of the photographing device is selected, a CPU 18 decides a drive clock of the image pickup element 15 accordingly and the clock is fed to the image pickup element 15 and the synchronization changeover circuit 18a via the TG 17. Since a cycle of a change in the luminous quantity of the light source 10 is coincident with that of the image pickup timing, the fluctuation in the level of the image pickup signal is reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a photographing device, more specifically,
An exposure unevenness prevention method and other performance for an image pickup apparatus to which an AC-driven light source is applied, such as resolution, S / N. The present invention relates to a method for preventing deterioration such as shading.

[0002]

2. Description of the Related Art Conventionally, as a light source used as a light source of an image pickup apparatus using a solid-state image pickup device, there is an AC drive type light source. There is a change in the amount of light in the AC driven light source, for example, light from a light source such as a metal halide lamp or a fluorescent lamp on the time axis. Generally, such light is called ripple light. FIG. 10 is a time chart of a light source drive signal, a light source light amount, and an image pickup signal of the AC drive system. As shown in this figure, the light amount waveform includes a ripple component in synchronization with the light source drive signal.

When an image is picked up by a CCD, which is an image pickup device, using the light source having the ripple light, the relationship between the ripple frequency of the light source and the exposure time of the image pickup circuit, for example, the shutter speed when an area sensor is applied. Due to the relationship, exposure unevenness occurs in the imaging output. For example, as the exposure unevenness, flicker may occur in the case of an area sensor, and streaks in the main scanning direction may occur in the case of a line sensor (see FIG. 11 described later).

The time chart of FIG. 10 also shows the change state of the image pickup signal level with respect to the change of the image pickup timing and the light amount of the light source. The high level and low level of the image pickup timing according to the image pickup timing shown in this figure. Each level period becomes an imaging period, and an imaging signal is captured. In the case of this figure, the period of the imaging timing is smaller than the ripple frequency of the light source, and the level of the imaging signal is low at the timing when the level of the light source light amount is low during the imaging period. This appears as the exposure unevenness.

FIG. 11 is a diagram showing the stripes of the image pickup screen due to the above-mentioned uneven exposure when a line sensor is used.
As shown in the figure, the two-dimensional image pickup screen 101 is obtained by scanning the line sensor 102 in one direction, that is, the sub-scanning direction. The axial direction of the line sensor 102 is the main scanning direction. In FIG. 10, when the image pickup signal level becomes low due to the image pickup unevenness as described above, black streaks 101a are formed on the image pickup screen 101 along the main scanning direction. It should be noted that white streaks occur in the main scanning direction at portions where the level of the image pickup signal is high.

Conventionally, as a measure against the occurrence of this exposure unevenness,
By changing the exposure time of the image pickup circuit, the exposure unevenness of the output, in the above example, the occurrence of flicker was prevented. For example, the one proposed in the flicker prevention system for a solid-state image pickup device disclosed in Japanese Patent Laid-Open No. 61-56915 prevents flicker by controlling the exposure amount by a lens diaphragm and electrically controlling the gain.

Here, a conventional image pickup device to which the CCD which is the solid-state image pickup device is applied will be described. Figure 12
FIG. 3 is a schematic block configuration diagram of the imaging device. In the present photographing device, the light of the light source 110 driven by the lamp power supply circuit 111 illuminates the film 112 as a subject. The subject light that has passed through the film 112 passes through the taking lens 113 and the diaphragm 114, and the CC
An image is formed on the image plane of D115. CCD115 is TG
The drive timing is controlled by the (timing) circuit 117, and the image pickup signal is subjected to processing such as gain control in the image pickup circuit 116 and output as an image pickup signal.

[0008]

However, in the flicker prevention system of the image pickup apparatus disclosed in Japanese Patent Laid-Open No. 61-56915 mentioned above, the exposure time, that is, the shutter speed is changed according to the ripple frequency. There was a drawback that the exposure time could not be selected. Further, when the exposure amount is controlled by the lens diaphragm, the lens is MTF depending on the diaphragm value.
Since (MODULATION TRANSFER FUNCTION) and the peripheral light amount change, the resolution characteristic and the shading characteristic change in the image formation information, and there is also a drawback that the image is picked up at almost or other than the best point. Further, when correcting shading, there is a drawback that a complicated circuit is required because the shading amount changes depending on the aperture value.

Now, changes in the MTF of the lens and the peripheral light amount depending on the aperture value will be described. FIG. 13 shows a change in MTF with respect to the spatial frequency in the photographing lens with a diaphragm as a parameter, and a deep diaphragm Ma 1 and an open diaphragm Mb of the diaphragm,
It is shown for the best aperture M0. Further, FIG. 14 is a diagram showing a change of the MTF at a certain frequency with respect to the diaphragm. As shown in the figure, the diaphragm opening side is deteriorated by aberration, and the deep diaphragm is deteriorated by diffraction phenomenon. Point P indicates the optimum position.

Next, the peripheral light amount drop of the image pickup screen will be described. FIG. 15 shows the change of the light amount on the CCD image forming surface. As shown in the figure, the image height 0 indicating the center is bright, and the amount of light decreases toward the image height 1 indicating the periphery.
FIG. 16 is a diagram showing a change in the amount of light at a predetermined position of the image height from the aperture open to the deep aperture. As shown in the figure, when the diaphragm is opened, the peripheral light amount further decreases.

As described above, it is understood that the MTF of the lens and the amount of peripheral light greatly change depending on the state of the diaphragm. Therefore, if the exposure unevenness due to the ripple of the light source is adjusted by the diaphragm, it will affect the MTF and the peripheral imaging screen state.

In addition, when the exposure amount control is performed by the electric gain control, the noise component in the signal is increased as well as the signal gain is increased, which causes a drawback of S / N deterioration. FIG. 17 is a diagram showing changes in the image pickup signal level before and after the gain correction, but as shown in this figure, the noise component is also amplified by the amplification during the gain correction.

The present invention has been made in order to solve the above-mentioned problems, and in an image pickup apparatus utilizing an AC drive power supply, it is possible to prevent the occurrence of exposure unevenness in the image pickup output when taking an image and to obtain a desired exposure. It is an object of the present invention to provide an image pickup apparatus capable of selecting time and preventing deterioration of other performances such as resolution, S / N, and shading.

[0014]

According to the present invention, there is provided an image pickup apparatus, wherein a power source driving means for driving a light source for projecting light for illuminating a subject by an alternating current, and an image pickup for obtaining a video signal corresponding to the image of the subject. The image pickup device driving means for driving the device, and the synchronization adjusting means for providing a predetermined periodic relationship between the driving phase of the image pickup device by the image pickup device driving means and the AC driving phase of the light source by the power supply driving means are provided. Is characterized by.

[0015]

By the synchronization adjusting means, image pickup is performed in a state in which a predetermined periodic relationship is established between the driving phase of the image pickup element by the image pickup element driving means and the AC driving phase of the light source by the power source driving means.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic block configuration diagram of an image pickup apparatus showing a first embodiment of the present invention. The photographing apparatus of the present embodiment has an AC drive light source 10 for illuminating an object, which is driven by a lamp power supply circuit 11 as an AC drive power supply driving means, and the light from the light source 10 is an image of an object. Film 1
2 is irradiated.

The subject light transmitted through the film 12 passes through the taking lens 13 and the diaphragm 14 and forms an image on the image forming surface of the CCD 15 as an image pickup device. CCD 15
The drive timing is controlled by a TG (timing) circuit 17 as an image pickup device driving unit, and the image pickup signal is subjected to processing such as gain control in the image pickup circuit 16 and output as an image pickup signal. The TG circuit 17 has a CPU 18 to which shutter speed information and mode setting information are input.
The above timing is controlled by.

It should be noted that the CPU 18 controls the drive phase of the AC drive light source 10 based on the mode setting information.
A synchronization switching circuit 18a, which is a synchronization relation switching means for selecting whether to turn on in synchronization with the CD drive phase or to turn on in an asynchronous state, is built in.

The lamp power supply circuit 11 has a built-in synchronization circuit 11a as a synchronization adjustment means. The synchronization circuit 11a has the TG circuit 17 when the mode setting is set to the synchronous drive side. Output by CCD
The light source 1 is synchronized with the drive phase related to the exposure timing of 15.
The lamp power supply circuit 11 is driven so that the lighting drive of 0 is performed. That is, the lamp drive timing of the AC drive light source 10 is adjusted to the exposure time of the image pickup circuit 16.

Specifically, the driving clock of the CCD 15 which is determined by selecting the exposure time of the photographing device is also sent to the lamp power supply circuit 11. The lamp power supply circuit 11 creates a light source drive clock signal synchronized with the drive clock of the CCD 15 that has been sent, and supplies it to the light source 10. The light source 10 emits light according to the light source drive clock signal.

FIG. 2 is a time chart showing the waveforms of the light source side drive signal and the light amount with respect to the CCD side image pickup timing.
It is As shown in the figure, the light source drive signal of the lamp power supply circuit 11 is matched with the clock for starting the exposure with reference to the image pickup timing of the CCD drive signal. As a result, the cycle of change in the light amount of the light source 10 coincides with the image pickup timing, the fluctuation in the level of the image pickup signal is reduced, and the image pickup output is not affected by the ripple of the light source.

In the image pickup apparatus of this embodiment, the image pickup timing of the CCD drive signal and the frequency ratio of the light source drive signal are set to 1: 1. As a modification, the frequency of the light source drive signal with respect to the image pickup timing frequency is set. Is also n times or n- (1/2) times, the fluctuation of the level signal of the image pickup signal can be suppressed, and uneven exposure due to ripple light can be eliminated.

If the asynchronous drive mode is set for the CPU 18, as shown in FIG.
The light source 10 is driven at a relatively high frequency with respect to the frequency of the imaging timing of the CD drive signal. Also in this case, the light source 1
Since the ripple component of 0 is averaged, the fluctuation in the level of the image pickup output of the CCD 15 is small and the uneven exposure is small. However, when the image pickup circuit 16 operates with a high-speed shutter, the light source 10 is driven at a considerably high speed.

In the image pickup apparatus according to the first embodiment of the present invention described above, the ripple countermeasure is performed by changing the frequency of the light source 10, so that a desired exposure time can be selected as the image pickup apparatus. Since the exposure time is selectable, there is no need for a lens diaphragm for controlling the exposure amount, electrical gain correction, and the like. Further, since it is not necessary to use the lens diaphragm for the exposure amount control, the position where the MTF is the best can be selected for the lens diaphragm. Also, the aperture of the lens at that time is closer to the deep aperture than the normal aperture, so the shading amount is
Relatively less. That is, S / N deterioration due to shading correction is reduced.

Furthermore, since the lens diaphragm can be used at a fixed position, shading does not change. Since the shading does not change, the shading correction circuit has a relatively simple structure. Similarly, since it is not necessary to use electrical gain correction for exposure amount control, the noise component in the signal is not lifted as the gain of the image pickup signal is increased, and S / N deterioration can be prevented. Also, the lamp drive circuit 1
Since the clock of the CCD 15 can be directly used as one clock, the timing can be set accurately and easily.

Next, a photographing apparatus showing the second embodiment of the present invention will be described. The image pickup apparatus of this embodiment is an image pickup apparatus that uses a light source with ripple light and moves a line sensor relative to a subject to capture image formation information. In such an apparatus, one main scanning exposure is performed. For timing,
The image pickup signal is spatially affected by the timing of the ripple light. Therefore, in the image pickup apparatus of the present embodiment, the image pickup output signal can be operated according to the purpose by intentionally operating the two timings.

FIG. 4 is a block diagram showing the main blocks of the image pickup apparatus of this embodiment. The image capturing apparatus of this embodiment is an apparatus that captures image information of the film 22 that is a subject by a line sensor type one-dimensional CCD 25 that is an image capturing element and outputs it as an image capturing signal.

That is, the light of the AC drive light source 20 for illuminating the object, which is driven by the lamp power supply circuit 26 as the AC drive power supply driving means, is the image film 2 to be the object.
Irradiate 2. The subject light transmitted through the film 22 is
An image is formed on the image forming surface of the CCD 25, which passes through the taking lens 23 and takes in line image information in the main scanning direction along the light receiving element array.

The image pickup output of the CCD 25 is outputted as an image pickup signal from an image pickup circuit (not shown). CCD25 above
Are fixedly supported on a linear stage 29 as an image pickup device moving means that is continuously moved and driven in a sub-scanning direction that is orthogonal to the main scanning direction.

The linear stage 29 is driven by a control circuit 28 via a linear stage drive circuit 27 and the light source 20 via a lamp drive circuit 21, and each one pixel line of the CCD 25 in the linear stage 28 is driven. And the AC drive cycle of the lamp drive circuit 21 is matched. The phase relationship between the two is set by the phase adjusting means 28a incorporated in the control circuit 28.

The set phase relationship will be described. Figure 5
Is T0 during the exposure time for one line of the stage 29.
(T1 to t5) shows the moving state of the CCD light receiving portion viewed from the main scanning direction. The light receiving portion of the CCD 25 is located at the position 25B after the exposure time T0 for one line from the initial position 25A.
Move to.

FIG. 6 is a sectional view of the optical system of the present photographing apparatus in a direction orthogonal to the main scanning direction. The exposure time T0 for one line is from position 25A to position 2A.
It shows a subject light receiving state in the CCD light receiving portion which moves to 5B. CC of the subject 22 during the exposure time T0
The subject portion corresponding to the D1 line is the ◯ mark portion 22a to the mark portion 22b.
The range RA changes from the range RA to the range RB between the mark portions 22b to the mark portion 22c. The CCD 25 has time points t1, t2, t
◯ mark portion 22a as shown at 3, t4 and t5
The subject information in each of the mark portions 22b to 22c is captured.

FIG. 7 shows the ◯ mark portion 22 when the light amount of the light source is constant.
From the range RA between the mark a and the mark part 22b to the range RB between the mark part 22b and the mark x mark 22c, the CCD output level indicating the spatial influence degree indicated by the exposure degree of the CCD output (exposure level) on the imaging position FIG. As shown in the figure, the CCD output characteristic is such that the exposure of the central portion (. Portion 22b) reaches a peak while moving from the range RA to the range RB during the one-line exposure operation. In such a state, the exposure time of only the image information of the central portion (· portion 22b) becomes long.

Therefore, in this photographing apparatus, the subject 2
In order to make the exposure amount for each point between the range RA and the range RB of 2 constant, the light amount of the light source 20 is shifted by 1/2 cycle,
The drive phase is controlled by the phase adjusting means 28a so as to decrease the exposure time T0 for one line at an intermediate point.

FIG. 8 shows the light quantity waveform and CC in this embodiment.
A chart of the D output waveform, showing a change in CCD output indicating the degree of spatial influence in a constant light quantity state, a controlled light source light quantity change when the light quantity is controlled as described above, and the control light quantity. 7 shows a level change of a CCD output signal indicating a spatial influence degree due to. In the present embodiment, the CC for each line feed pitch center position of the subject as shown in this figure
The D output level rarely rises.

According to the image pickup apparatus of the present embodiment, it is possible to reduce the influence on the linear stage movement position, and it becomes difficult to generate low frequency moire fringes due to point sampling. Further, it is possible to reduce the number of optical low pass filters.

Next, a modification of the image pickup apparatus of the second embodiment will be described. This modified example further emphasizes the high CCD output portion in the central portion of the 1-line exposure range shown in FIG. 7 so that the light source light amount reaches a peak at the CCD output peak position indicating the spatial influence. The phase adjustment means 28a of the control circuit 28 controls the drive phase of the light quantity so that it becomes the same phase as the CCD output indicating the degree of spatial influence.

FIG. 9 is a time chart of the light amount waveform and the CCD output waveform in the image pickup apparatus of the modified example, which shows the change of the CCD output indicating the degree of spatial influence and the spatial CCD output as described above. 3 shows a change in the light amount of the light source controlled in the same phase and a change in the level of the CCD output signal due to the control light amount. As shown in the figure, the CCD output level further increases at each center position of the line pitch of the subject. Therefore, according to the image pickup apparatus of this embodiment, a larger CCD output level can be obtained.

[0039]

As described above, according to the photographing apparatus of the first aspect of the present invention, in the image pickup apparatus having the light source of the AC drive system, the exposure unevenness countermeasure is realized in the state where the desired exposure time can be selected. In addition, it is possible to prevent deterioration in other performance such as resolution, S / N, and shading. Further, according to the image pickup apparatus of the second aspect of the present invention, the clock of the image pickup element can be directly used, so that the timing can be set accurately and easily. Further, claim 3 of the present invention
According to the image pickup apparatus described in (1), the exposure time selection range is widened. Further, according to the photographing apparatus of the fourth aspect of the present invention, the exposure time selection range is further widened, and the manufacturing is facilitated.

Further, according to the photographing apparatus of the fifth aspect of the present invention, it is possible to select the image quality of the capture screen according to the purpose. Further, according to the image-taking apparatus of the sixth aspect of the present invention, the moire component of the output signal is reduced, and the optical low-pass filter can be eliminated. Further, according to the image-taking apparatus of the seventh aspect of the present invention, the level of the output signal becomes large.

[Brief description of drawings]

FIG. 1 is a schematic block configuration diagram of an image capturing apparatus showing a first embodiment of the present invention.

2 is a time chart showing waveforms of a drive signal, a light amount, and an image pickup signal on the light source side when driven synchronously with the image pickup timing on the CCD side in the image pickup apparatus of FIG.

3 is a time chart showing waveforms of a drive signal, a light amount, and an image pickup signal on the light source side when driven asynchronously with respect to an image pickup timing on the CCD side in the image pickup apparatus of FIG. 1;
To.

FIG. 4 is a schematic block configuration diagram of an image pickup apparatus showing a second embodiment of the present invention.

5 is a diagram showing a moving state of the CCD light receiving unit viewed from the main scanning direction of T0 during the exposure time for one line in the image pickup apparatus of FIG.

FIG. 6 is a cross-sectional view of the optical system of the image capturing apparatus of FIG. 4 in a direction orthogonal to the main scanning direction.

FIG. 7 is a diagram showing a change in CCD output level indicating the degree of spatial influence in the photographing apparatus of FIG.

FIG. 8 is a light quantity waveform and CCD in the image capturing apparatus of FIG.
Output waveform time chart.

FIG. 9 is a time chart of a light amount waveform and a CCD output waveform in a modified example of the photographing device of FIG.

FIG. 10 is a time chart showing an AC drive type light source drive signal, a change in the light source light amount, an image pickup signal, and the like in a conventional photographing apparatus.

FIG. 11 is a diagram showing streaks on an image pickup screen due to uneven exposure in an image pickup apparatus using a conventional line sensor.

FIG. 12 is a schematic block configuration diagram of a conventional imaging device.

FIG. 13 is a diagram showing a change in MTF with respect to a spatial frequency in a conventional image capturing apparatus, using a diaphragm as a parameter.

FIG. 14 is a diagram showing a relationship between an aperture and an MTF at a certain frequency in a conventional imaging device.

FIG. 15 is a diagram showing a change in the amount of light on a CCD image forming surface in a conventional photographing device.

FIG. 16 is a diagram showing a change in the light amount when the aperture is changed from the wide open aperture to the deep aperture with respect to the light intensity at a certain image height position in the conventional imaging apparatus.

FIG. 17 is a diagram showing changes in the image pickup signal level before and after gain correction in the conventional imaging apparatus.

[Explanation of symbols]

10, 20 ...... Light source 11, 21 ...... Lamp drive circuit (power supply drive means) 11a ...... Synchronous circuit (synchronization adjustment means) 15, 25 ...... CCD (imaging device) 17 ...... ...... TG circuit ( Image pickup element driving means) 18a Synchronous switching circuit (synchronous relationship switching means) 27 ... Linear stage driving circuit (imaging element moving means) 28 ... Control circuit (phase adjusting means) 28a. ……… Phase adjustment means

Claims (7)

[Claims] 1. A power supply driving means for AC driving a light source for projecting light for illuminating a subject, an image pickup element driving means for driving an image pickup element to obtain a video signal corresponding to an image of the subject, An image pickup apparatus, comprising: a synchronization adjusting unit for providing a predetermined periodic relationship between a driving phase of the image pickup device driven by the image pickup device driving unit and a phase of AC driving of the light source by the power supply driving unit. 2. The synchronization adjusting means adopts a phase relating to an exposure timing of the image pickup element as a drive phase of the image pickup element by the image pickup element driving means, and depends on the drive phase of the image pickup element, the power source driving means. The image pickup apparatus according to claim 1, wherein the phase of AC drive of the power source is adjusted. 3. The synchronization adjusting means sets the frequency of AC driving of the power source by the power source driving means to n- (1/2) times or n times the driving frequency of the image pickup element by the image pickup element driving means. The photographing apparatus according to claim 1, wherein the photographing operation is performed as described above. However, n is a natural number. 4. A power supply driving means for AC driving a light source for projecting light for illuminating a subject, an image pickup element driving means for driving an image pickup element to obtain a video signal corresponding to the image of the subject, A synchronous relationship for making it possible to selectively switch whether to have a predetermined periodical relationship or a non-synchronous relationship between the driving phase of the image pickup device by the image pickup device driving means and the phase of AC driving of the light source by the power supply driving means. An image pickup apparatus comprising: a switching unit. 5. A power source driving means for alternating-current driving a light source for projecting light for illuminating an object, and an image pickup device for substituting an image sensor for obtaining an image signal corresponding to the image of the object. When the image pickup element moving means for moving in the scanning direction and the movement position of the image pickup element by the image pickup element moving means are regarded as one cycle of the movement unit in the sub-scanning direction corresponding to one pixel of the image pickup element, it is positional An image pickup apparatus comprising: a phase adjusting unit that selectively establishes a predetermined relationship between a phase and a phase of AC driving of a light source by the power supply driving unit. 6. The phase adjusting means is arranged such that the time corresponding to the peak of the light amount in the AC driving of the light source by the power source driving means,
6. The image pickup apparatus according to claim 5, wherein the image pickup device moving means has a relationship such that a moving position of the image pickup device by the image pickup device moving means substantially coincides with a time point when the image pickup device is at the start end position of the moving unit. 7. The phase adjusting means is arranged such that the time corresponding to the peak of the light amount in the AC driving of the light source by the power source driving means,
6. The image pickup apparatus according to claim 5, wherein the image pickup device moving means has a relationship such that a moving position of the image pickup device by the image pickup device moving means is substantially coincident with a time point when the image pickup device is moved to a central position of the moving unit.