JP4503733B2 - Imaging device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an imaging apparatus having a smear reduction function.
[0002]
[Prior art]
In a solid-state image pickup device using a CCD image pickup device or the like, a phenomenon peculiar to the solid-state image pickup device is a smear phenomenon that occurs when intense light is incident (more precisely, it is a phenomenon that occurs comprehensively by smear and blooming). However, in this specification, the image quality deterioration due to the common use by those skilled in the art is simply called smear). In other words, this smear phenomenon is caused by charges that are not trapped in the original charge accumulation region leaking into the vertical transfer path over the potential barrier, or diffraction components and multiple reflection components of incident light enter the vertical transfer path under the light shielding film. This occurs due to leakage and charge generation, etc., and when it is caused by normal steady light, this occurs over the vertical transfer period. For example, in the case of spot light, vertical stripes extending vertically are generated. , Image quality was severely impaired.
[0003]
There are several proposals for reducing this, such as signal correction and using an optical shutter, but the signal correction is not sufficient, and mechanical shutters offer controllability and reliability. However, the liquid crystal shutter uses polarized light, so that the transmittance is theoretically only 50% or less (actually lower).
[0004]
On the other hand, Japanese Utility Model Registration No. 2524634 discloses a liquid crystal which is interposed between a photographing optical system and a CCD image pickup device and which can switch a light diffusion state (high transmittance because a polarizing plate is not required). In the signal readout (CCD transfer) period that controls the element and causes smearing, the spot light is diffused to average the plate surface illuminance to lower the peak value and reduce smear (hereinafter referred to as “smear”). This is referred to as smear reduction imaging).
[0005]
[Problems to be solved by the invention]
By the way, since this prior art does not have the disadvantages of a mechanical shutter, it can be applied to, for example, high-speed continuous shooting and the like, and is excellent in that it can obtain a smear reduction effect while maintaining high transmittance. However, it has the following problems. That is, the reduction of smear by the diffusing means works extremely effectively for local smear due to local high brightness such as that caused by spot light, but when the illuminance of the plate surface (imaging surface) increases overall, The effect is insufficient for omnipresent smear that occurs when using a high-speed shutter (short-time exposure).
[0006]
This point will be described in detail. Although the shutter speed itself does not directly correlate with the smear level, it is presumed that a so-called appropriate exposure is given during general photographing. This is the case of plate surface illuminance at which a sufficient exposure amount can be obtained even with a short exposure. In this sense, there is a relationship of L = k / T (k is a constant determined by the sensitivity of the image sensor) between the average plate surface illuminance L and the exposure time T. Therefore, even if the local smear is reduced by the diffusing means, the exposure on a screen with a speed higher than a predetermined shutter speed (shorter time) causes the entire screen to have extremely high brightness, resulting in smearing and the lens flare effect. There was a problem that the whole image became white.
[0007]
In the above-mentioned utility model gazette, as a description relating to this, the right column of the second page, lines 39 to 41, states that “Smear occurs substantially uniformly over the entire screen, so that the signal processing circuit (3) The smear component can be easily removed at the time of processing the image signal in “.”. However, the publication does not disclose at all what the process for removing the smear component is, and under what conditions it should be applied. Such a problem remained unresolved.
[0008]
First, the description of the above publication suggests a technique for performing correction processing assuming that the smear component is substantially constant, but there is a problem that the actual smear component does not necessarily occur uniformly. That is, the diffusion degree of the diffusing element using liquid crystal may not always be sufficient. This is because, in order to perform smear reduction imaging, the response of the diffusion element must be fast, but in order to increase the response characteristic of the element, the distance between the electrodes = the thickness of the active part of the element (cell thickness) is reduced. That is essential. In addition, since the difference in refractive index depending on the wavelength of the active portion of the element, that is, the “dispersion” characteristic is generally larger than that of ordinary optical glass, it is preferable that the cell thickness is smaller (for example, several times) in order to reduce this influence. μm to several tens of μm). However, when the cell thickness is reduced, the degree of diffusion naturally decreases. Accordingly, sufficient image diffusion cannot be obtained, and the influence of the subject pattern may remain slightly, and it may not be considered uniform when the plate surface illuminance is high.
[0009]
Even if the diffusibility is sufficient, the peripheral light amount is considerably lower than the central light amount due to general lens characteristics. Accordingly, the generated smear also includes a considerably large shading, and when the plate surface illuminance is high, it may not be considered uniform.
[0010]
Secondly, when the smear component is removed by signal processing, there is a problem that noise of the image signal generally increases.
[0011]
The present invention has been made to solve the above-described problems in conventional imaging apparatuses, and is used in combination in consideration of the case where smear components do not necessarily occur uniformly when smear reduction imaging is performed. The purpose is to provide a high-quality image pickup device that does not cause image quality degradation due to smear by selecting and applying a specific smear correction signal processing technique, and in particular, noise of image signals accompanying signal processing Focusing on the increase problem, when the exposure time is equal to or greater than a predetermined value, by providing no smear correction by the specific signal processing, it is possible to provide a high-quality image pickup apparatus with little image quality degradation overall. Objective.
[0012]
[Means for Solving the Problems]
In order to solve the above problems, an invention according to claim 1 is directed to an imaging optical system capable of setting a state of an output optical image with respect to a planned focal plane to a subject imaging state and a subject image diffusion state, and the imaging optical system. An image pickup device that photoelectrically converts an output optical image and outputs the image signal as an image signal, and driving the image pickup device and controlling the image pickup optical system so that the image pickup optical system is moved to the subject during an accumulation period of the image signal to be read In an imaging state, during the readout period of the image signal, imaging control means for enabling smear reduction imaging with the imaging optical system in the subject image diffusion state, and a vertical block of the output signal of the imaging device by the smear reduction imaging A smear detecting means for detecting a smear component of the image sensor based on an output corresponding to a ranking period, and an effective signal output period based on the smear component detected by the smear detecting means. A smear correction means for correcting the effective image signal is an image pickup device output, quality acceptability of ubiquitous smear exposure time at the time of imaging of the imaging control unit has performed the smear reduction imaging control can not also be reduced by the smear reduction imaging When the effective image signal is corrected by the smear correction unit when the value is less than a predetermined value determined in accordance with the limit , the exposure time at the time of imaging is determined to correspond to the reduction effect of the smear reduction imaging If the it was the above, and constitutes the imaging apparatus in the smear correction control means for controlling so as not to perform the signal correction by the smear correction means.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Next, embodiments will be described. FIG. 1 is a block diagram showing a digital camera of a main embodiment of an imaging apparatus according to the present invention. 1 is an imaging lens composed of a front lens 1a and a rear lens 1b, 2 is a lens driving mechanism composed of a focus actuator 2a and a zoom actuator 2b, 3 is a movable diaphragm, 4 is an optical filter composed of a low-pass filter and an infrared cut filter, Reference numeral 5 denotes a CCD image pickup device, 6 denotes a CCD driver, 7 denotes a preprocess circuit including an A / D converter, 8 denotes a digital process circuit, which includes a memory as hardware and performs all digital process processing. 9 is a memory card interface, 10 is a memory card, 11 is an LCD image display system, 12 is a system controller including a microcomputer as a main configuration, 13 is an operation switch system, 14 is an operation display system including a display LCD, and 15 is an aperture actuator , 16 is an actuator driver, 17 is a light diffusing element, 18 is a light diffusing element driver, and 19 is an EEPROM.
[0014]
In the digital camera configured in this way, as described above, the light diffusing element 17 having a structure in which a so-called polymer dispersed liquid crystal (polymer network type) liquid crystal is sealed in a plate-like cell of optical glass with a transparent electrode is used as the imaging lens 1. Is provided in the vicinity of the movable diaphragm 3 inside. Next, the light diffusing element 17 will be described in more detail. The light diffusing element 17 is formed by bonding two optical glasses together to provide a parallel plate glass having a thickness of 0.9 mm as a whole, and has a flat liquid crystal enclosing portion having a thickness of 10 μm at the bonding portion. A transparent resin in which liquid crystal is dispersed is enclosed in the encapsulating portion to form an active portion as an element. The connection line drawn from the transparent electrode is connected to the light diffusing element driver 18 and driven by a known alternating current drive with a predetermined voltage.
[0015]
It should be noted that how to assign the diffusion state and the non-diffusion (through) state to the time of voltage application and non-application (0 voltage application in the present embodiment for discharging residual charges) is arbitrarily arbitrary. When combined with an optical viewfinder, this view is effective for making it possible to see the viewfinder even when the camera is turned off, or to eliminate the need to consume power when smear reduction imaging is not required. In the embodiment, non-diffusion is performed particularly when no voltage is applied. After the residual voltage is discharged once the zero voltage is applied, the passing state is maintained even if the power supply to the driver is stopped. It has become. For this purpose, it is needless to say that the effective refractive index of the liquid crystal corresponding to the medium and the resin corresponding to the medium are equal when no voltage is applied.
[0016]
Subsequently, the control related to the above embodiment will be described. In the digital camera of the present embodiment, the system controller 12 performs all the control in an integrated manner, and controls the movable diaphragm 3 and the drive (electronic shutter) of the CCD image sensor 5 by the CCD driver 6 to perform exposure. (Charge accumulation) and signal reading out, storing them in the digital process circuit 8 via the pre-process circuit 7, performing all necessary various signal processing in this digital process circuit 8, and then the memory card It is recorded in 10. The light diffusing element driver 18 is driven in accordance with the timing of exposure and signal readout, and the diffusion characteristics of the light diffusing element 17 are changed, so that smear reduction imaging can be performed. That is, while the photoelectric conversion charge of the subject image to be photographed is being accumulated, the light diffusing element 17 is left in a non-diffusing (through) state, and a transfer pulse TG to the CCD transfer path (vertical shift register) is output. At the same time, voltage application is started to make the diffusion state. However, it takes a considerable time from the start of driving until the light diffusing element 17 shifts to a sufficiently diffuse state. This transition time depends on the element material, applied voltage, and drive frequency, but is usually about several ms to several hundred ms. It also greatly depends on the thickness of the element (active part). In this embodiment, since the thickness is as thin as 10 μm, the transition time is as fast as 10 ms or less. Correspondingly, the readout of the imaging signal (signal charge CCD transfer) is 10 ms after the output of the transfer pulse TG. Start from the moment. Then, after the signal readout is completed, the voltage application to the light diffusing element 17 is quickly transferred to the pass-through state in a timely manner to prepare for the next photographing and eliminate unnecessary driving power. Thereafter, energization to the light diffusing element driver 18 may be stopped.
[0017]
At this time, if the transition time is a different value, the read start time may be set in accordance with this. At this time, the reading may be started with further delay, but in this embodiment, unnecessary delay is not performed in order to avoid an increase in dark current noise associated therewith.
[0018]
The digital camera according to the present embodiment that performs such smear reduction imaging includes a smear detection unit 8-1 and a smear correction unit 8-2 in the digital process circuit 8 at the same time, and as a part of signal processing. The function of detecting smear components and performing smear correction processing is provided. The smear correction process is applied when the exposure time during imaging is less than the smear limit exposure time Ts.
[0019]
Here, the smear limit exposure time Ts will be described. As described in the above-mentioned conventional problems, when maintaining the proper exposure relationship, the ubiquitous smear that cannot be reduced by the diffusing means increases as the exposure time becomes shorter. An image quality tolerance limit is set (for example, on the basis of the detection limit or less), and an exposure time corresponding to this is set as Ts. (Needless to say, it is set to a limit value that does not cause a problem even without smear correction, including the problem of insufficient diffusion uniformity during smear reduction imaging that becomes apparent when the plate surface illumination is high). If the exposure time is equal to or longer than Ts, the predetermined high image quality set at the design time is guaranteed. The value of Ts is stored in the EEPROM 19, and is referred to during the exposure control. Since EEPROM19 is used, it can be rewritten, and after confirming the market response, the guaranteed image quality level (corresponding to Ts) can be changed, or the specification can be changed by the user. Can be easily done.
[0020]
The smear correction processing method applied in the present embodiment is a smear detection unit 8-1 that detects a smear component of the image sensor 5 based on an output corresponding to a vertical blanking period of the output signal of the CCD image sensor 5. Based on the detected smear component, the smear correction unit 8-2 corrects an effective image signal that is an image sensor output during the effective signal output period, and specifically, VOB (vertical optical black detection pixel). The smear removal reference signal calculated from the output is subtracted from the effective image signal.
[0021]
That is, when an imaging output signal corresponding to one screen obtained by the smear reduction imaging is stored in a predetermined memory area of the digital process circuit 7, first, the smear detection unit 8-1 uses the VOB output to generate a smear removal reference signal. calculate. That is, the average value is obtained by taking the sum of every 12 pixels having the same horizontal address from the data of OB pixels having a plurality of lines (here, 12 lines) and dividing by the number of pixels. In other words, this smear removal reference signal is an image signal for one line corresponding to the average value of a plurality of VOB lines. Using the smear removal reference signal thus obtained, the smear correction unit 8-2 performs smear correction on the effective pixel signal. That is, the corrected output is obtained by subtracting the smear removal reference signal from each line data of the pixel signal read from the effective pixel portion. Needless to say, the subtraction is performed between data having the same horizontal address.
[0022]
At this time, since the VOB is a light-shielded pixel, its output signal should be 0 (aside from noise), and if it is not 0, it is a smear and the smear is removed by the above subtraction. be able to. This is also effective when smear does not occur uniformly over the entire screen. Here, since the smear removal signal used for subtraction is an image signal for one line as described above, it itself has noise. Therefore, at the time of subtraction, this noise component is superimposed on the effective image signal, which is a factor in image quality degradation. It should be noted that the average of 12 lines was calculated in calculating the smear removal reference signal in order to reduce this noise, but it is impossible to completely reduce it to zero.
[0023]
In view of this point, the digital camera of the present embodiment performs smear correction by the smear correction unit 8-2 under the control of the system controller 12 when the exposure time at the time of imaging is equal to or greater than the smear limit exposure time Ts. Is configured to not. With such a configuration, when the exposure time Ts is less than the exposure time Ts at which unacceptable image quality degradation occurs due to smear (in this case, the benefit of smear correction is greater than the disadvantage), the smear correction is performed to improve the image quality. Since the smear correction is not performed when the exposure time Ts is longer than the exposure time Ts at which image quality deterioration due to smear does not occur, high image quality is ensured in the sense that noise increase due to correction does not occur.
[0024]
The high-quality image signal imaged in this way is recorded in the memory card 10 or displayed on the LCD image display system 11 through various signal processing as appropriate. That is, the digital camera of the above embodiment can be applied to, for example, high-speed continuous shooting, and can obtain a smear reduction effect while maintaining high transmittance, and has high image quality with little image quality degradation overall. An imaging device.
[0025]
In addition to the above-described embodiments, various embodiments can be considered. For example, in the digital camera of the above embodiment, the smear correction is not performed when the exposure time is Ts or longer so as not to cause an increase in noise due to the correction. Focusing on the fact that an image quality equivalent to that in the case of Ts or more can be obtained, and if this is allowed, it may be configured to perform the same smear correction as in the case of less than Ts. By doing in this way, the case classification according to exposure time becomes unnecessary, and simplification of control and a structure is achieved.
[0026]
Although the above embodiment is applied to a digital (still image) camera, the present invention can also be applied to a moving image camera. In this case, since the subject image cannot be obtained in the image diffusion state, the output rate of the image is usually halved (30 fields / second in the case of NTSC conformance). This can be compensated by using a buffer memory. This configuration is often cited as one specific embodiment. In other words, the diffusion / non-diffusion of the light diffusing element is alternately switched for each field, and only the output signal read out in the diffusion state (this is the one accumulated in the non-diffusion state one field before) is effective. The image signal is stored in the buffer memory while being used as an image signal, and the image signal stored in the immediately preceding field is used again during the non-diffusion state.
[0027]
In the above embodiment, the smear limit exposure time Ts is stored in the EEPROM. However, it is obvious that the smear limit exposure time Ts may be replaced with an arbitrary memory.
[0028]
On the other hand, if this Ts storage means is also used as a memory used by the camera for other purposes (eg, pixel defect data storage of the image sensor, camera control program storage, etc.), the number of memory elements as hardware is increased. The present invention can be applied without any problem. This is also an embodiment.
[0029]
Although several embodiments of the present invention have been specifically shown above, it is needless to say that the present invention is not limited to these and can take any form as long as it is described in the claims. .
[0030]
【The invention's effect】
As described based on the embodiments above, the invention according to claim 1, ensuring high picture quality by performing the smear correction in the case of less than the exposure time image quality degradation unacceptable due uneven distribution smear, uneven distribution smear Since the smear correction is not performed when the exposure time is longer than the exposure time at which the image quality deterioration due to the correction does not occur, the noise increase due to the correction does not occur, so that it has an excellent effect that a high image quality can be ensured .
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a configuration of a digital camera according to an embodiment of an imaging apparatus according to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Imaging lens 1a Front ball 1b Rear ball 2 Lens drive mechanism 2a Focus actuator 2b Zoom actuator 3 Movable diaphragm 4 Optical filter 5 CCD image sensor 6 CCD driver 7 Pre-process circuit 8 Digital process circuit 8-1 Smear detection part 8-2 Smear detection part 8-2 Correction unit 9 Memory card interface
10 Memory card
11 LCD image display system
12 System controller
13 Operation switch system
14 Operation display system
15 Aperture actuator
16 Actuator driver
17 Light diffusing element
18 Light diffusing element driver
19 EEPROM

Claims (1)

An imaging optical system capable of setting the state of the output optical image with respect to the planned focal plane to a subject imaging state and a subject image diffusion state; and an imaging device that photoelectrically converts the output optical image of the imaging optical system and outputs the result as an image signal; The imaging optical system is controlled by controlling the driving of the imaging device and the imaging optical system so that the imaging optical system is in the subject imaging state during the accumulation period of the image signal to be read out, and the imaging optical during the readout period of the image signal. and imaging control means for enabling the smear reduction imaging the system as the subject image diffusing state, the smear component of the imaging device based on an output corresponding to the vertical blanking period of the output signal of the imaging device by the smear reduction imaging A smear detecting means for detecting, and a smear for correcting an effective image signal which is an image sensor output in an effective signal output period based on the smear component detected by the smear detecting means. A correction unit, wherein when the imaging control unit is less than the predetermined value determined corresponding to the image quality allowable limit of ubiquitous smear exposure time can not also be reduced by the smear reduction imaging at the time of imaging of performing the smear reduction imaging control If the effective image signal is corrected by the smear correction unit and the exposure time at the time of imaging is equal to or greater than a predetermined value determined in accordance with the reduction effect of the smear reduction imaging, the smear correction unit An image pickup apparatus comprising smear correction control means for controlling so as not to perform signal correction .

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