JP3547203B2 - Electronic exposure control device - Google Patents

Description

[0001]
[Industrial applications]
The present invention relates to an electronic exposure control device for an electronic still camera and a video camera using a CCD (solid-state imaging device) area sensor.
[0002]
[Prior art]
Conventionally, as an iris control method for an electronic still camera and a video camera, there is an iris control method in which a shutter is provided in an optical system, but recently, a timing (charge storage time) for directly discharging charges directly stored in a CCD (solid-state imaging device). The technology of an electronic iris control method (electronic exposure control, EE control) for electrically changing the exposure amount by controlling the electronic iris control has been developed. The technology of the electronic iris control method is disclosed in Japanese Patent Application Laid-Open No. 6-46309. It is disclosed in Japanese Unexamined Patent Publication No. Hei 6-46311 and Japanese Unexamined Patent Publication No. Hei 6-62324.
[0003]
According to Japanese Patent Laying-Open No. 6-46309, an integrating circuit for integrating a high-frequency component of a digital luminance signal output from a solid-state image sensor at a predetermined cycle is provided, and the output of the integrating circuit is used for autofocus control. Video cameras have been proposed.
Japanese Patent Application Laid-Open No. 6-46311 proposes a video camera that extracts a low-frequency component of a digital luminance signal output from a solid-state image sensor, integrates the signal at a predetermined cycle by an integrating circuit, and uses the output for iris control. ing.
According to Japanese Patent Application Laid-Open No. 6-62324, an error in the electronic iris control that shortens the charge accumulation time when the output of the solid-state imaging device is higher than the upper reference value and lengthens the charge accumulation time when the output is lower than the lower reference value. There has been proposed an electronic iris control circuit capable of increasing the control sensitivity without hunting at any shutter speed because the range (dead zone) can be narrowed according to the charge accumulation time.
[0004]
[Problems to be solved by the invention]
As the conventional electronic iris control method, the video cameras and electronic iris control circuits described in JP-A-6-46309, JP-A-6-46311, and JP-A-6-62324 are intended. An object of the present invention is to calculate an average luminance value of image data from an image sensor and perform autofocus or control a shutter speed so that the value is always constant. That is, these electronic iris control methods can always capture an image with the same brightness.
However, as in the example of the image of the backlight scenery shown in FIG. 15, light in a non-interest area such as sunlight promotes an increase in the average luminance value as compared with the object to be observed. As a result, the subject is dark and a sufficient dynamic range (level difference between maximum brightness and maximum darkness) cannot be obtained, resulting in an image that is difficult to see.
[0005]
In order to solve this problem of backlighting, the image is divided into several areas, and when calculating the average luminance value on the assumption that humans are often psychologically imaged so that the subject appears in the center of the image. A technique has also been devised in which a large weight is applied to the central area and a small weight is applied to the peripheral area, and in particular, an object at the center of the image is exposed.
However, if the luminance value of most of the image is large, such as a sentence image in which characters are written on a blank sheet, that is, if the assumption that a person attempts to capture the subject at the center of the image does not hold, like a backlight, Due to the halation of the portion, the aperture is narrowed down and a dark image is obtained. As a result, a blurred image in which the dynamic range between the character and the blank paper is not sufficiently obtained is obtained.
[0006]
SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and a first object of the present invention is to provide an imaging device in which the exposure amount is adjusted so that the dynamic range is maximized even when a backlight image and a text image are captured. It is an object of the present invention to provide an electronic exposure control device that can be used.
[0007]
A second object of the present invention is to provide backlighting and text imagelikeEven if the subject cannot be imaged with optimal exposure without halation, if the image cannot be captured with optimal exposure, the exposure is automatically adjusted to maximize the edge of the character without affecting the halation on the paper surface, and an image with legible characters is obtained. An object of the present invention is to provide an electronic exposure control device capable of imaging.
[0008]
A third object of the present invention is to compare the absolute value of the difference between the integrated value of the high-frequency component in the current field period and the integrated value of the high-frequency component in the previous field period to set the exposure amount at which the high-frequency component is maximized. And the absolute value of the differenceJudgment reference value that does not perform exposure control when exceeding a certain valueIs to provide an electronic exposure control device that can set an appropriate exposure amount while preventing hunting due to noise and flicker.
[0009]
[0010]
The present invention4The purpose of is to provide a means for presetting the range of the upper reference value of the brightness of the captured image, performing exposure control based on the result of the comparison judgment between the upper reference value and the lower reference value, and displaying an extremely white solid image and a black solid image. An object of the present invention is to provide an electronic exposure control device that prevents an image from being captured.
[0011]
The present invention5The objective of the present invention is to provide a means for presetting a range of an upper limit threshold and a lower limit threshold of an average brightness value of a captured image, and performing exposure control when the range exceeds the range of the upper threshold and the lower threshold, and An object of the present invention is to provide an electronic exposure control device capable of capturing an image with a simple exposure.
[0013]
The present invention6The object of the present invention is to provide a means for judging flicker and a means for storing the image of the previous field, and when a flicker occurs, switching to a previously stored image of the previous field and outputting the same to prevent an imaging error due to flicker. To provide an electronic exposure control device that can perform the above.
[0014]
The present invention7The purpose of the electronic exposure is to determine whether the image is adjusted to an optimal exposure amount regardless of the brightness of the subject while preventing an imaging error due to flicker by judging whether the image is a solid black image due to flicker or a black solid image with insufficient exposure. It is to provide a control device.
[0015]
[Means for Solving the Problems]
The present invention relates to an imaging signal output from a solid-state imaging device.Data obtained by A / D conversion ofDelay means for delaying the current time by one sampling period;Image data andDelayed one sampling periodimage dataPrimary differentiating means for obtaining a difference between the differential signal, a differential integrating means for integrating the differential signal for one field period, a second delay means for delaying an integrated output of the differential signal for one field period,1Field period delayedPrevious field periodIntegral value of difference signal and integral value of difference signal during current field periodWhenA comparison means for comparing the exposure control signal for controlling the exposure amount of the solid-state imaging device from the comparison result of the comparison means, and an exposure control means for outputting to the solid-state imaging device driving unit in synchronization with the field signal,
The exposure control unit controls the current exposure time of the solid-state imaging device when the comparison result of the comparison unit is larger than the integration value of the difference signal integrated during the previous field period. An electronic exposure control device comprising means for controlling in the opposite phase direction.
[0016]
Another invention is an imaging signal output from a solid-state imaging device.Data obtained by A / D conversion ofA high-pass filter for extracting the high-frequency component of the above, high-frequency integration means for integrating the extracted high-frequency component for one field period, delay means for delaying the integrated output of the high-frequency component for one field period,One field period before the previous field periodComparing means for comparing the integrated value of the high-frequency component with the integrated value of the high-frequency component during the current field period; Exposure control means for outputting to the element drive unit,
The exposure control means controls the current exposure time of the solid-state imaging device when the comparison result of the comparison means is that the integrated value of the high-frequency component integrated in the previous field period is greater than the integrated value of the high-frequency component integrated in the current field period. An electronic exposure control device comprising means for controlling in the opposite phase direction.
[0017]
Calculating means for calculating the absolute value of the difference between the integrated value of the high-frequency component during the current field period and the integrated value of the high-frequency component during the previous field period delayed by one field period; and the absolute value of the calculated differenceWhenA noise determination unit configured to determine a magnitude relationship with a predetermined determination reference value, wherein the exposure control unit determines that an absolute value of the calculated difference is equal to or smaller than the determination reference value.underWhen the comparison result of the comparison means is that the integrated value of the high-frequency component integrated in the previous field period is larger than the integrated value of the high-frequency component integrated in the current field period, the control of the current exposure time of the solid-state imaging device is performed in the opposite phase. It is preferable to provide a configuration including a control unit.
[0018]
[0019]
Image signal output from solid-state image sensorData obtained by A / D conversion ofIntegrating means for integrating the brightness, a brightness determining means for determining the brightness from a comparison between the integrated output and a preset darker lower reference value and a brighter upper reference value, and a determination result that the brightness is lower than the darker lower reference value. The exposure amount is controlled to be lighter when it is determined, and to be darker when the luminance is determined to be higher than the brighter upper reference value.Brightness control means for outputting an exposure control signalAnd from the brightness control meansExposure control signalAnd selector means for selecting an exposure control signal from the exposure control means and outputting the selected signal to the solid-state element driving section in synchronization with the field signal,
The selector means, when the average luminance value is lower than the dark lower reference value or higher than the bright upper reference value.From the brightness control meansSelect the exposure control signal, otherwiseExposure control signal from exposure control meansIs preferably selected and output to the solid-state imaging device driving unit.
[0020]
Calculating means for calculating the absolute value of the difference between the integrated output of the high-frequency component during the current field period and the integrated output delayed by one field period; and the absolute value of the difference calculated by the calculating means and a predetermined luminance stability criterion. A stable state judging means for judging a stable state by comparing values with an image signal output from a solid-state image sensorData obtained by A / D conversion ofIntegration control means for integrating the integrated output, a re-control determination means for determining whether or not to re-control the exposure by comparing the integrated output with a preset re-control lower reference value and a re-control upper reference value; and a stable state determination. Exposure determination means for outputting an exposure determination signal for stopping or continuing exposure control based on a logical determination of a stability determination signal output from the means and a re-control determination signal output from the re-control determination means; and the exposure control means It is preferable to further comprise a multiplexer for stopping or outputting an exposure control signal output from the controller to the solid-state imaging device driving unit based on the exposure determination signal.
[0021]
[0022]
A flicker determination integration means for integrating image data obtained by A / D conversion of an imaging signal output from the solid-state imaging device for one field period, and an integrated output from the flicker determination integration means on a lower side of a predetermined flicker. Standard valueWhenFlicker determination means for determining flicker by comparing and outputting a flicker determination signal, and image storage means for storing the image data based on the flicker determination signal,
When the flicker determination signal output from the flicker determination unit is a signal indicating a flicker phenomenon, the image storage unit is configured not to write the image but to retain the previously written image data. preferable.
[0023]
Based on the flicker determination signal output from the flicker determination means,imageThe apparatus further includes an imaging permission determination unit that outputs an imaging permission signal to the storage unit,
It is preferable that the imaging permission determination unit is configured to determine that the subject is a solid black image by detecting that a plurality of the flicker determination signals are continuously output, and to output an imaging permission signal to the imaging accumulation unit. .
[0024]
In the present invention, it is preferable to use a charge coupled device (CCD) as the solid-state imaging device, and to use a HIC (hybrid IC) as the solid-state imaging device driver and the high-pass filter (HPF).
A first delay unit, a primary differentiation unit, a difference integration unit, a second delay unit, a comparison unit, an exposure control unit, a high-frequency integration unit, a calculation unit,noiseDetermination means, coefficient setting means, subtraction means, brightness determination means, brightness control means, selector means, stable state determination means, re-control determination means, exposure setting means, interface means, flicker determination means, imaging storage means, imaging permission determination means The multiplexer is constituted by a microcomputer including a CPU, a ROM, a RAM, an I / O port, a shift register, a counter, and the like, and an LSI.
A personal computer is used as the host computer.
[0025]
[Action]
According to the configuration of the first aspect of the present invention, for example, even when a subject such as a backlight or a sentence image cannot be imaged with optimal exposure unless it is in the vicinity of halation, the exposure control means can control the difference integrated by the previous field period. If the integrated value of the signal is larger than the integrated value of the difference signal integrated in the current field period, the control is directed to shorten the exposure time of the solid-state imaging device at the present time, or to the control direction of shortening the exposure time. The exposure control signal is output to change the exposure time so that the exposure time can be controlled so that the dynamic range (level difference between the maximum brightness and the maximum darkness) of the imaging signal (image signal) is maximized. As a result, sharp images can be captured even with backlight or text images.
[0026]
According to the configuration of the second aspect of the present invention, for example, even when a subject such as a backlight or a sentence image cannot be imaged with optimal exposure unless it is in the vicinity of halation, the exposure control means can control the high frequency integrated over the previous field period. If the integrated value of the component is greater than the integrated value of the high-frequency component integrated during the current field period, the control is to shorten the exposure time of the solid-state image sensor at the current time, or to increase the control if the control is to shorten the exposure time. The exposure control signal is output to change the character, so that the high-frequency components of the image and the halation on the paper do not affect the edge amount, and the exposure is adjusted to maximize the edge of the character. Is easy to read.
[0027]
According to the configuration of claim 3 of the present invention, the absolute value of the difference between the integral value of the high-frequency component in the current field period and the integral value of the high-frequency component in the previous field period is compared to determine the exposure amount at which the high-frequency component is maximum. When setting, if the absolute value of the difference is less than the predetermined value, exposure control is not performed.Judgment reference valueBy setting, it is possible to set the exposure amount at which the high frequency component is maximized while preventing hunting due to noise and flicker. For example, as a method of searching for the exposure amount at which the high-frequency component becomes the maximum, the integral value of the high-frequency component is calculated for all the settable exposure amounts, and the exposure amount at which the integral value becomes the maximum value is obtained. The method of finding the value and changing the exposure amount slightly from the exposure amount at the time when the maximum value search was started, comparing the integrated values of each high-frequency component, and controlling the exposure aperture to the larger integrated amount to keep the maximum There is an estimation method (maximum value search method). The former method greatly flicks (flicker) because the exposure amount greatly changes during the search for the maximum value, and cannot be applied to a video camera. In the latter method, if the maximum value can be reliably obtained, the change in the exposure amount can be minimized. However, since the noise between the amount of exposure and the high-frequency component has noise, an accurate maximum value search cannot be performed.
Therefore, in the configuration of the third aspect, the determination reference value is set for the difference evaluation between the integrated value of the high-frequency component in the previous field and the integrated amount of the current high-frequency component,If exceeding the criterion valueThe difference is determined to be due to extraneous noise or the like, and is ignored, and the exposure control maintains the current direction, thereby performing exposure amount control that is strong against extraneous noise.
[0028]
[0029]
Of the present inventionClaim 4According to the configuration of (1), the brighter upper reference value and the darker lower reference value of the average brightness value of the image are set, and the brightness average value is lower than the darker lower reference value or higher than the brighter upper reference value. In such a case, the exposure can be forcibly corrected by the exposure control signal from the exposure control means, thereby preventing an extremely solid white image or a solid black image from being captured.
[0030]
Of the present inventionClaim 5According to the above configuration, the stable state is determined by comparing the average luminance of the image with the luminance stability reference value set in advance for the captured image, and the hunting is prevented by stopping the exposure control. Further, by comparing the preset re-control lower reference value and the preset re-control upper reference value, when the exposure amount needs to be adjusted again due to a change in the imaging target, the optimal exposure can be re-controlled.
[0031]
[0032]
Of the present inventionClaim 6According to the configuration of (1), there is provided a means for judging flicker and a means for storing the image of the previous field, and when a flicker occurs, switching to the previously stored image of the previous field and outputting the same to prevent an imaging error due to flicker. Can be prevented.
For example, in the case of the NTSC CCD drive, flicker of about 20 Hz occurs in the output from the CCD in a field unit in an environment illuminated by a 50 Hz fluorescent lamp, but an extremely black solid image due to the flicker phenomenon is discarded and stored in advance. Since the image is switched to the image of the previous field and output, an image with less influence of flicker can be captured.
[0033]
Of the present inventionClaim 7According to the configuration, it is possible to determine whether the image is a solid black image due to flicker or a black solid image with an insufficient exposure amount by detecting that a plurality of flicker determination signals are continuously output. An image adjusted to an optimal exposure amount can be obtained regardless of the brightness of the subject while preventing an imaging error due to flicker.
[0034]
【Example】
Hereinafter, the present invention will be described in detail based on embodiments shown in the drawings. The present invention is not limited by this. The electronic exposure control device of the present invention is mainly used for CCD exposure control of a CCD camera, an electronic still camera or the like.
FIG. 1 is a schematic view showing an embodiment in which the electronic exposure control device of the present invention is applied to a CCD camera connected to a host computer. In FIG. 1, reference numeral 1 denotes a CCD camera on which a CCD (charge coupled device) and an optical lens are mounted. Reference numeral 2 denotes a PCMCIA (Personal Computer Memory Card International Association) card having a built-in electronic exposure control device of the present invention, which includes an image processing unit 30 for processing an image signal output from the CCD camera 1 and an exposure control unit 20 of the present invention. (See FIG. 2). Reference numeral 3 denotes a signal cable for connecting various signals between the CCD camera 1 and the PCMCIA card 2. Reference numeral 4 denotes a host computer (personal computer) which takes in the image signal processed by the PCMCIA card 2 as image information and executes various processes such as editing, saving, and exchanging image information. Reference numeral 4a denotes a PCMCIA provided in the main body of the host computer 4. This is a card slot for the card 2.
[0035]
FIG. 2 is a block diagram showing a basic configuration in which the electronic exposure control device of the present invention is applied to a CCD camera control unit. In FIG. 2, light (imaging) collected by an optical lens 10 is converted into an imaging signal (analog image signal) of an electric signal by a CCD 11, and further converted to an AGC circuit (automatic gain control: automatic amplification control circuit) 12. Then, an appropriate bias cut and gain control are performed, and the data is converted into digital data ID (digital image signal) having 8-bit accuracy (0 to 255 gradations) by an A / D converter 13 having an 8-bit configuration. It is sent to the image processing unit 30 (camera image processing means).
[0036]
Here, 14 is an original oscillator for transmitting a basic clock signal CLK for driving the CCD 11, and 15 is a horizontal synchronizing signal which receives the basic clock signal from the original oscillator 14 and together with the CCD driving signal (swept pulse signal). HD and a CCD that generates a synchronization signal such as a vertical synchronization signal VD (field signal) and drives the CCD 11Drive part(Solid-state imaging device driving unit). The CCD drive unit 15 controls exposure by controlling the timing of the CCD drive signal based on two exposure control signals (EENR, EEUD) output from the exposure control unit (iris control unit) 20.
The AGC circuit 12, the A / D converter 13, the original oscillator 14, and the CCD driver 15 are composed of a HIC (hybrid IC) and a dedicated IC.
The exposure control unit 20 and the image processing unit 30 include a microcomputer including a CPU, a ROM, a RAM, an I / O port, a shift register, a counter, and the like, and an LSI.
[0037]
FIG. 3 is a block diagram illustrating a configuration of the exposure control unit according to the first embodiment of the present invention. 3, the digital data (image data) ID output from the A / D converter 13 shown in FIG.
The first delay means 101 samples the image data for one pixel and delays it. Next, the primary differentiating means 102 calculates the absolute value of the difference between the image data of one pixel sampling period at the current time and the image data sampled delayed by the first delay means 101.
Further, the output signal of the primary differentiating means 102 is integrated for one vertical synchronization time (one field period) by an integrator (difference integrating means) 103, and this integrated signal is output to the second delay means 104 and the comparing means 105. The second delay unit 104 outputs the integrated signal to the comparison unit 105 after delaying it by one field period. Here, VD is a vertical synchronization signal.
[0038]
Next, the comparison means 105 compares the integrated value of the integrated signal delayed by one field period with the integrated value of the integrated signal not delayed.
In the comparing means 105, for example, when the integrated value delayed by one field period is larger than the integrated value without delay, a high-level (TTL level) control signal is output to the exposure control means 106, and the exposure to the CCD driving unit 15 is performed. Notifies control reversal. In other words, it is considered that the integral value has decreased due to incorrect exposure control.
[0039]
Conversely, if the integrated value that has not been delayed is larger, it is determined that the control direction is correct, and a low-level (TTL level) control signal is output to continue the current exposure control.
In the exposure control means 106, when power is supplied to the apparatus or when a reset signal is input, the CCD driving unit 15 minimizes the timing of the pulse signal for sweeping out the CCD 11.(That is, the pulse width of the pulse signal sent from the CCD driving unit 15 to the CCD 11 shown in FIG. 2 is the minimum.)In other words, the CCD drive signal is initialized to the shortest exposure time.Exposure control is started to increase the signal width of the sweep pulse signal (that is, increase the pulse signal width of the pulse signal from the minimum width), that is, to increase the exposure time.
[0040]
The exposure control unit 106 interfaces with the CCD driving unit 15 using the logic of two exposure control signals EENR and EEUD, and the CCD driving unit 15 controls the shutter speed / exposure time by controlling the timing of the sweep pulse signal of the CCD 11. are doing.
The exposure control means 106 sets (EENR, EEUD) = (H, L) when the shutter speed is increased and the aperture is set to a darker aperture, and when the shutter speed is decreased and the aperture is set to a brighter aperture (EENR, EEUD). EEUD) = (L, H), and (EENR, EEUD) = (H, H) (here, H and L indicate TTL level signals) when the shutter speed is fixed for one field periodChange each timeOutput.
After the reset operation, the exposure control signals (EENR, EEUD) are inverted or held in synchronization with the rising edge of the vertical synchronizing signal VD based on the output signal output from the comparing means 105, and output to the CCD drive unit 15. .
[0041]
The CCD driving unit 15 drives the CCD 11 by generating a sweep pulse signal or the like, which is a driving signal of the CCD 11, from the basic clock signal of the original transmitter 14.
Timing control of sweep pulse signal is one fieldChanged and output per periodThe exposure time control signals (EENR, EEUD) are integrated, and the shutter speed is changed by one step in the next one field period depending on which signal is output longer.
The CCD driving unit 15 can logarithmically change the shutter speed by about 70 steps from 1/61 to 1 / 109,890 (s) by the exposure time control signal (EENR, EEUD). It is changed step by step.
[0042]
Therefore, if the exposure control unit is configured as in the first embodiment, for example, an imaging target such as a backlight and a text image must be in a halation state.BestExposure to maximize the dynamic range (level difference between maximum brightness and maximum darkness) of the image signal (image signal), ie, the one-field integrated value of the first derivative of the image data, even when the image cannot be captured by the appropriate exposure. By controlling the time, a sharp image can be captured even with a backlight or a sentence image.
[0043]
FIG. 4 is a block diagram showing an application configuration in which the exposure controller of the present invention is applied to a CCD camera controller. 4, the configurations and functions of the optical lens 10, the CCD 11, the AGC circuit 12, the A / D converter 13, the original oscillator 14, and the CCD driving unit 15 are the same as those in FIG.
The exposure control unit 20 differs in the units and functions thereof according to the embodiments described below.
As shown in FIG. 4, an HPF 21 (high-pass filter), an integrator 22 (high-frequency integration means), an integrator 23, an exposure setting means 24, an interface means 25, and a flicker determination means 26 connected to the exposure control section 20. The configuration and functions of the host computer 4 will be described in Examples 2 to 9 below.
[0044]
FIG. 5 is a block diagram illustrating a configuration of an exposure control unit according to the second embodiment of the present invention. In FIG. 5, the high-frequency component of the image data ID output from the A / D converter 13 shown in FIG. 4 is extracted by the HPF 21 and integrated by the integrator 22 for one field period.
The integration signal output from the integrator 22 shown in FIG.
Next, the delay means 201 delays the integrated signal output from the integrator 22 by one field period. The comparing means 202 compares the integrated value of the delayed integrated signal with the integrated value of the integrated signal without delay, and outputs a level H to the exposure control means 203 when the integrated value with delay is larger than the integrated value without delay, Notifies the control direction reversal.
In other words, it is considered that the integral value is reduced because the control direction is wrong. Conversely, if the integrated value that is not delayed is larger, it is determined that the control direction is correct, and the exposure control means 203 uses the exposure control signals (EENR, EEUD) so that exposure control is continued by outputting the level L. It controls the CCD driving unit 15.
[0045]
Therefore, if the exposure control unit has the configuration of the second embodiment, for example, even when the imaging target object cannot be imaged with optimal exposure without halation, such as a backlight image and a text image, the high-frequency component of the image, that is, In this embodiment, when an edge having a threshold value or more is detected and exposure control is performed so as to integrate for one field period and maximize it, halation on the paper surface does not affect the edge amount, and the edge portion of the character is maximized. The exposure amount is adjusted so that the character is easy to read.
[0046]
FIG. 6 is a block diagram illustrating a configuration of an exposure control unit according to the third embodiment of the present invention. In FIG. 6, high frequency components are extracted by the HPF 21 from the image data ID output from the A / D converter 13 shown in FIG. 4, and integrated by the integrator 22 (high frequency integration means) for one field period.
The integration signal output from the integrator 22 shown in FIG. Next, the delay means 301 delays the integrated signal output from the integrator 22 by one field period. The comparing means 302 compares the integrated value of the delayed integrated signal with the integrated value of the integrated signal without delay. If the integrated value after delay is larger than the integrated value without delay, the mask logic 305 (exposure determining means) To notify the reversal of the control direction. Conversely, if the integrated value without delay is larger, the control direction is determined to be correct and the level L is output.
[0047]
On the other hand, the arithmetic means 303 calculates the absolute value of the difference between the output from the delay means 301 and the signal without delay, and calculates its absolute value.Noise determination means 304Is entered. In the noise determination unit 304, the input is 700 (a constant set experimentally in advance).Criterion value that is)Judging that the influence of external noise is coming outOutput level H (1), if belowJudging that it is not affected by noiseThe level L (0) is output to the mask logic 305. In the mask logic 305Noise judgment meansThe signal output from the comparing means 302 is output to the exposure control means 306 only when the output from the level 304 is at the level L, and the level L is always output when the signal is at the level H.In other words, mask logic is used to prevent exposure control from being disrupted by the influence of external noise. H Ignore judgment when is entered L (Maintain current status) is output.
[0048]
Therefore, if the exposure control unit has the configuration of the third embodiment, it is possible to propose a maximum value search method that is not affected by external noise. In other words, the constant value is used to evaluate the difference between the integral value of the high-frequency component in the previous field and the integralSet the judgment reference value and if it exceeds the judgment reference valueThe difference is judged to be due to extraneous noise and ignored, and the aperture direction (whether bright or dark) is maintained in the current direction to adjust the exposure amount that is strong against noise. Can be.
[0049]
FIG. 7 is a block diagram illustrating a configuration of an exposure control unit according to the fourth embodiment of the present invention. 7, the high-frequency component of the image data ID output from the A / D converter 13 shown in FIG. 4 is extracted by the HPF 21 and integrated by the integrator 22 for one field period.
The integration signal output from the integrator 22 is input to the delay means 401.
Next, the delay means 401 delays the output of the integrator 22 by the field period set by the field coefficient setting means 402 (coefficient setting means). Next, the comparing means 403 compares the integrated value of the integrated signal from the integrator 22 with the integrated value of the delayed integrated signal, and when the delayed integrated value is larger than the integrated value without delay, the masking logic 404 A level H is output, the control direction is reversed, and if the integrated value that is not delayed is larger, the control direction is determined to be correct and a level L is output.
[0050]
On the other hand, in the field coefficient setting means 402,The absolute value of the difference between the integrated value of the integrated signal without delay and the integrated value of the delayed integrated signal output from the calculating means 407 (that is, the integrated value of the signal in the current field period and the integrated value of the signal in the previous field period) Absolute difference)The following equation (1) is calculated from the output to determine the field coefficient fk.
fk = k · | emax−edmax | / pixel ‥‥ (1)
In the above equation, the constant k is a factor that determines the speed of maximum value search and the noise sensitivity. emax is the integrated value of the signal in the current field period, edmax is the integrated value of the signal in the previous field period, and pixel is the number of effective pixels of the CCD. In this embodiment, since 640 × 480 pixels are cut out from the effective pixels of the CCD and one field period is set, pixel = 307,200 and k = 0.001 are set.
[0051]
The field coefficient fk determined here is a delay means401Is input toOn the other hand, it is input to the subtraction means 405 and subtracted one by one in synchronization with the vertical synchronization signal. The subtractor 405 outputs a level H to the mask logic 404 when the value becomes negative, and outputs a level L otherwise.The mask logic 404 outputs the output of the comparing means 403 as it is when the level H signal is output from the subtracting means 405, and otherwise outputs the level L to the exposure control means 406.
The operation means 407,Noise judgment meansThe functions of the operation unit 408 include the operation unit 303 shown in FIG.Noise judgment meansSince the function is the same as that of the function 304, the description is omitted.
[0052]
FIG. 8 is a graph showing the relationship between the exposure amount and the high frequency component. As shown in FIG. 8A, the maximum value of the high frequency component with respect to the exposure amount is not a simple relationship having only one extreme value, but has a false maximum point as shown in FIG. 8B. It can be complicated.
Therefore, if the exposure control unit is configured as in the fourth embodiment, if the difference between the integrated values of the high-frequency components of the previous field and the current field is large, the aperture control is performed at a coarse field interval because the distance is still far from the maximum point. Conversely, if the difference is small, the control point can be made finer from the characteristic that the current time is near the local maximum point, and the local maximum point can be reliably obtained. Further, since the control point is rough in a portion far from the maximum point, a maximum value search method capable of searching for the maximum point with high resistance to noise is obtained.
[0053]
FIG. 9 is a block diagram illustrating a configuration of an exposure control unit according to the fifth embodiment of the present invention. Further, FIG. 9 shows a configuration in which the configuration of the exposure control unit shown in FIGS. 4 and 7 further includes a luminance determination unit 501 (comparison unit), a luminance control unit 502 (protective exposure unit), and a selector unit 503. ing.
In FIG. 9, the integrated signal output from the integrator 23 in FIG. Exposure control signals (EENR, EEUD) output from the exposure control means 406 shown in FIG.
On the other hand, the luminance determination means 501 compares and determines the integrated signal output from the integrator 23 in FIG. 4 with a brighter upper reference value 200 and a darker lower reference value 70 of the preset luminance. The judgment result is input to the brightness control means 502. The brightness control unit 502 generates an exposure control signal (EENR, EEUD) based on the determination result of the brightness determination unit 501 and outputs the signal to the selector unit 503.
[0054]
When the determination result exceeds the brighter upper reference value, the brightness controller 502 outputs the exposure control signal (EENR, EEUD) = (H, L) and sets the brightness to a darker value. If the value is lower than the darker lower reference value, an exposure control signal (EENR, EEUD) = (L, H) is output to set a lighter value.
When the selector 503 receives the exposure control signal (EENR, EEUD) from the luminance controller 502, the selector 503 selects and outputs the exposure control signal. Otherwise, the selector 503 outputs the exposure control signal output from the exposure controller 406. (EENR, EEUD) is output as it is. An exposure control signal is output from the selector unit 503 to the CCD driving unit 15.
[0055]
Therefore, if the exposure control unit has the configuration of the fifth embodiment, the brighter upper reference value and the darker lower reference value of the average luminance value of the image are set, and the luminance average value falls below the lower reference value. When the value exceeds the upper reference value, the exposure control signal (EENR, EEUD) = (L, H) or (EENR, EEUD) = (H, L) for forcibly controlling the exposure is output, whereby the extreme value is output. This prevents a whiteout image or a solid black image from being captured.
[0056]
FIG. 10 is a block diagram illustrating a configuration of an exposure control unit according to a sixth embodiment of the present invention. FIG. 10 shows a configuration in which the configuration of the exposure control unit shown in FIGS. 4 and 7 further includes a control determination unit 601, a stable state determination unit 602, a mask logic 603 (exposure determination unit), and a multiplexer 604. I have.
In FIG. 10, the integration signal output from the integrator 23 of FIG. An operation signal output from the operation unit 407 shown in FIG. 7 is input to the stable state determination unit 602. An exposure control signal (EENR, EEUD) output from the exposure control means 406 shown in FIG.
[0057]
In the stable state determination means 602,FIG.Is compared with a preset stability reference value 80, and when the output signal SD falls below the stability reference value 80, it is determined that the apparatus is in a stable state, and a level H is output to the mask lossic 603. Otherwise, level L is output.
The re-control judging means 601 compares the integration signal from the integrator 23 shown in FIG. 4 with a preset re-control upper reference value 210 and a re-control lower reference value 100. , Or if it is lower than the re-control lower reference value 100, a level H is output to the mask logic 603, and otherwise a level L is output.
[0058]
In the mask logic 603, the output from the control determining means 601 and the output from the stable state determining means 602 are again used as shown in the truth table of FIG.Output signalIs output. FIG. 11 is a truth table of a control signal of the judgment control means in the sixth embodiment.
When the control signal from the mask logic 603 is L, the multiplexer 604 determines that the average luminance value of the image is in a stable state, and outputs an exposure control signal (EENR, EEUD) = (H, H) to stop the exposure control. Otherwise, the exposure control signals (EENR, EEUD) from the exposure control means 406 in FIG. 7 are output as they are.
[0059]
Therefore, when the exposure control unit is configured as in the sixth embodiment, the exposure amount is adjusted by the method of the second to fifth embodiments, and if the average luminance value of the image does not change much even when the exposure amount is changed, the exposure control unit is stable. Hunting is prevented by judging that the state is the state and stopping the exposure control.
Even when the exposure amount needs to be adjusted again due to a change in the imaging target after the stop, if the average luminance value of the captured image exceeds a certain range defined by the preset upper and lower thresholds, exposure control is performed again. Thus, even when the subject is newly changed such as when the CCD camera is moved, it is possible to perform a smooth and optimal exposure amount adjustment.
[0060]
Next, a configuration of an exposure control unit according to a seventh embodiment of the present invention will be described with reference to a block diagram of the exposure control unit illustrated in FIG. 4 and a time chart illustrated in FIG. As shown in FIG. 4, the exposure setting means 24 connected to the exposure control section is interfaced with the host computer 4 via the interface means 25.
The exposure setting means 24 includes a bright setting register wff and a dark setting register bff.
[0061]
FIG. 12 is a time chart showing the timing relationship of the exposure setting means in the seventh embodiment. FIG. 12A is a time chart at the time of setting brighter, and FIG.DarkIt is a time chart at the time of a setting. VD in the figure is a vertical synchronizing signal, and HD is a horizontal synchronizing signal. IOW is a bright / dark setting signal.
When an I / O access occurs from the host computer 4, the IOW signal (bright / dark setting signal) becomes level L,IOWAt the rising edge of the signal, a brighter setting register wff is set to level H when the user wants to set a lighter level, and a darker setting register bff is set to level H when the user wants to set a darker level.
[0062]
Next, the exposure control signal (EENR, EEUD) = (L, H) is output for one field period (one vertical synchronization period) from the falling edge of the vertical synchronization signal VD. , And outputs an exposure control signal (EENR, EEUD).
If neither is the case, the exposure control section outputs the output exposure control signals (EENR, EEUD) as they are.
Both the bright setting register and the dark setting register are cleared to level L at the rising edge of the vertical synchronization signal VD.
Therefore, if the exposure control unit is configured as in the seventh embodiment, in addition to the exposure adjustment of the methods of the second to sixth embodiments, a lighter or darker exposure can be set according to the user's preference.
[0063]
Next, the configuration of the exposure control unit according to the eighth embodiment of the present invention will be described with reference to the block diagram of the exposure control unit shown in FIG. 4 and the block diagram of the flicker determination unit shown in FIG. As shown in FIG. 4, an image is picked up from the CCD 11 by the means described in the second to seventh embodiments, the gain is controlled by the AGC circuit 12, and the A / D converter 13 outputs an 8-bit digital image signal ( The image data is converted to an image data (ID), and thereafter transmitted to the image processing unit 30. In the eighth embodiment, a flicker determination unit 26 is provided at the end of the output.
[0064]
FIG. 13 is a block diagram showing a configuration and operation of a flicker determination unit according to the eighth embodiment. In FIG. 13, VD indicates a vertical synchronization signal, ID indicates 8-bit image data, and Fr indicates a flicker detection signal. WE indicates a write enable terminal of the image storage unit 803 (imaging storage unit).
The image data ID and the vertical synchronization signal VD are input to the integrator 801. The integrator 801 integrates the input image data ID for one field period, and compares the integrated image data ID with the flicker lower threshold 30 at a flicker detector (lower comparator) 802. If the lower limit threshold is 30 or less, the flicker determination signal Fr is set to level H.
[0065]
The image storage unit 803 is configured by a normal static RAM, and the write enable terminal WE can be masked by the flicker determination signal Fr of the flicker detection unit 802. That is, when the flicker determination signal Fr of the flicker detection unit 802 is at the level H, the write enable terminal WE is always at the level H and the image is not written. On the other hand, since the static RAM previously stores the image data when the flicker determination signal Fr from the flicker detection unit 802 is at the level L, the solid black image due to the flicker phenomenon is discarded. By holding the image data of the field written in the field, it is possible to prevent an imaging error due to flicker.
[0066]
Therefore, when the exposure control unit is configured as in the eighth embodiment, when driving an NTSC CCD camera, flicker of about 20 Hz occurs in a field unit in the output from the CCD in an environment illuminated by a 50 Hz fluorescent lamp. In addition, an image of an extremely black solid image caused by flicker is discarded, and an image less affected by flicker can be captured.
[0067]
Next, regarding the configuration of the exposure control unit according to the ninth embodiment of the present invention, a block diagram of the exposure control unit illustrated in FIG.FIG.This will be described with reference to the block diagram of the flicker determination means shown in FIG. As shown in FIG. 4, an image is picked up from the CCD 11 by the means described in the second to seventh embodiments, the gain is controlled by the AGC circuit 12, and the A / D converter 13 outputs an 8-bit digital image signal ( The image data is converted to an image data (ID), and thereafter transmitted to the image processing unit 30. In the ninth embodiment, the flicker judging means 26 is provided before the output, which is the same as the configuration of the eighth embodiment.
[0068]
FIG. 14 is a block diagram showing the configuration and operation of the flicker determining means in the ninth embodiment. In the figure, Fr is a flicker determination signal 1205, VD is a vertical synchronizing signal, and Fmask is a flicker mask signal (imaging permission signal).
The flicker determination unit shown in FIG. 14 further includes an imaging permission determination unit including a ring buffer and a logic gate in addition to the flicker determination unit described in the eighth embodiment.
The flicker determination signal is input to a ring buffer 901 (shift register) including flip-flops FF1 to FF8. The output of each flip-flop is input to an 8-input AND gate 902, and when all the outputs have the level H, that is, when all the last 8 fields have a luminance value equal to or lower than the lower threshold of 30 or less, the original image is not a black solid image due to flicker but an original image. The image is determined to be a solid black image, and the flicker determination signal is masked by the logic 903.
[0069]
With this circuit, if the average luminance value in one field period of the image falls below the lower threshold value 30, and if there is at least one average luminance value exceeding the threshold value 30 in the last eight fields, the current field becomes black due to flicker. The image is determined to be an image, and a flicker mask signal Fmask for notifying the image storage unit 904 of the invalidity of the image data is issued.
Image storage means904IsExample 8The flicker mask signal Fmask according to the present embodiment is replaced with the flicker determination signal Fr according to the eighth embodiment and input to the image storage unit 904 in the same manner as described above.
[0070]
Therefore, if the exposure control unit is configured as in the eighth embodiment, an extremely black solid image due to flicker is discarded, but a black solid image due to insufficient exposure and a subject can simply be captured, thereby eliminating an imaging error due to flicker. Meanwhile, a normal dark image can be captured.
[0071]
【The invention's effect】
According to the present invention, the following effects can be obtained.
According to the configuration of the first aspect, by integrating the first derivative of the imaging signal output from the solid-state imaging device for one field period, the dynamic range of the image signal in one screen (the level of the maximum brightness and the maximum darkness) By performing the exposure control so that the difference) is maximized, an image with sharpness (shade difference) can be obtained. Even when a backlight image and a text image are captured, it is possible to capture an image automatically adjusted to the exposure amount that maximizes the dynamic range.
According to the configuration of the second aspect, the high-frequency component is extracted from the imaging signal output from the CCD solid-state imaging device, and the integration amount integrated for one field period is compared with the integration amount integrated in the same manner as one field before. By reversing the control direction of the exposure stop when the integral amount of the exposure is small, it is possible to automatically set the exposure amount that secures a sufficient dynamic range. Therefore, in the case of a subject such as a backlight or a sentence image, even if it is impossible to capture an image with optimal exposure unless it is in the vicinity of halation, an exposure amount that maximizes the edge portion of the character without affecting the halation on the paper surface. It is possible to capture an image in which characters are easy to read by automatic adjustment.
According to the configuration of the third aspect, when setting the exposure amount at which the high-frequency component becomes maximum by comparing the absolute value of the difference between the integrated value of the high-frequency component in the current field period and the integrated value of the high-frequency component in the previous field period. And the absolute value of the differenceWhen exceeding the judgment reference valueExposure controlDo not doThis makes it possible to set the exposure amount at which the high-frequency component is maximized while preventing hunting due to noise and flicker.
Claim 4According to the configuration of, the range of the upper reference value of the brightness of the captured image is set in advance, and the upper reference value and the means for performing the exposure control by comparing and determining the lower reference value, the extreme white solid image, It is possible to prevent a solid black image from being captured.
Claim 5According to the configuration of the above, the range of the upper limit threshold and the lower limit threshold of the average brightness value of the captured image is set in advance, and a unit that performs exposure control when the range exceeds the range of the upper limit threshold and the lower limit threshold is provided. An image can be taken with the optimum exposure to the change.
Claim 6In the digital still camera using the CCD of the NTSC system, the flicker development in which an extremely dark image is imaged at a fixed rate in a few fields due to a slight difference between the fluorescent lamp and the CCD driving frequency in the digital still camera using the CCD of the NTSC system. And means for accumulating the image of the previous field, and when a flicker occurs, switching to the previously stored image of the previous field and outputting the same can prevent an imaging error due to flicker.
Claim 7According to the configuration, by determining whether the image is a solid black image due to flicker or a black solid image having an insufficient exposure amount, an image adjusted to an optimal exposure amount can be obtained regardless of the brightness of the subject while preventing an imaging error due to flicker. .
[Brief description of the drawings]
FIG. 1 is a schematic view showing an embodiment in which an electronic exposure control device of the present invention is applied to a CCD camera connected to a host computer.
FIG. 2 is a block diagram showing a basic configuration in which the electronic exposure control device of the present invention is applied to a CCD camera control unit.
FIG. 3 is a block diagram illustrating a configuration of an exposure control unit according to the first embodiment of the present invention.
FIG. 4 is a block diagram showing an application configuration in which the exposure control unit of the present invention is applied to a CCD camera control unit.
FIG. 5 is a block diagram illustrating a configuration of an exposure control unit according to a second embodiment of the present invention.
FIG. 6 is a block diagram illustrating a configuration of an exposure control unit according to a third embodiment of the present invention.
FIG. 7 is a block diagram illustrating a configuration of an exposure control unit according to a fourth embodiment of the present invention.
FIG. 8 is a graph showing a relationship between an exposure amount and a high-frequency component.
FIG. 9 is a block diagram illustrating a configuration of an exposure control unit according to a fifth embodiment of the present invention.
FIG. 10 is a block diagram illustrating a configuration of an exposure control unit according to a sixth embodiment of the present invention.
FIG. 11 is a truth table of a control signal of a determination control unit according to the sixth embodiment.
FIG. 12 is a time chart illustrating a timing relationship of an exposure setting unit according to a seventh embodiment.
FIG. 13 is a block diagram illustrating a configuration and an operation of a flicker determination unit according to an eighth embodiment.
FIG. 14 is a block diagram illustrating a configuration and an operation of a flicker determination unit according to a ninth embodiment.
FIG. 15 is an explanatory diagram illustrating an example of imaging a backlight scene.
[Explanation of symbols]
1 CCD camera
2 PCMCIA
3 signal cable
4 Host computer
10 Optical lens
11 CCD
12 AGC circuit
13 A / D converter
14 Original transmitter
15 CCD drive unit
20 Exposure control unit
30 Image processing unit
ID image data
VD vertical sync signal
EEUD exposure control signal
EENR exposure control signal

Claims (7)

First delay means for delaying image data obtained by A / D conversion of an image signal output from the solid-state image sensor for one sampling period, and calculating a difference between the current time image data and the image data delayed for one sampling period. Primary differential means for obtaining, differential integrating means for integrating the differential signal for one field period, second delay means for delaying the integrated output of the differential signal for one field period, and difference between the previous field period delayed for one field period Comparing means for comparing the integrated value of the signal with the integrated value of the difference signal in the current field period; and synthesizing an exposure control signal for controlling the exposure amount of the solid-state imaging device from the result of the comparison by synchronizing with the field signal. Exposure control means for outputting to the element drive unit,
The exposure control unit controls the current exposure time of the solid-state imaging device when the comparison result of the comparison unit is larger than the integration value of the difference signal integrated during the previous field period. An electronic exposure control device, comprising: means for controlling in the opposite phase direction. A high-pass filter for extracting a high-frequency component of image data obtained by A / D-converting an imaging signal output from the solid-state imaging device; a high-frequency integration means for integrating the extracted high-frequency component for one field period; Delay means for delaying the output by one field period; comparison means for comparing the integrated value of the high-frequency component in the previous field period delayed by one field period with the integrated value of the high-frequency component in the current field period; Exposure control means for outputting an exposure control signal for controlling an exposure amount of the image sensor to the solid-state image sensor drive in synchronization with a field signal,
The exposure control means controls the current exposure time of the solid-state imaging device when the comparison result of the comparison means is that the integrated value of the high-frequency component integrated in the previous field period is greater than the integrated value of the high-frequency component integrated in the current field period. An electronic exposure control device, comprising: means for controlling in the opposite phase direction. A calculating means for calculating the absolute value of the difference between the integral value of the high-frequency component in the integration value and the one field period delayed by the previous field period of the high frequency components in the current field period, it is preset as the absolute value of the calculated difference Noise determination means for determining a magnitude relationship with the determined reference value,
Said exposure control means, the absolute value of the computed difference is under determination reference value or more, greater than the integrated value of the high-frequency component integration value obtained by integrating the current field period of the high frequency component comparison result is pre-field period the integral of the comparison means 3. The electronic exposure control device according to claim 2, further comprising means for controlling the current exposure time of the solid-state imaging device in a reverse phase direction in the event of the occurrence. Integrating means for integrating image data obtained by A / D conversion of an image signal output from the solid-state image sensor, and judging luminance from comparison between the integrated output and a preset dark lower limit reference value and preset bright upper limit reference value And a brightness determination unit that controls the exposure amount to be bright when the brightness is determined to be lower than the darker lower reference value and to be darker when the brightness is determined to be higher than the brighter upper reference value. Brightness control means for outputting an exposure control signal, and selector means for selecting one of the exposure control signal from the brightness control means and the exposure control signal from the exposure control means and outputting the selected signal to the solid-state element driving section in synchronization with a field signal And further comprising
The selector means selects the exposure control signal from the luminance control means when the average luminance value is equal to or less than the darker lower reference value or equal to or more than the brighter upper reference value, and otherwise selects the exposure control signal from the exposure control means. 3. The electronic exposure control device according to claim 2, wherein the electronic exposure control device selects and outputs the selected signal to a solid-state imaging device driving unit. Calculating means for calculating the absolute value of the difference between the integrated output of the high-frequency component during the current field period and the integrated output delayed by one field period; and the absolute value of the difference calculated by the calculating means and a predetermined luminance stability criterion. A stable state judging unit that judges a stable state by comparing values, an integrating unit that integrates image data obtained by A / D conversion of an image signal output from the solid-state image sensor, and an integral output and a preset integral output. Re-control determining means for determining whether or not to re-control exposure by comparing the re-control lower reference value and the re-control upper reference value; a stability determination signal output from the stable state determining means; Exposure determination means for outputting an exposure determination signal for stopping or continuing exposure control based on a logical determination of a re-control determination signal output from Electronic exposure control apparatus according to claim 2, further comprising a multiplexer for stopping or output based on the exposure determination signal an exposure control signal output to. Flicker determination integration means for integrating image data obtained by A / D conversion of an imaging signal output from the solid-state imaging element for one field period, and an integrated output from the flicker determination integration means on a lower side of a predetermined flicker. A flicker determination unit that determines flicker by comparing with a reference value and outputs a flicker determination signal; and an image storage unit that stores the image data based on the flicker determination signal,
When the flicker determination signal output from the flicker determination unit is a signal indicating a flicker phenomenon, the image storage unit does not write the image and holds the previously written image data. electronic exposure control apparatus according to any one of claims 1-5. An imaging permission determining unit that outputs an imaging permission signal to the image storage unit based on a flicker determination signal output from the flicker determining unit,
7. The electronic device according to claim 6, wherein the imaging permission determination unit determines that the subject is a solid black image by detecting that the plurality of flicker determination signals are output in succession, and outputs an imaging permission signal to the imaging accumulation unit. Exposure control device.

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