JP5906057B2 - Imaging apparatus and control method thereof - Google Patents

Description

  The present invention relates to an imaging apparatus and a control method thereof, and more particularly to an auto black balance adjustment technique.

  In the output signal of an imaging device such as a digital camera or a mobile phone, the level of the signal representing “black” changes due to the temperature rise of the image sensor or individual differences. Processing for correcting such a change in the black signal level is black balance adjustment processing. The black balance adjustment can be realized, for example, by adjusting an offset value added to the R pixel, G pixel, and B pixel signals output from the image sensor so that the color difference signal becomes 0 in a light-shielded state. In addition, an image pickup apparatus having an auto black balance adjustment (hereinafter referred to as ABB adjustment) function automatically determines an offset value (or a correction value of an offset value) for each color pixel signal from an image signal, and automatically adjusts the black balance. be able to.

  Since the ABB adjustment determines the offset value on the premise that the light is shielded from light, a correct offset value cannot be obtained when the ABB adjustment is performed in a state where the light is not shielded. Therefore, for example, it is known that ABB adjustment is performed when the luminance level of an image signal is lower than a predetermined value.

  For example, Patent Document 1 discloses a technique for automatically determining whether to adjust black balance or white balance according to a luminance signal level. Specifically, the white balance is adjusted if the luminance level is 50 [IRE] or more, the black balance is adjusted if it is 5 [IRE] or less, and is not adjusted if it is 5 to 50 [IRE]. Here, IRE (Institute of Radio Engineers) is a unit in which the luminance level of 100% white of a video signal is 100 [IRE].

Japanese Patent Laid-Open No. 10-211166

  However, in the method of Patent Document 1, when the luminance signal level is equal to or lower than a predetermined level, black balance adjustment is performed without considering other conditions. For example, the black balance is adjusted even when the incident light is attenuated by an aperture or an ND (Neutral Density) filter in the optical path and the luminance signal level becomes a predetermined level or less. Note that the ND filter is not only attached to the front end of the lens, but is often built in the imaging apparatus to be used in place of the diaphragm or to be used together with the diaphragm.

However, when the luminance signal level is below a predetermined level due to the influence of the diaphragm and the ND filter, the luminance signal level fluctuates due to a change in the environment, unlike a state where light is blocked by a lens barrier or a lens cap. For this reason, when the illumination is turned on or the surroundings become bright due to moving to a bright place, the luminance signal level may exceed a predetermined level during black balance adjustment. For example, even if the number [IRE] changes, the luminance signal level exceeds a predetermined level, so that it is possible that the user will not notice the environmental change during the black balance adjustment.
In such a case, it goes without saying that the accuracy of the black balance adjustment result is lowered.

  The present invention has been made in view of such a problem of the prior art, and an object thereof is to provide an imaging apparatus capable of performing more stable black balance adjustment and a control method thereof.

The above-described object is based on the evaluation value based on the image signal output from the image sensor and the predetermined black reference value, the correction value for adjusting the black balance of the image signal output from the image sensor and the image sensor. calculation means for calculating Te, and controls the dimming element to reduce the amount of light entering the imaging device, an imaging apparatus having a control means for controlling the dimming of incident light quantity by the dimming member, reduced The optical member includes an optical filter, and the calculating means calculates the correction value when the luminance value based on the image signal output from the imaging element is lower than a predetermined threshold value with the optical filter retracted from the optical path. This is achieved by an imaging device characterized in that it performs.

  With such a configuration, according to the present invention, more stable black balance adjustment can be performed.

1 is a schematic configuration diagram of a digital camera as an example of an imaging apparatus according to a first embodiment of the present invention. The flowchart which shows the method of ABB adjustment which concerns on 1st Embodiment of this invention. Schematic configuration diagram of a digital camera as an example of an imaging apparatus according to a second embodiment of the present invention The flowchart which shows the method of ABB adjustment which concerns on 2nd Embodiment of this invention.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.
<First Embodiment>
FIG. 1 is a schematic configuration diagram of a digital camera as an example of an imaging apparatus according to the first embodiment of the present invention. It is assumed that the digital camera of the present embodiment is of a type that can exchange lenses.

  The digital camera 100 includes an optical system 101, an ND unit 102, an imaging unit 103, an analog front end (hereinafter referred to as AFE) 104, a detection unit 105, a black balance (hereinafter referred to as BB) correction unit 106, a signal processing unit 107, and an operation unit 108. The system control unit 109 is included.

  1 shows a lens cap 110 attached to the tip of the optical system 101 and a body cap 111 attached to a lens mount (not shown) of the body when the optical system 101 is removed. Normally, the body cap 111 is removed when the optical system 101 is attached, and the lens cap 110 is also removed during photographing.

  The system control unit 109 controls the optical system 101, the ND unit 102, the imaging unit 103, the AFE 104, the detection unit 105, the BB correction unit 106, and the signal processing unit 107. Further, the system control unit 109 obtains a detection signal from the detection unit 105. The operation content of the operation unit 108 is also detected by the system control unit 109.

  The optical system 101 is a replaceable zoom lens having an aperture, a focusing lens, and a variable power lens and capable of autofocus control. The aperture ratio (aperture value) of the diaphragm, the position of the focusing lens, and the position of the variable power lens (lens magnification) can be controlled by the system control unit 109.

  The ND unit 102 inserts an ND filter into the optical path or retracts it from the optical path under the control of the system control unit 109. When the ND filter is inserted into the optical path, the amount of light incident on the imaging unit 103 decreases. In this embodiment, both the diaphragm and the ND filter function as a light reducing member that reduces incident light to the image sensor.

  The imaging unit 103 includes an imaging element such as a complementary metal oxide semiconductor (CMOS) image sensor or a charge coupled device (CCD) image sensor (not shown). The imaging unit 103 also includes a timing generator (TG).

  When a subject (not shown) is photographed, light that has passed through the optical system 101 and the ND unit 102 (an ND filter may not be inserted in the optical path) is imaged on an imaging element in the imaging unit 103. . The imaging device outputs an analog image signal having a voltage corresponding to the amount of light incident on each pixel during the accumulation (exposure) time determined by the system control unit 109 according to the camera settings.

  The AFE 104 performs analog-digital (A / D) conversion of the analog image signal to obtain a digital image signal (hereinafter referred to as image data). Further, signal amplification is performed in accordance with a command from the system control unit 109. The image data subjected to signal amplification is sent to the detection unit 105 and the BB correction unit 106.

  The detection unit 105 calculates the average value of each of the R pixel, G pixel, and B pixel and the average value of the luminance signal included in the luminance detection frame set by the system control unit 109 and transmits them to the system control unit 109. Note that the value of the luminance signal (luminance value) is obtained by performing a general calculation using the values of the R pixel, the G pixel, and the B pixel.

  The BB correction unit 106 adds an offset value to each of the R pixel, the G pixel, and the B pixel. The offset value is stored in the BB correction unit 106. The stored offset value can be changed by the system control unit 109. The corrected signal is transmitted to the signal processing unit 107.

  The signal processing unit 107 performs white balance adjustment, gamma correction, edge correction, and the like. The image data that has passed through the signal processing unit 107 is subjected to video signal processing, and is output to a display device (including a viewfinder) (not shown) included in the digital camera 100 or an external device.

  When a switch or touch panel included in the operation unit 108 is operated, a signal is sent to the system control unit 109, and a signal is sent from the system control unit 109 to each block in order to perform processing based on the signal.

The ABB adjustment operation in the present embodiment will be described with reference to the flowchart shown in FIG.
For example, when the menu button of the operation unit 108 is operated, the system control unit 109 displays a menu screen on the display device. The user can operate the arrow key and the execution key included in the operation unit 108 to instruct the imaging apparatus to execute the ABB adjustment. Alternatively, the operation unit 108 may include a button or key that instructs execution of ABB adjustment.

  For example, when execution of ABB adjustment is instructed, the system control unit 109 shields the user from a message such as “Attach a lens cap or body cap. Press the OK button when installation is complete.” Can be encouraged. Messages can be output by display or voice.

  When a confirmation input is made by the user (in this example, an OK button is pressed), the system control unit 109 starts ABB adjustment. First, the system control unit 109 detects whether the optical system 101 is attached. For example, the system control unit 109 transmits a command to the optical system 101 through the lens mount, and determines that the optical system 101 is attached if there is a correct response, and that the optical system 101 is not attached if there is no response.

  If it is determined that the optical system 101 is attached, the system control unit 109 opens the diaphragm of the optical system 101 and causes the ND unit 102 to retract the ND filter from the optical path (S201). If it is determined that the optical system 101 has been removed, the diaphragm cannot be controlled, and the system control unit 109 causes only the ND filter to be retracted.

  Next, the system control unit 109 compares the average luminance value acquired from the detection unit 105 with a preset light-shielding determination threshold value (S202). If the average luminance value is equal to or greater than the threshold value, the system control unit 109 determines that the light is not shielded (or is insufficiently shielded), and interrupts the ABB adjustment (S203). After the interruption, a message notifying that the ABB adjustment has been interrupted, such as “ABB adjustment has been interrupted due to insufficient light shielding”, is displayed or outputted (S204).

  On the other hand, when the average luminance value is lower than the threshold value, the system control unit 109 determines that the light is shielded (the light is sufficiently shielded), and starts the black balance adjustment. First, the system control unit 109 acquires an average value for each of R, G, and B pixels calculated by the detection unit 105 (S205). Then, the system control unit 109 calculates a difference between the predetermined black reference value and the average value as an offset value (S206). For example, if the black reference value is 256 and the average value of the acquired R is 250, the difference is 6, and the offset value added to R is +6. Thus, the offset value is a correction value for making the average value of each color pixel output in a light-shielded state equal to the black reference value.

  The system control unit 109 sets the offset value calculated for each color in the BB correction unit 106 (S207). If the output value of the BB correction unit 106 is the same as that at the time of ABB adjustment, the average value of the R pixel, the G pixel, and the B pixel is the black reference value 256. After setting the offset value, the system control unit 109 displays or outputs a message such as “ABB adjustment OK” indicating that the ABB adjustment is completed (S208). After completing the ABB adjustment, the system control unit 109 returns the control of the diaphragm and the ND filter to the normal control.

  In the present embodiment, as a case where the effect of the present invention is most obtained, the brightness level detected in a state where the dimming action by a dimming member such as a diaphragm or an ND filter is invalid is not more than a threshold value. As an example, the ABB adjustment is executed. However, the effect of the present invention can be obtained even if the light reducing action of the light reducing member is not completely invalidated.

  That is, if the ABB adjustment is executed on the condition that the detected luminance level is less than or equal to the threshold value in a state where the amount of reduction of the incident light amount by the light reducing member such as the diaphragm or the ND filter is less than the maximum amount, the light is not shielded. The possibility that the ABB adjustment is started in the state can be reduced.

  For example, when the ND filter is fixed, only the control for releasing the aperture may be performed. Further, the present invention can be applied even when an element capable of electrically changing the transmittance is provided in the optical path instead of a member inserted into or removed from the optical path, such as an ND filter. In this case, the luminance may be determined by setting the transmittance higher than the lowest state.

  In other words, more generally speaking, the brightness is determined by controlling the dimming rate due to the dimming action of the dimming member that reduces the amount of light incident on the image sensor to be not maximum, and thus the light is not shielded. The possibility of starting the ABB adjustment in the state can be reduced.

The detection signal is not limited to a value for each color, and a signal (evaluation value) that understands the balance (reciprocal relationship) of the values of the R pixel, the G pixel, and the B pixel may be obtained. Further, the correction method is not limited as long as the BB correction can be performed so that the value of the color signal output at the time of shading is close to zero.
In addition, instead of comparing the threshold value for shading determination and the average luminance value, a representative luminance value is selected from a plurality of luminance values acquired from the detection unit 105, and the representative luminance value is compared with the threshold value. It may be.

Second Embodiment
Next, a second embodiment of the present invention will be described. Since the image pickup apparatus according to the first embodiment does not include a light shielding unit, it is necessary to block incident light with another member such as a lens cap or a body cap. In the present embodiment, a case will be described in which the present invention is applied to an imaging apparatus that includes a light shielding unit and can shield the image sensor by the control of the system control unit 109.

  FIG. 3 shows a schematic configuration diagram of a digital camera 300 as an example of an imaging apparatus according to the present embodiment. In FIG. 3, the same reference numerals are given to the same components as those in FIG. 1, and duplicate descriptions are omitted. As is clear from a comparison between FIGS. 1 and 3, the camera according to the present embodiment includes a light shielding unit 301 between the ND unit 102 and the imaging unit 103. The light shielding unit 301 includes a light shielding member that can control blocking / non-blocking of incident light to the image sensor by the system control unit 109, such as a mechanical shutter.

  In a state where the light is shielded by the light shielding unit 301, an analog image signal without incident light is output from the imaging unit 103. Since other configurations are the same as those of the first embodiment, description thereof is omitted.

  The ABB adjustment operation in the present embodiment will be described with reference to the flowchart shown in FIG. In FIG. 4, the same reference numerals are assigned to the same components as those in FIG. In the present embodiment, after the ABB adjustment is started, the system control unit 109 first controls the light shielding unit 301 to set the light shielding state (S401). Since the subsequent steps are the same as those in the first embodiment, description thereof is omitted.

  If the method of the present embodiment is used, it is possible to reduce the possibility that the ABB adjustment is erroneously started when the light shielding member included in the light shielding unit 301 does not operate normally due to some problem and the light cannot be shielded.

  Although the mechanical shutter is taken as an example of the light shielding member, when the light can be completely shielded by the diaphragm mounted on the optical system 101, it may be shielded by controlling the diaphragm. When the diaphragm is used as a light shielding member in this way, the diaphragm cannot be opened, but the possibility of starting the ABB adjustment without being shielded can be realized only by controlling the ND filter.

Similarly to the first embodiment, in the present embodiment, the luminance is determined after controlling so that the dimming rate due to the dimming action of the dimming member that reduces the amount of light incident on the image sensor is not maximum. Good.
An application example in the first embodiment is also applicable to this embodiment.

  In the two embodiments described above, the control of the diaphragm and the ND filter is returned to the normal control after the ABB adjustment is finished. However, the control may be returned to the normal control before the ABB adjustment is finished. For example, if the exposure period (ABB adjustment exposure period) for obtaining the image data used by the detection unit 105 to calculate the average value of the R pixel, the G pixel, and the B pixel and the average value of the luminance signal ends, the light is blocked. Therefore, it is only necessary to return to the normal control after the end of the exposure period for ABB adjustment.

In the above-described two embodiments, the case where the present invention is applied to a digital camera incorporating an ND filter has been described. However, even if the ND filter is not incorporated, the light is not shielded only by controlling the diaphragm. Thus, the possibility of starting the ABB adjustment can be reduced.
In addition, the present invention can be applied to an image pickup apparatus with a built-in lens instead of a lens-exchangeable type as shown in the above two embodiments.

  The present invention has been described in detail on the basis of preferred embodiments. However, the present invention is not limited to these specific embodiments, and various forms can be applied to the present invention without departing from the gist of the present invention. included.

Claims (9)

An image sensor;
Calculation means for calculating a correction value for adjusting the black balance of the image signal output by the image sensor based on an evaluation value based on the image signal output by the image sensor and a predetermined reference value of black;
A control unit that controls a light reduction member that reduces the amount of incident light on the image sensor and controls a light reduction rate of the amount of incident light by the light reduction member,
The dimming member includes an optical filter;
The calculation means calculates the correction value when a luminance value based on an image signal output from the image sensor in a state where the optical filter is retracted from an optical path is lower than a predetermined threshold value. An imaging device. An image sensor;
Calculation means for calculating a correction value for adjusting the black balance of the image signal output by the image sensor based on an evaluation value based on the image signal output by the image sensor and a predetermined reference value of black;
A control unit that controls a light reduction member that reduces the amount of incident light on the image sensor and controls a light reduction rate of the amount of incident light by the light reduction member,
The dimming member includes an aperture;
It said calculation means, when the luminance value based on the image signal in which the diaphragm is output from the image sensor in a state of open is lower than the determined threshold Me pre, you and performs calculation of the correction value imaging device. An image sensor;
Calculation means for calculating a correction value for adjusting the black balance of the image signal output by the image sensor based on an evaluation value based on the image signal output by the image sensor and a predetermined reference value of black;
A control unit that controls a light reduction member that reduces the amount of incident light on the image sensor and controls a light reduction rate of the amount of incident light by the light reduction member,
The dimming member includes an optical filter and a diaphragm;
Wherein, prior to SL when the luminance value based on the image signal optical filter state and the diaphragm retracted from the optical path is output in a state of free from the image sensor is lower than a determined threshold Me pre, the correction it characterized in that to calculate the value imaging device. Furthermore, it has a light shielding means for switching between blocking and non-blocking of incident light to the image sensor,
The calculation means sets the light shielding means in a light shielding state, and a luminance value based on an image signal output from the imaging element in a state where the light attenuation rate of the incident light amount by the light reducing member is not maximum is greater than the predetermined threshold value . when low, the imaging apparatus according to any one of claims 1 to 3, characterized in that to calculate the correction value. An image sensor;
Calculation means for calculating a correction value for adjusting the black balance of the image signal output by the image sensor based on an evaluation value based on the image signal output by the image sensor and a predetermined reference value of black;
A control unit that controls a light reduction member that reduces the amount of incident light on the image sensor and controls a light reduction rate of the amount of incident light by the light reduction member,
The calculation means calculates the correction value when a luminance value based on an image signal output from the image sensor in a state where the dimming rate is minimum is lower than a predetermined threshold value. An imaging device. An image sensor ;
An optical filter that reduces the amount of light incident on the image sensor when inserted into an optical path ,
Control means, and controlling the optical filter in a state of being retracted from the optical path,
Wherein when the luminance value based on the image signal output from the image sensor in a state in which the optical filter is retracted from the optical path is less than the determined threshold Me pre calculation means, an image signal in which the image pickup device outputs the black And a step of calculating a correction value for adjusting the balance based on an evaluation value based on an image signal output from the image sensor and a predetermined black reference value. Method. An image sensor;
  A control method for an imaging apparatus having a diaphragm for adjusting the amount of light incident on the imaging element,
  A control means for controlling the aperture to an open state;
  When the luminance value based on the image signal output from the image sensor with the aperture opened is lower than a predetermined threshold, the calculation unit adjusts the black balance of the image signal output from the image sensor. And a step of calculating a correction value based on an evaluation value based on an image signal output from the image sensor and a predetermined black reference value. An image sensor;
  An optical filter that reduces the amount of light incident on the image sensor when inserted into the optical path;
  A control method for an imaging apparatus having a diaphragm for adjusting the amount of light incident on the imaging element,
  A control means for controlling the aperture to an open state;
  The control means controlling the optical filter in a state retracted from the optical path;
  When the luminance value based on the image signal output from the image sensor with the optical filter retracted from the optical path and the diaphragm open is lower than a predetermined threshold value, the calculation unit includes the image sensor And a step of calculating a correction value for adjusting the black balance of the output image signal based on an evaluation value based on the image signal output from the image sensor and a predetermined black reference value. A method for controlling the imaging apparatus. An image sensor;
  A method of controlling an imaging apparatus having a dimming member that reduces the amount of light incident on the imaging element,
  A step of controlling the dimming member in a state where the dimming rate of the incident light quantity by the dimming member is minimized,
  When the luminance value based on the image signal output from the image sensor in a state where the dimming rate is minimized is lower than a predetermined threshold value, the calculation unit calculates the black balance of the image signal output from the image sensor. A method for controlling an image pickup apparatus, comprising: calculating a correction value for adjustment based on an evaluation value based on an image signal output from the image pickup element and a predetermined black reference value.

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