JP2013219576A - Imaging apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an imaging apparatus that outputs an image with good visibility by suppressing deterioration of an image of a farther scene.SOLUTION: An imaging apparatus 10 includes an imaging section 1, an exposure control section 2, a video signal enlargement section 4 which performs enlargement processing on an image, a video signal correction section 5 which performs gradation correction on a video signal, and a luminance statistic information calculation section 6 which calculates luminance statistic information as to the video signal. The video signal correction section 5 makes corrections for movement to the center of a luminance distribution by enlarging gradations of a luminance region having large appearance frequency. A control section 7 performs control to make a gradation correction amount smaller as an image enlargement rate becomes larger.

Description

  The present invention relates to an imaging apparatus.

  Regarding exposure control and gradation control technology of an imaging device, for example, Patent Document 1 discloses that “the average luminance and luminance distribution range of a main subject are calculated based on an acquired image of the imaging device, and the calculated main subject luminance distribution range and , Determining the control target average luminance level of the subject based on the required number of gradations corresponding to the main subject, and executing exposure control so that the main subject has the control target average luminance level. For a subject image whose average luminance level is shifted, a gradation conversion process for setting the average luminance level at approximately the center of the output luminance distribution is described. This configuration states that “optimal control of exposure and generation of an output image with balanced brightness are possible” (see summary).

JP 2008-148180 A

  An imaging apparatus such as a digital camera or a digital video camera has an exposure control function. General exposure control is realized by measuring the amount of light within the angle of view and adjusting the gain from the aperture, electronic shutter, and image sensor using the result. As a result, even in a scene with a wide dynamic range in which a dark part and a bright part are mixed, an image with good visibility having no blackout or whiteout part can be obtained.

  The imaging device is further equipped with an image enlargement function. An optical lens is used as the magnifying means. However, since the optical lens is expensive and large, an magnifying method by image processing is adopted to view a further distant scene. This complements the signal between pixels after conversion into a digital signal. In the enlargement method using image processing, it is expected that distant scenes will be magnified and fine details can be seen, but on the other hand, noticeable noise is magnified in dark areas (low luminance areas), which may lead to image degradation. is there.

  In Patent Literature 1, exposure control is performed in accordance with the average luminance of the subject, and gradation conversion processing is performed to set the average luminance level at approximately the center of the output luminance distribution, thereby generating an output image with balanced brightness. It is something to try. However, there is no particular description regarding enlargement by image processing, and when tone conversion processing is performed on a dark part where noise is conspicuous, there is a possibility that noise will increase and the image will deteriorate.

  An object of the present invention is to provide an imaging apparatus that suppresses deterioration of an image of a farther scene and outputs an image with high visibility.

  In order to solve the above object, the configuration described in the claims is adopted. For example, an imaging apparatus according to the present invention includes an imaging unit that photoelectrically converts incident light from a subject and outputs it as a video signal, an exposure control unit that controls an exposure amount of the imaging unit, and a video signal that enlarges the captured image. An expansion unit, a video signal correction unit that performs gradation correction on the video signal from the video signal expansion unit, a luminance statistical information calculation unit that calculates luminance statistical information for the video signal from the video signal expansion unit, A control unit that controls the operation of each unit of the imaging apparatus. Then, the control unit changes the gradation correction amount performed by the video signal correction unit according to the luminance statistical information obtained from the luminance statistical information calculation unit and the image enlargement magnification performed by the video signal expansion unit.

  According to the present invention, it is possible to output an image with good visibility while suppressing deterioration of an image of a farther scene.

1 is a diagram illustrating a basic configuration of an imaging apparatus according to Embodiment 1. FIG. The figure which shows the principle of exposure control. The figure which shows the principle of gradation control. The figure which shows an example of the gradation correction | amendment in a present Example. The figure which shows the relationship between the magnification K of an image, and correction amount ((alpha), (beta), (gamma)). FIG. 6 is a diagram illustrating a basic configuration of an imaging apparatus according to a second embodiment. The figure which shows an example of exposure correction and gradation correction | amendment in a present Example.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram illustrating a basic configuration of the imaging apparatus according to the first embodiment. The imaging device 10 includes an imaging unit 1, an exposure control unit 2, a camera signal processing unit 3, a video signal enlargement unit 4, a video signal correction unit 5, a luminance statistical information calculation unit 6, and a control unit 7.

  The imaging unit 1 has an imaging element such as a charge coupled device (CCD) or a complementary metal oxide semiconductor (CMOS) in order to photograph a subject, photoelectrically converts incident light from the subject, and outputs it as a video signal. The imaging unit 1 includes a lens group including a zoom lens and a focus lens, an iris for adjusting an exposure amount, a shutter, a CDS (photoconductive effect element), an AGC (Automatic Gain Control), an AD converter, and the like.

  The exposure control unit 2 acquires information on the luminance distribution calculated from the video signal output from the imaging unit 1, and determines a target exposure amount based on this information. Then, the iris diaphragm, shutter timing, and AGC gain amount of the imaging unit 1 are controlled so that the actual exposure amount approaches the target exposure amount.

  The camera signal processing unit 3 performs digital signal processing such as separation processing into luminance signals and color signals, gamma processing, color difference conversion processing, and white balance correction processing on the video signal output from the imaging unit 1. The video signal enlargement unit 4 enlarges the image received from the camera signal processing unit 3 at a magnification K set by the control unit 7. The enlargement process is performed by complementing signals between pixels.

  The video signal correction unit 5 performs gradation correction processing on the video signal received from the video signal expansion unit 4 according to the correction amount γ set from the control unit 7. The gradation correction is to eliminate the unevenness of the luminance distribution by performing non-linear conversion such as enlarging the gradation of a part of luminance levels. Thereafter, the video signal is output to a video display device, a recording device, a moving image compression device, a PC, etc. (not shown).

  The luminance statistical information calculation unit 6 calculates the luminance statistical information S for the video signal received from the video signal expansion unit 4. Specifically, subject recognition is performed, and brightness statistical information is calculated for a region where the subject exists. The luminance statistical information S is information such as a histogram, a maximum value / minimum value, and an average luminance. The control unit 7 controls the operation of each unit of the imaging device 10. In particular, in this embodiment, the image enlargement factor K is set for the video signal enlargement unit 4 and the correction amount γ for the video signal correction unit 5 is determined based on the luminance statistical information S calculated by the luminance statistical information calculation unit 6. Set.

Here, the principle of exposure control performed by the exposure control unit 2 and gradation control performed by the video signal correction unit 5 will be described in comparison.
FIG. 2A is a diagram showing the principle of exposure control. The horizontal axis represents the amount of light incident on the image capturing unit 1 (brightness of the subject), and the vertical axis represents the output signal (luminance level) from the image capturing unit 1. The inclination (conversion coefficient) of the conversion line 100 depends on the exposure amount, and changes depending on settings such as the iris diaphragm and shutter timing of the imaging unit 1. When the amount of incident light is too small or too large, the output signal is saturated and becomes a black level (minimum luminance value) or a white level (maximum luminance value).

  In the exposure control, the exposure amount is adjusted so that the output signal is converted into a linear range between the black level and the white level according to the distribution of the amount of incident light on the imaging unit 1. That is, the inclination (conversion coefficient) of the straight line 100 is changed from α0 (normal value) by ± α and moved like the straight lines 101 and 101 ′. Alternatively, control is performed to change the position of the intercept (saturation start point) P from the black level by ± β from β0 (normal value). As a result, for example, when the brightness distribution of incident light is indicated by reference numeral 201, the luminance distribution of the video output signal is corrected as indicated by reference numeral 202 by switching to the conversion line 101 by exposure control. Hereinafter, the changes α and β of the conversion line 100 in exposure control are referred to as exposure correction amounts.

FIG. 2B is a diagram illustrating the principle of gradation control. The horizontal axis represents the input signal (brightness) to the video signal correction unit 5, and the vertical axis represents the output signal (brightness level) from the video signal correction unit 5. Normally, linear conversion represented by a straight line 100 (slope = 1) is performed between the two, but in gradation control, nonlinear conversion is performed in which the slope varies depending on the level of the input signal. That is, the intermediate portion of the conversion line 100 is displaced by ± γ to change it as curves 102 and 102 ′, and the inclination of the intermediate region is larger than 1 (enlarged gradation) or smaller than 1 (reduced gradation) ) Thereby, when the distribution of the input signal is biased, the region having a high appearance frequency can be moved to the center of the distribution by enlarging the gradation of the region having a high appearance frequency. For example, when the brightness distribution of the input signal is indicated by reference numeral 203, the luminance distribution of the video output signal is corrected as indicated by reference numeral 204 by switching to the conversion curve 102 by gradation control. Hereinafter, the change amount γ of the conversion line 100 in the gradation control is referred to as a gradation correction amount.
In this embodiment, the above gradation control is performed in association with image enlargement.

  FIG. 3 is a diagram illustrating an example of gradation correction in this embodiment. Reference numeral 301 in (a) is an example of the luminance statistical information S (luminance distribution) of the video signal output from the video signal expansion unit 4, and reference numeral 302 in (b) is the target of the luminance statistical information S after gradation correction. Show properties. The horizontal axis indicates the luminance value, and the vertical axis indicates the frequency of appearance in the video. The luminance statistical information S is calculated by the luminance statistical information calculation unit 6 and sent to the control unit 7.

  The video signal output from the video signal enlarging unit 4 is subjected to exposure control by the imaging unit 1 in the previous stage, but the luminance distribution is biased in a scene with a large contrast between light and dark in the screen. In (a), the portion 301a having a high appearance frequency is biased toward the low luminance side, and depending on the subject, an image in which blackout is conspicuous is not visible.

  In such a case, in order to improve the visibility, the control unit 7 controls the gradation correction so that the frequently occurring portion 301a (or the average luminance of the screen) is located at the center of the luminance distribution. Reference numeral 302 in (b) represents the target characteristic of the luminance statistical information S after gradation correction, and determines the amount of movement 303 for positioning the frequently occurring portion 301a at the reference numeral 302a that is the center of the luminance distribution. Then, the gradation correction amount γ corresponding to the movement amount 303 is determined from FIG. 2B and sent to the video signal correction unit 5.

  The video signal correction unit 5 corrects the gradation of the video signal according to the correction amount γ, and generates a video signal having target luminance statistical information indicated by reference numeral 302. In this way, even in a scene where the brightness distribution of the input signal has a large contrast and a black shadow as indicated by reference numeral 301, the black shadow can be eliminated by correcting the gradation of the low-luminance portion having a high appearance frequency. Here, the case where there is a blackout has been described, but the same applies to the case where there is a whiteout.

  The above is the description of the gradation correction operation performed by the video signal correction unit 5, but the control unit 7 controls gradation correction in association with image enlargement. When the magnification K set in the video signal enlargement unit 4 is 1, the control unit 7 moves the amount of movement so that the characteristic 301 of the luminance statistical information S becomes the target characteristic 302 as described with reference to FIG. 303 is determined and the video signal correction unit 5 is instructed with a gradation correction amount γ corresponding thereto. On the other hand, when the magnification K set in the video signal enlargement unit 4 is larger than 1, the gradation correction amount γ instructed to the video signal correction unit 5 is given smaller than the above value.

  FIG. 4 is a diagram showing the relationship between the image magnification K and the gradation correction amount γ. When the magnification K is 1, the correction amount γ (which is the maximum value) for setting the luminance statistical information S as the target characteristic is set as it is. As the magnification increases, the correction amount γ is decreased, and γ = 0 when the magnification is equal to or greater than a predetermined value (threshold value) A. This threshold A is determined from a magnification at which noise is determined to be conspicuous when gradation correction is applied. From the viewpoint of the above control, when the output image includes a blackout or whiteout portion, control is performed to reduce the blackout or whiteout portion as the image enlargement magnification decreases.

  According to this embodiment, it is possible to perform gradation control according to the luminance distribution of the area where the subject exists, and to correct the image to a suitable image with no blackout or whiteout. At that time, considering the image quality deterioration due to the gradation expansion for the noise that increases as the image expands, the gradation correction is performed in a range where the image quality deterioration is not conspicuous. It is possible to output an image with good visibility while suppressing deterioration.

  FIG. 5 is a diagram illustrating a basic configuration of the imaging apparatus according to the second embodiment. The imaging device 10 ′ has the same configuration as that of the first embodiment (FIG. 1), but the control unit 7 uses the luminance statistical information S obtained from the luminance statistical information calculation unit 6 to expose not only the video signal correction unit 5 but also the exposure. The control unit 2 is also controlled. The parts corresponding to those in FIG.

  FIG. 6 is a diagram showing an example of exposure correction and gradation correction in this embodiment. Reference numeral 601 in (a) is an example of luminance statistical information S (luminance distribution) of the video signal output from the video signal expansion unit 4, and reference numeral 602 in (b) indicates target characteristics of the luminance statistical information S after exposure correction. The reference numeral 603 in (c) indicates the target characteristic of the luminance statistical information S after gradation correction. In this embodiment, exposure control and gradation control are combined to generate an image with better visibility.

  The video signal output from the video signal enlarging unit 4 is uneven in luminance distribution in a scene having a large contrast between light and dark in the screen even if normal exposure control is performed. In (a), a portion having a high appearance frequency has a distribution biased to both sides of the high luminance side 601a and the low luminance side 601b. For this reason, the image has whiteout on the high luminance side and blackout on the low luminance side.

  In such a case, the control unit 7 first performs exposure correction control to move the portion 601a having a high appearance frequency to the center side of the luminance distribution in order to eliminate whiteout on the high luminance side. Reference numeral 602 in (b) indicates the target characteristic of the brightness statistical information S after exposure correction, and the moving amount 604 for locating the frequent part 601a toward the center of the brightness distribution and positioning it at the reference numeral 602a is determined. Then, exposure correction amounts α and β corresponding to the movement amount 604 are determined from FIG. 2A and sent to the exposure control unit 2.

  The exposure control unit 2 determines a target exposure amount based on the exposure correction amounts α and β, and adjusts the iris diaphragm, shutter timing, and AGC gain amount of the imaging unit 1. As a result, a video signal having target luminance statistical information indicated by reference numeral 602 is obtained, and whiteout on the high luminance side is eliminated. The control unit 7 may send information on the movement amount 604 to the exposure control unit 2 so that the exposure control unit 2 determines the exposure correction amounts α and β.

  In the luminance statistical information S indicated by reference numeral 602 obtained in (b), whiteout on the high luminance side is eliminated, but the phenomenon of blackout is worsening on the low luminance side. That is, the portion 601b having a high appearance frequency moves further to the low luminance side and exists as the reference numeral 602b. Therefore, the control unit 7 performs gradation correction control for moving the portion 602b having a high appearance frequency to the center side of the luminance distribution in order to improve blackout on the low luminance side. Reference numeral 603 in (c) indicates the target characteristic of the luminance statistical information S after gradation correction, and the amount of movement 605 for locating the high frequency portion 602b on the low luminance side is shifted to the central side of the luminance distribution and positioned at the reference numeral 603b. To do. Then, the gradation correction amount γ corresponding to the movement amount 605 is determined from FIG. 2B and sent to the video signal correction unit 5. Here, by performing effective gradation correction only on the low luminance side, the luminance distribution on the high luminance side, that is, the position of the portion 602a having a high appearance frequency is stored as it is as 603a.

  The video signal correction unit 5 corrects the gradation of the video signal on the low luminance side according to the correction amount γ, and generates a video signal having target luminance statistical information indicated by reference numeral 603. With the above-described operation, it is possible to obtain a video with high visibility without blackout or overexposure even in a scene where overexposure and overexposure can be seen with only normal exposure control. In this case, the whiteout is first eliminated and then the blackout is eliminated. However, the control can be performed in the reverse order.

  The above is the description of the operation combining the exposure correction and the gradation correction performed by the exposure control unit 2 and the video signal correction unit 5, and the control unit 7 controls these corrections in association with the enlargement of the image. When the magnification K set in the video signal enlargement unit 4 is 1, the control unit 7 moves so that the characteristic 601 of the luminance statistical information S becomes the target characteristic 602 as described with reference to FIG. 604 is determined, and exposure correction amounts α and β corresponding thereto are instructed to the exposure control unit 2. In addition, the movement amount 605 is determined so that the characteristic 602 of the luminance statistical information S after exposure correction becomes the target characteristic 603, and a corresponding gradation correction amount γ is instructed to the video signal correction unit 5. To do. On the other hand, when the magnification K set in the video signal enlargement unit 4 is larger than 1, the correction amounts α and β for the exposure control unit 2 and the correction amount γ for the video signal correction unit 5 are given smaller than the above values. To.

  The relationship between the enlargement magnification K and the correction amounts α, β, γ at that time is the same as in FIG. That is, when the magnification K is 1, the correction amounts α, β, and γ for setting the luminance statistical information S as the target characteristic are set as they are. The correction amount is decreased as the magnification K increases, and α, β, γ = 0 when the magnification is equal to or greater than a predetermined value (threshold value) A. The threshold value A may be given different values for exposure correction and gradation correction.

  According to the present embodiment, exposure control and gradation control can be executed in combination according to the luminance distribution of the area where the subject is present, and correction can be made to a suitable image without blackout or overexposure. At that time, taking into account image quality degradation due to tone expansion for noise that increases with image enlargement, exposure adjustment and tone correction are performed in a range where image quality degradation is not noticeable, so a farther scene It is possible to output an image with good visibility while suppressing deterioration of the image.

  In addition, this invention is not limited to an above-described Example, Various modifications are included. For example, the above-described embodiments have been described in detail for easy understanding of the present invention, and are not necessarily limited to those having all the configurations described. Further, a part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of one embodiment. Further, it is possible to add, delete, and replace other configurations for a part of the configuration of each embodiment.

  In addition, each of the above-described configurations may be configured such that some or all of them are configured by hardware, or are implemented by executing a program by a processor. Further, the control lines and information lines indicate what is considered necessary for the explanation, and not all the control lines and information lines on the product are necessarily shown. Actually, it may be considered that almost all the components are connected to each other.

1: imaging unit,
2: Exposure control unit,
3: Camera signal processing unit,
4: Video signal expansion section,
5: Video signal correction unit,
6: Luminance statistical information calculation unit,
7: Control unit,
10, 10 ′: imaging device,
K: Image magnification
S: Luminance statistics information,
α, β: exposure correction amount,
γ: gradation correction amount.

Claims (6)

In an imaging device that shoots an object and outputs an enlarged image,
An imaging unit that photoelectrically converts incident light from a subject and outputs it as a video signal;
An exposure control unit for controlling an exposure amount of the imaging unit;
A video signal enlarging unit for enlarging the captured image;
A video signal correction unit that performs gradation correction on the video signal from the video signal expansion unit;
A luminance statistical information calculation unit for calculating luminance statistical information for the video signal from the video signal expansion unit;
A control unit that controls the operation of each unit of the imaging device,
The control unit changes a gradation correction amount performed in the video signal correction unit according to the luminance statistical information obtained from the luminance statistical information calculation unit and an image enlargement magnification performed in the video signal expansion unit. An imaging device. The imaging device according to claim 1,
The control unit further changes an exposure correction amount performed by the exposure control unit in accordance with the luminance statistical information obtained from the luminance statistical information calculation unit and an image enlargement magnification performed by the video signal enlargement unit. An imaging device. The imaging device according to claim 1,
The video signal correction unit performs a correction to move the luminance region having a high appearance frequency to the center of the luminance distribution by enlarging the gradation of the luminance region having a high appearance frequency,
The image pickup apparatus according to claim 1, wherein the control unit controls the video signal correction unit to reduce the gradation correction amount as the image enlargement magnification in the video signal enlargement unit increases. The imaging device according to claim 2,
The exposure control unit performs correction for moving a luminance region having a large appearance frequency to the center of the luminance distribution by changing an exposure amount in the imaging unit,
The video signal correction unit performs a correction to move the luminance region having a high appearance frequency to the center of the luminance distribution by enlarging the gradation of the luminance region having a high appearance frequency,
The control unit controls the exposure control unit and the video signal correction unit to decrease the exposure correction amount and the gradation correction amount as the image enlargement magnification in the video signal enlargement unit increases. An imaging device that is characterized. In the imaging device according to claim 3 or 4,
When the image enlargement magnification in the video signal enlargement unit is equal to or greater than a threshold, the control unit applies the exposure correction amount or the exposure correction amount to the video signal correction unit or the exposure control unit and the video signal correction unit. And an image pickup apparatus that controls the gradation correction amount to be zero. In an imaging device that shoots an object and outputs an enlarged image,
An imaging unit that photoelectrically converts incident light from a subject and outputs it as a video signal;
An exposure control unit for controlling an exposure amount of the imaging unit;
A video signal enlarging unit for enlarging the captured image;
A video signal correction unit that performs gradation correction on the video signal from the video signal expansion unit;
A control unit that controls the operation of each unit of the imaging device,
When the image to be output includes a blackout or whiteout portion, the control unit controls to reduce the blackout or whiteout portion as the image enlargement magnification performed by the video signal enlargement unit decreases. An imaging apparatus characterized by that.

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