JP4996491B2 - Imaging device - Google Patents

Description

  The present invention relates to an imaging apparatus that captures an image of a target space, and more particularly to an imaging apparatus that is used to recognize an object that exists in the target space.

  2. Description of the Related Art Conventionally, various image processing apparatuses for recognizing an object in a target space (for example, face authentication) have been provided. In this type of image processing apparatus, a solid-state image sensor (for example, an image sensor) is used. The image pickup apparatus that has been used is widely used. In recognition of an object, a grayscale image is widely used. However, since the grayscale image reflects the light and darkness of the target space, fluctuations in ambient light (ambient light) (changes in the amount of ambient light) to be influenced. For this reason, in an image processing apparatus using an imaging apparatus that outputs a grayscale image, there has been a problem that the recognition rate of an object is reduced in a place where the fluctuation of ambient light is large.

  In view of such a problem, a light source unit that emits light to a target space such as a light emitting diode (LED) is provided, and a gray-scale image (image when the light source is turned on) captured when the light source unit is turned on, There has been proposed an image processing device using an imaging device that outputs a difference image (amplitude image) from a grayscale image (image when the light source is turned off) captured when the light is turned off (see, for example, Patent Document 1).

The image when the light source is on reflects the ambient light in the target space and the light emitted to the target space from the light source unit. The image when the light source is off reflects the ambient light in the target space. Since the difference image between the time image and the light source extinction image is an image that reflects only the light irradiated to the target space from the light source unit, the environment light can be changed by recognizing the object using the difference image. The object can be recognized without lowering the recognition rate even in a place where is large.
JP 2006-155422 A

  However, since the light source lighting image reflects the ambient light in the target space and the light applied to the target space from the light source unit as described above, the target space is bright (the amount of ambient light is large). May exceed the amount of charge that can be stored in a solid-state imaging device such as a CCD image sensor, and the luminance value (density value, luminance value) of the pixel may be saturated. When the luminance value of the pixel is saturated, there is a problem that a part of the difference image is crushed and the image quality of the difference image is deteriorated.

  The present invention has been made in view of the above points, and an object of the present invention is to provide an imaging apparatus capable of suppressing the influence of fluctuations in ambient light and improving the image quality.

In order to solve the above-described problem, in the invention of claim 1, an imaging unit that images a target space by arranging a plurality of photosensitive units that generate a light reception output according to the amount of received light, and irradiates the target space with light. A light source unit, an arithmetic processing unit that generates a difference image between an image when the light source is turned on and an image when the light source is turned off and an image when the light source is turned off and the image obtained when the light source is turned off. An exposure amount adjusting means for adjusting the exposure amount of the light source , and the arithmetic processing unit calculates an S / N ratio in each pixel from the luminance value of the image when the light source is turned on and the luminance value of the image when the light source is turned off. defining a pixel number counting unit that the S / N ratio is to count the number of pixels is less than the determination value, Oite the count result of the pixel number counting unit, the S / N ratio is the number of pixels is equal to or greater than the determination value so as to reduce the exposure amount when it is equal to or greater than the number, exposure adjustment Characterized in that it has an automatic exposure control unit for controlling the means.

According to the first aspect of the present invention, the light source on-time image is an image reflecting the ambient light in the target space and the light irradiated to the target space from the light source unit. Since it is a reflected image, the difference image between the image when the light source is turned on and the image when the light source is turned off is an image that reflects only the light irradiated to the target space from the light source unit. it is Ru can be. Further, the exposure amount is reduced when the number of pixels whose S / N ratio calculated from the brightness value of the image when the light source is turned on and the brightness value of the image when the light source is turned off is equal to or greater than a determination value is equal to or greater than a specified number. Thus, the exposure amount of the image pickup unit can be set within an appropriate range, so that the image quality can be improved.

According to a second aspect of the present invention, in the first aspect of the invention, the automatic exposure control unit is configured such that the number of pixels in which the luminance value in the light source lighting image is equal to or greater than a state determination threshold value continues for a predetermined time. If it exceeds, the specified number is increased .

According to the invention of claim 2, when the number of pixels whose luminance value in the light source lit image is greater than or equal to the threshold value for the state determination exceeds the specified number continues for a predetermined time, other unnecessary obstructions Since there is a high possibility that an object is reflected, and the prescribed number is increased so that the exposure amount is not adjusted in accordance with such an unnecessary object, it is possible to suppress deterioration in image quality.

According to a third aspect of the present invention, in the first or second aspect of the present invention, the pixel number counting unit is configured such that the maximum value of the luminance value in the image when the light source is turned off is equal to or less than a determination value for dark place determination and a predetermined time. Even if the determination value for dark place determination does not exceed even if it has elapsed, the maximum luminance value in the difference image is greater than or equal to the determination value for insufficient exposure amount determination, and the insufficient exposure amount determination even after a predetermined time has elapsed When it does not become less than the judgment value, the judgment value is lowered .

According to the invention of claim 3 , the maximum value of the luminance value in the image when the light source is turned off is equal to or less than the determination value for dark place determination , and does not exceed the determination value for dark place determination even after a predetermined time elapses. Since the ambient light is determined to be weak, the maximum brightness value in the difference image is equal to or greater than the determination value for determining the insufficient exposure amount , and does not become less than the determination value for determining the insufficient exposure amount even after a predetermined time has elapsed. In such a case, it is possible to reduce the exposure amount of the image pickup unit and set the exposure amount of the image pickup unit within an appropriate range by reducing the determination value. Can be improved.

According to a fourth aspect of the present invention, in the invention according to any one of the first to third aspects, the arithmetic processing unit creates a frequency distribution of luminance values of pixels in the difference image, and based on the created frequency distribution. An automatic gain control unit for adjusting the brightness of the difference image is provided.

According to the invention of claim 4 , the brightness of the difference image can be adjusted to an appropriate brightness.

  The present invention has an effect that the influence of fluctuations in ambient light can be suppressed and the image quality can be improved.

(Embodiment 1)
As shown in FIG. 1, the imaging device 1 of the present embodiment includes an imaging unit 2 that images a target space by arranging a plurality of photosensitive units (not shown) that generate a light reception output corresponding to the amount of received light, and imaging. A light source unit 3 that is arranged in the vicinity of the unit 2 and irradiates light on the target space; a lens unit 4 that forms an image of the target space on the imaging surface of the imaging unit 2; and the imaging unit 2 when the light source unit 3 is turned on. An arithmetic processing unit 5 that generates a difference image between the obtained light source lighting image and the light source extinguishing image obtained from the imaging unit 2 when the light source unit 3 is extinguished; a drive control unit 60 that controls the imaging unit 2; A lighting control unit 61 that performs lighting control of the light source unit 3, an incident light amount adjustment unit 62 that adjusts an incident light amount incident on the imaging surface of the imaging unit 2 from the lens unit 4, and face authentication that performs face authentication based on the difference image This is a so-called face authentication device including the unit 7.

  As the light source unit 3, various types can be used such as a plurality of light emitting diodes (LEDs) arranged on a single plane, a combination of a semiconductor laser and a diverging lens. As light emitted from the light source unit 3, infrared light or visible light can be employed. For example, if the light emitted from the light source unit 3 is infrared, the light source unit 3 will not be noticed even at night, so that the configuration is suitable for the purpose of a surveillance camera or the like. It becomes possible to obtain an image close to the state of the time. The lighting state of the light source unit 3 is controlled by the lighting control unit 61.

  The lighting control unit 61 drives the light source unit 3 with a modulation signal having a predetermined modulation frequency. A square wave is used for the modulation signal, the modulation frequency is selected from 10 to 100 kHz, for example, and the duty is 50%. Accordingly, the light source unit 3 repeats turning on and off alternately at the same time in a cycle of 10 to 100 μs. The cycle in which the light source unit 3 repeats turning on and off is set to a short cycle that cannot be recognized by human eyes. That is, the light source unit 3 is actually turned on and off repeatedly, but appears to be continuously turned on to human eyes. However, these numerical values are examples, and the modulation frequency can be set appropriately.

  The imaging unit 2 includes, for example, a light receiving element having a unit configuration that forms one photosensitive unit (not shown) and one charge accumulation unit (not shown). ) Are arranged on a single semiconductor substrate or the like (for example, a CCD image sensor). Note that this type of image sensor is not limited to a CCD image sensor, and a conventionally known one such as a CMOS image sensor can be adopted, and detailed description thereof is omitted.

  The imaging unit 2 can control the timing of charge extraction (image signal extraction), the timing of the electronic shutter, and the like, and the drive control unit 60 outputs the timing of charge extraction and the timing of the electronic shutter. Determined by the control signal. In the present embodiment, the drive control unit 60 causes the imaging unit 2 to output an image signal in synchronization with the blinking of the light source unit 3. Therefore, from the imaging unit 2, a light source lighting image composed of a gray image captured when the light source unit 3 is lit and a light source extinguishing image composed of a gray image captured when the light source unit 3 is unlit. Are output.

  An image signal (imaging signal) output from the imaging unit 2 is converted from an analog format to a digital format image signal by the AFE unit 8 and then input to the arithmetic processing unit 5. Note that the AFE unit 8 also performs correlated double sampling (CDS) that removes reset noise from the CCD image sensor and converts it to a baseband image signal, if necessary. Since this type of AFE unit 8 is conventionally well-known, detailed description thereof is omitted.

  The lens unit 4 includes, for example, a lens (not shown) for forming an image of a subject existing in the target space on the imaging surface of the imaging unit 2 and a diaphragm (iris) (not shown) for adjusting the amount of incident light. The Here, as the diaphragm, an aperture whose diameter can be adjusted by an external signal is adopted, and the external signal is given by the incident light amount adjusting unit 62. The lens unit 4 is not limited to a lens and a diaphragm. For example, instead of a diaphragm, a plurality of neutral density filters having different transmittances are provided, and which neutral density filter is used according to the external signal. For example, a neutral density filter including a liquid crystal filter whose transmittance is changed by the external signal can be employed.

  In the imaging apparatus 1 of the present embodiment, the timing of the electronic shutter of the imaging unit 2 is determined by the drive control unit 60, the brightness of the light source unit 3 is determined by the lighting control unit 61, and the lens unit 4 is determined by the incident light amount adjustment unit 62. (The amount of light incident on each light receiving element of the imaging unit 2) is determined. That is, the drive control unit 60, the lighting control unit 61, and the incident light amount adjustment unit 62 constitute an exposure amount adjustment unit 6 that adjusts the exposure amount of the imaging unit 2.

  The arithmetic processing unit 5 realizes various functions by executing, for example, a program stored in a memory with a microcomputer, and an image generation unit 50 that generates a difference image between the light source on image and the light source off image. A pixel number counting unit 51 that counts the number of pixels that satisfy the conditions set for exposure amount adjustment in the light source lighting image, and an automatic that controls the exposure amount adjusting unit 6 based on the count result of the pixel number counting unit 51 The exposure control unit 52 and an automatic gain control unit 53 that adjusts the brightness of the difference image are provided, and the difference image whose brightness is adjusted by the automatic gain control unit 53 is output to the face authentication unit 7.

  The image generation unit 50 determines the difference (in other words, the light source unit) between the light reception output of the photosensitive unit when the light source unit 3 is turned on (lighting period) and the light reception output of the photosensitive unit when the light source unit 3 is turned off (off period). The difference between the light reception output of each photosensitive unit when light is not irradiated from 3 to the target space and the light output of each photosensitive unit when light is irradiated from the light source unit 3 to each photosensitive unit (light reception) A difference image (amplitude image) as a luminance value of the element is generated. Here, since the light source unit 3 alternately turns on and off at the same time in a cycle of 10 to 100 μs, it is considered that the ambient light does not substantially change between the lighting period and the extinguishing period adjacent to each other. Therefore, by creating a differential image from the light source on-image and the light source off-image captured in the off period adjacent to the lighting period on which the light source on-image was captured, the difference image can be used for the fluctuation of ambient light. The effect can be removed.

  As the conditions set for the above-mentioned exposure amount adjustment, the pixel number counting unit 51 has a condition that the luminance value of the pixel is equal to or higher than a threshold value for determining the saturation of exposure amount (for determining the amount of exposure decrease), and the luminance value of the pixel. A condition is set such that it is equal to or greater than a threshold value for exposure amount shortage determination (for exposure amount increase determination). That is, the pixel number counting unit 51 counts the number of pixels whose luminance value is equal to or greater than the threshold value for determining exposure saturation and the number of pixels whose luminance value is equal to or greater than the threshold value for determining insufficient exposure amount in the light source lighting image. To do. However, the threshold value for determining the exposure amount saturation is set to a value larger than the threshold value for determining the insufficient exposure amount.

  The automatic exposure control unit (AE unit) 52 adjusts the exposure amount of the imaging unit 2 by controlling the exposure amount adjusting unit 6 based on the count result of the pixel number counting unit 51. In the present embodiment, the automatic exposure control unit 52 is configured such that the number of pixels counted by the pixel number counting unit 51 (the number of pixels whose luminance value is equal to or greater than the threshold value for determining exposure saturation) is a prescribed value for determining exposure amount reduction. When it is above, the exposure amount adjusting means 6 is controlled to decrease the exposure amount, and the number of pixels counted by the pixel number counting unit 51 (the number of pixels whose luminance value is equal to or greater than the threshold for determining insufficient exposure amount) Is equal to or less than the prescribed value for determining the exposure amount, the exposure amount adjusting means 6 is controlled to increase the exposure amount. The adjustment of the exposure amount of the imaging unit 2 is selected from the timing of the electronic shutter by the drive control unit 60, the dimming control of the light source unit 3 by the lighting control unit 61, and the adjustment of the incident light amount by the incident light amount adjustment unit 62. Or at least one. As described above, the adjustment of the exposure amount is any one of the timing of the electronic shutter by the drive control unit 60, the dimming control of the light source unit 3 by the lighting control unit 61, and the adjustment of the incident light amount by the incident light amount adjustment unit 62. However, a wide range of adjustments can be made by combining a plurality of them.

  The automatic gain control unit (AGC unit) 53 adjusts the luminance value of the difference image (brightness of the difference image). That is, the difference image created by the image generation unit 50 is an image in which only the light of the light source unit 3 is reflected by removing the ambient light from the light source lighting image. Since the brightness value of the pixel tends to be low and the entire image tends to be dark (see FIG. 2A), the brightness adjustment is performed by the automatic gain control unit 53. The automatic gain controller 53 creates a frequency distribution (histogram) of luminance values in the difference image when adjusting the brightness of the difference image. The automatic gain control unit 53 creates a frequency distribution indicating a frequency distribution of pixels whose luminance values are included in a predetermined range as shown in the graph of FIG. 3 (note that the frequency distribution shown in FIG. 3 is 12 bits). The luminance values shown are divided into 5 cases). More specifically, the automatic gain control unit 53 first creates a frequency distribution of the difference image in which the gain (gain) is set to a predetermined value. Here, if the gain is increased, the luminance value of each pixel of the difference image increases, so that the difference image becomes brighter as shown in FIGS. 2 (a) to 2 (c). ), The number of pixels having a high luminance value increases. 2A shows a difference image with a gain of 1 times, FIG. 2B shows a difference image with a gain of 4 times, and FIG. 2C shows a difference image with a gain of 16 times. 2D is a graph of the frequency distribution of the difference image having a gain of 1 ×, FIG. 2E is a graph of the frequency distribution of the difference image having a gain of 4 ×, and FIG. 2F is the frequency of the difference image having a gain of 16 ×. It is a graph of distribution.

  In the created frequency distribution, the automatic gain control unit 53 counts the number of pixels whose luminance value is equal to or higher than the threshold value for determining the upper limit of gain (in the example shown in FIG. 3, the number of pixels whose luminance value is 2048 to 4096). Is determined to exceed the specified value Th for determining the upper limit of gain. As a result, if the specified value Th for determining the upper limit of gain is not exceeded, the gain is increased, and the specified value Th for determining the upper limit of gain is exceeded. If so, the gain is reduced. The automatic gain control unit 53 repeatedly performs the determination using the frequency distribution as described above, so that the number of pixels whose luminance value is equal to or higher than the threshold value for determining the upper limit of gain does not exceed the specified value Th for determining the upper limit of gain. Choose the largest gain. Then, the automatic gain control unit 53 adjusts the brightness of the difference image with the selected gain, and then outputs the adjusted difference image to the face authentication unit 7.

  The face authentication unit 7 performs authentication (face authentication) by determining whether or not the face of the person to be authenticated is reflected in the image captured by the imaging unit 2, and outputs an authentication result. For example, the face authentication unit 7 performs a predetermined feature amount (from a binary image obtained by performing local spatial differentiation on the difference image given from the automatic gain control unit 53 using a Sobel filter or the like (see FIG. 3). In this embodiment, a feature amount of a person's face is extracted, and the similarity between the extracted feature amount and a template registered in advance is calculated. When the calculated similarity is equal to or greater than a predetermined value, the imaging unit 2 It is determined that the person to be authenticated is reflected in the image captured in step. Note that the authentication method in the face authentication unit 7 is not limited to the above example, and a conventionally known method can be adopted, and thus detailed description thereof is omitted.

  As described above, according to the imaging apparatus 1 of the present embodiment, the light source on-time image is an image in which the ambient light in the target space and the light irradiated on the target space from the light source unit 3 are reflected. Is an image that reflects only the ambient light in the target space, and therefore, the difference image between the light source on image and the light source off image is an image that reflects only the light emitted from the light source unit 3 to the target space. Pixels that can suppress the influence of fluctuations in ambient light and satisfy the conditions set for adjusting the exposure amount counted in one image selected from the image when the light source is turned on, the image when the light source is turned off, and the difference image Since the exposure amount of the imaging unit is adjusted based on the number of images, it is possible to set the exposure amount of the imaging unit 2 to an appropriate range, and thus it is possible to suppress the occurrence of white stripes and black blurring in the difference image. Can improve image quality. .

  In particular, when the number of pixels whose luminance value is greater than or equal to the threshold value for determining the exposure amount saturation, for example, the number of pixels whose light reception output is saturated or close to saturation is greater than or equal to the specified value for determining the exposure amount decrease, the exposure amount of the imaging unit 2 is decreased. As a result, the number of pixels in which the light reception output is saturated or close to saturation is reduced, so that it is possible to suppress the occurrence of white stripes or the like in the difference image, so that the image quality can be improved. Also, when the number of pixels whose luminance value is greater than or equal to the threshold for determining insufficient exposure amount is equal to or less than the prescribed value for determining increase in exposure amount, the exposure amount is increased to reduce the number of pixels having insufficient luminance value. The difference image can be brightened, and the occurrence of black blurring can be reduced. Note that the above threshold values (threshold value for exposure amount saturation determination and threshold value for insufficient exposure amount determination) and the above specified values (specified value for exposure amount decrease determination and specified value for exposure amount increase determination) are actually differences. What is necessary is just to set to a suitable value by performing the test etc. which produce an image.

  In addition, the arithmetic processing unit 5 has a frequency distribution of luminance values of pixels in the difference image, and has an automatic gain control unit 53 that adjusts the brightness of the difference image based on the created frequency distribution, and the image generation unit 50 Since the brightness adjustment is performed on the difference image created in step 1, the brightness of the difference image can be adjusted to an appropriate level.

  By the way, the amount of the reflected light of the light source unit 3 (light of the light source unit 3 reflected by the subject) that enters the imaging unit 2 when the light source unit 3 is turned on is inversely proportional to the square of the distance between the light source unit 3 and the subject. Therefore, the subject that exists in the target space becomes brighter as it is closer to the light source unit 3, that is, as it is closer to the imaging unit 2. For example, as illustrated in FIG. 4, when a person M, a plant P, and an object O exist in the target space, and the object O is closer to the imaging unit 2 than the person M and the plant P, the object is displayed in the light source lighting image. The luminance value of the pixel corresponding to O is much larger than the luminance value of the pixel corresponding to the person M and the plant P, and the luminance value of the pixel corresponding to the object O is saturated, but corresponds to the person M and the plant P. There may be a situation where the luminance value of the pixel is not saturated.

  In such a case, the number of pixels corresponding to the object O is counted as the number of pixels whose luminance value is equal to or greater than the threshold value for determining exposure saturation, so that the luminance value is not limited to the pixels corresponding to the object O. Even if there is no pixel that is equal to or greater than the threshold value for determining exposure saturation, if the number of pixels corresponding to the object O is equal to or greater than the prescribed value for determining exposure saturation, the automatic exposure controller 52 performs exposure. As a result, the luminance value of pixels other than the pixel corresponding to the object O (the pixel corresponding to the person M or the plant P) is excessively lowered in the difference image, and black blurring occurs. The difference image may be deteriorated.

  In view of the above points, it is preferable that the pixel number counting unit 51 does not count pixels whose luminance value is somewhat larger than the threshold for exposure amount saturation determination as invalid pixels. That is, it is preferable that the pixel number counting unit 51 does not count pixels having a luminance value equal to or greater than the threshold for determining invalid pixels that is greater than the threshold for determining exposure saturation.

  In this way, light is received by a pixel having a luminance value equal to or higher than the threshold for determining invalid pixels, such as specular reflection (for example, glasses worn by the person M or surrounding glass) or an object O that is too close to the imaging unit 2. Since it is possible not to count the pixels whose output has been saturated, the exposure amount of the imaging unit 2 is matched to the pixel whose light reception output has been saturated due to regular reflection or an object O that is too close to the imaging unit 2. Is adjusted, it is possible to suppress the difference image from becoming too dark, and it is possible to suppress the image quality of the difference image from being deteriorated by a subject that is not suitable as the subject of the imaging unit 2. .

  Note that the pixel number counting unit 51 in the present embodiment counts the number of pixels that satisfy the conditions set for adjusting the exposure amount in the light source on-image, but exposure is also performed on the light source off-image and the difference image. The number of pixels that satisfy the conditions set for the amount adjustment may be counted, or for the exposure amount adjustment in at least one image selected from the light source on image, the light source off image, and the difference image. The number of pixels that satisfy the set condition may be counted. This also applies to Embodiments 2 to 4 described later.

(Embodiment 2)
In the imaging apparatus 1 according to the present embodiment, the automatic exposure control unit 52 determines the above-described prescribed value (for exposure amount decrease determination) based on the temporal change in the number of pixels in which the luminance value in the image when the light source is turned on is equal to or greater than the threshold for state determination. This is different from the first embodiment in that the specified value) is adjusted. Since the configuration other than the automatic exposure control unit 52 in the imaging apparatus 1 of the present embodiment is the same as that of the first embodiment, the same components are denoted by the same reference numerals and the description and illustration thereof are omitted.

  The threshold for state determination is a value for determining whether or not the above-described object O (see FIG. 4) is reflected in the image when the light source is turned on, for example. If the number of pixels whose value is equal to or greater than the threshold for state determination does not change substantially even after a predetermined time has passed (it is not less than the specified number), that is, any of the images when the light source is turned on within the predetermined time If the number of pixels whose luminance value is equal to or greater than the threshold for state determination is equal to or greater than the specified number, it is determined that the object O is reflected in the image when the light source is turned on. When the automatic exposure control unit 52 determines that the object O is reflected in the image when the light source is turned on, the automatic exposure control unit 52 counts the number of pixels corresponding to the object O as a predetermined value for determining the amount of exposure to reduce the object. Ignore the number of pixels corresponding to O.

  Therefore, according to the imaging device 1 of the present embodiment, for example, when the number of pixels whose luminance value is equal to or greater than the threshold value for state determination hardly changes even after a predetermined time has elapsed, an obstacle or other difference It is determined that an unnecessary object is included in the image, and a predetermined value (in this embodiment, an exposure reduction determination is performed so that the exposure amount is not adjusted according to such an unnecessary object. Therefore, it is possible to suppress deterioration in image quality.

  In the present embodiment, the prescribed value for determining the exposure amount decrease is adjusted, but the prescribed value for determining the exposure amount increase may be adjusted. The threshold for state determination is a value used for determining whether or not an unnecessary object is included in an obstacle or other difference image, and may be set as appropriate according to the situation.

(Embodiment 3)
The imaging apparatus 1 according to the present embodiment is different from the first embodiment in that the pixel count unit 51 adjusts the threshold value based on the maximum luminance value and the temporal change in each of the image when the light source is turned off and the difference image. . Since the configuration other than the pixel number counting unit 51 in the imaging device 1 of the present embodiment is the same as that of the first embodiment, the same components are denoted by the same reference numerals and the description and illustration thereof are omitted.

  Hereinafter, the pixel number counting unit 51 in the present embodiment will be described in more detail. In the present embodiment, the pixel number counting unit 51 has a maximum luminance value equal to or lower than a determination value for dark place determination in an image when the light source is turned off, and does not exceed the determination value for dark place determination even if a predetermined time elapses. In this case, it is determined that the amount of ambient light is small (the ambient light is weak). In addition, the pixel number counting unit 51 in the present embodiment has a maximum luminance value in the difference image that is equal to or greater than a determination value for determining insufficient exposure and is less than a determination value for determining insufficient exposure even after a predetermined time has elapsed. If not, it is determined that the light amount of the light source unit 3 is excessive (the light of the light source unit 3 is too strong).

  Then, when the pixel number counting unit 51 in this embodiment determines that the amount of ambient light is small and determines that the light amount of the light source unit 3 is large, the threshold for exposure amount saturation determination is decreased. When the threshold value for exposure amount saturation determination is lowered, the number of pixels whose luminance value is equal to or greater than the threshold value for exposure amount saturation determination increases even though the luminance value of each pixel in the light source lighting image is the same. Therefore, before lowering the threshold for determining exposure saturation, even if the number of pixels whose luminance value is equal to or greater than the threshold for determining exposure saturation does not exceed the prescribed value for determining exposure reduction, exposure saturation determination As a result, the number of pixels whose luminance value is equal to or greater than the threshold value for determining exposure saturation exceeds the specified value for determining decrease in exposure amount, and the automatic exposure control unit 52 reduces the exposure amount. Control is made.

  Therefore, according to the imaging device 1 of the present embodiment, when the amount of ambient light is small and the light source unit 3 has too much light, the exposure amount of the imaging unit 2 is decreased and the exposure amount of the imaging unit 2 is reduced. An appropriate range can be set. At this time, if the exposure amount of the imaging unit 2 is reduced by reducing the brightness of the light source unit 3, the power required for lighting the light source unit 3 can be reduced, so that power consumption can be reduced. The amount of heat generated by the light source unit 3 can be reduced. As a result, when viewed from a long-term viewpoint, it is possible to suppress the deterioration of the light source unit 3 and to suppress the deterioration of the image quality due to the deterioration of the light source unit 3.

  In addition, the pixel number counting unit 51 in the present embodiment has a maximum value of the luminance value in the image when the light source is turned off is equal to or greater than a determination value for determining a bright place, and sets a determination value for determining a bright place even after a predetermined time has elapsed. If not, it may be determined that the amount of ambient light is large (the ambient light is strong), and the threshold for determining exposure saturation may be increased. In this case, even when the number of pixels whose luminance value is equal to or greater than the threshold for determining exposure saturation, it is difficult to exceed the prescribed value for determining decrease in exposure, and the exposure of the imaging unit 2 is difficult to decrease. This is useful when the threshold value for determining exposure saturation is set with some allowance for the capacity of the light receiving element of the imaging unit 2. In other words, by making it difficult to reduce the exposure amount of the image pickup unit 2, it is possible to use the capacity of the light receiving element of the image pickup unit 2 to the limit. It can be made difficult to deteriorate.

  Furthermore, by referring to the maximum value of the image when the light source is turned on and the time change thereof, it is possible to know how much exposure the imaging unit 2 is saturated, and thus, for each product of the image sensor used in the imaging unit 2. It is possible to adjust the exposure amount according to the difference in the saturation amount and dynamic range. That is, the pixel number counting unit 51 in the present embodiment is not limited to the maximum luminance value and its time change in the image when the light source is turned off and the difference image, but also the maximum value and its time change of the luminance value in the image when the light source is turned on. The threshold value may be adjusted based on the above. In short, the pixel number counting unit 51 in the present embodiment is based on the maximum value of the luminance value in at least one image selected from the light source on image, the light source off image, and the difference image, and the temporal change thereof. What is necessary is just to adjust a threshold value. Further, the threshold value to be adjusted is not limited to the threshold value for determining the exposure amount saturation, and the threshold value for determining the insufficient exposure amount may be adjusted.

  Note that the matters relating to the pixel number counting unit 51 in the present embodiment are also applicable to the second embodiment.

(Embodiment 4)
In the imaging apparatus 1 of the present embodiment, the operations of the pixel number counting unit 51 and the automatic exposure control unit 52 are different from those of the first embodiment, and the other configurations are the same as those of the first embodiment, and therefore the same configurations are the same. The description and illustration are omitted.

The pixel count unit 51 in this embodiment calculates the S / N ratio of each pixel from the luminance value of the image when the light source is turned on and the luminance value of the image when the light source is turned off, and the calculated S / N ratio is the exposure amount adjustment. Count the number of pixels that satisfy the conditions set for. Specifically, the pixel number counting unit 51 in the present embodiment employs a value obtained by dividing the luminance value of the image when the light source is turned on by the luminance value of the image when the light source is turned off as the S / N ratio. Then, the pixel number counting unit 51 in the present embodiment has the number of pixels whose S / N ratio is equal to or smaller than the first determination value and the second determination value that is larger than the first determination value. Count the number of pixels.

If the number of pixels having an S / N ratio equal to or smaller than the first determination value is equal to or greater than the specified number, the automatic exposure control unit 52 in this embodiment controls the exposure amount adjusting unit 6 to increase the exposure amount. If the number of pixels whose / N ratio is greater than or equal to the second determination value is greater than or equal to the specified number, the exposure amount adjustment unit 6 is controlled to reduce the exposure amount.

  According to the imaging apparatus 1 of the present embodiment described above, the exposure amount of the imaging unit 2 can be set within an appropriate range, and a difference image that accurately reflects the light of the light source unit 3 can be obtained. Thus, the image quality of the difference image can be improved.

  By the way, this embodiment and the imaging device 1 of Embodiments 1-3 mentioned above are integrated in the security system for apartment houses as shown, for example in FIG.

  The security system for apartments shown in FIG. 5 is installed in an apartment house such as a condominium. In addition to the imaging device 1, the lobby intercom 100, the alarm monitoring panel 110, the electric lock control unit 120, the elevator control panel 130, a delivery box control panel 140, a system control panel 150, a numeric keypad device 160, a housing information panel (not shown) installed in each dwelling unit, and the like.

  The lobby intercom 100 includes a camera that images the visitor, a call device for making a call between the alarm monitoring board 110 and the house information board, a numeric keypad for the visitor to enter a dwelling unit number of the visited residence, and the like. It is installed outside the common entrance 200 of the apartment house. When a visitor operates the numeric keypad of the lobby intercom 100 and inputs the dwelling unit number of the visited residence unit, the lobby intercom 100 passes through the alarm monitoring panel 110 to the housing information panel installed in the dwelling unit of the dwelling unit number. Thus, a call signal and a visitor image captured by the camera of the lobby intercom 100 are transmitted. Then, in the house information board that has received the call signal, an image received from the lobby intercom 100 is displayed on the display and a ringing tone is generated from the speaker. When the resident of the dwelling unit presses the response button on the house information board, a communication path is formed between the house information board and the lobby intercom, and the visitor and the resident use the lobby intercom 100 and the house information board, respectively. You can make a call. Since this type of lobby intercom 100, alarm monitoring panel 110, and house information panel are well known in the art, detailed illustration and description thereof will be omitted.

  The electric lock control panel 120 controls locking / unlocking of an electric lock (not shown) provided in the common entrance 200. The elevator control panel 130 controls the operation of an elevator (not shown) installed in the apartment house. The home delivery box control panel 140 controls locking / unlocking of home delivery boxes installed in the apartment house. The system control panel 150 causes the electric lock control panel 120 to unlock the electric lock or causes the elevator control panel 130 to operate the elevator according to the control command transmitted from the house information panel and the authentication result in the imaging device 1. The delivery box control panel 140 is made to unlock the delivery box. That is, when a resident of any dwelling unit operates the numeric keypad device 110 and inputs an ID number assigned to the resident, the imaging device 1 uses the template corresponding to the ID number received from the numeric keypad device 110 to The resident is authenticated, and if it can be authenticated, authenticable information is transmitted to the system control panel 150. When the system control panel 150 receives the information that can be authenticated from the imaging apparatus 1, the system control panel 150 causes the electric lock control panel 120 to unlock the electric lock, causes the elevator control panel 130 to operate the elevator, or causes the delivery box control panel 140 to perform delivery. Unlock the box. On the other hand, when the authentication by the imaging device 1 is impossible, the system control panel 150 receives the information indicating that the authentication is impossible from the imaging device 1 and does not unlock the electric lock to the electric lock control panel 120 and The elevator is not operated and the delivery box control panel 140 is not unlocked. In addition, since the electric lock control device 120, the elevator control panel 130, and the delivery box control panel 140 are conventionally well-known, detailed illustration and description thereof are omitted.

1 is a block diagram of an imaging apparatus according to Embodiment 1. FIG. (A)-(c) is the schematic of a difference image, (d)-(f) is a graph which shows frequency distribution. It is a graph which shows an example of frequency distribution. It is the schematic which shows an image at the time of light source lighting. It is a system configuration figure of a security system for apartment houses.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Imaging device 2 Imaging part 3 Light source part 5 Arithmetic processing part 6 Exposure amount adjustment means 7 Face authentication part 50 Image generation part 51 Pixel number count part 52 Automatic exposure control part

Claims (4)

Obtained from the imaging unit in which a plurality of photosensitive units that generate a light reception output corresponding to the amount of received light are arranged to image the target space, a light source unit that irradiates light to the target space, and the light source unit when the light source unit is turned on An arithmetic processing unit that generates a difference image between an image when the light source is turned on and an image when the light source is turned off when the light source unit is turned off, and an exposure amount adjusting unit that adjusts an exposure amount of the imaging unit,
The arithmetic processing unit calculates an S / N ratio in each pixel from the luminance value of the image when the light source is turned on and the luminance value of the image when the light source is turned off, and calculates the number of pixels where the S / N ratio is equal to or less than a determination value. a pixel number counting unit for counting, Oite the count result of the pixel number counting unit, as described above S / N ratio is reduced the amount of exposure if it is the number of pixels is equal to or greater than the determination value is more than the specified number, exposure An image pickup apparatus comprising: an automatic exposure control unit that controls the amount adjusting means. The automatic exposure control unit increases the prescribed number when the number of pixels whose luminance value in the light source lighting image is equal to or greater than a threshold for state determination exceeds the prescribed number continuously for a predetermined time. The imaging device according to claim 1. The pixel number counting unit is a case where the maximum value of the luminance value in the image when the light source is turned off is equal to or less than the determination value for dark place determination and does not exceed the determination value for dark place determination even if a predetermined time elapses. If the maximum brightness value in the difference image is equal to or greater than the determination value for insufficient exposure amount determination and does not become less than the determination value for insufficient exposure amount determination after a predetermined time, the determination value is lowered. The imaging device according to claim 1 or 2. The arithmetic processing unit includes an automatic gain control unit that creates a frequency distribution of luminance values of pixels in the difference image and adjusts the brightness of the difference image based on the created frequency distribution. The imaging device according to any one of claims 1 to 3 .

Images