JP2016173437A - Photometric device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a photometric device equipped with a low-pass filter and not having a focus adjustment mechanism, with which it is possible to recognize a subject with high accuracy even when a focus change occurs.SOLUTION: There are provided a finder optical system for observing a subject image in which the luminous flux of a subject having passed through a photographic lens is formed on a focusing screen, a photometric device for forming the subject image on the focusing screen secondarily in an optical path differing from the optical path of a finder and performing photometry, the photometric device comprising a photometric sensor for dividing the luminous flux of the subject image on the focusing screen into a plurality of areas and outputting a plurality of pieces of photometric information relating to luminance, a photometric lens for making the subject image on the focusing screen formed by the photometric sensor, subject recognition means for recognizing the color and shape of the subject using the output of the photometric sensor, a low-pass filter the spatial frequency limiting effect of which is variable, and a thermometer, with the spatial frequency limiting effect of the low-pass filter being varied in accordance with the output of the thermometer.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a photometric device that measures the luminance of a subject, and more particularly to a photometric device that includes a low-pass filter to reduce the influence of false colors in a photometric device capable of subject detection and color detection.

  Conventionally, photometry of a single-lens reflex camera measures the brightness of a subject image formed on a focusing screen by a photometric sensor installed around a pentaprism via a photometric lens. In recent years, an image sensor such as a CCD is used as the photometric sensor in addition to the image sensor, and the subject image formed on the focusing screen is captured, and the shape and color of the captured image are discriminated, so that the object recognition / color There is a photometry device that detects and improves the function. Normally, when the spatial frequency of the subject image has a response equal to or higher than the Nyquist frequency of the image sensor, a false color is generated, and there is a possibility that the correct color cannot be recognized on the sensor.

  When an image sensor is used as the photometric sensor, a high spatial frequency response is required for the photometric lens in order to perform subject recognition, so that false colors may occur as in the image sensor. When a false color occurs in the photometric sensor, there is a concern that the color of the subject cannot be recognized correctly and erroneous detection is caused. For this reason, an image sensor such as a CMOS used in an image pickup apparatus has an optical low-pass filter in the imaging optical path in order to suppress generation of false colors, or a digital low-pass filter is applied by image processing after imaging. Processing is in progress.

  The low-pass filter suppresses the generation of false colors by limiting the spatial frequency response of the lens and suppressing the high spatial frequency component of the subject image, but the resolution of the subject image is reduced and the image quality is reduced. A normal image pickup apparatus performs focus adjustment on a subject and always takes an image at a focus peak position. Therefore, image quality degradation due to a low-pass filter is not problematic in practice. However, it is difficult for the above-mentioned photometric device to mount a focus adjustment mechanism from the viewpoint of downsizing and cost reduction of the imaging device.

  However, if the temperature of the photometry device changes due to the change of the environmental temperature, the lens is out of focus, and the focus cannot be adjusted, so that the resolution of the subject imaged on the photometry sensor is reduced. Therefore, when the lens is out of focus, there is a possibility that the resolving power required for subject recognition cannot be obtained due to the reduction in resolving power due to the low focus filter effect in addition to the reduction in resolving power due to the lens defocusing.

  The following techniques have been proposed for preventing image quality degradation by a low-pass filter in an imaging apparatus that does not have a focus adjustment mechanism. In Patent Document 1, an optical low-pass filter with a variable spatial frequency limiting effect is provided, the in-focus state of the object to be photographed is detected, and the spatial frequency limiting effect of the low-pass filter is weakened according to the amount of deviation in the in-focus state. In addition, it is configured to suppress false color while suppressing a decrease in resolution.

JP-A-4-236585

  However, in the prior art disclosed in Patent Document 1 described above, it is necessary to always check the in-focus state. Usually, the in-focus state is not confirmed in the image captured by the photometric sensor. For this reason, adding a process for confirming the in-focus state may increase the photometric processing time, which may increase the release time lag. In addition, there is a concern that the power consumption increases when the process of photographing is shortened and the increase in the release time lag is suppressed by performing the confirmation process of the in-focus state.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a photometric device that can recognize a subject with high accuracy even when a focus change occurs due to a change in environmental temperature in a photometric device that includes a low-pass filter and does not have a focus adjustment mechanism. is there.

  In order to achieve the above object, the present invention provides a finder for observing a subject image formed by imaging a subject luminous flux that has passed through a photographic lens on a focusing screen disposed on a primary imaging plane. An optical system, a photometric device for performing secondary photometry on the subject image formed on the focusing screen in an optical path different from the optical path of the viewfinder, and the photometric device formed on the focusing screen A photometric sensor that divides the luminous flux of the subject image into a plurality of regions and outputs a plurality of photometric information relating to the luminance of the subject image, and a photometric lens that forms the subject image formed on the focusing screen on the photometric sensor Subject recognition means for recognizing the color and shape of the subject using the output of the photometric sensor, and a spatial frequency limiting effect A variable low-pass filter, and a thermometer, and wherein the changing the spatial frequency limiting effect of the low-pass filter in accordance with the output of the thermometer.

  In addition, the low-pass filter provides a spatial frequency limiting effect only when color information is used in the subject recognition unit.

  According to the present invention, it is possible to provide a photometric device capable of recognizing a subject with high accuracy by suppressing a reduction in resolution and the influence of false color even when a lens is defocused due to a change in environmental temperature.

The figure which showed the characteristic of the MTF change by temperature which considered MTF of the photometric lens single-piece | unit and low-pass filter based on embodiment of this invention Schematic which shows the structure of the imaging device based on embodiment of this invention Schematic showing the configuration of a photometric device according to an embodiment of the present invention The block diagram which shows the electrical constitution of the imaging device based on embodiment of this invention The figure which shows the characteristic of the low-pass filter based on embodiment of this invention 6 is a flowchart relating to photometry of the imaging apparatus according to the first embodiment of the present invention. Flowchart relating to photometry of the imaging apparatus according to the second embodiment of the present invention.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.
[Example 1]
FIG. 2 is a schematic diagram showing the configuration of the imaging apparatus according to the embodiment of the present invention. In FIG. 2, reference numeral 100 denotes an imaging apparatus main body. Reference numeral 101 denotes a CPU of the imaging apparatus. Reference numeral 112 denotes a photographer. Reference numeral 102 denotes an interchangeable photographic lens, which includes a lens group 113 that performs focusing and zooming, a lens driving unit 114 that drives the lens group 113, and a diaphragm device (not shown). Reference numeral 106 denotes an image sensor composed of an image sensor and its peripheral circuits.

  Reference numeral 103 denotes a main mirror, which is configured as a semi-transmissive mirror. Reference numeral 108 denotes a focusing screen, which is disposed on an imaging plane equivalent to the imaging plane of the image sensor 106 on which a subject image transmitted through the photographing lens 102 is formed. Reference numeral 118 denotes a subject optical path, and the light beam that has passed through the photographing lens 102 is reflected by the main mirror 103 and is primarily imaged on the focusing screen 108. Reference numeral 104 denotes a submirror. The subject luminous flux that has passed through the main mirror 103 is guided to the focus detection device 107 by the sub mirror 104, and a focus detection operation using a known phase difference detection method is performed.

  When the photographer 112 presses a later-described release switch (hereinafter referred to as SW) 205 when taking a picture, the main mirror 103 is automatically retracted from the viewfinder observation position to the outside of the subject optical path 118 of the subject luminous flux passing through the taking lens 102, and the taking lens. The image of the subject from 102 can be exposed to the image sensor 106. The focal plane shutter (hereinafter referred to as a shutter) 105 includes a magnet MG-1 that opens the front curtain when energized, and a magnet MG-2 that closes the rear curtain of the shutter 105 when energized. The subject luminous flux collected by the photographic lens 102 is controlled in light quantity by controlling the time (hereinafter referred to as shutter time) from the time when the shutter 105 starts running after the front curtain of the shutter 105 starts running. A photoelectric conversion process is performed as a subject image by 106. The image data after the photoelectric conversion process is recorded on a recording medium.

  Reference numeral 119 denotes a finder optical path, which indicates an optical path until the light beam from the focusing screen 108 is guided to the photographer 112. The pentaprism 109 changes the finder optical path 119 and corrects the subject image formed on the focusing screen 108 to an erect image. Reference numeral 111 denotes an eyepiece, which allows the photographer 112 to observe the subject image formed on the focusing screen 108. Reference numeral 110 denotes a photometric device, which is disposed on the upper side of the eyepiece lens 111. Here, the configuration of the photometric device 110 will be described with reference to FIG. FIG. 3 is a schematic view of a photometric device according to an embodiment of the present invention. Reference numeral 115 denotes a photometric lens. An optical low-pass filter 116 has a variable spatial frequency limiting effect.

  Details of the spatial frequency limiting effect will be described later. 117 is a photometric sensor. A thermometer (not shown) is also mounted on the photometric sensor 117, and the temperature in the vicinity of the photometric device 110 can be measured. Reference numeral 120 denotes a photometric light path. Among the light beams from the focusing screen 108, the light beam diffusing at a predetermined angle reaches the photometric device 110 via the pentaprism 109, and is narrowed by the photometric aperture 121. The light filtered by the photometric aperture 121 is subjected to secondary image formation on the chip surface of the photometric sensor 117 by the light filtered by the low pass filter 116 via the photometric lens 115. The photometric sensor 117 is an image sensor, and can perform subject recognition and subject brightness detection from color information and subject shape of a subject image formed on the chip surface.

  FIG. 4 is a block diagram showing an electrical configuration of the imaging apparatus according to the embodiment of the present invention. The CPU 101 includes an EEPROM 101a that is a non-volatile memory, performs processing based on a control program, transmits the processing result to each connected unit, and controls the entire imaging apparatus 100. An image sensor control unit 201 includes a timing generator (not shown), a noise removal / gain processing circuit, an A / D conversion circuit, and a pixel thinning processing circuit. The timing generator supplies a transfer clock signal and a shutter signal to the image sensor control unit 201.

  The noise removal / gain processing circuit performs noise removal and gain processing on the analog signal output from the image sensor 106. The A / D conversion circuit converts an analog signal into a 10-bit digital signal. The pixel thinning processing circuit performs pixel thinning processing in accordance with the resolution conversion instruction from the CPU 101. The image processing unit 202 performs image processing (gamma conversion, color space conversion, white balance, automatic exposure, flash correction, etc.) on the 10-bit digital signal output from the image sensor control unit 201, and YUV (4: 2: 2) Output as a format 8-bit digital signal.

  The focus detection device control unit 203 performs A / D conversion on the voltage obtained from the line CCD sensor of the focus detection device 107 and sends it to the CPU 101. The focus detection device control unit 203 also controls the light amount accumulation time and auto gain control of the line CCD sensor based on an instruction from the CPU 101. SW205 is a two-stage switch. Normally, when the first-stage switch (hereinafter referred to as SW1) is turned on, photometry and range-finding operations are started, and the second-stage switch (hereinafter referred to as SW2) is turned on. When turned on, the photographing operation is started. The battery 207 is configured as a rechargeable secondary battery (or dry battery).

  The DC / DC converter 206 receives a power supply from the battery 207, generates a plurality of power supplies by boosting and regulating, and supplies a power supply of a necessary voltage to the CPU 101 and each element. The DC / DC converter 206 can control the start and stop of each voltage supply by a control signal from the CPU 101. Further, the photometric device control unit 204 A / D converts the voltage obtained from the photometric sensor 117 and sends it to the CPU 101. The photometry control unit 204 also controls the light amount accumulation time and auto gain control of the photometry sensor 117 based on an instruction from the CPU 101. Further, the photometry control unit 204 also controls the spatial frequency limiting effect of the low-pass filter 116 based on an instruction from the CPU 101.

  Here, the frequency limiting effect of the low-pass filter 116 will be described. The purpose of mounting the low-pass filter is to reduce the false color by limiting the spatial frequency response of the lens with the low-pass filter as described above, cutting the high frequency component from the Nyquist frequency of the image sensor, and transmitting only the low frequency component. It is. In general, a birefringent plate such as a quartz plate is mainly used as an optical low-pass filter, and there is a type in which a birefringent plate and a quarter wavelength plate as a depolarizing plate are used in combination. The spatial frequency limiting effect of the low-pass filter is determined by the separation width d of the ordinary ray and the extraordinary ray due to the birefringence of the birefringent plate, and the separation width d can be expressed by the following equation.

n ₀ is the refractive index of the ordinary ray, the refractive index of n _e is the extraordinary ray, t represents the thickness of the low-pass filter. That is, the spatial frequency limiting effect by the low-pass filter is determined by the refractive index and the thickness. Further, the Nyquist frequency fn of the image sensor can be expressed by the following equation.

  P is the pixel pitch of the image sensor, and if the pixel pitch is known, the spatial frequency to be limited by the low-pass filter is known. That is, if a low-pass filter is set so that the separation width d> pixel pitch P, a spatial frequency limiting effect necessary for suppressing false colors can be obtained.

  The low-pass filter 116 in this embodiment has a variable spatial frequency limiting effect. Specifically, a low-pass filter in which a transparent electrode is formed on the inner surface of each of two quartz plates as shown in JP-A-4-236585 and a twisted nematic liquid crystal layer is provided between them is used. Thus, the spatial frequency limiting effect can be changed in two stages. When no voltage is applied to the low-pass filter 116 (hereinafter referred to as a low-pass filter OFF), the liquid crystal has a twisted nematic alignment and has optical rotation, so that there is no spatial frequency limiting effect.

  On the other hand, when a voltage is applied (hereinafter referred to as a low-pass filter ON), the twisted nematic arrangement loses its optical rotation, so that a spatial frequency limiting effect according to the separation width d of ordinary rays and extraordinary rays is produced. That is, by using the low-pass filter disclosed in Japanese Patent Laid-Open No. 4-236585, it is possible to select the presence or absence of the spatial frequency limiting effect by the low-pass filter depending on the presence or absence of voltage application. FIG. 5 is a diagram showing MTF (Modulation Transfer Function) at each frequency of the low-pass filter 116 in the present embodiment. The solid line is the MTF at each frequency when the low-pass filter is ON, and the dotted line is the MTF at each frequency when the low-pass filter is OFF. Further, a1 and a2 are MTFs of the photometric sensor 117 at the Nyquist frequency fn. By turning on and off the low-pass filter, a spatial frequency limiting effect as shown in FIG. 5 is produced, and a false color can be reduced.

  Next, a photometric operation sequence of the imaging apparatus according to the present embodiment will be described with reference to FIG. FIG. 6 is a flowchart showing a photometric operation sequence of the image pickup apparatus in the present embodiment. In S101, the power supply of the imaging apparatus 100 is turned on by a power switch (not shown). As a result of the power ON operation in S101, a voltage is applied to the low-pass filter 116 in S102, and the voltage is held in a state having a spatial frequency limiting effect. In S103, the photographer 112 operates SW205 to determine whether SW1 is turned on. If it is determined that SW1 is turned on, the process proceeds to S104. If it is turned off, the process waits until SW1 is turned on.

  In step S104, the photometry operation is started based on an instruction from the CPU 101. In S105, the temperature near the photometric sensor 117 is acquired by the thermometer mounted on the photometric sensor 117. In S106, the temperature in the vicinity of the photometric sensor 117 measured in S105 is compared with a threshold value recorded in advance in the EEPROM 101a. The threshold will be described later. If it is determined in S106 that the value is equal to or greater than the threshold value, the process proceeds to S107, the voltage of the low-pass filter 116 is turned OFF, the state is changed to a state having no spatial frequency limiting effect, and the process proceeds to S108. On the other hand, if it is determined in S106 that the voltage is equal to or lower than the threshold value, the process proceeds to S108 while the voltage is applied to the low-pass filter 116.

  In S108, accumulation of the photometric sensor 117 is started under conditions based on an instruction from the CPU 101. In S109, after the accumulation time instructed from the CPU 101 has elapsed, the accumulation of the photometric sensor 117 is terminated. In S110, a known subject recognition operation is performed using the output of the photometric sensor 117 accumulated up to S109 by the CPU 101. In S111, the CPU 101 determines the exposure based on the photometric algorithm of the imaging apparatus in response to the accumulation result in S109 and the subject recognition result in S110. The steps up to here are the photometric operation sequence of the present embodiment, and thereafter, the operation shifts to the normal photographing operation of the image pickup apparatus.

  Next, the temperature threshold value in S106 of FIG. 6 will be described. As described above, the photometric device 110 does not have a focus adjustment mechanism. Therefore, when a focus shift occurs due to a change in the environmental temperature, the resolution of the subject image formed on the photometric sensor 117 may be reduced. A factor causing the focus to be shifted due to the temperature is a temperature change in the refractive index of the glass material of the photometric lens 115. For the photometric lens 115, a plastic lens is often used from the viewpoint of cost and weight.

  The plastic lens has a larger refractive index change due to temperature change than a glass lens, and the Fno of the photometric lens 115 is also large in order to obtain a light amount, so that a focus shift due to temperature change affects. FIG. 1 is a diagram showing the MTF change due to the temperature change of the refractive index of the photometric lens 115 at the Nyquist frequency fn in this embodiment. The thin line indicates the MTF change due to the temperature of only the photometric lens 115. The thick line and the dotted line indicate the MTF in which the MTF of the low-pass filter when the low-pass filter is ON and OFF is added to the thin line, and represents the MTF of the photometric device 110.

  Here, a is an MTF for preventing the influence of false color. When the low-pass filter 116 is ON, the MTF is always equal to or lower than the MTFa, so that the influence of false color is suppressed regardless of the temperature change. The frequency limit is taken into account and the MTF is greatly reduced. On the other hand, when the low-pass filter is OFF, MTFa is exceeded during the temperature t, so that the influence of the false color occurs. However, the generation of the false color can be suppressed in a range other than the temperature t. Also, the MTF in the range other than the temperature t is higher when the low-pass filter is ON than when it is OFF.

  In other words, whether or not the threshold value in S106 is within the range of the temperature t, the low-pass filter 116 is turned on during the temperature t, and the low-pass filter 116 is turned off at other than the temperature t. While suppressing, it is possible to suppress a decrease in MTF due to the low-pass filter 116.

  As described above, in this embodiment, the temperature in the vicinity of the photometric device 110 is measured, and the frequency limiting effect of the low-pass filter 116 is changed according to the temperature measurement result. High-performance subject recognition can be performed while suppressing the influence of false colors.

[Example 2]
Next, a second embodiment of the present invention will be described. Note that the configuration of the imaging apparatus according to the second embodiment is the same as that described with reference to FIGS.

  A photometric operation sequence of the imaging apparatus according to the present embodiment will be described with reference to FIG. FIG. 7 is a flowchart showing a photometric operation sequence of the image pickup apparatus in the present embodiment.

  In S201, the power supply of the imaging apparatus 100 is turned on by a power switch (not shown). By the power ON operation of S201, a voltage is applied to the low pass filter 116 in S202, and the state is maintained in a state having a spatial frequency limiting effect. In S203, the photographer 112 operates SW205 to determine whether SW1 is turned on. If it is determined that SW1 is turned on, the process proceeds to S204, and if it is OFF, the system waits until SW1 is turned on.

  In step S204, a photometric operation is started based on an instruction from the CPU 101. In S205, it is determined whether the mode is to use the color information acquired by the photometry device 110. If it is determined that the color information is not used, the process proceeds to S208, where the voltage of the low-pass filter 116 is turned off, and the state is changed to a state having no spatial frequency limiting effect. On the other hand, when the color information is used, the process proceeds to S206, and the temperature near the photometric sensor 117 is acquired by the thermometer mounted on the photometric sensor 117. In S207, the temperature in the vicinity of the photometric sensor 117 measured in S206 is compared with a threshold value recorded in advance in the EEPROM 101a.

  The setting of the threshold value is the same as that described in the first embodiment, and a description thereof will be omitted. If it is determined in S207 that the value is equal to or greater than the threshold value, the process proceeds to S208, the voltage of the low-pass filter 116 is turned off, the state is changed to a state having no spatial frequency limiting effect, and the process proceeds to S209. On the other hand, if it is determined in S207 that it is equal to or less than the threshold value, the process proceeds to S209 while the voltage is applied to the low-pass filter 116.

  In step S209, accumulation of the photometric sensor 117 is started under conditions based on an instruction from the CPU 101. In S210, after the accumulation time instructed from the CPU 101 has elapsed, the accumulation of the photometric sensor 117 is terminated. In S211, the CPU 101 performs a known subject recognition operation using the output of the photometric sensor 117 accumulated up to S109. The operation sequence up to this point is the operation sequence of the present embodiment, and thereafter, the operation shifts to a normal imaging operation of the imaging apparatus.

  As described above, in this embodiment, when color information is not used, the low-pass filter 116 is turned off, so that the MTF reduction can be suppressed by the difference between the low-pass filter ON-OFF shown in FIG. Since the resolving power of the image formed on the sensor 117 is increased, highly accurate subject recognition can be performed. When color information is used, the temperature in the vicinity of the photometric device 110 is measured, and the frequency limiting effect of the low-pass filter 116 is changed according to the temperature measurement result. However, it is possible to perform high-performance subject recognition while suppressing the influence of false colors.

  The low-pass filter 116 according to the embodiment of the present invention is a step-by-step switching because the frequency limiting effect is a two-step switching. However, the low-pass filter 116 has a configuration as disclosed in Japanese Patent Application Laid-Open No. 61-268570. Alternatively, a low-pass filter that can change the frequency limiting effect may be used, and the frequency limiting effect may be continuously changed according to a temperature change. The low-pass filter 116 in the present embodiment uses an optical low-pass filter, but may be a known digital low-pass filter.

  As mentioned above, although preferable embodiment of this invention was described, this invention is not limited to these embodiment, A various deformation | transformation and change are possible within the range of the summary.

100 imaging device, 101 CPU, 110 photometric device, 115 photometric lens,
116 Low-pass filter, 117 Photometric sensor

Claims (2)

A finder optical system for observing a subject image formed by focusing the subject luminous flux that has passed through the photographing lens (102) on a focusing screen (108) disposed on a primary imaging plane, and the focusing screen A photometric device (110) for performing secondary photometry on the subject image formed above on an optical path different from the optical path of the viewfinder, and the photometric device is configured to detect the subject image formed on the focusing screen. A photometric sensor (117) that divides a light beam into a plurality of regions and outputs a plurality of photometric information relating to the luminance of the subject image, and a photometric lens that forms the subject image formed on the focusing screen on the photometric sensor ( 115), subject recognition means for recognizing the color and shape of the subject using the output of the photometric sensor, Several limiting effect a variable low-pass filter (116), and a thermometer, an imaging apparatus characterized by changing the spatial frequency limiting effect of the low-pass filter in accordance with the output of the thermometer. The imaging apparatus according to claim 1, wherein the low-pass filter imparts a spatial frequency limiting effect only when color information is used in the subject recognition unit.