JP5645190B2 - Flicker perception threshold measurement device, measurement method, and measurement program - Google Patents

Description

  The present invention relates to measurement of a threshold value (hereinafter also referred to as flicker perception threshold value) in which a person starts to perceive flickering with respect to a blinking stimulus, and can measure the threshold value in a short time at an appropriate distance. The present invention relates to a flicker perception threshold measurement device, a measurement method, and a measurement program.

  The present day is said to be a stress society, and there is a strong demand for objective measurement and evaluation methods for fatigue that can be used in daily life. Conventionally, a phenomenon in which the perception of “flicker” (flicker) when a person looks at a blinking light source changes depending on the degree of fatigue, in particular, the flicker frequency at the boundary (Critical Flicker Frequency: CFF) at which “flicker” can be perceived is fatigued. Quantitative evaluation of fatigue (flicker inspection) is performed using a phenomenon that decreases with increasing degree of fatigue. In the flicker test, as shown in FIG. 1, when the blinking frequency of the blinking light is temporally changed (monotonically increased or decreased) and presented to the subject, and the blinking is changed from an invisible state to a visible state, or When the blinking changes from the visible state to the invisible state, the frequency is measured by causing the subject to react such as pressing a button. FIG. 1 shows a measurement situation of five times. In other words, the frequency is presented to the subject by decreasing from a certain starting value fs, and the button is pressed when the subject perceives flicker in each measurement (time t1 to t5), and the frequencies f1 to f5 are respectively represented as CFFs. It shows the resulting situation. The flicker perception threshold (hereinafter also referred to as flicker value) is obtained, for example, as an average value of the obtained measurement values f1 to f5.

  The quantitative evaluation of the degree of fatigue using the flicker test is widely used particularly in the industrial hygiene field. However, a dedicated flicker value measuring device equipped with an LED or the like is necessary, and no one can easily carry out it on a daily basis.

  In contrast, the inventor of the present application enables a mental fatigue test based on the same flicker perception principle as the flicker test using an image display device having a fixed refresh rate such as a liquid crystal display and a CRT. (See Patent Documents 1 and 2 below). In this technique, instead of changing the blinking frequency of the blinking light used in the conventional flicker inspection, the flicker perception is generated by changing the contrast of the blinking light. This makes it possible to easily measure mental fatigue on a daily basis using a mobile terminal device such as a mobile phone, a personal computer, or the like.

For example, as shown in FIG. 2, the luminance of the image displayed on the image display device, to 0 from a maximum luminance _{Lon 0 (= Lon), Loff} 1, ···, Loff i, ···, Loff n = The image is displayed while decreasing at a constant ratio of 0. FIG. 2 shows a case where n gradations (for example, n = 256) are linearly changed in a period from t = 0 to T1. In FIG. 2, numbers “1” and “2” alternately attached along the time axis represent periods in which the first image with the maximum luminance and the second image with the luminance changed are displayed. Flickering is perceived when the contrast, which is the ratio (Loff / Lon) between the luminance value of the first image and the luminance value of the second image, is below a certain value. The contrast when flicker is perceived varies depending on the subject and the degree of fatigue.

  Further, Patent Document 2 discloses that objective measurement can be performed using two images as shown in FIG. 3 without subject's arbitraryness and measurement time can be shortened. The two images in FIG. 3 have different brightness values in the right sector. The fan-shaped region on the right side is a region where there is a contrast. When these images are displayed alternately, flickering can be perceived when the contrast of the right fan-shaped region falls below a certain value. A region in which contrast is to be provided is randomly determined from the four fan-shaped regions, and the subject is made to answer a region in which flicker is perceived (region in which the contrast is changed) while changing the contrast. Since it is possible to determine whether the answer is a correct answer or an incorrect answer, this makes it possible to objectively measure by eliminating the subject's arbitraryness. Furthermore, the measurement time can be shortened by measuring while adjusting the amount of change in contrast according to whether the answer is correct or incorrect.

JP 2010-088862 A International Publication No. 2011/030622 Pamphlet

  In the conventional flicker measuring apparatus as shown in FIG. 1, when measuring the point of transition from the state where the blinking is not visible to the state where it can be seen as a threshold value, it is usually the same fixed start so that any subject can be handled. Start the measurement from the point. Therefore, when measuring a plurality of times (usually 5 times), there is a problem that the measurement takes a long time. This also applies to the method using a contrast. According to the method disclosed in Patent Document 2, the measurement time can be shortened as compared with the conventional flicker measuring apparatus. However, it is desirable to be able to measure in a shorter time.

  Further, in the flicker test, it is necessary to perform measurement in a state where the distance between the subject and the measuring device (distance between the subject's eyes and the blinking stimulus) is properly maintained. If the distance is not appropriate, there is a problem that an accurate flicker perception threshold cannot be measured. Also, data measured at different distances cannot be handled equally. For example, there is a problem that sufficient accuracy cannot be obtained when the measurement data is compared with each other to determine the degree of fatigue of the subject.

  Therefore, an object of the present invention is to provide a measuring apparatus, a measuring method, and a measuring program that can measure the flicker perception threshold in a shorter time than before. It is another object of the present invention to provide a measuring apparatus, a measuring method, and a measuring program that can measure a flicker perception threshold at an appropriate distance.

  The above object can be achieved by the following.

  That is, the first method for measuring the flicker perception threshold according to the present invention is a method for measuring the flicker perception threshold of the subject by presenting the blinking stimulus to the subject, and the two images are displayed on the same image display surface. The step of presenting the blinking stimulus by alternately displaying the blinking stimulus at a certain frequency, and the boundary between the area where the subject perceives the flickering caused by the blinking stimulus and the area where the subject does not perceive the flickering while presenting the blinking stimulus. And a step of determining, as a flicker perception threshold, a luminance difference between positions on the two images corresponding to the specified boundary, one image of the two images is a predetermined region The brightness changes in the inside, and the brightness of the other image of the two images is constant in the area corresponding to the predetermined area.

  Preferably, the first method for measuring the flicker perception threshold is to measure the face of the subject at an appropriate distance of a measuring device that presents the flicker stimulus and measures the flicker perception threshold before the step of presenting the flicker stimulus. Imaging with the imaging device mounted on the device; extracting a face region from an image captured at an appropriate distance; and imaging a subject's face with the imaging device immediately after specifying the boundary; A step of extracting a face region from an image captured immediately after the step of specifying the boundary, a size of the face region extracted from an image captured immediately after the step of specifying the boundary, and an image captured at an appropriate distance And comparing the size of the face area extracted from the above and determining whether the distance between the eye of the subject and the blinking stimulus is appropriate when the boundary is designated.

  More preferably, the predetermined area is a band-shaped area, and the luminance of the predetermined area varies along the extending direction of the band-shaped area and is a constant value along the direction intersecting the extending direction.

  More preferably, the predetermined area is defined by one closed curve, and the luminance of the predetermined area is a constant value on a straight line connecting a predetermined point in the predetermined area and an arbitrary point on the outer periphery of the predetermined area, It changes along a circumference centered on a predetermined point.

  Preferably, the predetermined area is defined by one closed curve, and the luminance of the predetermined area changes along a straight line connecting a predetermined point in the predetermined area and an arbitrary point on the outer periphery of the predetermined area. It is a constant value along the circumference centered on.

  More preferably, the change in the luminance of the predetermined area is monotonously increasing or monotonically decreasing.

  The second method for measuring the flicker perception threshold according to the present invention is a method for measuring the flicker perception threshold of the subject by presenting a blinking stimulus to the subject, and using the face of the subject for the flicker perception threshold measurement. A step of imaging at an appropriate distance of the measuring device; a step of extracting a face region from an image captured at an appropriate distance; a step of presenting a blinking stimulus to the subject to measure the flicker perception threshold of the subject; and a flicker perception threshold Immediately after measuring the step, image the subject's face, extract the face region from the image captured immediately after measuring the flicker perception threshold, and extract from the image captured immediately after measuring the flicker perception threshold When the flicker perception threshold is measured by comparing the size of the face region obtained and the size of the face region extracted from the image captured at an appropriate distance, The distance between the flash stimulation with ocular examiner includes determining whether proper or not.

  The third method for measuring the flicker perception threshold according to the present invention is a method for measuring the flicker perception threshold of the subject by presenting the blinking stimulus to the subject, and presenting the flashing stimulus to the subject by the measuring device. Measuring the flicker perception threshold, immediately after measuring the flicker perception threshold, imaging the subject's face with the imaging device equipped in the measurement device, and from the image captured immediately after measuring the flicker perception threshold From the step of extracting the face area, the size of the face area extracted from the image captured immediately after measuring the flicker perception threshold, and the size of the face of the subject, the measurement distance is determined in consideration of the optical characteristics of the imaging device. Determining and determining whether the determined measurement distance is an appropriate distance in the measurement of the flicker perception threshold.

  The first measurement apparatus for flicker perception threshold according to the present invention presents a blinking stimulus and a display unit for presenting a blinking stimulus to a subject by alternately displaying two images at the same position at a constant frequency. And an operation unit for allowing the subject to designate a boundary between a region that perceives flickering caused by blinking stimulation and a region that does not perceive flickering, and the position of the position on the two images corresponding to the designated boundary is provided. The luminance difference is determined as a flicker perception threshold, and one of the two images changes in luminance within a predetermined area, and the other of the two images is within an area corresponding to the predetermined area. The brightness of is constant.

  A second flicker perception threshold measurement apparatus according to the present invention is a measurement apparatus that presents a blinking stimulus to a subject and measures the flicker perception threshold of the subject, and includes an imaging unit that images the face of the subject. A determination unit that uses the extracted face area to determine whether the distance between the subject's eyes and the blinking stimulus is appropriate when the flicker perception threshold is measured. And the determination unit immediately after measuring the flicker perception threshold, the size of the face region extracted by the extraction unit from the image captured by the imaging unit and the face of the subject by the imaging unit The size of the face area extracted by the extraction unit is compared with the image captured at the appropriate distance to determine whether the distance when the flicker perception threshold is measured is appropriate.

  A first flicker perception threshold measurement program according to the present invention displays two images alternately at a fixed frequency at the same position on a display unit on a computer or portable terminal device having an operation unit and a display unit. The function of presenting the blinking stimulus and the operation of the operation unit for designating the boundary between the area perceiving the flickering by the blinking stimulus and the area not perceiving the flickering by the subject in the state where the blinking stimulus is presented. An accepting function and a function of determining a luminance difference between positions on two images corresponding to a specified boundary as a flicker perception threshold, and one of the two images is within a predetermined area. The program for measuring a flicker perception threshold is characterized in that the luminance changes in the image and the luminance of the other image of the two images is constant in the region corresponding to the predetermined region.

  The second flicker perception threshold measurement program according to the present invention images a subject's face at an appropriate distance when the flicker perception threshold is measured by the imaging unit on a computer or portable terminal device including a display unit and an imaging unit. A function to extract a face region from an image captured at an appropriate distance, a function to measure a flicker perception threshold of the subject by presenting a blinking stimulus to the subject by a display unit, and immediately after measuring a flicker perception threshold In addition, the imaging unit captures the face of the subject, the function of extracting the face area from the image captured immediately after measuring the flicker perception threshold, and the image captured immediately after measuring the flicker perception threshold. The eye of the subject when the flicker perception threshold was measured by comparing the size of the detected face region with the size of the face region extracted from the image captured at an appropriate distance. The distance between the flashing stimulus to realize a function to determine whether proper or not.

  According to the present invention, various contrast differences are presented to the subject at a time by presenting the blinking stimulus using an image in which the luminance is two-dimensionally distributed, so that the area where the flicker is perceived and the area where the flicker is not perceived From the boundary, a flicker perception threshold can be determined. Since the subject can perceive the boundary immediately after the flashing stimulus is presented, the flicker perception threshold can be measured in a very short time. If a device capable of touch operation is used as a blinking stimulus display device, measurement within one second is possible.

  Also, by comparing the face area extracted from the image captured at the appropriate distance of the flicker threshold measurement device with the face area extracted from the image captured at the time of flicker threshold measurement, the measurement distance at the time of flicker threshold measurement is It can be determined whether or not it is appropriate. Therefore, data that has not been measured at an appropriate distance can be discarded, and all the data obtained is data that has been measured at an appropriate distance, so that the measured data can be compared with each other.

It is a graph which shows the change of the blink frequency in the measurement of the conventional flicker perception threshold. It is a graph which shows the change of the blink contrast in the measurement of the conventional flicker perception threshold. It is a figure which shows the image shown to a test subject, when contrast is measured as the conventional flicker perception threshold. It is a block diagram which shows the outline | summary of a structure of the measuring apparatus of the flicker perception threshold which concerns on the 1st Embodiment of this invention. It is a flowchart which shows the control structure of the program for implement | achieving the measuring method of the flicker perception threshold which concerns on the 1st Embodiment of this invention. It is a figure which shows two images shown to a test subject. It is a figure which shows two images shown to a test subject. It is a figure which shows the image shown to a test subject. It is a figure which shows the image shown to a test subject. It is a graph which shows the brightness | luminance change of the image shown to a test subject. It is a block diagram which shows the outline | summary of a structure of the measuring apparatus of the flicker perception threshold which concerns on the 2nd Embodiment of this invention. It is a flowchart which shows the control structure of the program for implement | achieving the measurement in an appropriate distance in the measurement of the flicker perception threshold which concerns on the 2nd Embodiment of this invention. It is a figure explaining a calibration. It is a figure explaining the determination method of measurement distance.

  In the following embodiments, the same parts are denoted by the same reference numerals. Their names and functions are also the same. Therefore, detailed description thereof will not be repeated.

(First embodiment)
Referring to FIG. 4, flicker perception threshold measurement apparatus 100 according to the first exemplary embodiment of the present invention includes an arithmetic processing unit (hereinafter referred to as CPU) 102 and a read-only memory (hereinafter referred to as ROM) 104. A rewritable memory (hereinafter referred to as RAM) 106, a recording unit 108, a timer 110, an interface unit (hereinafter referred to as IF unit) 112, a bus 114, a display unit 116, and an operation unit 118. The CPU 102 controls the entire measuring apparatus 100. The ROM 104 is a nonvolatile storage device, and stores a program and data for controlling the operation of the measurement device 100. The RAM 106 is a volatile storage device. The recording unit 108 is a non-volatile storage device that retains data even when power is cut off, and is, for example, a hard disk drive, a flash memory, or the like. The CPU 102 reads a program from the ROM 104 onto the RAM 106 via the bus 114, and executes the program using a part of the RAM 106 as a work area. CPU102 controls each part which comprises the measuring apparatus 100 according to a program.

  The timer 110 outputs time information using an internal clock. The IF unit 112 is an interface between the CPU 102, the display unit 116, and the operation unit 118. A CPU 102, ROM 104, RAM 106, recording unit 108, timer 110, and IF unit 112 are connected to the bus 114. Data (including control information) is exchanged between the units via the bus 114.

  The display unit 116 includes a display panel (liquid crystal panel or the like) for displaying an image and a drive unit for driving the display panel. The display unit 116 displays the image data transmitted via the IF unit 112 at a predetermined refresh rate. If the IF unit 112 and the drive unit are designed according to the format (specification) of the image signal transmitted between the IF unit 112 and the display unit 116, the image signal may be digital or analog. Good. The operation unit 118 includes keys, pads, and the like, and the subject operates the operation unit 118 to give an instruction to the measurement apparatus 100.

  As the measuring device 100, for example, a known computer or a mobile terminal device (a mobile phone, a PHS, a PDA, etc.) can be used.

  With reference to FIG. 5, the measurement of the flickering perception threshold using the measurement apparatus 100 will be described.

  In step 300, the CPU 102 reads two pieces of image data from the recording unit 108 into the RAM 106. Of the two images to be read, one image is an image including a predetermined two-dimensional region (hereinafter also referred to as a luminance change region) in which the luminance changes, and the other image corresponds to the luminance change region. It is an image in which the brightness of the region is uniform. For example, there are two images as shown in FIG. The first image 200 is composed of a horizontally long belt-like region 210 and a background region 212 thereof. The luminance values in the belt-like region 210 are distributed such that the luminance value of the left end region 202 is the largest, the luminance value decreases linearly as going to the right, and the luminance value becomes the smallest in the right end region 204. For example, in the case of an 8-bit 256 gradation image, the luminance value of the left end region 202 is 255, and the luminance value of the right end region 204 is 0. On the other hand, the luminance value of the region 222 corresponding to the belt-like region 210 of the second image 220 is constant, for example, 255. The luminance of the background region 212 of the first image 200 and the background region 224 of the second image 220 are both constant, for example, 255. Note that the gradation width (difference between the maximum luminance value and the minimum luminance value) is not limited to 8 bits (256 gradations) and is arbitrary. For example, it may be 3 to 7 or 9 to 11 bits (8, 16, 32, 64, 128, 512, 1024, 2048 gradations), or other values. Further, the difference in luminance value between adjacent regions may not be constant.

  In step 302, the CPU 102 acquires the current time from the timer 110 and stores it in the RAM 106, and then transmits the two image data alternately to the display unit 116 via the IF unit 112 at a predetermined cycle. The display unit 116 displays the received image data at a predetermined refresh rate (for example, 60 Hz) and presents it to the subject.

  The two images shown in FIG. 6 are alternately displayed on the display unit 116 by converting a conventional temporal contrast change (see FIG. 2) as a two-dimensional contrast distribution (two-dimensional distribution of luminance values). It will be presented at once. Therefore, the subject perceives flicker in a part of the luminance change region (band-like region 210) and does not perceive flicker in other regions. A boundary between a region where flicker can be perceived and a region where flicker cannot be perceived can be defined as a threshold for contrast change perception, that is, a flicker value. For example, when the luminance of the background area 212 is the same as that of the left end area 202, the subject cannot perceive flickering in the area P1 of the belt-like area 210, and in the area P2 (from the area 206 to the right end area 204). Perceive flicker. In this case, the boundary 208 is perceived. For example, when the luminance of the background area 212 is the same as that of the right end area 204, the subject perceives flickering in the area P1 of the belt-like area 210, and the area P2 (from the area 206 to the right end area 204). I can't perceive flicker. In this case as well, the subject perceives the boundary 208.

  In step 304, the CPU 102 determines whether or not the operation unit 118 has been operated by the subject and a point in the luminance change region has been designated. If it is determined that a point in the luminance change area is designated, information for identifying the designated point is stored in the RAM 106, and the process proceeds to step 310. If not operated, or if a point in the luminance change area is not designated even if operated, the process proceeds to step 306.

  The method for the subject to specify the boundary between the area where the flicker can be perceived and the area where the flicker cannot be perceived is as follows. The cursor such as an arrow is displayed on the display unit 116, the cursor is moved with the arrow key of the operation unit 118, and then the operation unit It is only necessary to press the 118 confirmation key. If a touch panel display is adopted as the display unit 116, the subject may touch the touch panel display and specify the boundary.

  In step 306, the CPU 102 acquires the current time from the timer 110 and determines whether or not a predetermined time T has elapsed from the time stored in the RAM 106 in step 302. When it is determined that the predetermined time T has elapsed, the process proceeds to step 310. If it is determined that the predetermined time T has not elapsed, the process returns to step 304. Accordingly, two images are alternately displayed for a predetermined time T, and the operation unit 118 is waited for being operated.

  When the predetermined time T has elapsed, in step 310, the CPU 102 stops displaying images, displays a predetermined message on the display unit 116, and proceeds to step 312. The predetermined message is, for example, a message indicating that the measurement could not be performed correctly, such as “Measurement failed”.

  In step 310, the CPU 102 reads the information specifying the designated point stored in the RAM 106 in step 304, determines the luminance value of the corresponding point on the displayed first image data, and stores the subject's flicker in the recording unit 108. Save as value.

  In step 312, the CPU 102 determines whether or not to end. If it is determined not to end, the process returns to step 300. For example, the CPU 102 displays a message such as “Do you want to measure again?” And the choices “Yes” and “No” on the display unit 116, and determines whether or not to end by the selection operation of the user. . When the user selects re-measurement, the processing after step 300 is repeated.

  As described above, the subject's flicker is displayed only once (within a predetermined time T) by blinking using the first image in which the luminance value is two-dimensionally distributed and the second image having a uniform luminance value. The value can be measured in a very short time. Since the subject can perceive the blinking region and the non-flashing region almost instantaneously, the measurement is completed in the time required for the subject to operate the operation unit 118 and specify the boundary. In order to shorten the operation time of the subject, it is preferable to employ a touch panel display as the display unit 116 so that the subject can directly specify the boundary by touching the blinking boundary.

  The image presented as the blinking stimulus is not limited to the image shown in FIG. An image as shown in FIG. 7 may be used. That is, the images 240 and 260 can be used as the first image and the second image, respectively. In the image 240, the luminance change region is a circular region, and the luminance value changes around the center (along the circumference). The brightness values in the brightness change area are distributed so that the brightness value of the fan-shaped area 242 is the largest, the brightness value decreases linearly as it moves clockwise, and the brightness value is the smallest in the fan-shaped area 244. ing. Note that the fan-shaped region 246 may be an arbitrary luminance value because it is a boundary between the region with the largest luminance value and the region with the smallest luminance value. For example, the same brightness value as that of the sector area 242, the same brightness value as that of the sector area 244, and the same brightness value as that of the background. In this case, the subject designates, for example, a radial line indicated by an arrow 250 as a boundary between a region where flicker can be perceived and a region where flicker cannot be perceived. The fan-shaped area may be a triangular area, and the luminance change area may be a polygonal area.

  Further, the luminance change region is not limited to the linear belt-like region as shown in FIG. 5 and may be a curve having an arbitrary width. For example, it may be a spiral belt-like region having both ends opened or an annular belt-like region having no open end as shown in FIG. 8 (FIG. 8 is a ring). Further, as shown in FIG. 9, the luminance change area may be a circular area whose luminance value changes in the radial direction from the center. In any of these images, the subject can specify the boundary between the area where flicker can be perceived and the area where flicker cannot be perceived.

  Further, the background area may be omitted. For example, if the luminance change area is a rectangle as shown in FIG. 6, an image in which the entire display screen is the luminance change area may be used.

  In the above description, the case where the change in the luminance value linearly increases or decreases along a predetermined direction on the two-dimensional surface has been described. However, the present invention is not limited to this. For example, as shown in FIG. 10, the change pattern of the luminance value is arbitrary. For example, even if the luminance value changes with a constant inclination like a line 500 or changes like a line segment with a plurality of inclinations like a line 502, the luminance value changes like a curve like lines 504 and 506. May be. Since the actual luminance value is expressed as a gradation value, it is a discrete value, for example, an integer value of 0 or more. Further, the change in the luminance value may not be monotonously decreased or monotonously increased. Lines including maximum values, minimum values, maximum values, or minimum values other than both ends of the luminance change region may be used, as indicated by lines 510, 512, and 514 in FIG. For example, when an image whose luminance value changes like the line 500 is used as the first image, the point A is designated as a boundary between a region where the flicker can be perceived and a region where the flicker cannot be perceived. On the other hand, when an image whose luminance value changes like the polygonal line 510 having the maximum luminance value near the center is used as the first image, the regions where the points B and C can perceive flicker and the region where the flicker cannot be perceived. Can be specified as a boundary. In this case, if the subject specifies at least one of point B and point C, the corresponding luminance value can be determined as the flicker value. Therefore, the luminance change region may be an arbitrary graphic (image) as long as the luminance value does not change rapidly in a narrow range (a pattern in which the subject can specify the boundary). Even if the subject perceives a plurality of boundaries between a region where flicker can be perceived and a region where flicker cannot be perceived, the corresponding luminance value can be determined as the flicker value by designating any one of the boundaries.

(Second Embodiment)
Next, a second embodiment of the present invention will be described.

  Referring to FIG. 11, flicker perception threshold measuring device 120 according to the second exemplary embodiment of the present invention includes CPU 102, ROM 104, RAM 106, recording unit 108, timer 110, IF unit 122, bus 114, and display unit 116. , An operation unit 118 and an imaging unit 124 are provided. The measuring apparatus 120 has a configuration in which an imaging unit 124 is added to the measuring apparatus 100 illustrated in FIG. The IF unit 122 is different from the IF unit 112 in that it performs an interface with the imaging unit 124, and thus is given a different reference. Here, description regarding the imaging unit 124 will be made, and redundant description will not be repeated.

  The imaging unit 124 is an image sensor (CCD, CMOS image sensor, etc.), for example, and performs imaging under the control of the CPU 102. Data output from the imaging unit 124 is transmitted to the RAM 106 via the IF unit 122 and stored as image data in the recording unit 108 as necessary. The imaging instruction is performed by the user operating the operation unit 118.

  With reference to FIG. 12, the measurement of the flickering perception threshold (flicker value) using the measuring device 120 will be described. Here, the flicker perception threshold is measured by the same method as in FIG. In FIG. 12, the same steps as those in the flowchart of FIG.

  In step 400, the CPU 102 performs calibration before performing actual measurement. Specifically, as shown in FIG. 13, the subject uses his / her measuring device 120 to photograph his / her face with the display unit 116 separated from his / her eyes by an appropriate distance (for example, 50 cm). . The CPU 102 controls the imaging unit 124 according to the operation of the operation unit 118 by the subject, performs imaging, and stores the image data in the recording unit 108. The CPU 102 performs image processing on the stored image data to extract a face area, and information on the size of the face area (for example, the length of the long side and the short side of the rectangle circumscribing the extracted area ( Pixel value)) is stored in the recording unit 108. Note that a known method may be used to extract a face from image data.

  In steps 300 to 308, a flicker value is measured by displaying a predetermined blinking image.

  When it is determined that a point in the luminance change region is designated by the operation of the operation unit 118 by the subject, in step 402, the CPU 102 controls the imaging unit 124 to perform imaging, and the captured image data is recorded in the recording unit 108. To record.

  In step 404, the CPU 102 performs image processing on the image data stored in the recording unit 108 in step 402 to extract a face area, and obtains the size of the face area. Further, the CPU 102 reads out the information on the size of the face area obtained in step 400 from the recording unit 108 and compares it with the obtained size of the face area, and compares the distance between the eye of the subject and the display unit 116 of the measuring device 120 ( It is determined whether or not (measurement distance) is appropriate. If it is determined that the distance is appropriate, the process proceeds to step 310, where a flicker value is obtained from the information for specifying the point specified in step 304 and stored in the recording unit 108. If it is not determined that the distance is appropriate, the process proceeds to step 308.

  When an object of the same size is imaged with one imaging device, the size of the object in the obtained image is (pixel) according to the distance between the object and the imaging device and the magnification of the optical system used for imaging. Value). Therefore, in step 402, when imaging is performed without changing the magnification of the measurement device 120 from the time of imaging at the appropriate distance in step 400, the size of the face region in the image captured at the appropriate distance in step 400 is If it is substantially equal to the size of the face area in the image captured at 402, it is measured at an appropriate distance (50 cm). For example, as illustrated in FIG. 14, when the center image is captured in step 400, if the image captured in step 402 is the leftmost image, the distance (for example, 100 cm) between the subject's eyes and the display unit 116. Is greater than the proper distance. In the case of the rightmost image, the distance (for example, 20 cm) between the subject's eyes and the display unit 116 is smaller than the appropriate distance. In Step 402, when the image is captured at the appropriate distance in Step 400 and the magnification of the measuring device 120 is changed, it is not appropriate to use the image captured in Step 402 as it is. In that case, the above comparison is performed using an image obtained by converting the image captured in step 402 into an image having a magnification equivalent to the magnification at the time of imaging at the appropriate distance in step 400.

  As described above, only the flicker value measured at an appropriate distance can be stored.

  In the above description, the case where imaging is performed when the subject operates the operation unit 118 has been described, but the present invention is not limited to this. For example, imaging may be performed at predetermined time intervals after the blinking stimulus is presented until the subject operates the operation unit 118. In that case, a face is extracted from the captured image, and if it is not an appropriate size compared to the reference size, a message that causes the display unit 116 to maintain an appropriate distance (for example, “Please bring your face closer”). , “Please keep your face away”).

  Moreover, when measuring with respect to the same test subject, it is not necessary to perform calibration (step 400) every time. If calibration is performed at least once and the result (which may be the captured image data itself or the size of the extracted face area) and the imaging magnification information are stored in the recording unit 108, they are used. Thus, it can be determined whether or not the flicker value is measured at an appropriate distance as described above. In this case, when the imaging magnification is different, it is necessary to convert the image to an equivalent magnification as described above. When there is a change that affects the face area extraction process, such as when the hairstyle is changed, it is preferable to perform calibration each time.

  It is also possible not to perform the calibration (step 400) at all. For example, a standard face size (average value or the like) obtained from a human body dimension database or the like is used. In the case of the Japanese, the distance from the top of the head to the jaw is about 24 cm for men, about 23 cm for women, and the head width is about 16 cm for men and about 15 cm for women. By using such data, if the subject's gender is specified, the size of the subject's face can be determined although it is an approximate value. Therefore, using the determined value and the optical characteristics of the imaging device, the measurement distance can be estimated from the size of the face area in the image of the subject imaged when measuring the flicker value, and measured at an appropriate distance. It can be determined whether or not. The optical characteristics of the imaging device include the focal length of the imaging device, the size and resolution of the image sensor (CCD, etc.), and the correspondence between the pixels of the image sensor and the pixels of the image data to be captured. (Not necessarily one to one). If the subject knows the size of his / her face, the value can be used to calculate the measurement distance in the same manner as described above.

  Note that the flicker value measurement method is not limited to the method shown in FIG. 5, but a conventional method of measuring a frequency (see FIG. 1) and a method of measuring a contrast with time (FIGS. 2 and 3). Reference).

  The present invention has been described above by describing the embodiment. However, the above-described embodiment is an exemplification, and the present invention is not limited to the above-described embodiment, and is implemented with various modifications. be able to.

100, 120 Flicker perception threshold measuring device 102 Arithmetic processing unit (CPU)
104 Read-only memory (ROM)
106 Rewritable memory (RAM)
108 Recording unit 110 Timer 112, 122 Interface unit (IF unit)
114 Bus 116 Display unit 118 Operation unit 124 Imaging unit 210, 240 First image 220, 260 Second image

Claims (8)

A method of measuring a flicker perception threshold of a subject by presenting a blinking stimulus to the subject,
Presenting the blinking stimulus by alternately displaying two images at the same position on the image display surface at a constant frequency;
Designating a point on the boundary between a region where the subject perceives flickering due to the flashing stimulus and a region where perceptual flickering is not perceived in the state where the flashing stimulus is presented;
Determining a luminance difference between positions on the two images corresponding to the designated point as a flicker perception threshold,
One of the two images changes in luminance within a predetermined area,
The flicker perception threshold value measuring method, wherein the other of the two images has a constant luminance in an area corresponding to the predetermined area. Prior to the step of presenting the flashing stimulus, the subject's face is imaged by an imaging device included in the measurement device at an appropriate distance of a measurement device that presents the flashing stimulus and measures the flicker perception threshold. Steps,
Extracting a face region from an image captured at an appropriate distance;
Immediately after the step of specifying the point , imaging the subject's face with the imaging device;
Extracting a face region from the image taken immediately after the step of specifying the point ;
Compared with the size of the face region extracted from the captured the image immediately after the step of specifying the point, the magnitude of the proper distances extracted from the captured the image in the face area, the point The method for measuring a flicker perception threshold according to claim 1, further comprising the step of determining whether or not a distance between the eye of the subject and the blinking stimulus is appropriate when designating the subject. The predetermined area is a belt-like area;
3. The flicker perception threshold according to claim 1, wherein the luminance of the predetermined region changes along the extending direction of the belt-like region and has a constant value along a direction intersecting the extending direction. Measuring method. The predetermined region is defined by a closed curve;
The luminance of the predetermined area is a constant value on a straight line connecting a predetermined point in the predetermined area and an arbitrary point on the outer periphery of the predetermined area, and the luminance around the predetermined point is a circle. The method for measuring a flicker perception threshold according to claim 1, wherein the flicker perception threshold is varied along the line. The predetermined region is defined by a closed curve;
The luminance of the predetermined area changes along a straight line connecting a predetermined point in the predetermined area and an arbitrary point on the outer periphery of the predetermined area, and along a circumference centered on the predetermined point. The method for measuring a flicker perception threshold according to claim 1 or 2, wherein the flicker perception threshold is a constant value.   The method for measuring a flicker perception threshold according to any one of claims 1 to 5, wherein the change in luminance of the predetermined region is monotonously increasing or monotonically decreasing. A display unit that presents a flashing stimulus to the subject by alternately displaying two images at a constant frequency at the same position;
In the state of presenting the blinking stimulus, the subject comprises an operation unit for causing the subject to specify a point on a boundary between a region that perceives flickering due to the blinking stimulus and a region that does not perceive flickering,
A luminance difference between positions on the two images corresponding to the designated point is determined as a flicker perception threshold;
One of the two images changes in luminance within a predetermined area,
An apparatus for measuring a flicker perception threshold, characterized in that the other of the two images has a constant luminance in an area corresponding to the predetermined area. To a computer or portable terminal device having an operation unit and a display unit,
A function of presenting a blinking stimulus by alternately displaying two images at a constant frequency at the same position on the display unit;
A function of accepting an operation of the operation unit for designating a point on a boundary between a region perceiving flicker due to the flashing stimulus and a region not perceiving flicker by the subject in a state where the flashing stimulus is presented;
A function of determining a luminance difference between positions on the two images corresponding to the designated point as a flicker perception threshold;
One of the two images changes in luminance within a predetermined area,
The flicker perception threshold value measurement program characterized in that the other of the two images has a constant luminance in an area corresponding to the predetermined area.

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