Optical waveform measuring device and measuring method

Abstract

The optical waveform measuring apparatus of the present application includes a detection unit (13) that detects a candidate of a light amount variation frequency of a measurement target (100), a frequency determination unit (14) that determines a light amount variation frequency based on the detected candidate of the light amount variation frequency, a measurement condition determination unit (15) that determines a measurement condition of optical waveform measurement based on the determined light amount variation frequency, and an acquisition unit (16) that acquires an optical waveform of the measurement target under the determined measurement condition. The measurement condition determination unit (15) determines a sampling frequency and a measurement point number such that a measurement time becomes an integral multiple of a period of the light amount variation frequency determined by the frequency determination unit (14).

Description

Technical Field

[0001] This invention relates to an optical waveform measuring device and a measuring method for measuring the optical waveform of objects such as displays. Background Technology

[0002] Generally, monitors such as those for personal computers update images according to the period of the vertical sync signal (Vsync), resulting in brightness fluctuations in the screen that occur periodically with the vertical sync signal. Furthermore, in the case of a liquid crystal display (LCD), the brightness fluctuation period becomes twice as low as that of an LCD because it employs a reverse drive that switches polarity between odd and even frames.

[0003] As a light measuring instrument for measuring the basic performance of such displays, there are known displays color analyzers (for example, the CA-410 manufactured by Konica Minolta Corporation). These displays color analyzers have an internal light sensor that can measure not only color or brightness, but also light waveform or flicker.

[0004] There are generally two ways to obtain light intensity: the successive acquisition method, which obtains instantaneous values, and the integral acquisition method, which obtains integral values ​​over a determined period of time. The successive acquisition method is characterized by its high speed, while the integral method is characterized by its excellent performance in low-brightness measurements.

[0005] In addition, frequency filtering is used as a means to make the characteristics of the acquired waveform more apparent. Filtering applies desired weights to each frequency component that constitutes the waveform. For example, in the case of a low-pass filter (LPF), high frequencies are attenuated relative to the signal frequency. This reduces high-frequency noise and allows for the reproduction of a smooth signal waveform. As another example, when a TCSF (temporal contrast sensitivity function) is used in the filter, a waveform corresponding to human visual characteristics can be reproduced.

[0006] In conventional optical waveform measurement devices, waveforms are obtained during a predetermined measurement period in the system, or waveforms for a period of time corresponding to the number of measurement points are obtained by the user inputting the number of measurement points.

[0007] The acquired waveform is processed by Discrete Fourier Transform (DFT) to transform it into a spectrum. The resulting spectrum reflects the filter's arbitrary frequency characteristics. Specifically, weighting is performed by multiplying each frequency. The filtered waveform is then obtained by performing an Inverse Fourier Transform (IDFT) on the weighted spectrum.

[0008] Furthermore, as an algorithm to reduce the computational processing of Discrete Fourier Transform and Inverse Fourier Transform, Fast Fourier Transform (FFT) is known. However, FFT can only process data points that are powers of 2 (data points = 2^3). d Such constraints exist. In order to reduce the computational load of Discrete Fourier Transform and Inverse Fourier Transform, the number of measurement points when acquiring waveforms is mostly set to a power of 2.

[0009] In addition, Patent Document 1 discloses the following technology: in an optical measurement device (splitter) equipped with an array detector, the measurement time value is determined by high-speed scanning, which enables the synchronization of time-discontinuous lighting sources.

[0010] Existing technical documents

[0011] Patent documents

[0012] Patent Document 1: U.S. Patent Publication No. 2005-0103979 Summary of the Invention

[0013] The problem that the invention aims to solve

[0014] Here, when the measurement time does not match the period of the emitted waveform (e.g., during Vsync) (and is not an integer multiple thereof), the light intensity values ​​at the beginning and end of the obtained waveform are inconsistent. Therefore, multiple frequency components associated with the measurement time are generated in the spectrum. The frequency component associated with the measurement time is 1 / measurement time × n, i.e., the frequency with one period equal to the measurement time and its higher harmonics.

[0015] If the spectrum is filtered, the filtered waveform (after weighting and inverse Fourier transform) will exhibit significant distortion at both the beginning and end of the waveform.

[0016] As a countermeasure, there is a known method to delete the front and back ends of the filtered waveform. However, due to the lack of generated data, it may be impossible to obtain the time domain information required for triggering measurements, which is not convenient.

[0017] As another countermeasure, a method using a window function that makes the data ends have the same value is disclosed. In this method, the acquired waveform is multiplied by the window function and then subjected to a discrete Fourier transform. Then, the waveform after weighted and inverse Fourier transform is divided by the window function to generate the filtered waveform.

[0018] However, in this method, the measurement error is amplified when divided by the window function, which also results in significant waveform distortion.

[0019] Furthermore, Patent Document 1 does not contain any description of optical waveform measurement or the aforementioned issues related to optical waveform measurement. Therefore, even if Patent Document 1 is consulted, the aforementioned issues cannot be resolved.

[0020] The present invention was made in view of the following technical background, and its purpose is to provide an optical waveform measurement device and method that can reduce the distortion of the filtered waveform.

[0021] Methods for solving problems

[0022] The above objectives are achieved through the following means.

[0023] (1) The optical waveform measuring device comprises: a detection unit for detecting candidates of optical quantity variation frequency of the object to be measured; a frequency determination unit for determining the optical quantity variation frequency based on the candidates of optical quantity variation frequency detected by the detection unit; a measurement condition determination unit for determining the measurement conditions for optical waveform measurement based on the optical quantity variation frequency determined by the frequency determination unit; and an acquisition unit for acquiring the optical waveform of the object to be measured under the measurement conditions determined by the measurement condition determination unit, wherein the measurement condition determination unit determines a sampling frequency and a number of measurement points in which the measurement time is an integer multiple of the period of the optical quantity variation frequency determined by the frequency determination unit.

[0024] (2) The optical waveform measuring device described in item 1 above, wherein the detection unit obtains waveform data of optical quantity variation by pre-measurement before optical waveform measurement, obtains spectrum data by performing Fourier transform processing on the waveform data, and detects candidates for optical quantity variation frequency based on the frequency of singularity point with intensity greater than adjacent frequency in the spectrum data.

[0025] (3) The optical waveform measuring device described in item 1 or item 2 above, wherein the frequency determining unit determines the candidate with the smallest frequency from the candidates of optical quantity variation frequencies as the optical quantity variation frequency.

[0026] (4) The optical waveform measuring device described in item 1 or item 2 above, wherein the device further comprises a selection unit that allows a user to select any candidate from the candidates of optical quantity variation frequencies detected by the detection unit, and the frequency determination unit determines the candidate selected by the user through the selection unit as the optical quantity variation frequency.

[0027] (5) The optical waveform measuring device described in item 1 or item 2 above, wherein the device includes an input unit in which a user can input the frequency of optical quantity variation, and the frequency determination unit determines the optical quantity variation frequency as the candidate closest to the optical quantity variation frequency input by the input unit among the candidates of optical quantity variation frequency detected by the detection unit.

[0028] (6) The optical waveform measuring device described in item 2 above, wherein the detection unit detects candidates for optical quantity variation frequencies by supplementation, the supplementation using the intensity of a frequency adjacent to a frequency that is a singularity with a greater intensity than the adjacent frequency in the spectrum data.

[0029] (7) The optical waveform measuring device described in item 1 above, wherein the detection unit obtains waveform data of optical quantity variation by pre-measurement before optical waveform measurement, and detects candidates of optical quantity variation frequency by autocorrelation method on the waveform data.

[0030] (8) The optical waveform measuring device described in any one of the preceding items 1 to 7, wherein the wave number of the optical waveform acquired by the acquiring unit varies according to the frequency of the optical quantity variation.

[0031] (9) The optical waveform measuring device described in any one of the preceding items 1 to 8, wherein it comprises a filtering processing unit, the filtering processing unit performs filtering processing on the optical waveform obtained by the acquisition unit, the number of measurement points is a power of 2 times m (m is an integer), and the number of measurement points is different before and after the filtering processing.

[0032] (10) The optical waveform measuring device in item 9 above, wherein the optical waveform before filtering based on the filtering processing unit is averaged in units of m and then filtered.

[0033] (11) A method for measuring optical waveforms, comprising: a detection step in which a detection unit detects candidates for the optical quantity variation frequency of a measurement object; a frequency determination step in which a frequency determination unit determines the optical quantity variation frequency based on the candidates for the optical quantity variation frequency detected by the detection step; a determination step in which a determination condition determination unit determines the determination conditions for measuring the optical waveform based on the optical quantity variation frequency determined by the frequency determination step; and an acquisition step in which the optical waveform of the measurement object is acquired under the determination conditions determined by the determination condition determination step, wherein in the determination condition determination step, a sampling frequency and a number of measurement points are determined such that the measurement time is an integer multiple of the period of the optical quantity variation frequency determined by the frequency determination step.

[0034] (12) The optical waveform measurement method described in item 11 above, wherein in the detection step, waveform data of optical quantity variation is obtained by pre-measurement before optical waveform measurement, and spectrum data is obtained by performing Fourier transform processing on the waveform data, and in the spectrum data, candidates for optical quantity variation frequency are detected based on the frequency of singularity point with intensity greater than adjacent frequency.

[0035] (13) The optical waveform measurement method described in item 11 or item 12 above, wherein, in the frequency determination step, the candidate with the smallest frequency is determined as the optical quantity variation frequency from the candidates of optical quantity variation frequencies.

[0036] (14) The optical waveform measurement method described in item 11 or 12 above, wherein, in the frequency determination step, the candidate selected by the user from the candidates of optical quantity variation frequencies detected by the detection step by the selection unit is determined as the optical quantity variation frequency.

[0037] (15) The optical waveform measurement method described in item 11 or item 12 above, wherein, in the frequency determination step, the candidate closest to the optical quantity variation frequency input by the user through the input unit among the candidates of optical quantity variation frequencies detected by the detection step is determined as the optical quantity variation frequency.

[0038] (16) The optical waveform measurement method described in item 12 above, wherein, in the detection step, candidates for optical quantity variation frequencies are detected by supplementation, the supplementation using the intensity of a frequency adjacent to a frequency that is a singularity with an intensity greater than that of an adjacent frequency in the spectral data.

[0039] (17) The optical waveform measurement method described in item 11 above, wherein in the detection step, waveform data of optical quantity variation is obtained by pre-measurement before optical waveform measurement, and candidate optical quantity variation frequency is detected by autocorrelation method on the waveform data.

[0040] (18) The optical waveform measurement method described in any one of the preceding items 11 to 17, wherein the wavenumber of the optical waveform obtained by the obtaining step varies according to the frequency of the light quantity variation.

[0041] (19) The optical waveform measurement method described in any one of the preceding items 11 to 18, wherein the method further comprises a filtering step of filtering the optical waveform obtained by the acquisition step, wherein the number of measurement points is a power of 2 times m (m is an integer), and the number of measurement points is different before and after the filtering step.

[0042] (20) The optical waveform measurement method described in item 19 above, wherein the optical waveform before filtering based on the filtering step is averaged in units of m and then filtered.

[0043] Invention Effects

[0044] According to the invention described in items (1) and (11) above, candidates for the light intensity variation frequency of the object to be measured are detected, and the light intensity variation frequency is determined based on the detected candidates. Based on the determined light intensity variation frequency, a sampling frequency and the number of measurement points are determined such that the measurement time is an integer multiple of the period of the determined light intensity variation frequency. Therefore, even if arbitrary frequency filtering is performed, distortion-free waveform acquisition is possible, and even if the frequency of the object to be measured is not known, the error can be minimized.

[0045] Furthermore, it is possible to correctly and easily derive the flicker index based on the IEC standard (Project No. 62341-6-3, 5.2.1 Flicker https: / / webstore.iec.ch / publication / 31171). Specifically, in the IEC standard, for a waveform filtered by TCSF, the flicker value is calculated as (maximum value - minimum value) / average value; however, to derive this flicker value, a correctly filtered waveform is required. Additionally, since the light intensity variation period is required in the derivation of the average value, this invention allows for easy derivation.

[0046] According to the invention described in paragraphs (2) and (12), waveform data of light quantity variation is obtained by pre-measurement before light waveform measurement, and spectrum data is obtained by performing Fourier transform on the waveform data. In the spectrum data, candidates for light quantity variation frequency are detected based on the frequency of the singular point with a greater intensity than the adjacent frequency. Therefore, it is possible to detect candidates corresponding to the actual light quantity variation frequency of the object being measured, and thus determine the light quantity variation frequency with high accuracy.

[0047] According to the invention described in paragraphs (3) and (13), since the candidate with the smallest frequency among the candidates of light intensity variation frequency is determined as the light intensity variation frequency, the light intensity variation frequency can be easily extracted.

[0048] According to the invention described in paragraphs (4) and (14), since the candidate selected by the user from the candidates of detected light intensity variation frequencies is determined as the light intensity variation frequency, it is possible to measure the light waveform of the frequency of interest to the user with high precision.

[0049] According to the invention described in paragraphs (5) and (15), since the candidate closest to the light quantity variation frequency input by the user is determined as the light quantity variation frequency among the candidates of detected light quantity variation frequency, it is possible to measure the light waveform near the frequency of interest to the user with high precision.

[0050] According to the invention described in the preceding paragraphs (6) and (16), by supplementing the frequency with the intensity of the frequency adjacent to the frequency of the singular point in the spectral data that is stronger than the adjacent frequency, the candidate of the light intensity variation frequency is detected, so that the light intensity variation frequency with high accuracy can be determined.

[0051] According to the invention described in paragraphs (7) and (17), waveform data of light intensity variation is obtained by pre-measurement before light waveform measurement, and candidates for the frequency of light intensity variation are detected by autocorrelation method on the waveform data, thereby shortening the pre-measurement time.

[0052] According to the invention described in the preceding items (8) and (18), since the wavenumber of the obtained optical waveform varies according to the frequency of the light quantity variation, it is possible to reduce waveform distortion and decrease period matching error.

[0053] According to the invention described in the preceding items (9) and (19), the number of measurement points is a power of 2 times m (m is an integer). The number of measurement points is different before and after the filtering process, so the increase of wave number can be avoided.

[0054] According to the invention described in the preceding items (10) and (20), since the optical waveform before filtering is averaged in units of m and then filtered, the noise of the waveform after filtering can be reduced. Attached Figure Description

[0055] Figure 1 This is a block diagram illustrating the functional structure of an optical waveform measuring device according to an embodiment of the present invention.

[0056] Figure 2 This is a flowchart representing the detection of candidates for light intensity variation frequency and the process for determining the light intensity variation frequency.

[0057] Figure 3 This is a diagram representing an example of the spectral analysis results of the obtained waveform data, i.e., spectral data.

[0058] Figure 4 This is a diagram used to illustrate a method for determining the measurement conditions.

[0059] Figure 5 This is a diagram used to illustrate other methods for determining the measurement conditions.

[0060] Figure 6 The waveforms after filtering are shown below: (A) shows the previous waveform, and (B) shows the waveform in this embodiment.

[0061] Figure 7 This is a diagram showing the display screen when the user selects from a candidate list of light intensity variation frequencies displayed on the display unit.

[0062] Figure 8 It is a diagram showing the display screen when the user inputs the designed value of the frequency of light intensity variation.

[0063] Figure 9 This is a structural diagram illustrating other embodiments of the present invention. Detailed Implementation

[0064] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

[0065] Figure 1 This is a block diagram illustrating the functional structure of an optical waveform measuring device 1 according to an embodiment of the present invention.

[0066] like Figure 1 As shown, the optical waveform measuring device 1 includes a light receiving unit 11, a data processing unit 12, a candidate detection unit 13, a frequency determination unit 14, a measurement condition determination unit 15, an optical waveform acquisition unit 16, a filtering processing unit 17, and a display unit 18.

[0067] The light-receiving unit 11 receives light from the object being measured, such as a display, and is equipped with a light-receiving sensor. The data processing unit 12 performs prescribed processing, such as amplification, on the light-receiving data in the light-receiving unit 11. The candidate detection unit 13 detects candidates for light intensity variation frequency based on the light-receiving data processed by the data processing unit 12, and the frequency determination unit 14 determines the light intensity variation frequency from the detected candidates.

[0068] The measurement condition determination unit 15 determines the sampling frequency and the number of measurement points based on the light intensity variation frequency determined by the frequency determination unit 14. In this embodiment, the sampling frequency and the number of measurement points are determined to be integer multiples of the period of the determined light intensity variation frequency.

[0069] The optical waveform acquisition unit 16 acquires an optical waveform using the sampling frequency and number of measurement points determined by the measurement condition determination unit 15. The filtering processing unit 17 performs filtering processing on the acquired optical waveform, and the display unit 18 displays the measurement results after filtering.

[0070] Next, the operation of the optical waveform measuring device 1 will be explained.

[0071] When the user sets the optical waveform measuring device 1 to the measuring position and indicates the start of the measurement by pressing the measurement start button or the like displayed on the display unit 18, the light receiving unit 11 receives the measuring light from the object being measured 100, such as the display. After the received light undergoes amplification and other prescribed data processing in the data processing unit 12, it is input to the candidate detection unit 13.

[0072] The candidate detection unit 13 detects candidates (hereinafter also referred to as candidate frequencies) of the light intensity variation frequency of the object 100 being measured, and the frequency determination unit 14 determines the light intensity variation frequency from the detected candidate frequencies.

[0073] Figure 2 The flowchart illustrates an example of candidate frequency detection and the determination process for the frequency of light intensity variation. In this embodiment, as an example of a candidate frequency detection method, a method based on waveform data of light intensity variation obtained through preliminary measurement is used to detect candidate frequencies. Frequencies above a certain threshold can also be used as candidate frequencies.

[0074] exist Figure 2 In the flowchart, when processing begins in step S01, light from the object being measured 100 is received through pre-measurement (prediction) to obtain waveform data of light intensity variation (step S02). Next, candidate frequencies are extracted (detected) (step S03). Specifically, the obtained waveform data is first subjected to spectral analysis (step S31). To shorten the prediction time, the frequency resolution can be set to a coarser value in the spectral analysis of the pre-measurement.

[0075] Figure 3 This represents an example of spectral data as a result of spectral analysis. Figure 3 The example illustrates the case where the frequency resolution is set to 2Hz. Additionally, in... Figure 2 In the example, 14Hz and 16Hz, 30Hz and 32Hz, 46Hz and 48Hz, and 60Hz and 62Hz of the spectral data are considered to be frequencies with greater intensity than their adjacent frequencies, i.e., singularities. It is believed that there are actual candidate frequencies with peak intensity near these singularities.

[0076] return Figure 2 The flowchart in extracting Figure 3 After identifying the singularity in the spectral data (step S32), the frequency is refined by supplementing the intensity of frequencies adjacent to the singularity (step S33). There are no limitations on the refinement based on the supplemented frequencies; it can be performed, for example, by centroid detection.

[0077] By refining the frequency range, the frequencies at which the intensity actually peaks are determined, and these frequencies are then listed as candidate frequencies. Candidate frequencies include the fundamental frequency and its higher harmonics.

[0078] Next, the light intensity variation frequency is determined from the list of candidate light intensity variation frequencies (step S04). As an example of a specific determination method, the minimum frequency in the candidates is determined as the light intensity variation frequency (step S41), and the detection of candidate frequencies and the determination of light intensity variation frequency are completed (step S05).

[0079] Thus, in this embodiment, waveform data of light intensity variation is obtained through prediction (preliminary measurement) before optical waveform measurement. Spectral data is obtained by performing Fourier transform processing on the waveform data. In the spectral data, candidate frequencies of light intensity variation are detected based on frequencies that are singular points with intensity greater than adjacent frequencies. Therefore, candidates corresponding to the actual light intensity variation frequency of the measured object can be detected. This allows for the determination of a highly accurate light intensity variation frequency. Furthermore, when the candidate with the smallest frequency among the candidate light intensity variation frequencies is determined as the light intensity variation frequency, the light intensity variation frequency can be easily extracted.

[0080] Based on the frequency of light intensity variation determined in this way, the measurement condition determination unit 15 determines the sampling frequency and the number of measurement points.

[0081] The relationship between the required measurement conditions is expressed as follows [Equation 1].

[0082] [Formula 1]

[0083] Measurement time T = Number of measurement points c / Sampling frequency fs ≒ Wavenumber n / Frequency of light intensity variation fv

[0084] (Where n and c are natural numbers)

[0085] The measurement conditions determine the wavenumber n, the number of measurement points c, and the sampling frequency fs, in order to satisfy the relationship shown in [Equation 1] above. That is, the sampling frequency fs and the number of measurement points c are determined to be integer multiples (n / fv) of the period of the light intensity variation frequency fv.

[0086] The error in period matching (=c / fs-n / fv) is preferably set to less than 1 / 10 of the period of light intensity variation, based on the reproducibility (distortion) of the filtered waveform. If adaptation to smooth waveforms with low noise is considered, it is more preferably set to less than 1 / 30. The determination of each parameter can be achieved by using a lookup table within the system.

[0087] Regarding the acquisition of light intensity, the following example illustrates the determination of measurement conditions in a successive acquisition method for obtaining instantaneous values. The sampling frequency fs in the successive method is a selectable frequency determined by the system. For this fs, as... Figure 4 As shown on the left side, n and c are chosen to satisfy [Equation 1]. The successive sampling method can achieve high-speed sampling, so it is generally fs >> fv, thus there is a tendency for the number of measurement points c to increase.

[0088] When using the Fast Fourier Transform in the calculation, the number of measurement points c is c = m × 2. d (m, d: natural numbers), such as Figure 4As shown on the right side, wavenumbers n, m, and d that satisfy [Equation 1] are selected for the number of measurement points c. By adding not only m = 1, which is an existing condition, but also m ≥ 2 to the conditions, the degree of freedom in selecting the wavenumber n is increased. If only m = 1 is an existing condition, then since fs ≥ fv, the wavenumber n or the number of measurement points c that satisfies [Equation 1] will become a very large value. As a result, the measurement time becomes longer and the computational load increases, and the advantages of the Fast Fourier Transform are not obtained.

[0089] Furthermore, the reason why the Fast Fourier Transform holds true when m≠1 will be explained later in the "Filtering Function". The value of m represents the rate of reduction in the effective sampling frequency of the filtered waveform, so the smaller value is preferred (explained later in the "Filtering Function"). For example, when the system's upper frequency limit is 2700Hz,

[0090] Light intensity variation frequency fv: 30Hz → wavenumber n: 16, number of measurement points c: 14336 (m=7, d=11), sampling frequency fs: 2700Hz

[0091] Light intensity variation frequency fv: 24Hz → wavenumber n: 11, number of measurement points c: 12288 (m=3, d=12), sampling frequency fs: 27000Hz

[0092] The following illustrates an example of the determination of measurement conditions in an integration method that obtains the integral value of the time determined by the acquisition of light intensity. While the sampling frequency fs of the integration method is difficult to increase in speed, the frequency setting generally offers high freedom and can be arbitrarily set. Therefore, the measurement conditions are as follows... Figure 5 As shown on the left side, for the target wave number n, c and fs that satisfy [Equation 1] are selected.

[0093] When using the Fast Fourier Transform in the calculation, the number of measurement points c is c = m × 2. d (m, d: natural numbers), such as Figure 5 As shown on the right side, n, m, and d are chosen to satisfy [Equation 1] for c. Here, the value of m is preferably set to m = 1 for the following reasons.

[0094] In the integration method, since fs has degrees of freedom, it is difficult to extend the measurement time even when m=1.

[0095] • When m≥2, the effective sampling frequency of the filtered waveform is lower than that of the acquired waveform (described later in "Filtering Processing Function").

[0096] To maintain a high fs near the system's upper limit, the wavenumber n varies depending on the frequency of light intensity variation. By changing the wavenumber n according to the frequency of light intensity variation, it is possible to reduce waveform distortion and decrease period matching error.

[0097] The following illustrates an example of measurement conditions. For instance, with a system upper frequency limit of 2700 Hz,

[0098] Light intensity variation frequency fv: 30Hz → wavenumber n: 12, number of measurement points c: 1024 (m=1, d=10), sampling frequency fs: 2560Hz

[0099] Light intensity variation frequency fv: 24Hz → wavenumber n: 18, number of measurement points c: 2048 (m=1, d=11), sampling frequency fs: 2731.667Hz

[0100] Under these determined measurement conditions, the optical waveform was obtained. The measurement of the optical waveform was performed in the same manner as before, therefore detailed descriptions are omitted.

[0101] After acquiring the optical waveform, the filtering processing unit 17 performs filtering processing on the acquired optical waveform. In the case of processing with the usual Discrete Fourier Transform (DFT) or Inverse Fourier Transform (IDFT), and in the case of m=1 in Fast Fourier Transform, the filtering processing is the same as before.

[0102] The following describes the filtering process for Fast Fourier Transform (FFT) with m ≥ 2. That is, preprocessing is required on the waveform obtained before the FFT. Preprocessing involves averaging or dividing every m data points starting from the first data point of the measured data (arranged in c order), compressing the number of data points to 1 / m. This compressed data number is then... d The waveform is processed by Fast Fourier Transform (DFT), weighted, and then by Inverse Fast Fourier Transform (IDFT) to generate the filtered waveform.

[0103] The aforementioned data compression is equivalent to setting the effective sampling frequency fs of the filtered waveform to 1 / m of the waveform's original value. Therefore, the value of m needs to be small enough not to affect the reproducibility of the filtered waveform. However, in the case of successive waves, fs ≥ fv, so this value of m has a relatively low impact on waveform reproduction. By compressing the data number to 1 / m, the number of measurement points differs before and after filtering, thus avoiding an increase in wavenumber. Furthermore, since filtering is performed after averaging the unfiltered waveform in units of m, the noise in the filtered waveform can be reduced.

[0104] Figure 6The waveform after filtering is shown. Figure (A) is a conventional waveform, and (B) is the waveform of this embodiment. In this embodiment, the measurement conditions are set in a manner that matches the frequency of light intensity variation, thus, compared to the conventional example, it becomes a waveform in which distortion is suppressed, especially at the beginning and end.

[0105] In this embodiment, candidate light intensity variation frequencies of the measured object 100 are detected, and the light intensity variation frequency is determined based on the detected candidates. Based on the determined light intensity variation frequency, a sampling frequency and the number of measurement points are determined so that the measurement time is an integer multiple of the period of the determined light intensity variation frequency. Therefore, even if arbitrary frequency filtering is performed, a distortion-free waveform can be obtained, and the error can be minimized even when the frequency of the measured object is not known. Furthermore, the flicker index based on the IEC standard can be correctly and easily derived. That is, in the IEC standard, for a waveform filtered by TCSF, the value obtained by calculating (maximum value - minimum value) / average value is used as the flicker value, but to derive this flicker value, a correctly filtered waveform is required. In addition, since the light intensity variation period is required in the derivation of the average value, it can be easily derived using this invention.

[0106] In the above embodiments, an example is shown where the smallest candidate frequency from a plurality of candidate frequencies is determined as the light intensity variation frequency, but the method for determining the light intensity variation frequency is not limited to this. Especially when users such as display designers perform light waveform measurements for verification, it is assumed that the user is aware of the light intensity variation frequency.

[0107] Therefore, as Figure 7 As shown, a list of detected candidate frequencies can also be displayed on display unit 18 along with messages such as "Please select a frequency," allowing the user to select the desired candidate. Figure 7 In the example, four candidate frequencies are shown, indicating that a candidate frequency of 15.36 Hz with an additional check has been selected. When any candidate frequency is selected, the selected candidate frequency is determined as the light intensity variation frequency.

[0108] In this way, by having the user select candidates and determining the frequency of the selected candidate as the frequency of light intensity variation, it is possible to measure the light waveform of the frequency of interest to the user with high precision.

[0109] Alternatively, the results of spectral analysis during the preliminary measurement can also be obtained. Figure 3The singularities shown in the spectral data are displayed as candidate frequencies for the user to select. In this case, the frequency of light intensity variation closest to the selected singularity is determined as the frequency of light intensity variation that forms the basis for determining the frequency resolution. However, in terms of displaying the correct candidate frequencies, it is preferable that the displayed candidate list is based on a supplementary, refined list of candidate frequencies.

[0110] Alternatively, it can be displayed not as a list of candidate frequencies, but as follows: Figure 8 As shown, input field 18a is displayed along with messages such as "Please select frequency," allowing the user to directly input the design value for the light intensity variation frequency. In this case, the candidate frequency closest to the input frequency is selected as the light intensity variation frequency from the candidate frequencies. Thus, even when the user inputs the light intensity variation frequency and the candidate frequency closest to the input light intensity variation frequency is selected as the light intensity variation frequency, it also has the effect of being able to measure the light waveform near the frequency of interest to the user with high precision.

[0111] Furthermore, in the above embodiment, a waveform data of light intensity variation was obtained by pre-measurement before optical waveform measurement, and spectral data was obtained by performing Fourier transform processing on the obtained waveform data. In the spectral data, a candidate frequency was detected based on the frequency of the singular point that is stronger than the adjacent frequency. However, the detection of candidate frequencies can also be done by other methods.

[0112] For example, waveform data of light intensity variations can be obtained through preliminary measurements before light waveform measurement, and the variation period (frequency) can be directly calculated by analyzing the obtained waveform data. One example is the autocorrelation method for waveform data. This method extracts the periodicity of the data by calculating the correlation coefficient between the waveform data of light intensity variations and data separated from the waveform data by time intervals, and then detects candidate frequencies. Other methods include period extraction methods based on image analysis that utilize feature points of the waveform data.

[0113] Detection of light intensity variation frequency based on waveform data analysis has the effect of shortening the preparation and measurement time, but the computational load increases.

[0114] The above describes one embodiment of the present invention, but the present invention is not limited to the above embodiment. For example, the candidate detection unit 13 can be configured using the function of a conventional optical waveform measurement device that obtains spectral data by performing Fourier transform processing on waveform data of light intensity variation, or it can be configured by separately providing a dedicated circuit for candidate detection.

[0115] In addition, such as Figure 9As shown, a personal computer 200 can also be used to construct an optical waveform measurement device. In this case, the personal computer 200 can obtain the light received data of the object 100 from the existing optical waveform measurement device 300, and perform candidate frequency detection, determination of light intensity variation frequency, determination of measurement conditions, etc.

[0116] Furthermore, the optical waveform measurement step does not need to be performed consecutively with the frequency detection step, the frequency determination step, and the measurement condition determination step. For example, the frequency detection step, the frequency determination step, and the measurement condition determination step can be performed first to obtain the measurement condition data, and then the optical measurement can be performed only using the obtained measurement conditions.

[0117] Furthermore, the determined measurement conditions can be recorded and stored in the optical waveform measuring device or an external recording device (such as a personal computer) connected to the optical waveform measuring device. By recording and storing the measurement conditions, when optical waveform measurements need to be performed again, the processes of detecting candidates for light intensity variation frequency, determining the light intensity variation frequency, and determining the measurement conditions can be omitted, thereby shortening the time required for optical waveform measurements.

[0118] This application is accompanied by the priority claim of Japanese Patent Application No. 2020-095517, filed on June 1, 2020, the disclosure of which directly constitutes a part of this application.

[0119] Industrial availability

[0120] This invention can be used when measuring the optical waveform of objects such as displays.

[0121] Label Explanation

[0122] 1 Optical waveform measuring device; 11 Light receiving unit; 13 Candidate detection unit; 14 Frequency determination unit; 15 Measurement condition determination unit; 16 Filtering unit; 17 Optical waveform acquisition unit; 18 Display unit; 100 Measured object; 200 Personal computer.

Claims

1. An optical waveform measuring device, comprising: The detection unit detects candidates for the frequency of light intensity variation of the object being measured; The frequency determination unit determines the light intensity variation frequency based on the candidate light intensity variation frequencies detected by the detection unit. The measurement condition determination unit determines the measurement conditions for light waveform measurement based on the light quantity variation frequency determined by the frequency determination unit. The acquisition unit acquires the optical waveform of the object to be measured under the measurement conditions determined by the measurement condition determination unit. as well as The filtering unit performs filtering processing on the optical waveform acquired by the acquisition unit. The measurement condition determination unit determines the measurement time to be an integer multiple of the period of the light quantity variation frequency determined by the frequency determination unit, and the sampling frequency and the number of measurement points.

2. The optical waveform measuring device according to claim 1, wherein, The detection unit Waveform data of light intensity variation are obtained through preliminary measurements before optical waveform measurement. Spectral data is obtained by performing a Fourier transform on the waveform data. In the spectral data, candidates for frequencies of light intensity variation are detected based on the frequencies that are singular points with greater intensity than adjacent frequencies.

3. The optical waveform measuring device according to claim 1 or claim 2, wherein, The frequency determination unit selects the candidate with the smallest frequency from the candidates for light intensity variation frequency as the light intensity variation frequency.

4. The optical waveform measuring device according to claim 1 or claim 2, wherein, The system includes a selection unit that allows the user to choose any candidate from the candidates of light intensity variation frequencies detected by the detection unit. The frequency determination unit determines the candidate selected by the user through the selection unit as the light intensity variation frequency.

5. The optical waveform measuring device according to claim 1 or claim 2, wherein, It has an input unit that allows users to input the frequency of light intensity variations. The frequency determination unit determines the light quantity change frequency as the candidate light quantity change frequency that is closest to the light quantity change frequency input by the input unit among the candidates detected by the detection unit.

6. The optical waveform measuring device according to claim 2, wherein, The detection unit detects candidates for light intensity variation frequencies by supplementing the frequency with the intensity of frequencies adjacent to frequencies that are singularities with a higher intensity than adjacent frequencies in the spectral data.

7. The optical waveform measuring device according to claim 1, wherein, The detection unit Waveform data of light intensity variation are obtained through preliminary measurements before optical waveform measurement. Candidates for the frequency of light intensity variation are detected by autocorrelation of the waveform data.

8. The optical waveform measuring device according to any one of claims 1, 2, 6, and 7, wherein, The wavenumber of the optical waveform acquired by the acquisition unit varies according to the frequency of the light intensity variation.

9. The optical waveform measuring device according to any one of claims 1, 2, 6, and 7, wherein, The number of measurement points is m times a power of 2, and the number of measurement points differs before and after filtering, where m is an integer.

10. The optical waveform measuring device according to claim 9, wherein, The optical waveform before filtering based on the filtering unit is averaged in units of m, and then filtered.

11. A method for measuring optical waveforms, comprising: The detection step involves the detection unit detecting candidate frequencies of light intensity variation in the object being measured. The frequency determination step involves the frequency determination unit determining the light intensity variation frequency based on candidates of light intensity variation frequencies detected by the detection step. The determination step and the measurement condition determination unit determine the measurement conditions for the optical waveform measurement based on the frequency of light quantity variation determined by the frequency determination step. The acquisition step involves acquiring the optical waveform of the object being measured under the measurement conditions determined by the measurement condition determination step; and The filtering step involves filtering the optical waveform obtained in the acquisition step. In the measurement condition determination step, the measurement time is determined to be an integer multiple of the period of the light intensity variation frequency determined by the frequency determination step, and the sampling frequency and number of measurement points are determined.

12. The optical waveform measurement method according to claim 11, wherein, In the detection step, Waveform data of light intensity variation are obtained through preliminary measurements before optical waveform measurement. Spectral data is obtained by performing a Fourier transform on the waveform data. In the spectral data, candidates for frequencies of light intensity variation are detected based on the frequencies that are singular points with greater intensity than adjacent frequencies.

13. The optical waveform measurement method according to claim 11 or claim 12, wherein, In the frequency determination step, the candidate with the smallest frequency from the candidates for light intensity variation frequency is determined as the light intensity variation frequency.

14. The optical waveform measurement method according to claim 11 or claim 12, wherein, In the frequency determination step, the candidate selected by the user from the candidates of light intensity variation frequencies detected by the detection step through the selection unit is determined as the light intensity variation frequency.

15. The optical waveform measurement method according to claim 11 or claim 12, wherein, In the frequency determination step, the candidate that is closest to the light intensity variation frequency input by the user through the input unit among the candidates for light intensity variation frequency detected by the detection step is determined as the light intensity variation frequency.

16. The optical waveform measurement method according to claim 12, wherein, In the detection step, candidates for light intensity variation frequencies are detected by supplementation, which uses the intensity of frequencies adjacent to frequencies that are singularities with a higher intensity than adjacent frequencies in the spectral data.

17. The optical waveform measurement method according to claim 11, wherein, In the detection step, Waveform data of light intensity variation are obtained through preliminary measurements before optical waveform measurement. Candidates for the frequency of light intensity variation are detected by autocorrelation of the waveform data.

18. The optical waveform measurement method according to any one of claims 11, 12, 16, and 17, wherein, The wavenumber of the optical waveform obtained by the acquisition step varies according to the frequency of the light intensity variation.

19. The optical waveform measurement method according to any one of claims 11, 12, 16, and 17, wherein, The number of measurement points is m times a power of 2, and the number of measurement points differs before and after filtering, where m is an integer.

20. The optical waveform measurement method according to claim 19, wherein, The optical waveform before filtering based on the filtering process is averaged in units of m, and then filtered.

Images