Optical radiation measurement method

Abstract

The invention provides an optical radiation measurement method, which is characterized in that light from a measured object enters an optical detection unit through a color wheel, three or more channels are uniformly distributed on the circumference of the same radius of the color wheel, and each channel is provided with a color filter or a through hole without any color filter; the measurement process specifically comprises the following steps: S1, in the measurement process, a color wheel continuously rotates to sequentially cut each channel into a light path, and a light detection unit converts an obtained light signal into an electric signal to obtain a group of waveform data of the electric signal changing along with time; and S2, performing demodulation calculation on the waveform data obtained in the step S1 by using the shape function under each channel to obtain the average optical power or the total energy of the measured object under each channel. According to the technical scheme, the problems that in the prior art, beam splitting measurement is high in alignment requirement and low in sensitivity, and color wheel rotation measurement is low in speed can be effectively solved.

Description

Technical Field

[0001] The invention relates to the field of photoelectric testing, and in particular to a method for measuring optical radiation. Background Art

[0002] Colorimeter is a common instrument used to measure optical parameters such as brightness and chromaticity of light sources, and is widely used in the fields of display and lighting. Colorimeter generally adopts the following technical solution: the light of the object to be measured is incident on one end of the bundled optical fiber after passing through the objective lens, and the other end of the optical fiber disperses the received light beam. The dispersed sub-light beams are received by the corresponding photoelectric sensors after passing through color filters with different spectral transmittances. According to the intensity of the light signal detected by different photoelectric sensors, the light power or energy under each color filter is calculated, thereby obtaining the optical parameters such as brightness and chromaticity of the object to be measured. This method has the advantages of fast test speed and little influence by the angle of incident light, but it has extremely high requirements for the alignment of the optical fiber bundle with the filter and the photoelectric sensor. If the alignment is inaccurate, it may cause a large deviation in the test results. In addition, the sampling method of optical fiber splitting has low sensitivity and poor accuracy when measuring low-brightness signals.

[0003] Using a color filter wheel is also a common method in colorimetry. A color filter is set on the color wheel. The light of the object to be measured passes through the objective lens and then passes through each filter on the color wheel to enter the light sensor. This method has a high sensitivity, but the measurement speed is slow, especially when the object to be measured changes over time. It is often necessary to stop measuring after turning to a certain filter. This takes a long time to measure and has low measurement efficiency. It is not suitable for production line inspection and other occasions. Summary of the invention

[0004] In view of the shortcomings of the prior art, the present invention provides a method for measuring optical radiation, aiming to solve the problems in the prior art of using traditional optical fiber bundle measurement, such as high alignment requirements and low sensitivity, especially insufficient accuracy in low brightness environments, and slow speed and low efficiency of color wheel rotation measurement.

[0005] In order to achieve the above object, the present invention provides a method for measuring optical radiation, wherein light from the object to be measured is incident on a light detection unit through a color wheel, and three or more channels are evenly distributed on the same radius of the color wheel, wherein a color filter or a through hole is arranged on each channel; the measurement process specifically includes:

[0006] S1: During the measurement process, the color wheel rotates continuously to cut each channel into the light path in turn, and the light detection unit converts the obtained light signal into an electrical signal to obtain a set of waveform data of the electrical signal changing with time;

[0007] S2: Demodulate and calculate the waveform data obtained in S1 using the shape function under each channel to obtain the average optical power or total energy of the object under test under each channel.

[0008] In this technical solution, the color wheel rotates continuously, cutting each channel into the optical path at a time. This dynamic measurement method avoids the inefficient process of stopping to switch color filters during traditional measurement, significantly improving the measurement efficiency. In addition, since the color wheel rotates continuously and evenly, and each channel is evenly distributed, the requirements for the alignment accuracy between the light detection unit and the color wheel are reduced, simplifying the calibration process before measurement. The application of dynamic measurement and waveform data demodulation significantly improves the measurement speed, which is suitable for occasions that require fast response and continuous monitoring, such as production line detection.

[0009] In the above technical solution, the color filter can be a color filter that simulates the stimulation function of the human eye, such as the design of X / Y / Z three channels, which can better simulate the human eye's perception of color and perform corresponding optical parameter measurements; the color filter can also be designed as four channels or more channels. The design of the multi-channel color filter can divide the spectral range more finely, so that each channel can more accurately capture the light within a specific wavelength range, so that when measuring the measured object such as LED, its spectral characteristics can be more comprehensively covered, thereby improving the measurement accuracy and reliability, and suitable for different measurement needs. In practical applications, the appropriate number of color filter channels can be selected according to specific needs and measurement requirements. A color filter that matches the human eye's light efficiency function V(λ), or a color filter that matches the CIE color matching function x(λ), y(λ) and z(λ), or a bandpass color filter can be selectively arranged on each channel to achieve more accurate measurement and evaluation. A transparent glass slide that transmits (all) visible light can be provided on the above through hole to keep the light path consistent with other color filters.

[0010] As a technical solution, in step S1, the color wheel speed is set according to the modulation period of the object to be measured; wherein the color wheel speed is known, or before step S1, the designated channel is cut into the optical path and the waveform data measured by the light detection unit is analyzed to obtain the modulation period of the object to be measured. When the modulation period of the object to be measured is unknown, the designated channel is cut into the optical path so that the channel receives the optical signal from the object to be measured to initialize the measurement process and ensure that the subsequent analysis has a stable starting point; generally, the designated channel is generally a through-hole channel to obtain the complete optical waveform of the object to be measured. To further ensure accuracy, the modulation period is set so that each channel passes through time to cover at least one period of modulation of the object to be measured. In order to achieve this goal, the rotation period of the color wheel is set to an integer multiple of the modulation period and the multiple is greater than the number of channels on the color wheel, so that the phase of the optical waveform received at the same position on the color wheel during the rotation process is the same to ensure the repeatability of the measurement; and each channel has enough time to be cut into the optical path for measurement, so that each channel can fully receive the optical signal of the object to be measured, while avoiding signal overlap or omission caused by too fast rotation speed. Taking 4 channels as an example, the rotation period of the color wheel is usually at least 4 times or more of the modulation period. Considering the gaps between the color filters in the color wheel, if the total gap time is less than the time it takes for a channel to pass through, then in order to ensure measurement accuracy, the rotation period of the color wheel should be at least 5 times the modulation period. If the total gap time is equivalent to the time it takes for a channel to pass through the optical path, in order to ensure the continuity and accuracy of the measurement, the rotation period of the color wheel needs to be longer, at least 8 times the modulation period.

[0011] The modulation period calculation of the measured object specifically includes: performing Fourier transform on the optical waveform data obtained under the specified channel to obtain:

[0012]

[0013] Where ω0 is the fundamental angular frequency, X k is the amplitude.

[0014] The fundamental frequency The modulation signal period is

[0015] As a technical solution, the relative physical positions of the color filters are known in advance. By obtaining the position information of one of the color filters and combining the relative physical positions of the color filters and the rotation speed of the color wheel, the intervals corresponding to the through holes and each filter channel in the signal time domain space can be analyzed; the signal sum, average value or peak value in each interval is calculated to obtain the three stimulus values.

[0016] As another technical solution, the color wheel is provided with one or more position sensors, and the position information of the position sensors in the color wheel is used to mark the waveform data collected in step S2 to identify the signal areas corresponding to different color wheel channels.

[0017] It should be noted that when the light of the object under test itself changes with the time period, since the interval signals corresponding to each filter channel are difficult to guarantee to be full-cycle signals, and the attenuation degree of RGB components is different, the method of directly obtaining the three stimulus values ​​by summing, averaging or peaking the signals in each interval may have large errors. Therefore, the signals obtained from each channel can be restored, specifically including: obtaining the shape function of each channel on the color wheel, and demodulating the waveform of the object under test under each filter or through hole by using the shape function in step S2, and obtaining the average optical power or total energy of the object under test under each channel. The shape function describes the time domain characteristics of the light signal when it passes through a specific filter or through hole, including signal attenuation, phase shift and possible waveform distortion.

[0018] In the above technical solution, the shape function can be calculated by simulation based on the shape and size of each channel on the color wheel and the shape and size of the light spot incident on the color wheel. For example, when the light spot channels are all rectangular, the shape function is a trigonometric function or a trapezoidal function.

[0019] In another technical solution, the shape functions of the above-mentioned channels can also be obtained by a light source with known optical power and modulation function, or by a light source with known tristimulus values; for example, when the frequency is 0 Hz, the light source is a constant DC light source; when the frequency is 120 Hz and the initial phase is 0, the waveform of the light source is a sine wave; the specific steps are:

[0020] A1: Turn on the light source and set the color wheel speed;

[0021] A2: The light detection unit measures the light signal obtained in step A1 and converts it into electrical signals S0, S1, S2, ..., S n , then the relationship between the electrical signal and time is the channel shape function;

[0022] A3: During the actual test, the rotation speed of the color wheel may change due to the modulation period of the signal. Therefore, the actual shape function can be obtained by proportional stretching based on the ratio of the actual rotation speed to the rotation speed set when the shape factor is first measured.

[0023] Furthermore, in A1, the shape functions under different rotation directions can be directly obtained by cutting the through holes in the color wheel into the light path from left to right or from right to left.

[0024] In another technical solution, when the optical signal of the measured object itself changes with the time period, the shape function can also be obtained by fitting according to the peak change of the waveform data measured in step S1, and the specific steps are as follows:

[0025] B1: Test the actual modulation signal and obtain the intervals corresponding to the through holes and each color filter channel according to the above technical solution;

[0026] B2: Get the peak points P0P1P1...P of the signal in the corresponding interval of each channel m P0P1P1...P m Remove it and it will no longer be

[0027] The extreme points on the envelope surface are removed, and the extreme points P0'P1'P2'...P on the envelope surface are retained. n ';

[0028] B3: Use P0'P1'P2'...P n 'Perform linear, cubic spline interpolation or polynomial fitting to obtain the shape function within the interval.

[0029] As a technical solution, the electrical signal obtained by the above-mentioned light detection unit is converted into waveform data after passing through an analog low-pass filter. The cutoff frequency of the analog filter is higher than the product of the inverse of the color wheel rotation period and the number of channels on the color wheel and lower than the modulation period of the object under test. The electrical signal obtained by the light detection unit is processed through an analog low-pass filter to remove high-frequency noise and retain low-frequency information useful for subsequent data processing.

[0030] As a technical solution, the demodulation calculation in step S2 specifically includes: taking the ratio of each point on the shape function to the peak value of the shape function as a restoration coefficient, dividing the value of each point of the waveform under each color filter or through hole by the restoration coefficient. This division operation is equivalent to "reverse attenuation" of the waveform to restore the intensity of the signal before passing through the color filter or through hole to obtain a restored signal.

[0031] As a technical solution, a light source with known optical power and modulation function is measured to calibrate the measured value of the average optical power or total energy described in step S2, thereby further ensuring the accuracy and reliability of the measurement.

[0032] As a technical solution, the object to be measured is a display screen, and a higher-precision measurement method is used to obtain reference tristimulus values ​​of each primary color and mixed color of the display screen at one or more grayscales; the measured tristimulus values ​​of the display screen at the same grayscale are measured using steps S1 and S2, and the measured tristimulus values ​​are calibrated using the reference tristimulus values ​​to obtain the responsiveness to the primary colors under each color filter channel. The above-mentioned display screen can be a display screen that emits primary colors and mixed colors. Specifically, taking an RGBW4-color display screen as an example, a higher-precision measurement method (such as spectral method) and steps S1 and S2 are used to measure the tristimulus values ​​Q at the same position under the screen of R(255,0,0), G(0,255,0), B(0,0,255), and W(255,255,255) respectively. RGBW and P RGBW , the correction matrix is ​​calculated by the following formula:

[0033] C=Q RGBW *P RGBW -1

[0034] ………………………………(2)

[0035] in,

[0036] Then the correction matrix C is used to correct the tristimulus values ​​X measured at any gray scale in step S1 and step S2. T ,Y T ,Z T For calibration, the formula is as follows:

[0037]

[0038] Where X T ',Y T ',Z T ' is the calibrated tristimulus value.

[0039] Furthermore, in order to improve the measurement efficiency, rapid measurement can be achieved by establishing a correction coefficient database. Specifically, the correction coefficients are established according to the above technical solution by selecting different types of display screens at different grayscales. When measuring the display screen to be tested, the relevant correction coefficients are retrieved by the three stimulus values ​​measured by step S1 and step S2, and the calibrated three stimulus values ​​are obtained by calculation.

[0040] As a technical solution, in scenarios where test timeliness is not a high requirement, such as measuring and analyzing the brightness and color of display screens in laboratories, measurements can also be performed using low-speed sampling.

[0041] Beneficial effects of the invention: The invention provides a method for measuring optical radiation, in which the light from the object to be measured is incident on the optical detection unit through the color wheel, and the difficulty of alignment is greatly reduced; and the light efficiency is effectively improved, the detection sensitivity of weak signals is enhanced, and the brightness and chromaticity measurement accuracy of weak signals is improved. The method of using continuous testing and processing and analyzing the signals to obtain the three stimulus values ​​of the object to be measured can effectively shorten the test time and improve the test efficiency, and is suitable for a variety of application scenarios, especially those that require fast response and efficient measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Attached Figure 1 A schematic diagram of a measurement signal in an embodiment of the present invention;

[0043] Attached Figure 2 A schematic diagram of a restoration signal in an embodiment of the present invention;

[0044] Attached Figure 3 Schematic diagram of channel signal extreme value point distribution in an embodiment of the present invention;

[0045] Attached Figure 4 Schematic diagram of channel signal envelope fitting in an embodiment of the present invention;

[0046] Attached Figure 5 A schematic diagram of a measurement signal in another embodiment of the present invention;

[0047] Attached Figure 6 FIG. 1 is a schematic diagram of a restoration signal in another embodiment of the present invention. DETAILED DESCRIPTION

[0048] Embodiment 1

[0049] This embodiment provides a method for measuring optical radiation. Light from a measured object is incident on a light detection unit through a color wheel. Four channels are evenly distributed on a circle with the same radius of the color wheel. Three of the channels are provided with different bandpass filters, and another channel is provided with a transparent glass slide that transmits visible light. The measurement process specifically includes:

[0050] C1: First, the through-hole channel is cut into the optical path, and the waveform data measured by the light detection unit is analyzed to obtain the modulation period of the object under test; in this embodiment, the gap setting of each color filter in the color wheel is considered, and the rotation period of the color wheel is set to 8 times the modulation period. The modulation period calculation of the object under test mainly includes Fourier transforming the periodic light waveform data obtained under the through-hole channel to obtain Where ω0 is the fundamental angular frequency, X k is the amplitude; then the fundamental frequency The modulation signal period is

[0051] C2: During the measurement process, the color wheel rotates continuously to cut each channel into the light path in turn. The light detection unit converts the obtained light signal into an electrical signal to obtain a set of waveform data of the electrical signal changing with time, such as Figure 1 shown.

[0052] C3: The shape function of each channel is obtained by simulation calculation according to the shape size of each channel on the color wheel and the shape size of the light spot incident on the color wheel, wherein the shape function used for simulation calculation is a high-order polynomial function; the waveform data obtained in C2 is demodulated and calculated using the shape function of each channel, and the ratio of each point on the shape function to the peak value of the shape function is used as the restoration coefficient, and the value of each point of the waveform under each color filter or through hole is divided by the restoration coefficient to obtain the restored signal, such as Figure 2 As shown, the average optical power or total energy of the measured object under each channel is obtained. It should be noted that one or more position sensors are provided on the color wheel, and the position information from the position sensor to the center of the optical path in the color wheel is used to mark the collected waveform data to identify the signal area corresponding to different color wheel channels.

[0053] C4: Measure a constant DC light source with known tristimulus values ​​to calibrate the average optical power or total energy measured in step C3 to further ensure the accuracy and reliability of the measurement. Specifically, the tristimulus values ​​X of the known light source are s , Y s , Z s The light detection unit is used to measure the average optical power of the light emitted by the light source through the three channels X / Y / Z, respectively. sx , P sy , P sz , then the calibration coefficient k x , k y and k z It can be obtained by the following formula:

[0054]

[0055] The average optical powers of the light emitted by the object under test through the three channels X / Y / Z obtained according to steps C1-C3 are P tx , P ty , P tz ; Use the calibration coefficients to calculate the three stimulus values ​​of the actual object being measured:

[0056]

[0057] It should be noted that, since the optical signal of the measured object itself changes with the time period, the shape function in the above step C3 can also be obtained by fitting according to the peak change of the waveform data measured in step C2, and the steps are as follows:

[0058] D1: After setting the rotation speed of the color wheel according to the modulation period of the object to be tested, the actual modulation signal is tested, and the intervals corresponding to the through holes and each color filter channel are obtained according to the above technical solution;

[0059] D2: Get the peak points P0P1P1...P of the signal in the corresponding interval of each channel m , for P0P1P1...P m Eliminate the extreme points that are not on the envelope surface, and retain the extreme points P0'P1'P2'...P on the envelope surface n ',like Figure 3 As shown;

[0060] D3: Use P0'P1'P2'...P n 'Perform linear, cubic spline interpolation or polynomial fitting to obtain the shape function within the interval, such as Figure 4 shown.

[0061] Embodiment 2

[0062] This embodiment provides another method for measuring optical radiation, in which light from the object to be measured is incident on the light detection unit through the color wheel, and four channels are evenly distributed on the same radius of the color wheel, three of which are arranged with different bandpass color filters, and the other channel is a through hole without any color filter. Different from the first embodiment, this embodiment adopts a low-speed sampling method for measurement; the electrical signal obtained by the light detection unit first passes through an analog low-pass filter and then undergoes analog-to-digital conversion to obtain waveform data, and the cutoff frequency of the analog filter is higher than the product of the inverse of the color wheel rotation period and the number of channels on the color wheel but lower than the modulation period of the object to be measured.

[0063] In this embodiment, the measured object is an RGBW 4-color display screen. First, the reference tristimulus values ​​of each primary color and mixed color of the display screen at one or more grayscales are obtained by spectral method. Each channel is sequentially cut into the optical path by low-speed sampling or stop-and-go mode. Referring to steps C1 and C2, the tristimulus values ​​Q of the same position under the screen of R (255, 0, 0), G (0, 255, 0), B (0, 0, 255), and W (255, 255, 255) are measured respectively. RGBW and P RGBW , use the reference tristimulus values ​​to calibrate the measured tristimulus values, and obtain the responsiveness to the primary colors under each filter channel; the correction matrix C is calculated by the following formula:

[0064] C=Q RGBW *P RGBW -1

[0065] in,

[0066] The correction matrix C is used to correct the tristimulus value X measured at any gray scale. T ,Y T ,Z T For calibration, the formula is as follows:

[0067]

[0068] Among them, X T ',Y T ',Z T ' is the calibrated tristimulus value.

[0069] This implementation is suitable for scenarios where the test timeliness is not high, such as laboratory measurement and analysis of the brightness and color of the display screen, and measurement through low-speed sampling or rotation and stop. When each channel color wheel channel corresponds to more than 20 or more periodic signals, such as Figure 5 As shown, the three stimulus values ​​can be solved by taking the average value, summing up, or filtering and taking the peak value. The schematic diagram obtained after taking the average value for each channel is as follows Figure 6 shown.

[0070] The specific implementation of the present invention is described above in conjunction with the accompanying drawings, but it should be understood by those skilled in the art that the above embodiments are only for illustration and not for limiting the scope of the present invention. It should be understood by those skilled in the art that the above embodiments may be modified without departing from the scope and spirit of the present invention. The protection scope of the present invention is defined by the appended claims.

Claims

1. A method for measuring optical radiation, characterized in that: The light from the object to be measured is incident on the light detection unit through the color wheel, and three or more channels are evenly distributed on the same radius of the color wheel, and a color filter or a through hole is arranged on each channel; the measurement process specifically includes: S1: During the measurement process, the color wheel rotates continuously to cut each channel into the light path in turn, and the light detection unit converts the obtained light signal into an electrical signal to obtain a set of waveform data of the electrical signal changing with time; S2: Demodulate and calculate the waveform data obtained in S1 using the shape function under each channel to obtain the average optical power or total energy of the object under test under each channel.

2. The optical radiation measurement method according to claim 1, characterized in that: In step S1, the color wheel speed is set according to the modulation period of the object to be measured; the color wheel speed is known, or before step S1, a designated channel is cut into the optical path and the modulation period of the object to be measured is obtained by analyzing the waveform data measured by the light detection unit.

3. The optical radiation measurement method according to claim 1, characterized in that: The shape function of each channel in step S2 is obtained by simulation calculation according to the shape size of the channel and the shape size of the light spot incident on the color wheel.

4. The optical radiation measurement method according to claim 1, characterized in that: The shape function of each channel in step S2 is obtained by measuring a light source with known optical power and modulation function.

5. The optical radiation measurement method according to claim 1, characterized in that: The shape function of each channel in step S2 is obtained by fitting according to the peak value change of the waveform data measured in step S1.

6. A method for measuring optical radiation according to claim 1 or 2, characterized in that: The electrical signal acquired by the light detection unit is converted into waveform data after passing through an analog low-pass filter. The cutoff frequency of the analog filter is higher than the product of the inverse of the color wheel rotation period and the number of channels on the color wheel but lower than the modulation period of the object being measured.

7. A method for measuring optical radiation according to claim 1, 2, 3 or 4, characterized in that: The demodulation calculation in step S2 specifically includes: taking the ratio of each point on the shape function to the peak value of the shape function as a restoration coefficient, dividing the value of each point of the waveform under each color filter or through hole by the restoration coefficient to obtain a restored signal.

8. A method for measuring optical radiation according to any one of claims 1 to 5, characterized in that: The color wheel is provided with one or more position sensors, and the waveform data collected in step S2 is annotated using the position information of the position sensors in the color wheel to identify signal areas corresponding to different color wheel channels.

9. A method for measuring optical radiation according to any one of claims 1 to 6, characterized in that: A light source with known optical power and modulation function is measured to calibrate the measured value of the average optical power or total energy in step S2.

10. A method for measuring optical radiation according to any one of claims 1 to 8, characterized in that: The object to be measured is a display screen, and reference tristimulus values ​​of each primary color and mixed color of the display screen at one or more grayscales are obtained by a more precise measurement method; the measured tristimulus values ​​of the display screen at the same grayscale are measured by using steps S1 and S2, and the measured tristimulus values ​​are calibrated using the reference tristimulus values ​​to obtain the responsiveness to the primary colors under each color filter channel.

11. A method for measuring optical radiation according to any one of claims 1 to 8, characterized in that: The through hole is provided with a transparent wave plate which transmits visible light.

Images