This application is the 35 U.S.C. §371 national stage of PCT application PCT/CN2009/000865, filed Aug. 3, 2009, the disclosure of which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a light-measuring system and method thereof. More particularly, the present invention relates to a light-measuring method and a light-measuring system with a look-up table based on a light spectrum model.
2. Description of the Prior Art
In prior art, a to-be-measured light may be measured according to the roles developed by the Commission Internationale de l'Eclairage (CIE) in 1931. The to-be-measured light is measured by the light-measuring device to obtain the tri-stimulus value. Then, the color coordinates will be obtained. However, it is difficult to manufacture the optical filters which meet three standard color-matching functions
Thus, the variations of the light-sensing element cannot be removed. In fact, the actual color-matching functions shall be normalized in measurement for decreasing the variations of the actual color-matching functions and the standard color-matching functions. In practice, a known light may be normalized. For example, an regulation constants Ai of an A light (Ai=∫λ1λ2SA(λ)
A four-color matrix method developed by Yoshihiro Ohno in 1997 (IS&T fifth color image conference 1997), is applied to correct three regulation coefficients by using the white light combined by the red light, green light and blue light. Accordingly, the chromaticity of the monochromatic light can be measured accurately. However, for the light spectrum with large variations, the errors of the light cannot be ignored.
To sum up, the errors of the light-measuring device cannot be removed in prior art. Additionally, if the variations of light spectrum used by the to-be-measured light and the normalization are too large, the errors of measuring the color coordinates will become lager.
A scope of the invention is to provide a method of constructing light-measuring look-up table, a light-measuring method and a light-measuring system. The color of the light with a spectral feature can be modeled, can be measured with a high accuracy. In the invention, the relationship between the spectrum parameters, light-measuring system and the standard color coordinates can be constructed in advance. So that, the light-measuring system can determine the accurate estimated color coordinate according to the relationship without standard color matching functions. Additionally, the spectrum parameters of the to-be-measured light can be determined with the estimated color coordinate at the same time. That is to say, the analogue light spectrum of the to-be-measured light can be constructed. According to the analogue light spectrums (or the spectrum parameters) and the standard color-matching functions, the actual stimulus value of the light-measuring system can be corrected. Then, the luminance can be obtained. Accordingly, the invention provides color measurement with high accuracy.
In an embodiment, the method of constructing light-measuring look-up table comprises the following steps of: measuring a light-measuring system for obtaining three actual color-matching functions of the light-measuring system; normalizing three actual color-matching functions by a standard light; calculating the plurality of look-up color coordinates according to a plurality of the spectrum parameters and the three actual color-matching functions; and calculating a plurality of reference color coordinates according to the plurality of spectrum parameters and the three standard color-matching functions, wherein each spectrum parameter corresponds to one of the plurality of look-up color coordinates and one of the plurality of reference color coordinates.
Wherein, the light spectrum model can be used to represent the actual spectrum of the to-be-measured light and shown in the forms of two variables. One is central wavelength variable, another is half-power full waviness width variable (Full-width half maximum). In other words, each spectrum parameter comprises a central wavelength value and a half-power full waviness width variable value, for representing a specific light spectrum. Each specific light spectrum corresponds to a look-up color coordinate calculated by the actual color-matching functions and a reference color coordinate calculated by the standard color-matching functions. Thus, the relationship between the look-up color coordinate and the reference color coordinate will be constructed by the spectrum parameters.
In the embodiment, the light-measuring system comprises a light-sensing module, a storage module and a processing module. The light-sensing module comprises a light filtration element and a light-sensing element. The light-sensing module produces three actual stimulus values by sensing at least one of the to-be-measured lights at the same time. The storage module is used to store a look-up table. The processing module is coupled to the light-sensing module and the storage. The processing module produces three actual stimulus values by capturing the photoelectric converting signal from the light-sensing module and determines the estimated color coordinates of the to-be-measured light according to the look-up table. The processing module can determine the spectrum parameters of the to-be-measured light and the estimated luminance of the to-be-measured light according to the standard color-matching functions.
Accordingly, in the embodiment, the light-measuring method comprises the following steps of: the light-measuring system measures the to-be-measured light for obtaining the three actual stimulus values according to the light-sensing module; the processing module calculates an actual color coordinate according to the three actual stimulus values; the processing module compares the actual color coordinates to the plurality of look-up color coordinates of the look-up table stored in the storage module, for determining at least one of the look-up color coordinates matched with the actual color coordinates; the processing module determines an estimated color coordinate according to at least one of the reference color coordinates of at least one of the matched look-up color coordinates, then the processing module determines a to-be-measured light spectrum parameters according to at least one of the spectrum parameters of at least one of the look-up color coordinates; the processing module calculates an adjustment coefficient or a ratio for correcting the actual stimulus values corresponding to the actual color-matching functions, according to the analogue light spectrum, one of the three actual color-matching functions and the standard color-matching functions corresponding to the actual color-matching functions. Finally, an estimated luminance can be obtained.
To sum up, the light-measuring system and the light-measuring method can determine the to-be-measured light spectrum parameters, accurate color coordinates and the luminance according to the look-up table constructed by the light spectrum model of the to-be-measured light. Accordingly, the to-be-measured light spectrum parameters, accurate color coordinates and the luminance can be determined by referring table easily and the easy calculating steps. Briefly, the look-up table can be constructed in advance for the known spectral features of the to-be-measured light. The actual measuring system and the standard measuring system can be connected so that the error can be removed. Additionally, the color values can also be measured with high accuracy to prove the error of the actual color-matching functions and standard color-matching functions. Specially, the spectral features of the quantity production of the light, such as LED, LCD or other monochromatic light, are similar. The product can be modeled according to the same spectral feature. The difference of the product can be covered by the spectrum parameters.
The advantage and spirit of the invention may be understood by the following recitations together with the appended drawings.
Please refer to
Wherein, the light spectrum model 1 represents the spectral features of the to-be-measured light 3, the spectrum parameters are variable set of the light spectrum model. For example, when the to-be-measured light 3 is a monochromatic LED, the variable of the light spectrum model can be represented as a central wavelength variable λ0 (or a wavelength λp with maximum power) and a half-power full waviness width variable Δλf. As shown in
The asymmetric spectrum can be represented as the following types of:
wherein λ≦λL or λ≧λH, S51(λL)=S51(λH)=0.5 Incidentally, the light spectrum model can be, but not limited to the said types. The model can be a derivation which depends on the actual spectral feature of the to-be-measured light 3 or a model which can be explained directly as the set of the numeric value.
In the manufacturing, the possible situations of the to-be-measured light 3 can be covered by the light spectrum model according to the suitable light spectrum model. The sets of the variables in the look-up table 126 are the spectrum parameters λ0 and Δλf. The actual color-matching functions of the light-measuring system 1 and the light spectrum model shall be calculated in advance to obtain the look-up color coordinates. Each look-up color coordinate corresponds to a specific light spectrum, or a spectrum parameter. Then, each light spectrum (spectrum parameter) and the CIE 1931 standard color-matching functions shall be calculated to obtain the corresponding reference color coordinates. The results of the calculation construct the look-up table 126. According to the look-up table 126, the look-up color coordinates are compared to the actual color coordinates of the to-be-measured light 3 to determine the reference color coordinates. Additionally, the standard color coordinates will be obtained. That is to say, if the spectral feature of the to-be-measured light 3 and the any light spectrum are the same, the standard color coordinates of the to-be-measured light 3 and the reference color coordinates of the light spectrums are almost the same. Furthermore, the look-up table 126 shall be constructed in the light-measuring process and storied in the storage module 124 for the post process.
Please refer to
To be noticed, the normalizations of the actual color-matching functions Xr(λ), Yr(λ) and Zr(λ) are based on correcting or reducing the differences between the actual color-matching functions and the standard color-matching functions (
As shown in step S104, a plurality of look-up stimulus values
Please refer to
To be supplemented, although the effect of the spectral amplitude has not been considered in the formula of the look-up stimulus values
For example, the ranges of the look-up color coordinate xidx and yidx are 0≦xidx≦0.73 and 0≦yidx≦0.83. If the color coordinate shall be obtained with an accuracy of 0.001, the amount of corresponding spectrum parameters λ0 and Δλf are about 3×105((½)×(0.73/0.001)×(0.83/0.001)≈3×105)). However, the half-power full waviness width variable of the LED is about 50 nm ( 1/7 of the waviness width of the visible ray), so the amount of spectrum parameters λ0 and Δλf are 5×104. For example, if the central wave length of the LED ranges from 400 nm to 700 nm, the half-power full waviness width ranges from 20 nm to 50 nm, when the variable interval of the central wave length λ0 is equal to 0.25 nm, the variable interval of the full waviness width Δλf is equal to 0.5 nm, the look-up table 126 will be constructed with 8×104((350/0.25)×(30/0.5)≈8×104) spectrum parameters λ0 and Δλf which is larger than 5×104. That is to say, the look-up table 126 can be constructed with an accuracy which is larger than 0.001. If the more accurate color coordinate is obtained, the variable intervals of the central wave length λ0 and the full waviness width Δλf shall be decreased.
Please refer to
Then, as shown in step S200, the processing module 122 determines at least one of the look-up color coordinates xidx and yidx of the matched actual color coordinate xM and yM according to the actual color coordinate xM, yM and look-up table 126. Then, as shown in step S204, the processing module 122 determines the to-be-measured light spectrum parameters λ0* and Δλf* according to at least one of the spectrum parameters λ0 and Δλf of the matched look-up color coordinate xidx and yidx. The to-be-measured light spectrum parameters λ0* and Δλf* can be represented as the spectral feature of the to-be-measured light 3. That is to say, the to-be-measured light 3 can be represented as the light spectrum AsSt(λ, λ0*, Δλf*), wherein As is the spectral amplitude of the to-be-measured light 3.
To be supplemented, the value of the matched result can be different. If the expected difference value compared to the look-up color coordinate xidx and yidx can be accepted, the result can match with the look-up color coordinate xidx and yidx. That is to say, each look-up color coordinate xidx and yidx has a certain coverage, if the actual color coordinate xM and yM is located in a certain coverage of look-up color coordinate xidx and yidx, the actual color coordinate can be thought that locates between two look-up color coordinate xidx and yidx or matches with the two look-up color coordinate xidx and yidx. At least one of the look-up color coordinate xidx and yidx will become a basis of determining the to-be-measured light spectrum parameters λ0* and Δλf* in step S204. That is to say, the look-up color coordinate xidx and yidx shall be determined in step S202. Additionally, the look-up color coordinate xidx and yidx can be thought that matches with the actual color coordinate xM and yM.
For example, if the actual color coordinate xM and yM locates between the look-up color coordinate x2, y2 and look-up color coordinate x3, y3 in
Of cause, the invention can be, but not limited to linear interpolation. The look-up color coordinates x2, y2, x3 and y3 can be thought as matched actual color coordinate xM and yM. In principle, if the sampling intervals of the look-up color coordinate xidx and yidx are small, the linear interpolation will be accurate.
Please refer to
XMS, YMS and ZMS are standard stimulus values of the standard color-matching functions
Thus, as shown in step S208, the processing module 122 calculates the estimated color coordinate xEST, yEST and zEST of the to-be-measured light 3 according to the three actual stimulus values XM, YM and ZM corrected by the three values ΔX, ΔY and ΔZ. The formulas are:
xEST=(XM+ΔX)/(XM+ΔX+YM+ΔY+ZM+ΔZ);
yEST=(YM+ΔY)/(XM+ΔX+YM+ΔY+ZM+ΔZ);
zEST=(ZM+ΔZ)/(XM+ΔX+YM+ΔY+ZM+ΔZ)o
The estimated color coordinate xEST, yEST and zEST is the measuring result of the color coordinate of the light-measuring system 1. Additionally, in step S206, if the three are defined as Δ
In step S208, the estimated color coordinates xEST, yEST and zEST of the to-be-measured light 3 can be obtained by the following formulas:
Please refer to
The Δ
According to the first preferred embodiment of the invention, the light-measuring system 1 uses the stimulus light spectrum AsSt(λ, λ0*, Δλf*) (or St(λ, λ0*, Δλf*) calculated with the actual color-matching functions
The processing module 122 further calculates the estimated color coordinate xEST, yEST and zEST according to the analogue standard stimulus values
To be supplemented, the calculating ways in step S208a are different from the ways in step S208, but the formulas are all represented as the estimated color coordinate xEST, yEST and zEST of the to-be-measured light 3, so that the xEST, yEST and zEST are represented as the same symbol. Additionally, because the estimated color coordinates xEST, yEST and zEST are dimensionless, the estimated color coordinates xEST, yEST and zEST can be calculated by the said analogue standard stimulus values
Please refer to
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As shown in step S212, the processing module 122 calculates the error values Δ
Then, as shown in S214, the processing module 122 calculates the estimated luminance IEST of the to-be-measured light 3 according to the error values Δ
IEST=YM×(1Δ
Please refer to
According to the look-up table 126, in step S212, the processing module 122 determines error values Δ
Please refer to
By using the logic of determining the to-be-measured light spectrum parameters λ0* and Δλf*, the processing module 122 determines a specific ratio according to at least one of the reference ratios of at least one of the matched spectrum parameters λ0 and Δλf. So the estimated luminance IEST can be represented as IEST=YM×(1+γ*).
Please refer to
Please refer to
In step S214a, the processing module 122 calculates the estimated luminance IEST of the to-be-measured light 3 according to the analogue standard stimulus values
IEST=YM×(
Analogue standard stimulus values
and reference stimulus values. Then, the ratios (reference adjustment coefficients k) can be integrated into the look-up table 126, as shown in
Please refer to
In details, the analogue stimulus values YSIM about the analogue light spectrum AsSt(λ, λ0*, Δλf*) can be constructed according to the to-be-measured light spectrum parameters λ0* and Δλf*. The formula is:
Because the light spectrum model St(λ, λ0, Δλ) is constructed according to the to-be-measured light 3, the light spectrum model St(λ, λ0, Δλ) can be thought as the spectral feature of the actual to-be-measured light 3. Accordingly, the actual stimulus values YM can be represented by the analogue stimulus values YSIM. Then, the spectral amplitude As can be obtained by the following formula:
Of course, As can be obtained by the integration of the XM/
The said embodiments are explained the ways of determining the estimated color coordinates xEST, yEST, zEST and estimated luminance IEST. In practice, the ways of determining the estimated color coordinates can be, but not limited to the said embodiments . Additionally, the embodiments take single to-be-measured light for examples, but in practice, the plurality of to-be-measured lights can also be measured at the same time.
Please refer to
The LCD 7 is set in two-dimension. The images of the plurality of to-be-measured light at the CCD 56 are two-dimensional. The CCD 56, comprises a plurality of light-sensing units (not shown in figures), can sense the light and transmit the photoelectric conversion signal to the processing module. The process of the photoelectric conversion signal (such as actual stimulus values) and the determining process of the estimated color coordinate and the estimated luminance are the same, and it will no longer be explained. Each to-be-measured light of the LED 7 does not correspond to a light-sensing unit necessarily, but each to-be-measured light can be distinguished by pixel processing. Then, the corresponding estimated color coordinate and the estimated luminance can be calculated. In principle, the configuration density of the light-sensing units of the CCD 56 is larger than the configuration density of the to-be-measured light of the LCD 7, so that the plurality of to-be-measured light CCD 56 can provide a high discrimination. That is to say, the light-measuring system 5 can use the method of measuring single light to measure estimated color coordinates and the estimated luminance of the each corresponding light-sensing unit. Furthermore, calculating average color coordinate and the color-profile of each light by a software and obtaining the estimated color coordinates and the estimated luminance of the to-be-measured light.
To be supplemented, the to-be-measured light is set in two-dimension, so that the to-be-measured light can also be set in one-dimension, such as the LED is set along a straight line or a curve. Additionally, although the spectral responses of the light-sensing units are almost the same, the light-sensing units are disposed at different places and affected by the lens 52 and the light filter, so that the photosensitivity of the light-sensing units are different. Thus, the light-measuring system 5 can be calibrated with a flat-field calibration. That is to say, each light-sensing unit can be illuminated by a uniform light to obtain the value of each light-sensing unit. Then, a flat-field calibration coefficient can be produced corresponding to each light-sensing unit to compensate for the difference of the photosensitivity. The flat-field calibration coefficients can form a light-sensing adjusting table and the light-sensing adjusting table can be merged into the look-up table 126. Thus, compensating the photoelectric conversion signal according to the corresponding flat-field calibration coefficients before processing the photoelectric conversion signal. Then, processing the signal and calculating the estimated color coordinate and estimated luminance. Otherwise, processing the photoelectric conversion signal directly and calculating the estimated color coordinate and estimated luminance. The calculation of the estimated luminance shall be corrected by the corresponding flat-field calibration coefficient.
To sum up, the light-measuring system and the light-measuring method can determine the to-be-measured light spectrum parameters, accurate color coordinates and the luminance according to the look-up table constructed by the light spectrum model of the to-be-measured light. Accordingly, the to-be-measured light spectrum parameters, accurate color coordinates and the luminance can be determined by referring table easily and the easy calculating steps. Briefly, the look-up table can be constructed in advance for the known spectral features of the to-be-measured light. The actual measuring system and the standard measuring system can be connected so that the error can be removed. Additionally, the color values can also be measured with high accuracy.
With the example and explanations above, the features and spirits of the invention will be hopefully well described. Those skilled in the art will readily observe that numerous modifications and alterations of the device may be made while retaining the teaching of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.
Number | Date | Country | Kind |
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2009 1 0005886 | Feb 2009 | CN | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/CN2009/000865 | 8/3/2009 | WO | 00 | 8/9/2011 |
Publishing Document | Publishing Date | Country | Kind |
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WO2010/091539 | 8/19/2010 | WO | A |
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