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Gamut Correction

Gamut Correction

Nov 16, 2017

  When the gamut correction is carried out in LED, the target brightness of each LED should be determined besides the range of the target color gamut. The brightness of LED can be directly represented by the Y value in the three stimulus value, and the chromaticity can be represented by the color coordinate formula (1) in the CIE1931XYZ color space.


  In color gamut correction, all LED brightness should be consistent, so the target value can be selected minimum values of all the LED in the brightness, as in Table 1 red LED as an example, the minimum value of 31 Y, the target color coordinates of (0.687, 0.3105), the color coordinate type (1) can be calculated. To obtain the target when the red color of the three stimulus values for:

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  In this paper, XR, YR and ZR are used to represent the target three stimulus value of red LED. Xr, Yr and Zr represent the current three stimulus values of red LED, and the LED of other colors make similar definitions.

  It can be known from the linear mathematical model of formula (2) and formula (3) that when the luminous intensity of LED changes, its three stimulus value also changes linearly. Before correction, the red LED luminescence can be expressed as:

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 The red color gamut of new correction, is passed to a display three colors LED pixel multiplied by the coefficient in different expressed by emitting a combination of three color LED to replace the original red light red color as LED alone, three of the three primary colors of light stimulation LED value should be red color the three target stimuli, it can be described as:

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 In formula (7), when kr1=1, kr2=0, kr3=0, that is, the formula (6) represents the red LED in front of the school alone luminous situation, the solution formula (7) can be obtained:

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  The correction coefficient of the red LED can be obtained by the formula (8), and the theoretical three stimulus value for the new red primary color is p when the gray level is :

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 A similar correction of the red, green and blue LED in Table 1 can be obtained with correction coefficients kg1, kg2, kG3 and blue LED correction coefficients kg1, kg2, kG3 for green LED. It should be noted that when the display pixel needs to display the highest gray level "white field", the red LED brightness in the white field comes from the red primary color, the green primary color and the blue primary color, respectively.

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In the formula (5), is likely to make the correction of Y "R of the single color value is set as a result of excessive kr1+kg1+kb1 is larger than 1, the type (10) in the required X value is larger than the maximum brightness, red LED obviously, it is necessary to avoid, this situation the white balance later in the discussion.


Color gamut correction results as shown in Figure 3 and table 1 shows that the actual measurement of three stimulus values between the target and three stimulus values of the brightness difference is less than 3%, close to the measurement accuracy of the equipment, the primary color coordinates relative correction before the aggregation degree was obviously improved, difference between actual color coordinates and color coordinates of the target is close to 0.05[3].


Need to note is that the final is closely related with the accuracy of the correction effect correction system used in this paper, the correction system of accuracy of 10bit, when the correction precision of the system is small enough, the LED color coordinate theory after correction of aggregation as a "point", the correction accuracy will further improve.

 

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