International hydrographic organization specifications for chart content and display aspects of ecdis
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S-52 Appendix 2 - IHO
| L r , L b , and L g are the luminance outputs of the colour producing elements at the screen and A -1 is the inverse of the matrix A for the colour coordinates of the colour producing elements, given by 69 S, Edition 6.0 March 2010 = b b g g r r b b g g r r y z y z y z y x y x y x A 1 where x and y are the CIE chromaticities of the red, green, and blue phosphors, and x + y + z = 1 The tristimulus values, X, Y, Z are derived from the CIE coordinate defined colour as follows Y y y x Z Luminance) L Y Y y x X − − = = = 1 ( The required luminances are then derived from an interpolation of the monitor gamma function data, and RGB DAC values are achieved. These DAC values are automatically fed into the Presentation Library routine to give the correct colour table values. B Example Assume principal colour producing element chromaticities as measured from the colorimeter 070 0 , 100 0 590 0 , 300 0 360 0 , 600 0 = = = = = = b b g g r r y x y x y x "Using these values, and the equation z = 1-x-y to generate matrix A = 86 11 186 111 1 1 1 429 1 508 667 1 A By inversion, − − − − = − 0852 0187 0055 0175 4429 1 8646 0677 4242 8590 1 A 70 S, Edition 6.0 March 2010 If the required colour for the screen has CIE coordinates of x = .28, y = .31 and L = 45 cd/m 2 Then, 52 59 and 45 , 64 40 = − − = = = = Y y y x Z Y Y y x X Calculate the required luminances from each colour producing element by the first equation = − Z Y X A L L L b g r 1 This results in luminance values for the colour producing elements as follows L r = 11.80 cd/m 2 , L g = 28.75 cd/m 2 , L b = 4.56 cd/m 2 The corresponding DAC values are calculated by interpolation of the gamma function derived for the red, green, and blue guns of the monitor. For example, in the case of a Hitachi CRT monitor recently calibrated, the DAC values were R = 183, GB. Other monitors will have different values" B Verification Calculation This section discusses the calculation for converting the separate luminances of red, green, and blue for the given test colour to CIE coordinates in x, y, and L. The verification calculation is essentially the reverse of the calibration calculation discussed in section B. The known data are the colour coordinates of the colour producing element, and the red, green, and blue luminance components of each colour to be measured. The desired output are the colour coordinates and luminance for each colour. Given the relationship between luminances of each colour, L r , L g , and L b , matrix A containing the phosphor coordinate data, and X, Y, and Z (from which x, y, and L are derived) the following equation is derived = Z Y X A L L L b g r X, Y, and Z can be calculated. 71 S, Edition 6.0 March 2010 Note that from B above A is the matrix of the cromaticities coordinates given by = b b g g r r b b g g r r y z y z y z y x y x y x A 1 1 1 x and y can be obtained from X, Y, and Z by the following equations + + = Z X Z Y Y X x 1 and + + = Z X Z Y Z X y 1 Note from B that Luminance, L = Y These equations then give the formulas necessary to calculate the chromaticity coordinates and luminance, x, y, and L, for any given color, where the contributions of red, green, and blue luminance and the chromaticity coordinates are known. Download 0.98 Mb. Share with your friends:
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