International hydrographic organization specifications for chart content and display aspects of ecdis

B.4 Calculations to achieve Correct Colours

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S-52 Appendix 2 - IHO
S-52 Appendix 2 - IHO

B.4
Calculations to achieve Correct Colours The colours for ECDIS are specified in CIE x, y, L coordinates, and the system that outputs the colours to the monitor uses RGB values. A calculation is performed to compute the correct RGB values to yield the correct colour (in CIE x, y, L) on the screen. At the end of the measurement sequence, there are two sets of data collected - a set of RGB coordinates for the principal colour elements of the monitor x r
y
r
), (x
g
y
g
), (x
b

y
b
)} and a set of gamma function data in the form of (DAC Value, L out) for each of red, green and blue. The data should consist of about 23 sets of numbers for each colour. The calculation routine uses this data to calculate the correct RGB values that correspond to the desired x, y, L coordinate description. The calculation details are handled by a computer program that is part of the Presentation Library. This procedure described here details the user input and output procedure for using the program. In addition, the mathematical basis for the

64 S, Edition 6.0 March 2010 calculations is explained in section BB Calibration computations using the CIE2RGB software in the Presentation Library A utility exists in the Presentation Library called CIE2RGB which will take a series of
CIE colour coordinates and luminance values and convert them to RGB DAC values for use in ECDIS, according to the specific calibration characteristics of the monitor used. Instructions for using this utility are appended to this Annex in section B.

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