International hydrographic organization specifications for chart content and display aspects of ecdis
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S-52 Appendix 2 - IHO
| B.3 Data Collection The data collection consists of two parts measuring the CIE chromaticity coordinates of the principal colour producing elements and measuring the gamma function of the principal colour producing elements. B Principal colour producing element Chromaticities The principal colour producing element chromaticities can be measured directly by the photometer (e.g. Minolta CS 100) as follows .1 Put a square of pure red on the screen (DAC values of (255,0,0). This square should be as large as possible, covering at least ten times the sampling area of the photometer, and preferably covering at least 80% of the screen. .2 With the photometer normal to the screen and pointing at the centre, with light shielding in place and the room darkened, measure the red chromaticity directly according to the colourimeter manufacturer's instructions. .3 Repeat steps 1 and 2 for green and blue, using DAC values of (0,255,0) and (0,0,255) respectively. Principal colour producing element chromaticities maybe available from the monitor vendor. These data maybe used instead of measuring the chromaticities directly, as long as the data takes into account the effect of the monitor faceplate. 63 S, Edition 6.0 March 2010 B Measurement of the Gamma of the principal colour producing elements B The principal colour producing elements have typically anon linear transfer characteristic describing the relationship between the R, GB input values and the light output on the face of the monitor. This is called the Gamma Function or Gamma of the monitor. This transfer characteristic is used to select the proper mixing of colours to create the correct combined colour on the screen. B The Gamma is measured for each principal colour producing element separately. A test square in the centre of the screen of size at least 5 cm by 5 cm (but not exceeding 25% of the area of the screen) should be used for this calibration. The screen outside the test area should remain black. Use a sensitive radiometer for this measurement (e.g. Graseby 370). Setup the radiometer head contacting the centre of the screen. Ensure that the instrument is always pointed at the same part of the screen for the entire series of measurements (red, green and blue. Put shields in place to block any stray light and darken the room to black. B Start with the red colour. Drive the monitor with DAC values starting at (0, 0, 0) and increasing to (255, 0, 0). Increase in increments of 8 for the low values (below 100) and in increments of 16 for the higher values. (There is no harm in using a smaller increment if desired) Record the light output in candelas per square metre (if available) against each DAC value. Otherwise, (for example in the case of the Graseby with radiometric head) record the output reading in amperes. Then, when the maximum DAC value is achieved, use a calibrated photometer/colorimeter (e.g. Minolta CS 100) to take a luminance reading. This luminance reading is then used to develop a conversion factor to convert from the radiometer's ampere reading to candelas per square metre. B Repeat the measurement sequence for each of the other two colours. Repeat the photometer calibration for each of the other colours as well. B To prepare the radiometer output data for processing, convert it from nano amperes to candelas per square metre using the calibration constants derived above for each phosphor colour. Download 0.98 Mb. Share with your friends:
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