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In this paper, a method for retrieving the line charge density and the current of a downward leader based on ground observations of lightning images and electric field changes was proposed and examined. The method was then applied to two downward negative leaders in a rocket-triggered lightning discharge with measurements of broadband interferometric images and electric field changes at close distance. Only the descending channel portion between about 900–400 m high of the two leaders were analyzed, where the channel was in free air rather than the trace of triggering wire. The line charge density for both leaders showed a general increasing trend with a big impulsive change around 500 m high, as the leaders moved downward, which was in good agreement with the prediction of existing downward leader models. The range of the line charge density was similar for the two leaders (−0.03 to −0.32 mC/m and −0.02 to −0.33 mC/m, respectively). The impulsive change of the line charge density was corresponding to a sharp turn of the leader channel around 500 m high, which may imply that the sharp turn of the leader channel was probably associated with a pre-existing local positive space charge pocket. The estimated leader currents for two leaders (−20 to −315 A and −77 to −541 A, respectively) were also in good agreement with independent estimations in the literature. [ABSTRACT FROM AUTHOR]

With rapidly advancing computer technology, the demand for color images is growing with time for both quantity and quality, especially for various display panels. The purpose of this paper is to develop color calibration methods with hardware and software compensations for a surrounding true-color LED display system to enhance the performance of the true-color image display. To have an even LED lighting-time control and a linear relationship between RGB input value and output luminance, pulsewidth modulation driving schemes are employed in driving LED display. The color calibration techniques also include gamma correction for gradation of the luminance, compensation for the RGB input values on the basis of LED white point, and weighting filter to eliminate the interference from the adjacent LEDs. The experimental results indicate that the color-calibrated LED display system offers a very wide color gamut, and gives a great enhancement in color saturation and brilliance. For the color-calibrated LED display system, the display quality is obviously improved, and it exhibits a colorful and saturated color display. [ABSTRACT FROM PUBLISHER]