| Summary: | 碩士 === 國立臺灣科技大學 === 電子工程系 === 94 === As brightness of LEDs is brighter and brighter, making LED projector is possible. Taking the place of conventional UHP (ultra high pressure) lamp with LEDs reduces the projector size and system complexity. The major advantages of LEDs are natural pure color, long lifetime, low power consumption, small size, and high brightness. LEDs also has defects, one is low lux value, it limits LED projector to perform only in absolutely dark room, another is the suitable projection distance is below 1 meter. The reason is that illuminance varys with inversely proportional to the square of projection distance, and gathering efficiency of LED projector is not good enough. Additionally, power and brightness of LEDs are not high enough to be an illuminant source at present. If so, the projection image will be not large.
The major research of this article is solving the problem of low sensitivity of measuring device at dim levels, that will cause inaccurate tristimulus, and explained below：
When digital input values are zero, display still outputs light. The phenomenon is referred to as display’s black level. The basic reason is internal scattering. The black level will cause chromaticity variation. It is already known measuring black level precisely in colorimetric characterization is very important. The low instrument sensitivity for black level had been solved and proposed. Unfortunately, output tristimulus for dim levels of LED projector are especially low. Measuring device is not sensitive enough for low digital values, not only black level.
To improve accuracy, two proposed method are employed. One is black level estimation, another is cutting black level into respective contribution of each channel. For dim levels problem, a routine procedure including proposed black level estimation and nonlinear interpolation of low output tristimulus in place of raw data is proposed, namely tristimulus of every dim level output as well as black level are corrected.
In addition to sensitivity problem, primary additivity, color gamut, contrast, uniformity, temporal stability, spectral stability, spatial non-uniformity, channel independency, spatial independency are measured, All the characteristics are compared to data in a paper about colorimetric characteristics of a LCD projector. Color prediction accuracy of various model are compared eventually, and we probed into possibility of reducing large number of measuring data and time.
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