Dynamic contrast in a projection system
Publication Date: 2004-Feb-25
The IP.com Prior Art Database
Dynamic contrast in a projection system.
The invention relates to a projection system for displaying image information comprising an illumination system for generating a light beam, a modulation system for modulating the generated light beam and a projection lens for projecting the modulated light beam on a screen. The modulation system comprises a transmissive or reflective liquid crystal display panel for modulating the light beam. According to the invention the modulation system further comprises an electrochromic device and a controller for adapting the transmission of the electrochromic device in dependence of a brightness signal controlling the liquid crystal display panel in order to improve the contrast level. The electrochromic device can be positioned between the liquid crystal display panel and the projection lens or between the projection lens and the screen.
Fig.1 shows an example of an electrochromic device 1 that can be used in the projection system. The electrochromic device 1 comprises of two glass substrates 2, 3 between which the following layers are present: a transparent ITO layer 4, an ion- storage layer 5, an ion conducting electrolyte layer 6, an electrochromic electrode layer 7 and a transparent ITO layer 8. In operation, a voltage difference 9 is supplied to the transparent ITO layers 4,8, so that an electric field is present between these ITO layers. Due to the electric field ions move from the electrolyte layer 6 into or out of the electrochromic layer 7 in dependence of the direction of the electric field. The optical properties i.e.transmission, reflection and absorption of the electrochomic electrolyte layer 7 varies in dependence of the electron density in the electrochromic material.
Fig.2 shows a projection system 20 comprising a light source 21, a reflector 22 which reflects the larger portion of the light to the integrator system. The integrator system comprises segmented lens plates 22, 23 and forms a light beam directed to the liquid crystal panel 25. A polarization converting system 24 is present between the intragrator system 22,23 and the liquid crystal panel 25 for converting the random polarization of the light beam in a first linear polarization direction. The liquid crystal panel 25 modulates the polarization direction of the light beam in accordance with the ima...