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Single Panel DMD projector with improved gamma and high brightness

IP.com Disclosure Number: IPCOM000014657D
Original Publication Date: 2000-Mar-01
Included in the Prior Art Database: 2003-Jun-20

Publishing Venue

IBM

Abstract

Single Panel DMD projector having improved color depth and high brightness Disclosed is a technique to improve color depth of a Single Panel Digital Micromirror Device (DMD) projector without sacrificing brightness. In a single Panel DMD projection system, a color wheel is used to create a full color projected image Fig-2). The color wheel is a red, green and blue, filter system which spins at 60 Hz to give 180 color fields a second (Fig-3). As DMD is a bi-stable device, gray scale is achieved through a digital technique called pulse width modulation (PWM). With PWM, grayscales are generated by varying the the time mirror is ON (Fig-4). Color depth is limitted by the micromirror switching time. For computor image such as business graphics, gamma correction is not required and 8-bit color depth is achieved by PWM (Fig-5a). But video signals typically have gamma correction applied to them to compensate for the non-linear characteristics of the CRT receiver. Degamma will be achieved by controlling ON time duty in the conventional single DMD projector. But it will reduce the color depth (Fig-5b). Adding a Rotating Neutral Density (ND) wheel (Fig-6,Fig-7,Fig-8) will introduce natural degamma characteristics without reducing color depth (Fig-9). But a half of light will be lost at ND filter and the projection image becomes dark. Disclosed technique is to improve color depth with ND wheel, preventing brightness loss, by utilizing Two-zoned DMD.