Other

Hughes-Jvc Technology Corporation

James G Hagerman

A system for measuring the illumination uniformity of a liquid light value (LCLV) for a LCLV projector includes a projection device including a first LCLV. The projection device reflects light from the first LCLV to form an image on a screen. An image sensing device senses illumination values for a plurality portions of said image. A processor is coupled to the image sensing device and the projection device. The processor determines an optimum voltage bias which provides a maximum illumination for the plurality of image pixels. The illumination uniformity measuring system can independently measure the illumination non-uniformity of the LCLV and illumination non-uniformity resulting from other sources such as projection lens roll-off, screen gain, and other illumination non-uniformities. Using the measured illumination non-uniformity, a correction system can improve the quality of the displayed image.

Method and apparatus for measuring illumination uniformity of a liquid

Improved bias drive and noise reduction techniques for use with and image projector, such as a liquid crystal light valve image projector. A bias drive circuit produces a square wave-like signal to drive the liquid crystal light valve, for example, with a square wave signal. The square wave-like signal is phase-locked to the vertical refresh (vertical sync) signal of the projector. A frequency synthesizer is used to drive the bias drive circuit wherein the noise is interlaced by using every other field as the sync reference input to the bias drive circuit. The bias drive circuit is unique in how it reduces unwanted visual noise effects in a displayed image by waveshaping the drive signal and interlacing and phase-locking it to the vertical refresh signal of the projector. These aspects of the present invention combine to virtually eliminate visual noise in the projected image. An optional variable gain circuit may be provided that provides the ability to set the amplitude of the bias provided by the bias drive circuit to the cut-in operating point of the liquid crystal light valve.

Bias drive and noise reduction in image projectors

Apparatus that implements a nonlinear transfer function (gain) that provides for gamma correction of nonlinear image projectors. The nonlinearity of the transfer function is designed to compensate for the nonlinearity of a nonlinear light modulator, such as a liquid crystal light valve and cathode ray tube combination, for example, that is used in the image projector. The gamma correction circuit comprises a plurality of amplifiers that include current sources coupled together to sum their output currents, and each amplifier is adapted to implement a predetermined transfer function, and provide differing levels of current. An optional output resistor may be employed to convert the composite output current into a corresponding output voltage. Each of the plurality of amplifiers typically comprises first and second emitter coupled pair transistors plus their associated current sources. The present invention corrects the grey scale linearity of the image projector in which it is employed. The amplifier configuration of the circuit does not use feedback, so its processing bandwidth remains high. The present invention also produces 'soft' breakpoints, creating a relatively smooth transfer function. The gamma correction circuit of the present invention is useful in any application using a nonlinear amplifier. The present gamma correction circuit may also be used in any image projector or display using liquid crystal or other nonlinear imaging technology. If gamma correction is used in conjunction with dynamic threshold correction then the gamma correction is made dynamic by adding the threshold correction signal to the base of one of the transistors in the gamma correction circuitry.

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San Diego, CA, United States of America

James G Hagerman