Abstract: An image capture system comprises a camera configured to capture an image of a whiteboard, or similar, viewed from an acute angle. A linear polarizer has a surface substantially perpendicular to a plane of the board and an axis of polarization substantially perpendicular to the plane of the board or within 30° of the perpendicular to the plane of the board. The camera is configured to capture the image of the board through the polarizer. A normal to the polarizer is directed in a different direction to a direction defined by an optic axis of the camera.

Abstract: An image capture system comprises a camera configured to capture an image of a whiteboard, or similar, viewed from an acute angle. A linear polarizer has a surface substantially perpendicular to a plane of the board and an axis of polarization substantially perpendicular to the plane of the board or within 30° of the perpendicular to the plane of the board. The camera is configured to capture the image of the board through the polarizer. A normal to the polarizer is directed in a different direction to a direction defined by an optic axis of the camera.

Abstract: A method of capturing writing or drawing on a whiteboard comprises inputting camera data for a succession of image frames of the whiteboard, and processing data from said image frames to remove parts of the image frames corresponding to parts of a user or user pen writing or drawing on the whiteboard. The processing involves filtering to distinguish between i) motion of the user/user pen parts in the image frames, and ii) writing/drawing image information in the image frames which appears or changes during said writing or drawing but which is thereafter substantially unchanging. The filtered data defines captured writing or drawing from the whiteboard.

Abstract: We describe a method of capturing writing or drawing on a whiteboard. The method comprises: inputting camera data for a succession of image frames, wherein the camera data is from a camera directed towards the whiteboard and the image frames comprise successive images of the whiteboard from the camera; and user filter processing data from said image frames to remove parts of said image frames corresponding to parts of a user or user pen writing or drawing on said whiteboard. The user-filter processing comprises filtering to distinguish between motion of the user/user pen parts in the image frames and writing/drawing image information in the image frames which appears or changes during said writing or drawing but which is thereafter substantially unchanging. The method outputs writing/drawing data from the user filter-processing, this defining captured writing or drawing from the whiteboard.

Abstract: A "Y" connected three port circulator is disclosed having three transmission mediums interconnected at a bias terminal to form a reciprocal "Y" connection having three distal terminals; a capacitor connecting the bias terminal to ground; and three non-reciprocal coupling circuits, one connected between each pair of distal terminals.

Abstract: A variable attenuator having first and second branch circuits configured in bridged T, T or PI topologies, each of the branch circuits having at least one voltage variable FET resistor. The voltage variable FET resistor includes a FET network comprising a plurality of FET segments each of which have a predetermined gate width and a voltage divider network including a plurality of fixed resistors coupled to the gates of the plurality of FET segments for providing a different predetermined gate voltage to each of the FET segments. The gate width of each of the FET segments and the resistance of each of the fixed resistors is chosen to provide a predetermined relationship between the control voltage and the channel resistance of the voltage variable FET resistor, to thereby provide a preselected relationship between the control voltage applied to the first branch circuit and the attenuation ratio of the attenuator.

Abstract: A voltage variable FET resistor includes a FET network comprising a plurality of FET segments each of which have a predetermined gate width and a voltage divider network including a plurality of fixed resistors coupled to the gates of the plurality of FET segments for providing a different gate width of each of the FET segments and the resistance of each of the fixed resistors is chosen to provide a predetermined relationship between the control voltage and the channel resistance of the voltage variable FET resistor.