Northrop Grumman Systems Corporation

Dean L Weideman

Harold J Orlando

Lawrence M Scherr

An apparatus and method for removing offset and shading from a video signal include a filter that convolves the video signal with a second derivative. The derivative can include first and second non-zero values centered about a third non-zero value, zero-filling between the first and third values, and zero-filling between the second and third values. The filter can be applied to Modulation Transfer Function measurement of an electro-optical sensor, in which offset and shading are removed from the sensor's video signal prior to Fourier analysis. Filtering and Fourier analysis are performed by a digital signal processor, which allows the measurement to be fully automated.

Apparatus and method for removing offset and shading from a video signal

This is a target projector projecting a vertical line source of infrared energy for testing of thermal imaging sensors. A vertical wire of a material which heats and emits infrared energy when an electrical current is passed therethrough is heated by a DC source. There is a projector for intercepting a portion of infrared energy from the wire, for passing only a line source beam portion which comprises a narrow beam of about 10 milliradians width and subtends a vertical angle of about 40.degree., and for directing the narrow beam on an optical center line of a thermal imaging sensor being tested. One type of projector comprises a narrow vertical mirror oriented about a longitudinal axis of rotation which is in a common plane with the wire disposed between 4' and 10' from the wire and rotatable about the axis of rotation to project the line source beam in a desired direction. In another projector, the mirror is replaced by a slit. The wire and projector in combination are also rotatable to a position 45.degree. from vertical so that dead channels of a sensor tied to adjacent live channels can be identified.

Infrared line source projector

A method of optimizing the optical focus of an electro-optical sensor in preparation for accurately measuring an optical parameter thereof of the type including, but not limited to, dynamic range, modulation transfer function, minimum resolvable temperature difference and field of view, includes changing a focus of the sensor on a target image viewed by the sensor while obtaining successive output images produced by the sensor, constructing respective image vectors from respective ones of the output images, for each one of the image vectors transforming the image vector by transform to produce a transformed image vector of elements whose values correspond to spatial frequency content computing a sum of squares of elements of the transformed image vector to produce a focus metric and identifying the focus of the recorded image corresponding to the greatest focus metric as being the optimum focus.

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Lomita, CA, United States of America

Dean L Weideman