Patent ID: 6141046
Filing Date: 2000-10-31
Classification: G06K,H04N

Abstract:
An electronic camera for producing a digital image whose contrast is nearly constant over a field of view, comprising:a camera circuit including an image sensor and an adjustable shutter speed control, said camera circuit being configured to output an analog image signal;an optical assembly defining an optical axis and configured to define a field of view and a depth of field for image capture by said image sensor;a plurality of light sources positioned approximately in a ring concentric with said optical assembly;at least one annular lens shaped to project light from said light sources in a light pattern whose form remains approximately constant and consistent from center to edge through said depth of field;a video gain circuit configured to receive said analog image signal and to output an amplified analog image signal;an analog-to-digital converter including an A/D gain controller responsive to an A/D reference input and configured to convert said amplified analog image signal from said image sensor to a digital image signal;a lens attenuation evaluator circuit configured to output to said A/D reference input a correction signal varying as a function of angle from said optical axis; andan intensity evaluator circuit configured to receive said digital image signal for each image capture and to provide a plurality of intensity-dependent control signals;said intensity evaluator circuit being connected to transmit a corresponding one of said control signals to said shutter speed control, said video gain circuit, and said lens attenuation evaluator circuit,such that overall gain control in said camera is obtained by controlling in combination shutter speed, video gain, and analog-to-digital converter gain, responsive to evaluation of image brightness.