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13 October 2005 Scale factor in digital cameras
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For objects on a plane, a "scale factor" relates the physical dimensions of the objects to the corresponding dimensions in a camera image. This scale factor may be the only calibration parameter of importance in many test applications. The scale factor depends on the angular size of a pixel of the camera, and also on the range to the object plane. A measurement procedure is presented for the determination of scale factor to high precision, based on the translation of a large-area target by a precision translator. A correlation analysis of the images of a translated target against a reference image is used to extract image shifts and the scale factor. The precision of the measurement is limited by the translator accuracy, camera noise and various other secondary factors. This measurement depends on the target being translated in a plane perpendicular to the optic axis of the camera, so that the scale factor is constant during the translation. The method can be extended to inward-looking 3D camera networks and can, under suitable constraints, yield both scale factor and transcription angle.
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Anthony P. Badali, Yahui Zhang, Peter Carr, Paul J. Thomas, and Richard I. Hornsey "Scale factor in digital cameras", Proc. SPIE 5969, Photonic Applications in Biosensing and Imaging, 59692B (13 October 2005);

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