This work was supported in part by NIH. The method described is patent pending.
Image processing -- Digital techniques, Semiconductors -- Optical properties, Electric currents -- Measurement, CCD cameras -- Calibration
Dark current is caused by electrons that are thermally exited into the conduction band. These electrons are collected by the well of the CCD and add a false signal to the chip. We will present an algorithm that automatically corrects for dark current. It uses a calibration protocol to characterize the image sensor for different temperatures. For a given exposure time, the dark current of every pixel is characteristic of a specific temperature. The dark current of every pixel can therefore be used as an indicator of the temperature. Hot pixels have the highest signal-to-noise ratio and are the best temperature sensors. We use the dark current of a several hundred hot pixels to sense the chip temperature and predict the dark current of all pixels on the chip. Dark current computation is not a new concept, but our approach is unique. Some advantages of our method include applicability for poorly temperature-controlled camera systems and the possibility of ex post facto dark current correction.
Ralf Widenhorn, Armin Rest, Morley M. Blouke, Richard L. Berry, and Erik Bodegoma, "Computation of dark frames in digital imagers," Sensors, Cameras, and Systems for Scientific/Industrial Applications VIII, Morley M. Blouke, Editor, 650103, SPIE Proceedings Vol. 6501. Copyright 2007 Society of Photo-Optical Instrumentation Engineers. One print or electronic copy may be made for personal use only. Systematic electronic or print reproduction and distribution, duplication of any material in this paper for a fee or for commercial purposes, or modification of the content of the paper are prohibited. http://dx.doi.org/10.1117/12.714784