CCD Base Line Subtraction Algorithms

High statistics astronomical surveys require photometric accuracy on a few percent level. The accuracy of sensor calibration procedures should match this goal. The first step in calibration procedures is the base line subtraction. The accuracy and robustness of different base line subtraction techniques used for Charge Coupled Device (CCD) sensors are discussed. A specialized algorithm for base line subtraction in CCD images containing sparse signals was developed. This algorithm does not require taking separate bias exposures. Statistical properties of the algorithm and the algorithm performance on (55)Fe data are presented. This algorithm is compared with the bias exposures approach. Details of the bias exposure analysis are also discussed.