CCD base line subtraction algorithms

High statistics astronomical surveys require higher accuracy of sensor calibration procedures. 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. The specialized algorithm of the base line subtraction for CCD images containing sparse signals was developed and is discussed in section 3. This algorithm does not require taking additional bias exposures and uses data from the same image. Statistical properties of the algorithm are discussed in section 3. The algorithm performance on ⁵⁵Fe data and comparison with bias exposures approach is presented in section 4. Details of the bias exposure analysis are presented in section 2.