... Previous: Residual Bias Removal in HST NICMOS Images . ... Bias frames taken with CCDs should be homogeneous in intensity. ... Using a large number of bias frames obtained in one specific run, the time-dependent pattern was found to be built up of a fixed one-dimensional periodic function whose phase-shift varies from row to row. It was successfully removed from calibration and science frames through the use of pre- and upscan ``bias'' pixels available in each of these frames. ...