Correcting the NICMOS count-rate dependent non-linearity

We describe a routine to correct NICMOS imaging data for the NICMOS count-rate dependent non-linearity recently discovered by Bohlin et al. (2005) and quantified by de Jong et al. (2006) and Bohlin et al. (2006). The routine has been implemented in the python scripting language and is callable from the shell command line and from iraf. The routine corrects NICMOS count-rate images assuming the non-linearity follows a powerlaw behavior. The wavelength dependence of the non-linearity is interpolated between the measured points of de Jong et al. (2006) and Bohlin et al. (2006) if necessary. The count rates in the output images are modified and hence the standard NICMOS calibration zero-points are no longer valid. New calibration zero-points have been derived from standard star images corrected with the routine. The routine was tested on the lamp-on/off data used in de Jong et al. (2006) to measure the non-linearity effect. We apply the correction to the NGC1850 stellar cluster field and the Hubble Ultra Deep Field (HUDF) to show the magnitude offsets expected due to the non-linearity on objects with a range in luminosity and surface brightness.