fitsh- a software package for image processing

In this paper we describe the main features of the software package named fitsh, intended to provide a standalone environment for analysis of data acquired by imaging astronomical detectors. The package both provides utilities for the full pipeline of subsequent related data-processing steps (including image calibration, astrometry, source identification, photometry, differential analysis, low-level arithmetic operations, multiple-image combinations, spatial transformations and interpolations) and aids the interpretation of the (mainly photometric and/or astrometric) results. The package also features a consistent implementation of photometry based on image subtraction, point spread function fitting and aperture photometry and provides easy-to-use interfaces for comparisons and for picking the most suitable method for a particular problem. The set of utilities found in this package is built on top of the commonly used UNIX/POSIX shells (hence the name of the package); therefore, both frequently used and well-documented tools for such environments can be exploited and managing a massive amount of data is rather convenient.