CCDPACK Overview

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CCD data reduction

CCDPACK is a package of programs for reducing images taken by CCD-like detectors.

Users of CCDPACK see the package as:

  1. A complete set of basic tools that can be controlled from the command line or from scripts.
  2. An easy to use X windows interface for controlling automated reductions.

The X windows interface is designed to help those with little, or no, knowledge of the package or CCD reduction, to start working effectively as quickly as possible. It concentrates on the organisation and categorisation of data, rather than the ins and outs of how and when to run the individual programs, any necessary processing steps are deduced and executed automatically.

The more basic command-line programs cover:

  1. Bias estimation and removal.
  2. Dark counts and pre-flash correction.
  3. Flatfield calibration and correction.
  4. Image registration.
  5. Image resampling.
  6. Image combination and normalization.

Supporting facilities are also provided for controlling such things as the automation of stages 1, 2 and 3.

All the basic CCDPACK programs are designed for processing large quantities of data and consequently process whole lists of images and record their progress using a integral logging system. They also allow: defect information to be stored very concisely as text descriptions, the generation and subsequent propagation of data errors and can use many different image combination methods (mean, median etc.).

The registration of many images with different scale factors and orientations can be performed at once. More commonly if the images have the same scale and orientation, but have different origins, then they can be registered either "automatically" or graphically with a minimum of effort.

The main window of the CCDPACK GUI. Note that the "Help" menu has been pulled down. "On Context" tells you how to get help on any part of the window. "On Window" describes this window in overview. "On CCDPACK" access the main CCDPACK document.

Another snapshot of the CCDPACK GUI. This window allows the selection of a known CCD camera. If the images where taken on the WHT after 1994, then they can be reduced automatically. All that is necessary is to identify the data files (this is done in a separate window).

If the CCD used isn't already known to CCDPACK, then it is necessary to supply some information about it. The most important parameters are the extents of the light-sensitive area and the bias strips. If these are not known, then help is at hand -- in this window the image can be panned and zoomed and any of the required regions identified by dragging the mouse over them.

This picture shows the result of "automatically" aligning eight images that have different origins. The marked stars have been detected and identified across all the images "automatically". The registering transformations derived from the knowledge of which star is which on each frame have then been used to resample the images so that they are aligned. The images have then been combined into a single "mosaic". The mosaic is not "flat" because of exposure and sky brightness variations.

This picture is the same data as shown before, except that it has now been "normalized", correcting for any changes in exposure and sky brightness (any visible variations are now due to noise changes due to the different number and quality of images present at each point).

CCDPACK is documented in the "Starlink User Note No. 139". This is available on the WWW at:

Hardcopy can also be obtained from this document.


Questions or comments to:

Copyright © 2005 Central Laboratory of the Research Councils
Copyright © 2006 Particle Physics and Astronomy Research Council
Copyright © 2008-2009 Science and Technlogy Facilities Council
Copyright © 2009-2013 Peter W. Draper
Last modified: 02-Jun-2016
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