Extracts sources from astronomical images.


EXTRACTOR is a program for detecting and measuring the properties of all the sources on an astronomical image. It offers a large range of configuration options for controlling the way that objects are detected and the measurements that are made of them.

The source measurements are written to a catalogue (which can be of several different formats), so that they can be analysed (possibly by a catalogue handling package like CURSA – SUN/190).

EXTRACTOR, is based on the SExtractor program which is described in the SExtractor’s User Guide (MUD/165). Consult this about all the various options that are available and for the rationale behind the program.


extract image config [keywords] [name] [value]


The name of the image which contains the objects you wanted detected and parameterised. If you have initialised the CONVERT package (see SUN/55) then you may process foreign formats, such as FITS and IRAF.

Using this parameter you may give two image files. The first image will be used for detection and parameterising and the second will be used to actually measure the data values. Using this method allows you to measure the same objects many images, or to use a high signal to noise image to determine the measurement regions on a low signal to noise image


The name of the file that contains the many program parameters (things like the threshold for object detection). This is initially a file named default.sex that can be found in the directory $EXTRACTOR_DIR/config. To modify the parameters used by this program, you must take a copy of this file and edit it. Guidance about the values that parameters can take may be found in this file as well as in the associated SExtractor documentation (see MUD/165).

The measurements made are determined by a list of parameters in the file
$EXTRACTOR_DIR/config/default.param. Again if you want measurements that are not available by default, you must take a copy of this file and edit it. Remember to also change default.sex to use this file (otherwise you will continue to use the system-wide defaults).

One off modifications of parameters can be made using the KEYWORDS, NAME and VALUE parameters.


Whether you want to enter a series of parameter names and values interactively. If TRUE then the parameters NAME and VALUE are used to cyclically prompt for program parameters and the values you want to use. To end the cycle respond with a null symbol (!)


The name of a preferences parameter that you want to set interactively. Respond with ! when you have no more to enter. [!]
The value of the parameter you have just specified using the NAME prompt. [!]