GNU Astronomy Utilities

7.3.1 Invoking Segment

Segment will identify substructure within the detected regions of an input image. Segment’s output labels can be directly used for measurements (for example, with MakeCatalog). The executable name is astsegment with the following general template

$ astsegment [OPTION ...] InputImage.fits

One line examples:

## Segment NoiseChisel's detected regions.
$ astsegment default-noisechisel-output.fits

## Use a hand-input S/N value for keeping true clumps
## (avoid finding the S/N using the undetected regions).
$ astsegment nc-out.fits --clumpsnthresh=10

## Inspect all the segmentation steps after changing a parameter.
$ astsegment input.fits --snquant=0.9 --checksegmentaion

## Use the fixed value of 0.01 for the input's Sky standard deviation
## (in the units of the input), and assume all the pixels are a
## detection (for example, a large structure extending over the whole
## image), and only keep clumps with S/N>10 as true clumps.
$ astsegment in.fits --std=0.01 --detection=all --clumpsnthresh=10

If Segment is to do processing (for example, you do not want to get help, or see the values of each option), at least one input dataset is necessary along with detection and error information, either as separate datasets (per-pixel) or fixed values, see Segment input. Segment shares a large set of common operations with other Gnuastro programs, mainly regarding input/output, general processing steps, and general operating modes. To help in a unified experience between all of Gnuastro’s programs, these common operations have the same names and defined in Common options.

As in all Gnuastro programs, options can also be given to Segment in configuration files. For a thorough description of Gnuastro’s configuration file parsing, please see Configuration files. All of Segment’s options with a short description are also always available on the command-line with the --help option, see Getting help. To inspect the option values without actually running Segment, append your command with --printparams (or -P).

To help in easy navigation between Segment’s options, they are separately discussed in the three sub-sections below: Segment input discusses how you can customize the inputs to Segment. Segmentation options is devoted to options specific to the high-level segmentation process. Finally, in Segment output, we will discuss options that affect Segment’s output.