Spectral Extraction Quick Start

Specreduce provides flexible functionality for extracting a 1D spectrum from a 2D spectral image, including steps for determining the trace of a spectrum, background subtraction, and extraction.

Tracing

The specreduce.tracing module defines the trace of a spectrum on the 2D image. These traces can either be determined semi-automatically or manually, and are provided as the inputs for the remaining steps of the extraction process. Supported trace types include:

• ArrayTrace

• FlatTrace

• FitTrace

Each of these trace classes takes the 2D spectral image as input, as well as additional information needed to define or determine the trace (see the API docs above for required parameters for each of the available trace classes):

trace = specreduce.tracing.FlatTrace(image, 15)

Background

The specreduce.background module generates and subtracts a background image from the input 2D spectral image. The Background object is defined by one or more windows, and can be generated with:

• Background

• Background.one_sided

• Background.two_sided

The center of the window can either be passed as a float/integer or as a trace:

bg = specreduce.tracing.Background.one_sided(image, trace, separation=5, width=2)

or, equivalently:

bg = specreduce.tracing.Background.one_sided(image, 15, separation=5, width=2)

The background image can be accessed via bkg_image and the background-subtracted image via sub_image (or image - bg).

The background and trace steps can be done iteratively, to refine an automated trace using the background-subtracted image as input.

Extraction

The specreduce.extract module extracts a 1D spectrum from an input 2D spectrum (likely a background-extracted spectrum from the previous step) and a defined window, using one of the implemented methods:

• BoxcarExtract

• HorneExtract

Each of these takes the input image and trace as inputs (see the API above for other required and optional parameters):

extract = specreduce.extract.BoxcarExtract(image-bg, trace, width=3)
spectrum = extract.spectrum

The returned extract object contains all the set options. The extracted 1D spectrum can be accessed via the spectrum property or by calling the extract object (which also allows temporarily overriding any values):

spectrum2 = extract(width=6)

Example Workflow

This will produce a 1D spectrum, with flux in units of the 2D spectrum. The wavelength units will be pixels. Wavelength and flux calibration steps are not included here.

Putting all these steps together, a simple extraction process might look something like:

from specreduce.trace import FlatTrace
from specreduce.background import Background
from specreduce.extract import BoxcarExtract

trace = FlatTrace(image, 15)
bg = Background.two_sided(image, trace, separation=5, width=2)
extract = BoxcarExtract(image-bg, trace, width=3)
spectrum = extract.spectrum