3.1.13. findStripes
Locate and fit stripes in flat field spectrum.
Starting in the central column, the algorithm identifies peaks and
traces each stripe to the edge of the detector by following the
brightest pixels along each order. It then fits a polynomial to each
stripe. To improve algorithm stability, the image is first median
filtered and then smoothed with a gaussian. It not only eliminates
noise, but also ensures that the cross-section profile of the flat
becomes peaked in the middle, which helps to identify the center of
each stripe. Choose gauss_filter_sigma accordingly. To avoid
false positives, only peaks above a certain (relative) intensity
threshold are used.
3.1.13.1. Parameters
- adinputslist of
AstroData MX flat frames. Each frame is either a DFFFD flat, an FDDDF flat, or a combined FFFFF flat.
- suffixstr
Suffix to be added to output files.
- deg_polynomialint
Degree of the polynomial fit to each stripe.
- med_filterint
Median filter window size applied before peak detection.
- gauss_filter_sigmafloat
Sigma of the gaussian filter used to smooth the image before peak detection.
- min_peakfloat
Minimum peak height, relative to the frame maximum, for a stripe to be accepted.
3.1.13.2. Returns
- list of
AstroData The input frame with the following extension added:
STRIPES_LOC: per-fiber polynomial coefficients tracing each stripe. This extension temporarily holds the fits-unsavable fiber information before it is utilized and then removed.
3.1.13.3. Parameter defaults and options
suffix '' Filename suffix
deg_polynomial 5 Degree of polynomial fit
med_filter 1 Median filter parameter
gauss_filter_sigma 3.5 Gaussian filter sigma
min_peak 0.008 Minimum relative peak height
3.1.13.4. Algorithm
Todo
add description
3.1.13.5. Issues and Limitations
Todo
add description