measure_fwhm

poppy.measure_fwhm(HDUlist_or_filename, ext=0, center=None, plot=False, threshold=0.1)

Improved version of measuring FWHM, without any binning of image data.

Method: Pick out the image pixels which are above some threshold relative to the peak intensity, then fit a Gaussian to those. Infer the FWHM based on the width of the Gaussian.

HDUlist_or_filename : string

what it sounds like.

ext : int

Extension in FITS file

center : tuple of floats

Coordinates (x,y) of PSF center, in pixel units. Default is image center.

threshold : float

Fraction relative to the peak pixel that is used to select the bright peak pixels used in fitting the Gaussian. Default is 0.1, i.e. pixels brighter that 0.1 of the maximum will be included. This is chosen semi-arbitrarily to include most of the peak but exclude the first Airy ring for typical cases.

plot : bool

Display a diagnostic plot.

fwhm : float

FWHM in arcseconds