def feature_extent(sphere, config, nfringes=20):
'''Radius of holographic feature in pixels'''
s = Sphere()
s.a_p = sphere.a_p
s.n_p = sphere.n_p
s.z_p = sphere.z_p
h = LMHologram(coordinates=np.arange(300))
h.instrument.properties = config['instrument']
h.particle = sphere
# roughly estimate radii of zero crossings
b = h.hologram() - 1.
ndx = np.where(np.diff(np.sign(b)))[0] + 1
return float(ndx[nfringes])
from pylorenzmie.theory.Sphere import Sphere
import matplotlib.pyplot as plt
# Create coordinate grid for image
x = np.arange(0, 201)
y = np.arange(0, 201)
xv, yv = np.meshgrid(x, y)
xv = xv.flatten()
yv = yv.flatten()
zv = np.zeros_like(xv)
coordinates = np.stack((xv, yv, zv))
# Place a sphere in the field of view, above the focal plane
particle = Sphere()
particle.r_p = [125, 75, 100]
particle.a_p = 0.5
particle.n_p = 1.45
# Form image with default instrument
instrument = Instrument()
instrument.magnification = 0.135
instrument.wavelength = 0.447
instrument.n_m = 1.335
k = instrument.wavenumber()
# Use Generalized Lorenz-Mie theory to compute field
kernel = CudaGeneralizedLorenzMie(coordinates=coordinates,
particle=particle,
instrument=instrument)
field = kernel.field()
# Compute hologram from field and show it
field *= np.complex64(np.exp(-1.j * k * particle.z_p))
field[0, :] += 1.
hologram = np.sum(np.real(field * np.conj(field)), axis=0)