记录numpy下制作圆形或扇形mask-20201110

记录numpy下制作圆形或扇形mask
Mask a circular sector in a numpy array

import numpy as np
def sector_mask(shape,centre,radius,angle_range):
    """
    Return a boolean mask for a circular sector. The start/stop angles in  
    `angle_range` should be given in clockwise order.
    """
    x,y = np.ogrid[:shape[0],:shape[1]]
    cx,cy = centre
    tmin,tmax = np.deg2rad(angle_range)
    # ensure stop angle > start angle
    if tmax < tmin:
            tmax += 2*np.pi
    # convert cartesian --> polar coordinates
    r2 = (x-cx)*(x-cx) + (y-cy)*(y-cy)
    theta = np.arctan2(x-cx,y-cy) - tmin
    # wrap angles between 0 and 2*pi
    theta %= (2*np.pi)
    # circular mask
    circmask = r2 <= radius*radius
    # angular mask
    anglemask = theta <= (tmax-tmin)
    return circmask*anglemask
    
from matplotlib import pyplot as pp
from scipy.misc import lena

matrix = lena()  # np.ones(500,500)
mask = sector_mask(matrix.shape,(200,100),300,(0,50))
matrix[~mask] = 0
pp.imshow(matrix)
pp.show()