Source code for ecpi.common.num.extrapolate_image

'''Extrapolate tools
'''

import numpy as np
from scipy.interpolate import interp2d


def extrapolate_edge(image):
    """Extrapolate edges of an image so as to 
    find the image value at the edge of outer pixels.
    
    :param image: image to process of size MxN.
    :type image: array2D(float) 
    :return: image of size (M+2)x(N+2). 
    :rtype: array2D(float)
    """
    # interpolate original image.
    x = np.linspace(0, image.shape[0] - 1, image.shape[0])
    y = np.linspace(0, image.shape[1] - 1, image.shape[1])
    f = interp2d(x, y, image.T, kind='cubic')
    
    # create extrapolated image.
    x_new = np.linspace(-1, image.shape[0], image.shape[0] + 2)
    y_new = np.linspace(-1, image.shape[1], image.shape[1] + 2)
    img_new = f(x_new, y_new)
    return img_new.T