def grid_distortion(img, num_steps=10, xsteps=[], ysteps=[], interpolation=cv2.INTER_LINEAR,
                    border_mode=cv2.BORDER_REFLECT_101, value=None):
    """
    Reference:
        http://pythology.blogspot.sg/2014/03/interpolation-on-regular-distorted-grid.html
    """
    height, width = img.shape[:2]

    x_step = width // num_steps
    xx = np.zeros(width, np.float32)
    prev = 0
    for idx, x in enumerate(range(0, width, x_step)):
        start = x
        end = x + x_step
        if end > width:
            end = width
            cur = width
        else:
            cur = prev + x_step * xsteps[idx]

        xx[start:end] = np.linspace(prev, cur, end - start)
        prev = cur

    y_step = height // num_steps
    yy = np.zeros(height, np.float32)
    prev = 0
    for idx, y in enumerate(range(0, height, y_step)):
        start = y
        end = y + y_step
        if end > height:
            end = height
            cur = height
        else:
            cur = prev + y_step * ysteps[idx]

        yy[start:end] = np.linspace(prev, cur, end - start)
        prev = cur

    map_x, map_y = np.meshgrid(xx, yy)
    map_x = map_x.astype(np.float32)
    map_y = map_y.astype(np.float32)
    img = cv2.remap(img, map_x, map_y, interpolation=interpolation, borderMode=border_mode, borderValue=value)
    return img