get_up_mask.py

import numpy as np


def get_up_mask(height: int, width: int) -> np.ndarray:
    """
    Get the mask corresponding to the projection of the UP cubeface
    on the equirectangular image
    """
    mask = np.zeros((height, width // 4), bool)
    
    # Get the mask above a single cubeface
    theta = sample_pixels(-np.pi/4, np.pi/4, width // 4)
    phi = -np.arctan(np.cos(theta))
    phi_idx = ((phi/np.pi + 0.5) * height).astype(int)
    for i, j in enumerate(phi_idx):
        mask[:j, i] = True
    
    # Repeat 4 times and roll by a half-cubeface
    up_mask = np.tile(mask, 4)
    return np.roll(up_mask, width // 8, axis=1)