import cv2


def bgr_to_yuv420(bgr_img):
    # Step 1: Convert BGR to YUV 4:4:4
    yuv_img = cv2.cvtColor(bgr_img, cv2.COLOR_BGR2YUV)

    # Step 2: Extract Y, U, V channels
    Y, U, V = cv2.split(yuv_img)

    # Step 3: Downsample U and V channels (Subsample by a factor of 2)
    U_downsampled = cv2.resize(U, (U.shape[1] // 2, U.shape[0] // 2), interpolation=cv2.INTER_LINEAR)
    V_downsampled = cv2.resize(V, (V.shape[1] // 2, V.shape[0] // 2), interpolation=cv2.INTER_LINEAR)

    # Step 4: Combine Y, U_downsampled, V_downsampled to get YUV 4:2:0 format
    return Y, U_downsampled, V_downsampled