def channel_squeeze(x,
                    channels_per_group):
    """
    Channel squeeze operation.

    Parameters:
    ----------
    x : NDArray
        Input tensor.
    channels_per_group : int
        Number of channels per group.

    Returns:
    -------
    NDArray
        Resulted tensor.
    """
    return x.reshape((0, -4, channels_per_group, -1, -2)).sum(axis=2)