def get_op_bbox(frame):
    """
    Arguments: 
        frame: dictionary of joint indices to normalized coords [x, y, conf]. ie {0: [.5, .5, .98]}
    Returns:
        4 normalized bounding box coordinates x1, x2, y1, y2
    """
    x1 = 1
    x2 = 0
    y1 = 1
    y2 = 0
    for key in frame:
        joint = frame[key]
        if len(joint) != 0:
            if (joint[0] != 0):
                x1 = min(x1, joint[0])
                x2 = max(x2, joint[0])
            if (joint[1] != 0):
                y1 = min(y1, joint[1])
                y2 = max(y2, joint[1])
        
    return x1, x2, y1, y2