sample.py

#!/usr/bin/env python
# -*- coding: utf-8 -*-


import rospy
from sensor_msgs.msg import Image
from cv_bridge import CvBridge

def callback(msg):
    rospy.loginfo(msg.width)
    try:
        frame = CvBridge().imgmsg_to_cv2(msg, "bgr8")
    except:
        rospy.logerr('error occured')
        
    # 今までのYOLOの処理

def main():
    rospy.init_node('sample')
    sub = rospy.Subscriber('~input`, Image, callback, queue_size=1)
    rospy.spin()


if __name__ == '__main__':
    main()