Example 4.2 question

In the solution.
if( blob_position > 1000 ):
rospy.loginfo(“TURN RIGHT”)
turn = -1.0
# turn left if we set off the right cliff sensor
if( blob_position < 900 ):
rospy.loginfo(“TURN LEFT”)
turn = 1.0
. Is 1000 and 900 for the center of the image width?

Mine robot keeps turning to much away from the ball. Does anybody know what the problem could be?