Question: Calculate the ratio of the total number of images with an object class of "man" and "person".
SQL: SELECT CAST(COUNT(CASE WHEN T2.OBJ_CLASS = 'man' THEN 1 ELSE 0 END) AS REAL) / COUNT(CASE WHEN T2.OBJ_CLASS = 'person' THEN 1 ELSE 0 END) FROM IMG_OBJ AS T1 INNER JOIN OBJ_CLASSES AS T2 ON T1.OBJ_CLASS_ID = T2.OBJ_CLASS_ID