How many white objects are there in image no.2347915?
white objects refers to ATT_CLASS = 'white'; image no.2347915 refers to IMG_ID = 2347915
SELECT SUM(CASE WHEN T2.ATT_CLASS = 'white' THEN 1 ELSE 0 END) FROM IMG_OBJ_ATT AS T1 INNER JOIN ATT_CLASSES AS T2 ON T1.ATT_CLASS_ID = T2.ATT_CLASS_ID WHERE T1.IMG_ID = 2347915