Omnivision Technology shares are off 6.2% to $20.90 and option volume is 3x the daily average. Volume leaders are the Sep $21 & $24 calls which have each traded 2,000 contracts,(largest block was 1,800 lot) in looks like a purchase of the spread. But prior open interest is sufficient to cover and this could closing a bear spread initiated on 8/12 when stock was trading $22.40.