RealD Inc. late Wednesday said that it had commenced its previously announced secondary offering of more than 7.8 million shares of its common stock by some existing stockholders.

The Los Angeles developer of 3-D movie projection technology, which raised $200 million of its own in a July initial public offering, won’t be getting any proceeds from this sale, it said. The selling stockholders are expected to grant underwriters a 30-day over-allotments option to purchase an additional 1.17 shares if necessary.

The secondary offering, first announced Nov. 23, is being managed by J.P. Morgan Securities LLC, Piper Jaffray & Co., William Blair & Co. L.L.C., Stifel Nicolaus Weisel and BMO Capital Markets Corp.

Shares were down 42 cents, or $1.5 percent, to $28.49 in midday trading on the New York Stock Exchange.