Sony Corp's Sony Pictures on Thursday became the sixth major studio to support a theater-chain upgrade to digitally convert 20,000 U.S. and Canadian cinema screens, at an estimated cost of more than $1 billion.

Other studios announced in October they would back a theater-upgrade program with the Digital Cinema Implementation Partners (DCIP), a group of theater chains comprising Regal Entertainment Group, Cinemark Holdings Inc and AMC Entertainment Inc.

The other studios include Walt Disney Co, Viacom Inc Paramount Pictures, News Corp's Twentieth Century Fox, General Electric Co's Universal Pictures and Lions Gate Entertainment.

In October, the DCIP estimated it could complete the conversion within 3 to 3-1/2 years of a start date in early 2009, although some of the conversions have gotten pushed back due to the credit crisis.

Once outfitted with digital projectors, theaters can then be modified to show 3-D films.

Hollywood studios are investing heavily in 3-D on expectations these films will draw bigger audiences at premium ticket prices.

(Reporting by Susan Zeidler; Editing by Gary Hill)