The top grosser of the year is about to become the top homevideo seller of the year. During its first week of release, “The Dark Knight” sold more than13.5 million discs across all retail channels worldwide, and set impressive standards for the next-gen Blu-ray format.According to Warners, “The Dark Knight” sold more than 1.7 million Blu-ray discs worldwide its first week. Although comparisons are tricky given the elusiveness of worldwide sales data, “The Dark Knight” is now considered the undisputed Blu-ray champ, given the strong bow. The studio also projects that “The Dark Knight” will become the bestselling 2008 title overall this week. Consumers have bought more than 10 million copies of the pic, with the remainder of purchases by rental outlets. Warners released “The Dark Knight” in six territories last week — U.S., Canada, U.K., Japan, Benelux and Australia — and included purchases from all those regions in its worldwide tallies. The homevid bow of “The Dark Knight” has been closely watched due to concerns over how the economy would affect DVD and Blu-ray purchases. With the homevid biz running behind last year, there has been added pressure on big releases this holiday season to hit their marks. Last week, Warners said U.S. consumers bought 3 million copies of “The Dark Knight” on Dec. 9, its first day in stores, with another 2.5 million believed to go into U.S. rental stores.