Sony is taking a novel approach to marketing its new 4k Ultra HD TV sets: the company is placing microscopic ads on tennis star Anne Keothavong during the Wimbledon tennis championship. The tournament is being filmed in 4k for the first time ever this year and viewers will only be able to fully discern the ads with a 4k Ultra HD television.

On Monday, Sony launched two new flagship 4k Ultra HD sets: the 55X9 BRAVIA and 65X9 BRAVIA. In addition, two of the company's 4k cameras will be used to film the matches at Wimbledon. The "microtising" campaign involves only Keothavong, but Sony stated that it might replicate the ads for future events that are filmed in 4k.

"With more footage being generated in 4k people are going to see every single detail and get much closer to the action," said Paul Gyles, head of marketing for Sony Televisions. "We thought we'd push it to the limit by running a microtising campaign - proving that Sony televisions can pick up on the smallest details."

Keothavong is the fifth-ranked tennis player in the UK and so far, she appears to be having fun with the tiny ads.

"This is a real laugh, I've got a lot of friends and family paying attention to the smallest detail - I've had it on my shoe laces, my index finger and the hem of my skirt, but there are a few hidden places no one has noticed yet," Keothavong said.

4k Ultra HD offers four times the resolution of a conventional HD television. The technology is still very new and consequently very expensive. Sony's new sets, which were just recently unveiled in January at the Consumer Electronics Show, will be priced at around $5,000 for a 55-inch model and $7,000 for the 65-inch version.