Novak Djokovic and Serena Williams were honored Tuesday as the International Tennis Federation's world champions for 2012.Djokovic won the men's award for the second straight year, while Williams took the honor for the third time in her career.Djokovic won the Australian Open and was runner-up at the French Open and U.S. Open. He finished the season No. 1 in the ATP rankings with six tour titles.Williams won Wimbledon, the U.S. Open and the Olympic gold medal. She had a tour-best 58-4 record and seven titles.American twins Bob and Mike Bryan were named men's doubles world champions for the ninth time in 10 years, while Sara Errani and Roberta Vinci of Italy took the women's doubles award.Filip Peliwo of Canada and Taylor Townsend of the U.S. were named junior world champions.Esther Vergeer of Netherlands won the women's wheelchair tennis award for the 13th consecutive year. Stephane Houde of France was named the men's winner.