The 35-year-old actress admitted that it didn't take much convincing by Testino - who also photographed Prince William and Kate on their wedding day - for her to strip off for the shoot.
Appearing at the El Museo del Barrio gala on Thursday, where she presented the photographer with an award honouring his career, she explained, 'You know that his biggest strength without fail is making women look beautiful.
'When Mario turns to you and says, 'It's beautiful, but I think it?would work better naked, no?' How can one refuse?
'No matter what insecurities about oneself a subject may have, Mario makes them go away like a magician. One moment you are in the hair and makeup chair fully clothed and wishing you had smoother skin, longer legs and smaller feet and then Mario comes in and in that charming way he takes you by the hand and says, 'Don't worry it's going to be amazing.''
Testino agreed that getting Winslet to pose for his Todo o Nada exhibit in Rome was easy.
'I said to her, I want you to pose nude for this exhibition. And she was like, 'Oh, OK, Mario.' She said yes right away.'