Instead, the moment you walk in you're hit with bright orange and blue walls, text, arrows and of course portraits, 100 from the gallery's collection showing everyone from Barry Humphries to Megan Gale partially unclothed.

Bare: Degrees of Undress is meant to be fun and it's hard not to smile while wandering around a show that deliberately puts a shirtless portrait of soccer star Harry Kewell next to a naked photo of art collector David Walsh.

The show brings together every piece from the gallery's collection, and one loan piece, with an element of bareness.

It means that some sitters are completely naked and exposed and others are totally clothed with only a shoulder or bare legs on display.

The gallery's director Angus Trumble believes the new show will appeal to everybody, after all we all have to take our clothes off at some point.

"It's something we live with, it's so fundamental to human life," he said.

"Even just the visibility of parts of the body that are normally unclad like hands and faces we process rather differently from feet and shoulders and the lower back.

"Everything in the show really delves into that question of what kind of clothing nakedness provides, is it an alluring thing or is it a vulnerability, a performance, a private thing that we're permitted to view discreetly or not?"

For those expecting to see lots of naked celebrities you might be disappointed.

Trumble admits the audience might be surprised by how clothed some of the portraits are, but as the title suggests the exhibition is about "degrees" of bareness and the narrative behind the decision to expose or not expose the body.

"It's one of the most ambitious shows to be constituted completely from within the collection, the rigour of the thinking behind it is testimony to the versatility of the collection," he said.

Earlier in the year it was the audience who was invited to bare all to experience the James Turrell retrospective in the nude at the National Gallery, but Trumble said despite the subject matter there were no plans for "audience participation" in the portrait gallery's show, for one thing it's the wrong season.

"At the present moment you need to rug up to see Bare," he said.

Curator Penny Grist said the show will be a rich experience for everyone from art history students to families - especially with the online game allowing the audience to find out their nude alter ego from art history.

She worked with Tim Moore to design the show with its distinctive colourful setting.

"What we were aiming for is an exhibition where you can visually understand why we were placing these works together and read the yellow meta-text to get the fundamental context behind it," she said.

"The fundamental concept as well as the interpretation comes through in every aspect of the design."

Bare is on at the portrait gallery until November 15, entry is free.