HISTORIC images of Edinburgh's post-war cultural Renaissance will displayed on the architecture of one of its most famous squares for the music and light show which will open the city's International Festival this year.

Buildings on three sides of St Andrew Square, in the New Town, will be the canvass for Bloom, an immersive "magical digital installation" which will tell the story of the history of the 70 years of the festival and the city's status as the mother of worldwide arts festivals.

The event will take place on two nights, rather than the one originally printed in the EIF programme, and will now take place on August 4 and 5, from 10pm.

Three sides of the famous square, which is not a Fringe venue this year, will be closed for the two hour shows, which will not tell a narrative but display a loop of around 15 minutes of images and music.

Unlike the Harmonium Project in 2015 and Deep Time in 2016, the audience will be able to move around and see different parts of the show at different times - and all entry is free, but ticketed.

Like the first two opening nights of the EIF under director Fergus Linehan, the display has been designed by 59 Productions, and will have music from the award winning composer Nick Powell.

The light show, which can be viewed from any part of the closed roads, or the paths inside the gardens of St Andrew Square, is intended to be seen by the audience as they move around the historic site.

Leo Warner, director of Bloom, said there will be no advised "direction of travel" around the square and the experience will differ depending on when and where you stand.

He said the details of the animations and light projections are only just beginning to be detailed and animated by his team, but he said he thought the show, reflecting the history of the festival and its birth in the post-war period, would be "emotional".

Mr Warner said: "We want to look at the city historically, and give some sense of the desolation of the Second World War, and then how the festival ignited a spark which has grown until this day - I hope its emotional, I hope people will see this sense of a dialogue with this very specific environment, and I hope also it is a lot of fun."

Mr Warner added: "We have 3D mapped the entire square, and will be projecting onto the perimeters and the column [the Melville Monument] and is the most challenging work we have done so far."

The fourth, eastern, side of the square, which includes the tram line, will not be closed for the event.

Bloom will "chart the joyful transformation of Edinburgh, from the darkness and division of the post-war years to the colour and vibrancy of today’s Festival City.

"Bloom draws upon the architectural beauty of the new town, Edinburgh’s rich cultural heritage and the technological innovation for which the city is renowned."

He added: "We faced a challenge in conceiving a new piece befitting the significance of this anniversary year.

"We decided to place audiences inside the event, encompassing them within nearly half a linear kilometre of projection-mapped architecture and bespoke lighting fixtures, and use music, sound and light to tell a story celebrating the 70 year history of the International Festival and the associated Edinburgh festivals, and the immeasurable impact that it has had on the cultural world."

The event, over two nights for the first time, is being sponsored by Standard Life.

Mr Linehan said: "Since 1947 the International Festival has welcomed the world to Edinburgh, creating an electric atmosphere in this city which has radiated back out across the globe.

"That energy has transformed Edinburgh and sparked not only the development of the Festival City we know today, but the creation of countless other festivals around the world.

"We’ll experience that transformative power first-hand in Bloom."

Entrance to the show will be free, but to guarantee access from the 10pm start, a limited amount of tickets will be available from the festival's website from July 3.

Ticket holders will have access to the arena from 9pm.

Non-ticket holders will be admitted from 10.30pm on a first-come, first-served basis.

Professor Dorothy Miell, Vice-Principal and Head of the College of Arts Humanities and Social Sciences at the University of Edinburgh, said: "We are delighted to collaborate once again to create this spectacular opening event.

"Our world-class researchers in digital media, design informatics and biological sciences will assist in shaping this epic artwork, and our archives will help tell the story of how the Festival has inspired a blossoming of creativity within the city and beyond."