A 16 billion pixel image of Leonardo da Vinci's Last Supper has been posted on the internet, allowing art lovers close up details of the 15th Century work.

The image is 1,600 times stronger than those taken with a typical 10 million pixel digital camera.

Experts will be able to see segments as though just centimetres away and examine details otherwise unavailable.

The posting comes amid claims a new system aimed at protecting the piece from Milan's pollution is not working.

The work is displayed in the Italian city's Church of Santa Maria delle Grazie.

Peeled off

Art curator Alberto Artioli told Associated Press news agency the new internet resolution avoided the graininess when zooming in to regular photographs.

It is visible at www.haltadefinizione.com.

"You can see how Leonardo made the cups transparent, something you can't ordinarily see," he said. "You can also note the state of degradation the painting is in."

That degradation has been the subject of controversy this week.

An Italian newspaper, Corriere della Sera, reported that a sophisticated monitoring and filtration system introduced during a restoration of the chapel in the late 1990s was not preventing particles or substances that could damage the work being brought in by visitors.

The Last Supper was painted by Leonardo da Vinci at the end of the 15th Century and, because of the experimental techniques he used, parts of the masterpiece subsequently peeled off and were badly damaged.

The BBC's Frances Kennedy says the paper reported that equipment monitoring air quality inside the refectory showed that levels of fine particle pollution had tripled in the past two years.

It quoted experts suggesting these particles could settle on the work, eventually creating a dark misty layer.

However, Milan's cultural commissioner said the threat was non-existent.

More than 350,000 people visit the painting each year.