PARIS - An intense and controversial restoration of the last great work by Leonardo da Vinci went before the public Thursday at the Louvre Museum, revealing "The Virgin and Child with Saint Anne" in the full panoply of hues and detail painted by the Renaissance master 500 years ago.

The 18-month-long restoration of the painting that Leonardo labored on for 20 years until his death in 1519 will go a long way to raising "Saint Anne" to its place as one of the most influential Florentine paintings of its time and a step toward the high Renaissance of Michelangelo.

The cleaning has endowed the painting portraying the Virgin Mary with her mother Saint Anne and the infant Jesus with new life and luminosity. Dull, faded hues were transformed into vivid browns and lapis lazuli that had visitors awe-struck.

"It's unbelievable, so beautiful. Now you have that same feeling as when you enter Michelangelo's restored Sistine Chapel. Look at the blue!" one visitor, Odile Celier, 66, said Wednesday.

The exhibit brings together some 130 preparatory drawings and studies by Leonardo and his apprentices - something curator Vincent Delieuvin likened to "a police investigation" - tracing the painting's conception and revealing to experts today the entire development over the last 20 years of Leonardo's life.

Almost like detective work, the impressive display of sketch books and mathematical diagrams hold clues not just to unlocking the art behind the painting, but - for the man who was more famous in his day as an engineer - the years of scientific research that defined his work.

"The exhibit is a science workshop," Delieuvin said. "For Leonardo, art is founded on theoretical knowledge of nature and its functioning."

In one carnet spilling with mathematical sketches, we see how over several years he painstakingly studied light refracting from opaque objects. It decodes the technique that made Leonardo famous. The Saint Anne painting is a glowing example clearly seen in the blue opaque mantle with its almost imperceptible play on light and shadow.

The key to the hazy realism of the tree, too, with the subtle contrast of light in its leaves was cracked by infrared used during the restoration. To get this effect, Leonardo first painted the entire tree structure in full and only afterwards painted the foliage on top.

Another notebook astounds in its detailed analysis of water and air compression that shows the thinking that went into creating the sweeping blue and gray mountains rising up behind Saint Anne and child.

Like the novel "The da Vinci Code," the restoration of the master's last work has been accompanied by high-level intrigue worthy of a political thriller.

Seventeen years ago, the Louvre abandoned an attempt to clean the painting amid fears over how the solvents were affecting the sfumato, a painting technique that Leonardo mastered.

After the cleaning was eventually given the green light in 2009, two of France's top art experts - Jean-Pierre Cuzin and Segolene Bergeon Langle - resigned last year from the Louvre advisory committee responsible for the restoration, amid reports they were outraged that restorers were over-cleaning the work to a brightness Leonardo never intended.