One look at a panoramic cityscape is all it takes for the image to be etched in British artist Stephen Wiltshire's memory for the rest of his life.
More astounding is the fact that the 40-year-old savant, who is autistic, can draw a city he has seen right down to the finest detail even 20 years after a single visit.
His sister Annette, 42, says: "Once he has absorbed the view and memorised it, that's it - he's got it forever."
Diagnosed with autism when he was three - he could not speak fully till he was nine - the artist is internationally renowned for his amazing ability to draw detailed cityscapes from memory after viewing them just once.
His talent has allowed him to travel the world and sketch the skylines of major cities such as London, New York, Shanghai, Tokyo and Hong Kong.
He is in Singapore for the first time to draw its cityscape at the event See The Big Picture, as part of Singapore Press Holdings' 30th anniversary celebrations.
Since Wednesday, he has been drawing an aerial view of the city on a 4m-by-1m canvas from 10am to 5pm every day, in full public view, at the main atrium of Paragon shopping centre.
Before beginning his sketch, he was taken on an hour-long helicopter ride on Tuesday to view Singapore's skyline.
He will be at Paragon until tomorrow, which is when he is slated to complete the artwork. It will be presented to President Tony Tan Keng Yam in September as a gift to Singapore for its 50th birthday next year.
When Life! visited Paragon on Wednesday at noon, the black benches in front of the stage were packed with people, while others stood around watching him draw. Despite the large turnout, the artist was unfazed.
Sitting on a high chair and plugged into music from his iPhone, he appeared to be in a world of his own as he slowly but steadily sketched out areas of Singapore's landscape for seven hours straight, save for an hour's break at 1.30pm daily.
Wiltshire, who tends to speak slowly, was in good spirits. "It is a pleasure drawing in front of an audience and not at all stressful. I always listen to music when I draw because it makes me feel good and allows me to concentrate," he says.
He enjoys listening to a wide range of tunes, including rock 'n' roll, Motown, funk, soul, rhythm, blues and pop.
He adds: "The cityscape was so beautiful and nice. But Singapore is sometimes difficult to draw, like the details of the residential areas."
By 5pm yesterday, he had completed two-thirds of the drawing.
Dealing with her brother's autism during a time when the condition was almost unheard of was difficult, says Ms Wiltshire. This was especially so as their father, an electrician had died in a motorbike accident in 1976, a year before he was diagnosed.
She says: "Autism in the 1970s was a taboo subject and a lot of parents who had autistic children were embarrassed. There were no books or schooling on how to go about handling it so we just did the best we could."
It was her mother who kept the family together. She raised them on her own and Ms Wiltshire vaguely recalls her taking on a part-time job in the evenings to support them.
"After my father died, my mum had two choices - either to give up or be strong and bring us up in the best way possible. She made us independent."
Their mother Geneva, 68, has retired and now lives with her son in London.
Understandably, the two siblings share a close bond. Ms Wiltshire accompanies her brother on all his travels. She manages his artistic affairs, such as running his art gallery in London and organising commissions and exhibitions.
She is also a jewellery designer who produces modern Art Deco pieces in her free time. She lives with her husband, a 37-year-old software programmer, in London. They have no children.
"My mother said to us that people and friends would come and go, but no matter what happens, we would always have one another. I've stuck to that to this day."
With his impressive gallery of intricate panoramic commissions and originals of his work fetching thousands of pounds each, Wiltshire has certainly come a long way.
Born in London in 1974, he attended Queensmill School, a special school for autistic children, when he was five. It was there that he uncovered his talent.
The bachelor says: "I would use crayons, pencils and felt-tip pens to draw animals, cars, London transport buses and landmarks such as the Big Ben and Tower Bridge."
After winning several children's art competitions, he sold his first drawing of Salisbury Cathedral at age eight to former British prime minister Edward Heath.
He came to wider public attention in 1987 after an appearance in a BBC programme called The Foolish Wise Ones, on autistic savants, which led to him being referred to as "the best child artist in Britain" by the late Hugh Casson, a former president of London's Royal Academy of Arts.
In 2005, he was commissioned by organisations and individuals to undertake panoramic drawings of 10 world cities, starting with a 10m-long canvas of the Tokyo skyline, all sketched from memory.
With art having changed his life remarkably, it is no surprise that Wiltshire wants to keep doing it for as long as he lives.
"Drawing makes me feel good and excited. I want to keep doing the best I can and never stop," he says, adding that he would love to visit the cities of Montreal, Dallas, Houston and Boston for his next projects.
He says the most difficult drawing he has completed so far is of the city of Jerusalem in Israel.
"There was a lot of information and residential places to remember. I could not understand many of the names and areas because they were all in Hebrew."
He is well aware that his is no ordinary gift.
Asked to name the most important person in his life, he declares matter-of-factly: "Me, I am the most important person. I'm a genius."
His sister says: "I think he's become much more confident because he is truly in his element. The main thing is that he enjoys what he is doing and gets to travel to places he only ever dreamt of before."
She adds: "There used to be doubts over his future, but I guess he's the one having the last laugh now."