In Western countries, outdoor advertising posters and signs are often thought of as visual pollution, cluttering up the streetscape and countryside. But in India, where the spiritual pervades everything, this brand of street art holds a deeper and more complex meaning.

For decades, garishly hand-painted billboards have been a ubiquitous feature of India's urban landscape, advertising everything from hair products to Bollywood hits. Drawing deeply upon religious and mythological sources, they have long embodied a part of the national soul. But today this art form is disappearing – collateral damage in the country's battle for the spoils of globalization.

In Painted Nation, award-winning Toronto filmmaker Cyrus Sundar Singh takes an affectionate look at India's vanishing street art, its gifted creators, and its once-powerful place in the national culture.

As a youngster in Chennai, India, Singh was mesmerized by “the hand-painted landscape” all around him: trucks adorned with colourful gods and goddesses to protect their drivers from mishap; billboards and hoardings whose bold images promoted movies, toothpaste and political parties. Each was a one-of-a-kind work of art.

In this programme, Singh meets some of the great masters of the form, like Balkrishna Vaidya, who has been creating Bollywood movie billboards for more than 50 years, or Aykan, the prolific genius behind the ad campaigns of the filmmaker's youth.

In a country where religion intertwines deeply with politics and culture, it is only natural that commercial art should be informed by spirituality. The father of modern Indian street art was painter Raja Ravi Varma (1848-1906), who brought Western techniques to his “brilliantly gaudy” depictions of scenes from Hindu myth. Varma's images of gods and goddesses have influenced subsequent generations of Indian painters. And Hindu deities have appeared on billboards and posters as frequently as film stars.

As Singh tours present-day India to meet the great street artists, he discovers that their craft is becoming obsolete. With the country of his birth rapidly evolving into an economic superpower, hand-painted signs have given way to digital images imprinted on vinyl posters. Instead of selling soap and shampoo to ordinary folk, billboards now pitch cars, cell phones and other luxury goods for India's burgeoning middle class.

India's street painters are a dying breed. It is inevitable, perhaps, that such a utilitarian art form should become a victim of economic progress. Still, artists like Aykan wonder if Indian culture isn't losing just a little piece of its soul. “How,” he asks, “can you get a god's picture from a computer?”