Suman Moitra, who has directed Hindi docu-feature "Bestseller", said the film focuses on Asia's largest red light district Sonagachhi in Kolkata and talks about the life of its inmates.
The film was shot real time in its dingy lanes and bylanes for over two months.
Moitra, who assisted Vishal Bharadwaj in "Omkara" said, "Bestseller" is made in the thriller format. It is based on the fictional life of a kothi malkin in the red light area and her writer sister who too is forced to join the flesh trade.
"Bestseller" was released in 1,000 theatres across country on February 26, Moitra said adding it will now visit the world festival circuits.
"'Bestseller' brings out in the open the dark underbelly of the city. It was a challenge to capture the body language, ambience and expletive-filled dialect spoken by the people in that belt," Moitra told PTI.
The director himself made a recce of the place, talked to sex workers before shooting the film for over two months in the area.
"One of our crew members who had lived for a considerable time in those areas helped a lot during and before outdoor shoots," he said.
Actor Wry Mukherjee, who essayed the role of the owner of the brothel where all the action takes place, said she had interacted with the sex workers for days. "I found they were not just women soliciting customers on the street but also mothers, wives and home makers in other times of day.
"I think these ladies are the most courageous human beings in the world. We, the normal people have less than five per cent of such courage," she said.
Moitra said the cast and crew of the film spent days in the red-light area to perfect their mannerisms.
The crew also got help from NGO 'Durbar Mahila Samanwaya Committee' which is a forum for the thousands of sex workers of Sonagachhi and works for them.