Berg has been working on Janis: Little Girl Blue since 2007.
Letters home give a revealing insight into a complicated woman.
The woman behind the fiery voice has never ceased to fascinate.
Yet since Janis Joplin's tragic death in 1970 at the age of 27, filmmakers have struggled to turn her life into a feature film. Award-winning documentary director Amy Berg was up for the challenge.
The Los Angeles-born 45-year-old had taken on tough subjects before, in 2012's West of Memphis (about the West Memphis Three case, which involved three teenagers jailed for the murder of three boy scouts) and 2006's Oscar-nominated Deliver Us from Evil about child abuse by a Catholic priest.
Berg has been working on Janis: Little Girl Blue since 2007. The key into the singer's life came on the discovery of letters revealing her inner world, the unearthing of previously unseen concert footage and details surrounding the man in her life at the time of her death.
"The movie is the story of who Janis Joplin was and what she was trying to achieve in her short career," Berg explains of a movie she describes as 90 per cent Janis.
"I wanted her to narrate the story so it was useful having interviews and this amazing unseen footage, including her concert at Woodstock, to show her different incarnations. I chose the music based on personal stories that resonate with the music."
The film follows Joplin growing up in conservative Texas, eventually heading to San Francisco, where she dove headlong into city's burgeoning counter-culture and joining her first band, Big Brother and the Holding Company.
"Janis became more herself on stage; it was her way to liberate herself," says Berg. "But she had this sense that she'd betrayed her family, so she kept writing them letters to try to stay connected."
Joplin struggled to find love and the film traces her relationship with David Niehaus, whom she met in Brazil and described to Rolling Stone as "a big bear of a beatnik" .
Niehaus grew tired of Joplin's heroin habit and had taken off to Kathmandu.
"I think David Niehaus was the missed opportunity for her and I think that relationship shows how famous she was and how difficult it is for a female who's that big of a rock star to have a personal life.
"But he was stronger than any of the other men she met and he offered her many things she was looking for at that point."
Alone in a Los Angeles motel following a recording session, Joplin died of a heroin overdose.
Her death made her an early member of the so-called 27 club - rock figures who died at that age.
"You can't blame the industry for her death, because she embraced the industry and she embraced fame," Berg says.
"If anything, I made this film to dispel the myth because I don't like to see Janis locked into cliche of the 27 club, to be remembered as a woman who overdosed on heroin in a hotel room. I wanted to show her as a talented woman and artist.
"Her history and experiences made her this powerful performer. She left a powerful statement for women, as she was basically the first female rock star."
Lowdown
Who: Director Amy Berg What: Janis: Little Girl Blue Where: Screening as part of the Autumn Event at the Civic on April 14 and Academy on April 24.