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Renée Zellweger knows what it's like to be a public target. At 50, she's lived half her life in the spotlight, weathering tabloid stories about her weight, plastic surgery and high-­profile relationships (Jim Carrey, Kenny Chesney).

So when it came to playing Judy Garland — whose struggle with substance abuse, financial troubles and custody battles were all grist for the mill — little surprised the actress. She wasn't even shocked to learn that in the last years of Garland's life, British audiences pelted her with bread rolls when they were displeased with her performance.

"It wasn't shocking because I've never known any different," Zellweger said. "It might have been a little less direct then than it can be today, where you will be unapologetically asked about the nature or health of your personal, intimate relationships and the private choices you make."

In director Rupert Goold's "Judy," which opens Sept. 27, Zellweger plays Garland in the final months of her life.

It's 1968, and the "Wizard of Oz" star at 46 is no longer America's sweetheart. Millions of dollars in debt, she's in London, the only place she can find a paying gig. Away from her children, she's drinking heavily and popping the pills that Hollywood studios forced on her during her adolescence. She turns up late or out-of-tune during her sold-out run at the cabaret club Talk of the Town, inviting scorn from critics and ticket holders. (Garland died in June 1969.)

In writing the screenplay, based on playwright Peter Quilter's 2005 musical "End of the Rainbow," Tom Edge ("The Crown," "Lovesick") did not reach out to Garland's family.

Edge said that because Garland's younger daughter Lorna Luft had written a memoir, 1998's "Me and My Shadows," he felt "a little distance" from the children would prove useful in remaining neutral. Older daughter Liza Minnelli recently said, "I do not approve nor sanction the upcoming film about Judy Garland in any way."

Zellweger, however, said she felt torn about speaking to Garland's kids.

"I wanted to reach out not to ask questions, except to maybe ask what they would like or hope to see," she said.

"I figured that whatever was for public consumption, they had already shared at this point. I could find that. I wouldn't dream of calling and asking, 'Hey, what else can you share here? Because that'd be so helpful.' To me, what they haven't shared is treasure and that belongs to them, and that's where it should stay."

The actress tried to connect with Minnelli through a mutual friend but wasn't successful. Luft was diagnosed with a brain tumor just as filming began.

"That was a time for her and her family, not for a stranger to approach her about things that ultimately don't matter, right?" Zellweger said. Instead, she dug into publicly available material, watching old films, listening to concert recordings and reading numerous Garland biographies, some written by those who claimed to be close to her, including her last husband, Mickey Deans.

"Every night, there was something new to go to sleep with, reading and watching to make sure there wasn't a tiny little gemstone hidden in the mix," she said. "But considering the source was a challenge — trying to understand the truth or the depth of the relationship. Having had some experience with that myself, maybe I knew to sniff it out and be skeptical about 'firsthand accounts.' Everybody has a bad day and can be misunderstood."

Goold said he liked the idea of Zellweger as Garland because he thought she could channel Garland's warmer side. But he also didn't want the "Bridget Jones" star to do a note-for-note impression.

"That's what people do on cruise ships," Goold said.

Zellweger has sung in films before, most memorably as Roxie Hart in the 2002 adaptation of "Chicago." But she said she was scared when Goold requested that she belt out Garland's classics on set instead of recording them in a studio before filming.

"There was freedom in knowing [she had] nights where there were misses and compromise and inability to access her full instrument," Zellweger acknowledged, referring to the decline in Garland's vocal abilities. "Having that in the back of my mind was liberating. I could just be. It also brought a little bit of truth to the experience, because from my understanding, she was afraid that she would not perform at the level to which people had expected from her, and she experienced stage fright. So the mix made it very real and true."

Unlike in the play, Edge said, he included a glimpse of Garland's adolescence in the film to give audiences a sense of what she overcame. MGM studio head Louis B. Mayer referred to her as his "little hunchback," and Garland revealed later in life that he touched her inappropriately.

"I think she certainly felt like the way that she was treated in those studio days was at least partly responsible for the things she struggled with later in life," Goold said. "The pity of it is that this terrifically funny and talented and charismatic kid ended up on the other side of that system carrying so much damage. Yet at the same time, she endured and found her way back to her audience."