Sasha Pieterse says she wanted to play a dual role in The Image of You because the film blends familiar storytelling genres, while keeping viewers in suspense.

"I was flipping through the script and liked it and whatever, but I was like, 'I know what's gonna happen here,' and when THAT twist hit and I didn't [know], I loved it."

The Pretty Little Liars and Inherent Vice alum was excited about the project after her initial reading of the screenplay and couldn't stop thinking about it.

"I was in the shower like, 'Oh, I know how I would do that scene...'" she recalled. "I was dreaming about it. It was just one of those things where I felt like I knew exactly what it could be and I wanted to be the one to do it."

Nestor Carbonell and Mira Sorvino play the women's conflicted parents, while Michele Nordin plays Nick's disapproving sister, Rebecca.

"Quite a lot does need to be re-imagined," Parks, an executive producer on the film, said about bringing her original story to the screen.

The ending of the film departs from the one in the book, but Parks doesn't mind seeing plot points change.

"What's intrinsic is the character and, in this case, the 'characters' because they are twins --physically identical, but, in terms of emotions and experiences, very, very different," Parks said.

"Both are really complex. Anna is sweet and wholesome and naive, and we have Zoe who is sexy and crazy, a little bit crazy, and certainly disruptive," she added. "I didn't want to lose that. I wanted that sort of punch that she delivers, and, luckily, we cast Sasha, who could deliver on both of those fronts."

Pieterse's script was covered in post-it notes intended to help her keep the two characters straight.

"I had it all color coordinated," the actress said.

For scenes that showed the twins together, a body double was used with Pieterse's performance digitally added to the film later.

"Once we completed that, we switch over, and I become the different character and she would switch over, as well," Pieterse said.

The fact that the characters' hair, makeup and clothing were so dissimilar was also a huge help.

"I could just sit there and watch the transformation, watch the red lips come on," Pieterse said about her preparation to play Zoe.

"It just felt natural and i never was like, 'OK, who am I?' and, 'What am I?' It just kind of came out. When I turned into Zoe, I was Zoe, and it was very empowering, and a fun contrast," she added. "It's a different perspective of the same scene. You're looking at it completely differently from somebody else's perspective, so I loved it."

Nick almost seems like different men, as well, depending on whom he is with.

"He acted a certain way with Anna, and I think it really worked, and when I became Zoe, I kind of took control," Pieterse said.

"It got that natural reaction," she added.

Some of the scenes they had together were intense and the fact that they had become good friends during production made getting through the darker material easier to navigate.

"Parker's hilarious. We had such a good time on that. We laughed so hard and that's what you need off camera," Pieterse said.

"We have a lot of similarities," she added. "We've both been with our partners for a long time, we're married, we've got kids and I think it just immediately sets the tone."

Parks said the main theme of artifice that runs through her book and movie extends to Nick.

"He isn't able to be his entire self with either one of them and, so, he also has a duality. The entire book is about people's duality," she added. "Even the parents act differently depending on which daughter they are dealing with."