On July 26, Warner Bros. Animation will release a film adaptation of what is perhaps the most famous—and infamous—Batman graphic novel of all time: Alan Moore and Brian Bolland’s bestselling The Killing Joke. The subject of a 2015 cover controversy, the graphic novel follows Batman as he attempts to catch the Joker after a series of crimes against police commissioner Jim Gordon and his family, including notoriously shooting and paralyzing the original Batgirl, Barbara Gordon.

Publishers Weekly talked with animator, writer, and artist Bruce Timm—one of the showrunners of Batman: The Animated Series and co-director and co-producer of The Killing Joke—in advance of the film’s Friday screening at San Diego Comic-Con to discuss adapting a classic story, trying to animate a master comics artist’s style, and more.

What was it like to adapt The Killing Joke—a classic batman graphic novel known for its controversial and disturbing plot—to screen?

Having been down this road before [when adapting Batman: Year One for film], I’m not too terribly worried about it, but at the same time, we just want to do an honest adaptation of it. At the other end of it, though, is the fact that this is a comic that is obviously very disturbing. Honestly, myself, I was always kind of freaked out about it, even back in the day when I first read it. So adapting it always kind of terrified me on one level—it’s a pretty extreme subject matter, so do we somehow try to tone it down to make it a little more “palatable,” or do we just do it the way it is? And [the latter] is what we ended up doing. Even though there are story elements that have always bothered me, we made the decision kind of early on that we weren’t going to try to put our own spin on it, and basically, being the classic that it is, we needed to stay true to the source material.

There’s a prologue to the film that gives Barbara Gordon a new story and provides context for what her character endures at the hands of the Joker. Why did you decide to include it?

One of the things that always kind of disturbed me [about the graphic novel] on a kind of visceral, unconscious level was that years before people coined the term, “women in refrigerators,” I was very much aware that Barbara was a plot device in the story. She wasn’t a genuine human being. She was there to be maimed by the Joker to, you know, enrage Batman and drive Commissioner Gordon insane, and the last time we see her in the comic, she is basically a victim. She was crippled and in the hospital and that’s it! And so I thought, OK, well, if we have all of this extra story time to mess around with, instead of just expanding The Killing Joke story by inserting a bunch of different sequences in among the existing comic sequences, why don’t we do an entire prologue that is basically all about Barbara.

This is part original work and part adaptation. Did you find that your creative process for different parts of it were different because one was an adaptation and one was your own work based on another work?

Definitely. On one hand, The Killing Joke part of it kind of took care of itself. That’s the beauty of doing an adaptation—you have a template to work from. You can tweak, but especially with a comic that is as perfectly drawn as this one, half of the work is done for you. Instead of asking, “OK, there’s this story B where such and such happens, what’s the best way to visualize that,” all you’ve got to do is look at the comic, and if it ain’t broke, don’t fix it. Whereas, in the prologue that’s all new, and it’s going to be a prologue to one of the most famous Batman stories of all time, and we thought, we’re going to have to make sure that this is as good as we can make it because it’s going to share screen time with The Killing Joke.

You’ve worked in film for a while, but you’ve also worked in comics. Do you have a different strategy for how you write for each?

The biggest change I always think of is that in a comic, you can stare at each individual image for as long as you’d like. The editor is not going to move you along. You could just sit there and stare at each drawing so that each drawing is as good as it can be on its own. But at the same time, it still has to link up to the whole. It still has to flow, and the rhythm of it has to do its storytelling thing, without an orchestra backing it up or a really good actor reading the lines.

The Killing Joke author Alan Moore has had some less-than-favorable responses to a number of the film adaptations of his work. Are you at all worried about his response?

No. Because on one hand, a lot of the adaptations of his stuff has been really bad. He’s got deeper issues going on with DC Comics in general, going back many, many years, and we’ve been quite public about that. In some interviews, he says he never watches the movies based on his stuff. The fact that it got made at all just bothers him, so I’m not worried that he’s going to see the movie and dislike it or like it. He may never comment on it one way or the other, and that’s fine too. The other weird thing about it is that this particular project is one that he has gone back and said, and said, “Yeah, that’s not my favorite of my works. There’s things I did in there that I shouldn’t have done.” I’m more concerned with what [artist] Brian Bolland thinks of it, frankly.

What were some of the biggest challenges that you faced in adapting this work?

The biggest challenge was how to do a style for the film that was animated and also still somewhat recalled the comic. Bolland has an almost photographically realistic style, which is absolutely antithetical to animation. If you had enough time and money—if you had, like, four years to devote to making a movie—you could hire the best people in the world and make them do every scene over and over and over again until it absolutely looks like Brian Bolland drawings on the screen, But short of that, there’s not really anything you can do. At the same time, we did want to at least use his style as a starting place. He has a very specific design for the Joker, which, after ending up on the screen, frankly doesn’t look like Brian Bolland drew it.

But he does have the pompadour. He does have the smile that is unique to Brian Bolland’s vision. The kind of beady, creepy eyes. We tried to mimic that without trying to draw it exactly the way that he does. The same thing with Batman. Nobody here on our staff has the kind of draftsmanship that Brian does, and we can’t expect people in Japan to be able to mimic it either. But there were certain stylistic things—the way he draws the ears on Batman’s cowl, the way he draws sheens on gloves and pants. And so there were certain things that we tried to stylistically mimic, and then everything else had to be simplified and broken down into a formula that could be reproduced overseas, which always is the challenge when we do an adaptation of any comic artist’s work.