When photographer Andrew Cowen sat down for a yarn with his friend, the cartoonist Matthew Martin, he hadn't planned on a photo shoot, but that's how the day ended up.

Cowen rolled up his lights and his camera and began shooting, as the two men chatted about this and that.

It wasn't until later, flicking through the results, that he discovered the one image that truly captured Martin's essence.

The judges of this year's National Photographic Portrait Prize agreed, and named Cowen's image the winner.

"I wasn't attempting to achieve that moment, but that moment came, and in the edit, I thought there was an intensity in this picture and it tells something about Matthew that is true," Cowen said at the gallery yesterday.

"Matthew has the capacity to be introspective and dark when he wants to be...It's got a grittiness to it without being full-on.''

Gallery director Angus Trumble described Cowen's image as a work of "supreme elegance and quality, disarming intensity, acuity and fineness of texture".

But Cowen said the image's spare composition was down to discipline and a lack of paraphernalia in his approach to photography.

"Digital cameras do 95 per cent of the stuff for you if you want them to. People's skills I think are actually decreasing, but I didn't come from that world," he said.

Although he has been a finalist in the prize before, he said this year's win was especially pleasing because it was an image of a friend.

He and Martin have sons the same age and both hail from Adelaide originally.

"We spent a lot of time together. I think now if the kids weren't friends we'd hang out," he said.

"I emailed a copy [of the image] to Matthew after we shot it, and his wife saw it and went, 'You've got him'."

Cowen will take home $25,000 as prize money, which he says will go towards funding future projects.

The winner was chosen from 45 finalists, which in turn were whittled down from 1400 entries.

One of the three judges, curator Chris Chapman, said it had been particularly difficult to choose a winner.

"For us in the end, with the portrait of Matthew Martin, it was a combination of a really strong, minimal style and a real sense of the person," he said.

The mood of the show is also noticeably dark this year; the prize runner up is a self-portrait by Melbourne photographer David Apostol, depicting him in a dingy kitchen leaning towards an open oven.

The image was one in a series the artist created to explore his own depression and anxiety.

At the gallery yesterday, Apostol, who works as a tram driver to fund his art, said he was overwhelmed that his image had been selected as a finalist.

"They were never really meant to be shown. I did them for me," he said of his series dealing with suicide.

"This one is the easiest to look at for me because the other ones in the series are far more revealing and very, for me, confronting... I try not to look at them too often. I'm proud because it helped me through, it was art therapy."

The National Photographic Portrait Prize 2014 is showing at the National Portrait Gallery until June 9.