Have you ever walked around an art gallery and thought, "Why does everyone look so miserable?"
Twitter user Olly Gibbs has. And so, during a recent visit to Amsterdam's Rijksmuseum, he came up with a solution to brighten up some of the portraits.
It involved FaceApp - which uses facial recognition software to make a person's face look older, younger, or even a different gender.
One other thing it can do, though, is make a person smile.
"The idea started in the tower of the Old Church," he told Dutch newspaper deVerdieping Trouw.
"I took a picture with my girlfriend of the beautiful view over Amsterdam, but I laughed because I'm afraid of heights. She said that there was an app that my grimace could be transformed into a brilliant smile."
You can guess what happened next.
The couple then visited the Rijksmuseum and had the idea they could apply the same smiles to some of the less than happy faces on display.
"They looked like me on that tower... [so] my girlfriend then thought it would be fun to use the app to cheer them a little," Olly said.
"We then had a lot of time in the museum and walked around to find the most grumpy faces."
As anyone who's ever seen a portrait can confirm, finding grumpy-looking faces was not difficult.
Olly had a wealth of material to choose from, and didn't even limit himself to paintings. Why not apply it to sculptures too?
Olly told the newspaper he'd be happy if the craze helped attract more people to museums.
We're certainly sold. Grab your phone and meet us at the National Portrait Gallery.