TOKYO — Japanese police have arrested five porn movie producers and a member of an industry self-censorship group on charges their films were too graphic, police said Monday.

Sexual images are widely available in Japan but only as long as they do not expose human genitalia.

To circumvent the law, adult film and magazine makers have created industry groups that impose self-censorship, mostly by blurring out images of genitalia through mosaic patterns.

But Katsumi Ono, 51, a member of the Nihon Ethics of Video Association, was arrested Saturday for alleged laxity in screening seven porn films.

Police said he helped filmmakers, including Yoshitaka Haga, 80, chairman of a porn manufacturer, distribute movies in which genitalia was not fully pixelated.

Police said Monday that they also arrested Haga and four other producers.

Ono’s self-censorship group said in a statement that it “strongly protests” the arrests.

“The recent incident was a violation of freedom of expression and people’s rights to know and watch,” it said.

Ono is believed to have been lax about the guidelines to help distributors compete better against start-up porn makers that tend to sell more graphic material via the Internet, which is more difficult to regulate.

In the movies in question, the mosaic patterns on the genitalia were reportedly too easy to see through.

“The titles did have mosaic patterns,” said a member of the self-censorship group. “We believe it was within the range of public tolerance.”

Sexually oriented pictures and films are openly sold in Japan, where it is not an unusual sight to see men flipping through adult magazines on packed commuter trains.

Last month, Japan’s Supreme Court handed a significant victory to a movie distributor by lifting a ban by customs officers, who had confiscated his personal copy of a book from late US photographer Robert Mapplethorpe that depicted male genitals.