Intensifying its smartphone battle with Apple, Samsung unveiled the feature-rich Galaxy S4, with groundbreaking eye motion technology to let users control key functions at a glance.

In one highlight, sensors in the S4 detect when a person looks away from a video and then pauses play until the distraction has passed and eyes are once again directed at the screen. The eye motion technology can also screen through emails.

The South Korean consumer electronics giant introduced the Galaxy S4 Thursday on the stage of New York City's Radio City Music Hall and said the smartphones would roll out in 155 countries in late April. Pricing was not disclosed.

"For each of us, life is a journey," said Samsung mobile communications division head JK Shin. "What we want is a device that can join us on that journey; a companion that helps us experience life in the fullest."

S4 features include a high-definition, five-inch (12.7-centimeter) screen, enhanced picture-taking capabilities and the capacity to translate to and from nine languages.

"It is now clearly Samsung's flagship device; jam-packed with technology," said Gartner analyst Michael Gartenberg.

"The question is how many of these features will resonate with consumers."

Samsung played up its online hub for music, books, and video and the ease with which the S4 can share video with televisions made by the company.

"At this point, smartphones are all about software and ecosystems; showing up with compelling hardware is the expected starting point," Gartenberg said.

"This is about a Samsung ecosystem that happens to be built on Android."

Samsung is the biggest and most successful maker of smartphones powered by Android software that Google makes available for free.

Samsung has become the top smartphone maker worldwide with a 29 percent market share, according to IDC, while in the US market Apple remains the king and sells more than one of every three mobile phones.

The Galaxy S3 has sold more than 40 million worldwide since its launch last May and has some analysts debating which of the two firms is ahead in innovation.

"We are always listening to learn from people around the world about what kind of progress they really want," Shin said.

Samsung stressed innovation as it continues to defend itself against charges made by Apple in public and in lawsuits that the South Korean rival has copied the California company's creations.

The S4 is thinner than its predecessor and weighs just 130 grams despite having a bigger screen and battery.

The smartphone also boasts a "dual camera" function that lets the front and rear-facing cameras be used simultaneously for pictures or videos that combine images of subjects with that of the photographer.

A Group Play function lets S4 handsets close to one another share music, photos, documents or games, or even work in unison as a sound system for a song.

An S Translator feature lets people speak or enter text in one tongue and have it instantly converted to another.

S4 sensors combined with S Health software enable handsets to be used to track exercise, eating, heart rate and other fitness factors.

The handsets were also designed to measure temperature and humidity to help people "understand what is going on around them."

Samsung also took aim at the trend of people using their own smartphones for work with the addition of new Knox software that builds a secure wall between personal and business data on handsets.

"The Samsung Galaxy S4 is very good, but looks like an evolution to the S3, not a revolution," said technology analyst Jeff Kagan.

Apple, which is known for keeping its plans private, is believed to be working on its own upgrades, including a new version of the iconic iPhone. But Apple shares have slumped some 40 percent from highs hit last year.