Samsung Galaxy S4 eye-tracking smartphone unveiled

Samsung has launched a smartphone which allows users to control its 5in (12.5cm) screen using only their eyes.

The Galaxy S4 follows on from last year's S3, a product that sold over 40 million units worldwide.

At a lavish, Broadway-themed event in New York, the company also demonstrated the phone's ability to take two different pictures at once.

Analysts widely regard Samsung to be the biggest challenger to Apple's dominance of mobile products.

The Galaxy S4 will be rolled out globally at the end of April.

Following the launch, shares in Samsung fell 1.7% in early trade in Seoul on Friday amid worries the market for phone upgrades was "flattening out".

The company's head of mobile communications, JK Shin said 327 mobile operators in 155 countries will carry the handset.

The device will be made available in two colours, white and black

In the UK, Vodafone, Three, Orange, T-Mobile and EE have all announced plans to offer the device on their networks.

Through a series of role-playing scenes, the South Korean firm demonstrated the phone's key features.

Much was made of the device's ability to be controlled without touching it.

Using "Smart pause", the user can pause a video by looking away from the screen.

Additionally, the "Smart Scroll" software analyses the user's eyes and wrist to scroll through emails and other content.

'Gimmicky'

"The debut of nifty eye motion-sensitive controls to allow users to pause video and scroll through pages using eye movements alone is smart," said telecoms expert Ernest Doku from uSwitch.com.

"For commuters crammed in trains - or just those who love a bit of futuristic tech that makes their lives easier - this novel feature will really help the Galaxy S4 to stand out."

However, Charles Golvin from Forrester Research worried the swathes of new features may alienate some customers.

"The larger question is how much of this stuff can people actually use," he told the BBC.

"There's no question that there's a lot of powerful technology and innovative features - but whether people will care about them or use them I'm not sure.

"Including an image of yourself in a picture that you're taking for someone else - yes, I think that's a bit gimmicky.

"But on the video side, for a live chat where it's compositing you and your image to show both you and what you're seeing - that's not a gimmick."

Lighter and thinner

In another scene, depicting a backpacker in Shanghai, the phone was shown to translate English text into Chinese speech - before translating Chinese speech back into English text.

The dual camera function takes pictures using both rear and front cameras

The dual camera feature makes use of the device's front and rear cameras simultaneously, blending the pictures together to make sure the picture taker is not "left out".

The rear has a 13 megapixel camera, while the user-facing camera captures pictures at 2 megapixels.

The phone weighs 130g, and is 7.9mm thick - making it slightly lighter and thinner than the S3.

The device uses Samsung's HD AMOLED technology, giving the S4's screen - which is marginally bigger than the S3's - a resolution of 441 pixels-per-inch.

As predicted by several industry experts before the event, most of the presentation focused on the phone's software rather than hardware.

As well as the "touchless" technology, the company also introduced the Samsung Hub - a multimedia storage facility that can be shared across multiple Samsung devices.