This week, Samsung revealed the Galaxy S9 and S9+ flagship smartphones at a media event in Barcelona, Spain. The two handsets replace the year-old S8 and S8+, and go into battle against the Apple iPhone X and Google Pixel 2 and 2 XL.

On the surface, the S9 duo look almost identical to their predecessors, but there are some key differences and major improvements - both inside and out.

Samsung Galaxy S9 vs S8: Design and appearance

The S9 and S9+ look very similar to the S8 and S8+, but there are some crucial differences and useful upgrades. For example, the bezels of the new pair are slightly smaller than before, making the screens seem larger.

More importantly, Samsung has listened to feedback and relocated the fingerprint sensor. It now sits below the rear camera instead of next to it, making it easier to reach with your index finger.

Read More: Samsung Galaxy S9 creates 'AR Emoji' which look just like you

Finally, the S9 is available in a new color called Lilac Purple, which is sold alongside Midnight Black and Coral Blue; a Titanium Gray version is available in some markets, but not the US.

Welcome similarities between the S8 and S9 include expandable storage (this time up to 400GB if you have a micro SD card that large), a headphone jack and IP68 waterproofing.

The Samsung Galaxy S9 and larger Galaxy S9+GearBrain

Samsung Galaxy S9 vs S8: Camera

This is where there are some major differences between the S8 and S9 - and also between the S9 and S9+.

The rear camera of both new models is the first on any smartphone to offer two different apertures. These are F1.5 and F2.4, with the former letting in lost of light for improved nighttime photography, while the latter has the speed to work best in brighter situations.

In its F1.5 setting, the camera is claimed by Samsung to let in 28 percent more light than the F1.7 camera of the Galaxy S8, while the F2.4 mode helps to prevent over exposure on sunny days. The camera app switches between the two apertures automatically, although in manual mode you can control this yourself. The camera can only use one of these two apertures, with nothing in-between, but it's still a marked improvement over all other smartphones.

The S9's relocated fingerprint sensor is easier to useGearBrain

The rear camera sensors is 12-megapixels on both the S9 and S9+ (the same as before), with dual-pixel technology, faster focusing, a claimed 30 percent improvement in low-light performance, and the ability to record slow-motion video at a hugely impressive 960 frames per second. However, that is only available at 720p HD, and you need a lot of light to get the best results. Still, being able to stretch 0.2 seconds of real-time into six seconds of footage is mightily impressive. The S8 could only manage 240 frames per second at the same resolution.

Samsung says the S9 takes 12 photos when you press the shutter button, which are then analyzed and combined to produce the perfect shot; for comparison, the S8 only took three at time. The S9 can do this because, for the first time, Samsung has given the camera its own dedicated RAM.

The S9+ has a second rear camera lens, set at F2.4, and just as with the Galaxy Note 8 this is used to offer 2x telescopic zooming, and enables a background blur effect with portrait photos.

Both the S9 and S9+ have the same 8-megapixel front camera with F1.7 aperture and autofocus as the S8 last year.

AR Emoji

Not to be outdone by the iPhone X and its Animoji feature, Samsung has created AR Emoji for the S9 and S9+. TAke a selfie, and this feature automatically creates 18 animated emojis which look like you. You can adjust the skin tone and hair, then add glasses and change your emoji's clothes, then import it to your keyboard. From there - and unlike Animoji on the iPhone X - they can be sent to any contacts via Facebook Messenger and WhatsApp.

AR Emoji are a countrerstrike against Animoji on the iPhone XGearBrain

Dolby Atmos

Samsung has added a second loudspeaker to the Galaxy S9, where the earpiece is, to give stereo sound when held in landscape. Samsung claims the S9 is 40 percent louder than the S8, but more impressive than that is Dolby Atmos, which adds a genuine element of surround sound to the handset. We watched a quick Atmos demo and, having seen the same video on our cinema system at home we were pleasantly surprised at the width of sound produced by the S9.

Sure, there's no sound behind you and it doesn't bounce effects off the ceiling like a true Atmos setup, but it's impressive for a smartphone nonetheless.

Samsung Galaxy S9 vs S8: Display

Nothing is new here. The S9 and S9+ have the same screen sizes and resolutions as their predecessors, which means 5.8 inches for the S9 and 6.2 inches for the S9+. Both have a resolution of 2960 x 1440. As before, the screen are curved at their edges when held in portrait.

The S9 is available in lilac, blue and black in the USGearBrain

Samsung Galaxy S9 vs S8: Processor, RAM and battery

In the US, the Galaxy S9 has a Qualcomm Snapdragon 845 processor with 4GB of RAM, while the S9+ gets the same processor but 6GB of RAM. Battery sizes are the same as last year, at 3,000mAh and 3,500mAh respectively.

Galaxy S9 price and release date

The Galaxy S9 and S9+ are priced at $719.99 and $839.99 unlocked. Pre-orders open on March 2 and the phones go on sale on March 16.

For more on the differences between the S8 and S9, here is a useful infographic produced by Samsung:

Samsung