Samsung recently unveiled its latest and greatest Android flagships in the form of the Galaxy S9 and Galaxy S9 Plus, debuting a product family that has much more differences across its models than the 2017 Galaxy S8 lineup did. Even so much as a glance at the two devices makes one thing obvious - the Galaxy S9 Plus has an extra camera on the back. While having additional hardware is an advantage, it's what that second camera enables what truly matters. In the case of the Galaxy S9 Plus, that answer is rather straightforward - Portrait Mode. Or, how Samsung calls it - Live Focus.
Getting a shot of a subject that's perfectly in focus and manages to pop up and really dominate the frame due to their background being blurred is a complicated task for smartphones as their camera sensors are so tiny that most image settings usually result in either a perfectly focused shot or a perfectly unfocused one. Some manufacturers managed to circumvent those physical limitations by using two cameras to create depth maps of images before they're taken which figure out what the subject's supposed to be and help the imaging software blur out the rest. In fact, with the exception of Google's machine learning magic utilized by the Pixel flagships, that's exactly how the so-called portrait modes are done on every smartphone. It's what Samsung did with the Galaxy Note 8 and what the Galaxy S9 Plus is repeating, albeit with even more versatility due to the variable aperture of its primary lens.
As the Galaxy S9 lacks a secondary camera on its back panel, it also doesn't have the physical capabilities to create detailed depth maps that make portrait mode achievable by any manufacturer that isn't Google. Due to that state of affairs, the device is still limited to the Selective Focus mode that can often deliver comparable results but not of the in-camera variety. Instead, the mode takes a burst of shots with different focus points and provides users with the ability to change the focus area as part of a straightforward post-processing action that stitches all of those images together. In many cases, this mode will deliver similar results to the Live Focus one but is objectively worse due to not being instant in nature. Selective Focus has been supported by single-lens Samsung smartphones since the Galaxy S5 released in early 2014 and while the hardware has improved, the overall principles and limitations of the technology remain the same.