"For shallow depth-of-field, synthetic defocusing is not the same as real optical defocusing, but the visual effect is similar enough to achieve the same goal, of directing your attention towards the main subject," wrote Google engineers Marc Levoy and Yael Pritch in a research blog back in October.
While Portrait Mode has been an exclusive to the Pixel 2 family, the Camera NX mod has now been updated to bring similar functionality to older Google smartphones. Camera NX V7.3 modifies the existing Google Camera app, and can be side-loaded onto 2016-era Pixel smartphones along with the Nexus 5X and Nexus 6P. No rooting is required to get Portrait Mode goodness on these devices.
"Portrait mode will replace the Lens-blur mode in the menu, it provides the face-retouching feature on both front and back camera, and it needs a human face to do the portrait effect job," writes Camera NX developer Charles Chow. "It will take two burst photos, one is normal ZSL HDR+ photos, the other is applied the portrait effect. if no human face shows up, you will get one normal photo."
You can download Camera NX V7.3, which is based on Google Camera 5.1.016, right here.