The Photobooth mode on the Google Pixel 3 and Pixel 3 XL camera app makes it easier for individuals, couples and even groups to snap selfies. Found in the Pixel Camera app under the "More" category, once you tap on Photobooth and click on the shutter, a selfie won't be snapped until the camera is steady and everyone has a nice expression with their eyes open. And in the latest version of the app (found in the Google Play Store), Photobooth added some expressions that will set off the shutter automatically.
As Google explains, it worked with photographers to come up with five expressions that will automatically set off the shutter and capture a picture. The five are "smiles, tongue-out, kissy/duck face, puffy-cheeks, and surprise." Machine Learning is used to score a frame and the shutter is triggered when the combination of the weighted expressions score and the kiss score surpass a certain level. A bar at the top of the screen (remember, these are selfies) grows in length when the photo quality score increases and the selfie is ready to be taken automatically. The length of the bar is small when there are no faces clearly seen. It expands when there are faces seen, but they are not paying attention to the camera, and when the faces paying attention but not making key expressions. The bar hits its maximum length when the faces are paying attention with key expressions. At that point, the shutter automatically snaps and the selfie is captured.
Note that Photobooth is only available for the Pixel 3 and Pixel 3 XL. Earlier Pixel models don't have the dual selfie snappers found on the latest models. That is important because Photobooth is designed to work with the wide-angle front-facing camera.