Portrait Mode

Portrait Mode is a feature introduced in the iPhone 7 Plus that utilizes a combination of technologies to improve the appearance of close subjects in photography.

History
Digital cameras that support portrait mode will open the of the lens to narrow the  to draw attention to the subject in the photo.

iPhone support
Due to limitations in the small sizes (and apertures) of cameras in smartphones, supported devices from Apple will generate a with photos taken in Portrait Mode. This can be generated through the following methods:


 * Multi-camera systems: Depth data calculated from variances in image data from the different cameras (e.g. wide and telephoto).
 * Single-camera systems: Depth data calculated through a machine learning algorithm. This version of the feature is most effective on human faces and is limited to the iPhone X R and 2nd generation iPhone SE.
 * Depth sensors: Depth data is gathered from a front-facing TrueDepth camera or a rear-facing LiDAR sensor.

The above features may be supplemented by algorithms. The depth map can then be used to blur or remove the background around the subject.

iPad support
Portait Mode is only supported by the front-facing TrueDepth cameras of recent iPad Pro models. The mode was found not to function with the rear-facing cameras of any iPad model, regardless of the number of cameras or sensors.

Articles

 * How To Use iPhone Portrait Mode To Shoot Stunning Portrait Photos by Kate Wesson at iPhone Photography School (2019-10-22)
 * 13 Tips For Stunning Portrait Photography On iPhone by Karyn Teno (2018-10-18)