THE EVOLUTION OF ZOOM CAMERA TECHNOLOGIES IN SMARTPHONES
Zoom is a commonly used photography feature; it allows the user to shift smoothly from a long shot to a close-up and vice versa. Optical zoom employs camera optics (a lens) to magnify the object, while digital zoom crops and up scales the input image. Unlike optical zoom, digital zoom reduces resolution and, as a result, diminishes image quality.
In recent years, mobile devices, such as smartphones, have become ubiquitous. Such devices typically include two compact cameras, a main rear-facing camera, and a secondary front-facing camera. Most compact cameras are designed with the traditional structure of a digital still camera – i.e., they comprise a lens placed on top of an image sensor. The lens focuses the incoming light to create an image of a scene on the sensor.
The dimensions of these cameras are largely determined by the size of the sensor and by the size of the lens. The size of the lens is mainly defined by the focal length (f) of the lens and the desired field of view (FoV ). These properties are usually tied together such that the sensor size is proportional to FoV * f . A larger focal length results in a higher zoom factor and a longer lens, which necessitates a thicker camera.
As smartphone manufacturers are constantly striving to make their products thinner, a compact camera’s height becomes a limiting factor. Several approaches have been proposed to reduce compact camera height to alleviate this constraint. Nonetheless, due to the above limitation, traditional compact camera performance is very limited; the severe height restriction eliminates any distinct performance enhancement – in particular, an optical zoom feature.
This paper covers the entire evolution of zoom cameras in smartphones, from early days of the Samsung Galaxy K-zoom, through the latest iPhones and the Samsung Note8, to the future of folded zoom cameras. It also explains some of the mobile photography fundamentals and how vendors strike a fine balance between them.