Camera: Hardware And Software
Apple upgraded the rear iSight camera sensor on the iPhone 4s to 8MP three years ago. Since then, we’ve seen smartphone camera pixel counts steadily increase to over 20MP, however, pixel count held steady on the iPhone 5 and 5s.
While pixel density didn’t change on the 5s, it did receive a new sensor with larger pixels (1.5µm versus the 1.4µm in the iPhone 5) to improve low-light performance. The aperture was also changed from f/2.4 to f/2.2, allowing more light to hit the sensor. The other significant change was the addition of the dual-LED True Tone flash, which blends the light from two different color LEDs to achieve better color balance.
The rear camera on the iPhone 6 uses the same optics as the 5s, and while the sensor is new, its specifications are also the same as the 5s. This new sensor contains Focus Pixels, which is just Apple’s fancy name for a technology known as phase detection autofocus (PDAF). PDAF is common in DSLR cameras and is also used in the Samsung Galaxy S5.
Previous iPhones used contrast detection autofocus, where the image signal processor (ISP) compares the change in contrast of nearby pixels at various focal distances. Focus is achieved when contrast is maximized. While less costly to implement, this method doesn’t work well in low-light conditions and is comparatively slower than other methods.
PDAF, however, is a more reliable autofocus process and achieves focus much more quickly than the contrast detection method. It works in a manner similar to an optical rangefinder. Incoming light is refracted by microlenses and the resulting images are superimposed on the AF sensor. The distance between light intensity peaks is measured, and then the ISP uses this data to determine if the image is in focus. Unlike the contrast detection method, which doesn’t know exactly how much to adjust the lens to improve focus, the PDAF method calculates the necessary adjustment, which is the secret to its speed.
The other new rear camera feature is exclusive to the iPhone 6 Plus: optical image stabilization (OIS). With OIS, the gyroscope and M8 motion coprocessor feed motion data to the ISP within the A8 SoC, which controls a voice coil in the camera that physically moves the lens assembly. This helps compensate for small vibrations caused by shaky hands to reduce motion blur for low-light images. It’s also more effective than the electronic image stabilization used on previous iPhones and still used on the iPhone 6.
The front-facing FaceTime HD camera also gets a new sensor, although it maintains the same 1.2MP resolution and 1.9μm pixels as the camera in the iPhone 5s. Aperture size is now f/2.2, improving low-light performance. There’s also better face detection and a new burst mode capable of taking 10 photos per second.
The A8’s ISP gets some enhancements, enabling new features and boosting video capture speeds. The iSight camera now captures HD video at 1080p/60 FPS, and slow-motion 720p video at either 120 or 240 FPS. The higher frame rate for HD video helps action scenes look smoother. Video on the go is further improved by cinematic video stabilization, which uses software to reduce small, jittery movement and helps keep the video looking steady.
The Camera app remains largely unchanged in iOS 8, still functioning as a point-and-shoot camera. However, tapping the screen now shows an exposure control next to the focus box. Sliding the control lightens or darkens the photo or video by up to four f-stops in each direction. There’s also a shot timer that can be set for either a three- or 10-second delay, and a new mode for shooting time-lapse videos. Unfortunately, the time-lapse feature doesn’t provide any control over the playback speed or duration of capture. Depending on how much action is in a scene, the default playback speed isn’t always appropriate.
The only other addition to the interface is a toggle in the lower-right corner for setting the recording speed when shooting slow motion video. Unfortunately, there isn’t a similar toggle when shooting HD video. Instead, the option to record 60 FPS video resides in the “Photos & Camera” section in the Settings app.
The Photos app gains some new image editing options for adjusting brightness and color. You can either use a simple slider and let the Photos app handle the details, or you can expand the menu to access manual controls.
With iOS 8 it’s now possible to take and share photos directly from the Lock screen. Tapping the share button and entering your passcode or using Touch ID accesses the sharing options. It's a simple change, but a big improvement in usability.