The horizontal and vertical measurement of a screen creates what is called an aspect ratio. Although it may seem like a simple cosmetic choice, the aspect ratio on the iPhone has an impact on how you view movies, shows and pictures. The iPhone 4 and 4S both use a 3.5-inch Retina display that is wider than it is tall, creating the illusion of a widescreen display.
Users of the iPhone 4 and 4S are familiar with the orientation feature of the device. Rotating the iPhone into the horizontal plane takes widescreen content from your movies, YouTube or sports highlight and shifts it in the proper orientation to fill the screen entirely or almost entirely. Flipping it vertically into the "Portrait" position leaves large black spaces above and below a stamp-sized rectangular image in the middle. If the iPhone were to alter the shape and size of on-screen content to fit while vertical, those images would be tall and skinny with much of the scene cut off.
Impact on Digital Images
Although the iPhone 4 and 4s employ a digital camera, the 3:2 aspect ratio is shared by 35mm film-based cameras. The way an iPhone takes a picture or shoots a movie is clearly designed for display on the phone itself. Viewing the 3:2 aspect ratio picture or video remains in that shape when seen on a computer monitor or television. However, the on-screen images are not distorted to fit the screen, with proper proportion and geometry maintained.
Movies and Television Shows
Watching a movie on the iPhone 4 or 4s typically involves a black bar top and bottom, framing the image. This is present because, although the movie or TV show was most likely shot with an elongated screen in mind, the iPhone 4/4s does not quite fit that standard exactly. Since commercially released movies and TV shows may be shot with a variety of subtle differences in aspect ratio, the actual size of the letterbox bars on the screen may vary. Common widescreen ratios are 2.35:1, 1.85:1, 1.78.1 and 4:3. As with movies and pictures shot and taken with the iPhone, this does not impact the geometry of the characters and object on-screen. You can double-tap on the screen to "zoom" the screen to eliminate or reduce the letterbox bars, at some loss of visual quality.
Apps as Aspect Ratio
The iPhone's screen measurements are 3 inches wide by 2 inches tall, creating a 1.5:1 aspect ratio. You may see this written as 3:2, with either being an accepted description. App developers design their software to accommodate this ratio, often creating a separate version for the iPad. In most cases, apps for the phone completely fit the screen, making the impact of that ratio transparent for daily use. The fact that apps normally fill the entire screen gives the illusion of a 16-by-9 widescreen, high definition television.
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