The aspect ratio refers to the proportions of the height and width of an image. It defines its overall shape, and it is usually shown as W
16:9 works great for TVs since that is the format modern TV shows are delivered on, but most movies are made using the cinema standard, which is 21:9. 21:9 is much wider, so parts of the screen need to be filled with black bars above and below the image in order to fit most TVs. These horizontal bars a called "letterboxes". Similar to movies, TV shows used to be made using a 4:3 aspect ratio, which is a lot more square than current TVs (this is why 16:9 is often called a widescreen aspect ratio). To fit modern TVs, vertical black bars or "
|4:3||1.33:1||Standard Channels||Old TVs|
|16:9||1.77:1||HD Channels||The majority of HDTVs|
|21:9||2.35:1||Most movies||Most theaters|
|14:10||1.4:1||IMAX Film||Very few theaters|
|19:10||1.9:1||IMAX Digital||Most IMAX theaters|
Black bars appear when the aspect ratio of the content playing isn't matched with the aspect ratio of the TV.
Depending on the type of mismatch between the picture and the display's ratio, the black bars appear in different places. Content wider than the screen it is played on will have horizontal black bars, while content that is taller will use vertical bars. The following picture shows the black bars for various televisions and aspect ratios (4:3, 16:9 and 21:9). All televisions have the same diagonal length.
If you do not like having black bars, you have two options available within the settings of your TV: cropping or stretching.
Different TVs have different settings for this, so here's a table with the different options found on different brands, as well as their specific name. Some of them have two types of zoom; either two levels of crop or one of them combines both zoom and stretch at the same time.
|Sony||Full||Zoom||Wide Zoom (Zoom+Stretch)|
|Samsung||Fit to screen||Zoom/Position||N/A|
|LG||16:9||All Direction Zoom||Vertical Zoom (Zoom+Vertical Stretch)|
|TCL||Stretch||Zoom||Normal (Overscan feature)|
IMAX movies and theaters are a complete ecosystem that encompasses everything from cameras, speakers, room shapes, screen finishes and even film types. More importantly though, part of IMAX's proprietary system is their own aspect ratio. IMAX has a few different ratios used now to accommodate for different types of rooms, but there are two major ones: 1.9:1 and 1.4:1.
Most movies today that use IMAX still are filmed with a mixture of 21:9 ratio and 1.4:1 IMAX. As seen in the picture above, IMAX content fills up the entirety of the 16:9 screen. The image itself goes beyond the height of a 16:9 TV, but it is cropped in Blu-ray films to fit the screen. You don't get the whole experience, but you still get a more complete picture than if it was letterboxed to the standard cinema ratio.
21:9 TVs were made a few years ago and were aimed at cinephiles since they match the standard motion pictures aspect ratio and allow you to watch movies from edge to edge of your screen. They aren't available anymore, and they were rare even at the time of their release. Unless you only turn on your TV to watch movies, you're better off with a standard 16:9 TV. Watching normal TV shows on a cinema-wide screen causes it to show black bars on either side, which isn't great. This reduces the viewing area for 16:9 content considerably. A 58" 21:9 television corresponds to the same viewing area as a 47" TV for 16:9 content, as you can see in the illustration.
TV shows are made and distributed using a 16:9 aspect ratio, and every TV sold today uses the same. Movies are usually found with a 21:9 ratio, however, which causes them to have black bars above and below the pictures on standard TVs. Some PC monitors share that ratio, but it isn't very practical on a TV since normal content would have vertical bars.