Aspect Ratio

画面宽高比 (Aspect Ratio) is the ratio of a display’s width to its height, typically expressed as 4:3, 16:9, or 2.39:1. It describes the composition and shape of the final image but does not directly indicate the number of pixels. The same 16:9 aspect ratio can correspond to 720p, 1080p, 4K, or other resolutions.

In digital video, there are also storage aspect ratios and pixel aspect ratios. DVDs often store 4:3 and 16:9 images at 720×576 or 720×480, relying on non-square pixels to scale horizontally during playback; The display aspect ratio is determined by both the storage dimensions and the pixel aspect ratio. Ignoring the pixel aspect ratio can cause characters to appear narrower or wider. Common film aspect ratios include 1.85:1 and 2.39:1. When widescreen movies are displayed on a 16:9 screen, black bars are typically added at the top and bottom; when 4:3 content is displayed on a 16:9 screen, black bars may be left on the sides. Black bars may be generated in real time by the player or may already be encoded into the video; the latter consumes usable pixels.

The aspect ratios 2.35:1, 2.39:1, and 2.40:1 are often used interchangeably in release notes, but the corresponding historical standards and actual cropping may differ slightly. Values calculated by media tools based on the effective frame or container metadata may also vary due to black bars, sampling errors, and rounding. Changing the aspect ratio can be achieved through cropping, adding borders, distortion, or recomposition, and the results are not equivalent. Open format, masked format, and anamorphic widescreen also involve the filming and projection processes; the final video aspect ratio alone cannot prove the original photographic aspect ratio.