Confusion With Display Aspect Ratio
Pixel Aspect Ratio is often confused with different types of image aspect ratios; the ratio of the image width and height. Due to non-squareness of pixels in Standard-definition TV, there are two types of such aspect ratios: Storage Aspect Ratio (SAR) and Display Aspect Ratio (abbreviated DAR, also known as Image Aspect Ratio and Picture Aspect Ratio). Note that both Picture Aspect Ratio and Pixel Aspect Ratio can be abbreviated into PAR. This article reserves the acronym PAR for Pixel Aspect Ratio and instead, uses the term "Display Aspect Ratio" and the acronym "DAR" where appropriate.
Storage Aspect Ratio is the ratio of the image width to height in pixels, and can be easily calculated from the video file. Display Aspect Ratio is the ratio of image width to height (in a unit of length such as centimeters or inches) when displayed on screen, and is calculated from the combination of Pixel Aspect Ratio and Storage Aspect Ratio.
However, users who know the definition of these concepts may get confused as well. Poorly crafted user-interfaces or poorly written documentations can easily cause such confusion: Some video-editing software applications often ask users to specify an "Aspect Ratio" for their video file, presenting him or her with the choices of "4:3" and "16:9". Sometimes, these choices may be "PAL 4:3", "NTSC 4:3", "PAL 16:9" and "NTSC 16:9". In such situations, the video editing program is implicitly asking for the Pixel Aspect Ratio of the video file by asking for information about the video system from which the video file originated. The program then uses a table (similar to the one below) to determine the correct pixel aspect ratio value.
Generally speaking, to avoid confusion, it can be assumed that video editing products never ask for the Storage Aspect Ratio as they can directly retrieve or calculate it. Nonsquare-pixel–aware applications also need only to ask for either Pixel Aspect Ratio or Display Aspect Ratio, from either of which they can calculate the other.
Read more about this topic: Pixel Aspect Ratio
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