Understanding pixel aspect ratios

You may already be familiar with image aspect ratios, but did you know that pixels can have various aspect ratios too? If you have ever worked with a drawing or graphics program on a computer, you’re probably familiar with pixels. A pixel is the smallest piece of a digital image. Thousands — or even millions — of uniquely colored pixels combine in a grid to form an image on a television or computer screen. On computer displays, pixels are square. But in standard video, pixels are rectangular. In NTSC video, pixels are taller than they are wide, and in PAL or SECAM, pixels are wider than they are tall. Pixel aspect ratios become an issue when you start using still images created as computer graphics — for example, a JPEG photo you took with a digital camera and imported into your computer — in projects that also contain standard video. If you don’t prepare the still graphic carefully, it could appear distorted when viewed on a TV.