Learn about pixel aspect ratio and how to avoid images appearing distorted.
The pixel aspect ratio describes the ratio of width to height of a single pixel in a frame. The pixels that make up a frame have a pixel aspect ratio (sometimes referred to as PAR). Pixel aspect ratios vary because different video systems make various assumptions about the number of pixels that are required to fill a frame.
For example, many computer video standards define a 4:3 aspect ratio frame as 640x480 pixels high, which results in square pixels. The computer video pixels have a pixel aspect ratio of 1:1 (square).
Video standards such as DV NTSC define a 4:3 aspect ratio frame as 720x480 pixels, which results in narrower, rectangular pixels. The DV NTSC pixels have a pixel aspect ratio of 0.91 (non-square). DV pixels, which are always rectangular, are vertically oriented in systems producing NTSC video and horizontally oriented in systems producing PAL video. Premiere Pro displays clip pixel aspect ratio next to the clip image thumbnail in the Project panel.
The clean aperture is the portion of the image that is free from artifacts and distortions that appear at the edges of an image. The production aperture is the entire image.
A. 4:3 square-pixel image displayed on 4:3 square-pixel (computer) monitor B. 4:3 square-pixel image interpreted correctly for display on 4:3 non-square pixel (TV) monitor C. 4:3 square-pixel image interpreted incorrectly for display on 4:3 non-square pixel (TV) monitor
Distorted images
If you display rectangular pixels on a square-pixel monitor without alteration, images appear distorted.
For example, circles distort into ovals. However, when displayed on a broadcast monitor, the images appear correctly proportioned because broadcast monitors use rectangular pixels.
Premiere Pro can display and output clips of various pixel aspect ratios without distortion. But you could occasionally encounter a distorted clip if Premiere Pro interprets pixel aspect ratio incorrectly. You can correct the distortion of an individual clip by manually specifying the source clip pixel aspect ratio in the Interpret Footage (Clip > Modify > Interpret Footage) dialog box.
