Aspect ratios

An aspect ratio specifies the ratio of width to height. Video and still picture frames have a frame aspect ratio, and the pixels that make up the frame have a pixel aspect ratio. You record video for television in either a 4:3 or 16:9 frame aspect ratio. Additionally, different video recording standards use different pixel aspect ratios.

You set the frame and pixel aspect ratios for a Premiere Pro project when you create it. Once these ratios are set, you cannot change them for that project. You can, however, use assets created with different aspect ratios in that project.

Premiere Pro automatically tries to compensate for the pixel aspect ratio of source files. If an asset still appears distorted, you can manually specify its pixel aspect ratio. Reconcile pixel aspect ratios before reconciling frame aspect ratios, because an incorrect frame aspect ratios can result from a misinterpreted pixel aspect ratio.

Frame aspect ratio

Frame aspect ratio describes the ratio of width to height in the dimensions of an image. For example, DV NTSC has a frame aspect ratio of 4:3 (or 4.0 width by 3.0 height). A typical widescreen frame has a frame aspect ratio of 16:9. Many cameras that have a widescreen mode can record using the 16:9 aspect ratio. Many films have been shot using even wider aspect ratios.

A 4:3 frame aspect ratio (left), and wider 16:9 frame aspect ratio (right)

When you import clips shot in one frame aspect ratio into a project that uses another frame aspect ratio, you decide how to reconcile the different values. For example, two common techniques are used for showing a 16:9 movie on a 4:3 standard television. You can fit the entire width of the 16:9 movie frame within the 4:3 television frame. This placement leaves black bands above and below the movie frame, called letterboxing. Alternatively, you can fill the 4:3 frame vertically with the entire height of the 16:9 frame. Then, you pan the horizontal position of the 16:9 frame within the narrower 4:3 frame so that important action always remains inside the 4:3 frame. This techniques is called pan & scan. In Premiere Pro, you can implement either technique by using Motion effect properties such as Position and Scale.

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NTSC displays

A.

16:9 NTSC footage

B.

DVD player display using original widescreen format on widescreen TV screen

C.

16:9 image on a 4:3 TV screen cropped using automatic pan and scan

D.

16:9 image on a 4:3 TV screen using automatic letterboxing to reduce overall frame size and display entire image

Pixel aspect ratio

For a video that explains the basics of pixel aspect ratios, see the Adobe website.

Pixel aspect ratio describes the ratio of width to height of a single pixel in a frame. Pixel aspect ratios vary because different video systems make various assumptions about the number of pixels required to fill a frame. For example, many computer video standards define a 4:3 aspect ratio frame as 640 pixels wide by 480 pixels high, which results in square pixels. Video standards such as DV NTSC define a 4:3 aspect ratio frame as 720x480 pixels, which results in narrower, rectangular pixels because where more pixels lie within the same frame width. The computer video pixels in this example have a pixel aspect ratio of 1:1 (square). The DV NTSC pixels have a pixel aspect ratio of 0.91 (nonsquare). 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.

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. Premiere Pro attempts to automatically reconcile them with the pixel aspect ratio of your project.

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 dialog box. You can correct similar misinterpretations of groups of same-size files by editing the file Interpretation Rules.txt.

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Pixel and frame aspect ratios

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

Many graphics and animation programs generate square-pixel assets meant for display on square-pixel computer monitors. Premiere Pro, however, typically generates files with non-square pixels for display on television sets. Premiere Pro automatically conforms square-pixel assets to the project pixel aspect ratio. After the asset is conformed, however, it no longer has its original frame aspect ratio. Also, its frame aspect ratio is not likely to match that of the project, even if it did before it was conformed.

For example, suppose you generate a square-pixel asset at 720x540 and import it into a Premiere Pro DV project with an aspect ratio of 720x540. In this case, the asset is wider than the screen when it is conformed. You can use the Scale control to set the size of the asset frame within the project frame. However, to preserve the asset frame aspect ratio, Premiere Pro often either crops the asset or frames it within black bars.

You can prevent this cropping and framing by carefully generating assets from your square-pixel graphics or animation programs. Choose a frame aspect ratio that, when conformed, matches the project frame size exactly. For best results, use programs such as Adobe Photoshop® and Adobe After Effects® that include pixel aspect ratio settings. Set the frame dimensions and pixel aspect ratio to match the dimensions of your project. If the pixel aspect ratio setting is unavailable in your program, do not try to match the frame dimensions (for example, 720x540). Instead, ensure that the overall frame aspect ratio matches that of your project (for example, 4:3 or 16:9). Premiere Pro automatically adjusts the video so that it is not distorted.

Premiere Pro automatically attempts to preserve the frame aspect ratio of imported assets, sometimes changing the pixel aspect ratio, the frame dimensions, or both so that the asset does not appear cropped or distorted when used in a sequence. Assets created in an Adobe Creative Suite application contain metadata that allows Premiere Pro to make the calculations automatically and precisely. For assets lacking this metadata, Premiere Pro applies a set of rules to interpret pixel aspect ratio.

When you capture or import NTSC footage with the ATSC frame size of 704x480, the D1 frame size of 720x486, or the DV frame size of 720x480, Premiere Pro automatically sets the pixel aspect ratio for that asset to D1/DV NTSC (0.91). When you capture or import footage with the HD frame size of 1440x1080, Premiere Pro automatically sets the pixel aspect ratio for that file to HD 1080 Anamorphic (1.33). When you capture or import PAL footage with the D1 or DV resolution of 720x576, Premiere Pro automatically sets the pixel aspect ratio for that file to D1/DV PAL (1.094).

For other frame sizes, Premiere Pro assumes that the asset was designed with square pixels and changes the pixel aspect ratio and frame dimensions in a way that preserves the asset image aspect ratio. If the imported asset is distorted, you can change the pixel aspect ratio manually.

When you drag an asset into a sequence, Premiere Pro centers the asset in the program frame by default. Depending on its frame size, the resulting image could be too small or overcropped for the needs of the project. If so, you can change its scale. You can do this manually or have Premiere Pro do it automatically whenever you drag an asset into a sequence.

It is always a good idea to make sure that files are interpreted correctly. You can read asset frame dimensions and pixel aspect ratio near the preview thumbnail and in the Video Info column of the Project panel. You can also find this data in the asset Properties dialog box, the Interpret Footage dialog box, and the Info panel.

1. Select the still image in the Project panel.
2. Choose File > Interpret Footage.
3. Select an option in the Pixel Aspect Ratio section, and click OK.
4. Select one of the following:

   Use Pixel Aspect Ratio From File

   Uses the original aspect ratio saved with the still image.

   Conform To

   Lets you choose from a list of standard aspect ratios.

   Note: When using Photoshop to generate images for use in video projects, it’s best to use the Photoshop preset named for the video format you’ll use. Using the preset ensures that your images are generated with the correct aspect ratio.

1. Open a text editor.
2. From within the text editor, go to the Premiere Pro Plug-ins folder.
3. Open the file named Interpretation Rules.txt.
4. Edit the rule that you want to modify, and choose Save.