Adobe Premiere Elements 12 - Manual (Page 59)

Working with aspect ratios and field options
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Understanding aspect ratios
Capturing or adding various aspect ratios
View a project’s aspect ratio
Adjust pixel aspect ratio for a still image or source clip
Use square-pixel files in a D1 or DV project
Set field options for imported interlaced video
Understanding aspect ratios
The aspect ratio specifies the ratio of width to height. Video frames have an aspect ratio (frame aspect ratio) as do the pixels that make up the
frame (pixel aspect ratio). Some video camcorders can record various frame aspect ratios, and the NTSC and PAL video standards use different
pixel aspect ratios. If an image of a circle appears oval-shaped, there can be a mismatch between the aspect ratios of the image and your project.
Premiere Elements automatically attempts to detect and compensate for the pixel aspect ratio of source clips so that distortion doesn’t occur. If a
clip appears distorted in Premiere Elements, you can manually change its pixel aspect ratio. It's important to reconcile pixel aspect ratios before
reconciling frame aspect ratios. Misinterpretation of a source clip’s aspect ratio causes incorrect frame 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). For comparison, a typical widescreen frame has a frame aspect ratio of 16:9; many camcorders that have a widescreen
mode can record using this aspect ratio. Many films are shot using even wider aspect ratios.
A 4:3 frame aspect ratio (left), and a wider 16:9 frame aspect ratio (right)
When you add clips into a project with a different frame aspect ratio, decide how to reconcile the different values. You can show a widescreen
movie with a 16:9 frame aspect ratio on a standard TV with a 4:3 frame aspect ratio in two ways. Use the Letterboxing technique to fit the entire
width of the 16:9 frame into a black 4:3 frame. Black bands appear above and below the widescreen frame.
Alternatively, use the Pan and scan technique to fill the 4:3 frame with only a selected area of the 16:9 frame. Although this technique eliminates
the black bars, it also eliminates part of the action. Premiere Elements automatically letterboxes any 16:9 footage that you add into a 4:3 aspect
ratio project.
Pixel aspect ratio
Pixel aspect ratio describes the ratio of width to height in a single pixel of a frame. Pixel aspect ratios vary because different video systems make
different assumptions about the number of pixels required to fill a frame. For example, many computer video standards define a frame that has a
4:3 aspect ratio as 640 x 480 pixels. Pixels that are square, which have an aspect ratio themselves of 1:1, perfectly fill the horizontal and vertical
space the frame defines. However, video standards such as DV NTSC (standard for DV camcorders in the U.S.) define a 4:3 aspect ratio frame as
720 x 480 pixels. Consequently, to fit all of these pixels in the frame, the pixels must be narrower than the square pixels. These narrow pixels are
called rectangular pixels, and they have an aspect ratio of 0.9:1, or 0.9 as they are commonly called. DV pixels are vertically oriented in systems
producing NTSC video and horizontally oriented in systems producing PAL video. Premiere Elements displays a clip’s pixel aspect ratio next to the
clip’s image thumbnail in the Project Assets panel.
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