Historically, the National Television Systems Committee (NTSC) in the United States adopted an aspect ratio of 4:3 for television images because the motion picture industry had earlier adopted the same aspect ratio for movies after determining that viewers preferred a rectangular image that had a greater width than height. Television standards organizations throughout the rest of the world have also adopted the 4:3 aspect ratio. With the advent of high definition television, such as the High Definition terrestrial broadcast system proposed by the Grand Alliance and described in the 1994 Proceedings of the National Association of Broadcasters, 48th Annual Broadcast Engineering Conference Proceedings, Mar. 20–24, 1994, content providers now offer high definition television programming having a 16:9 aspect ratio for display on wide screen television display devices.
While the market for high definition wide screen television display devices continues to grow, there remains a large embedded base of standard television display devices that can only display images having a 4:3 aspect ratio. To facilitate formatting of a wide screen video image having a 16:9 aspect ratio for display on a television display device that can only display images having a 4:3 aspect ratio, providers of wide screen content often encode a pixel coordinate within each individual frame to enable image format conversion by a “pan and scan” operation. Likewise, years from now when the embedded base of 16:9 aspect ratio display devices becomes large, video content from the 4:3 aspect ratio era will ultimately continue to be broadcast. Thus, a need will likewise exist for cropping a 4:3 aspect ratio image to fit within a video screen having a 16:9 aspect ratio.
The term “pan and scan” refers to a well-known technique for capturing a fixed-size window within a digital wide screen video image frame by effectively panning a row of picture elements (pixels) within the window and then scanning to the next row to commence a subsequent panning operation and so on. As described, the image capture window associated with the pan and scan format operation has a prescribed size. Thus, a single pixel coordinate, typically referred to as the “pan and scan pixel coordinate” will define such a window. In practice, the pan and scan pixel coordinate defines the center of the window. The location established for the pan and scan pixel coordinate affects what portion of the wide screen image remains after formatting. For example, establishing the location of the pan and scan pixel coordinate at the center of the wide screen image typically yields a formatted image that will not contain any activity occurring at the edges of image. To avoid such difficulties, some providers of video image content embed pan and scan pixel coordinates to facilitate formatting. However, because video image content is dynamic, such content providers must often embed a pan and scan pixel coordinate in each successive image frame to enable faithful formatting. Providing such pan and scan pixel coordinates has proven a very tedious process so only few content providers actually do so.
There, there is a need for a technique for automatically establishing a pan and scan pixel coordinate that overcomes the disadvantage of the prior art.