Image Processing Reference
does this as the switch takes place in the scanning circuits in some models. Sometimes the
electronics make a loud electrical crackling noise as the voltages change.
Ideally this would be done digitally and the TV scan circuits would simply continue
scanning a constant-sized raster.
This is covered in more detail in Chapter 39, which discusses some advanced topics
related to hidden data signals.
Film Aspect Ratio Formats on TV
Many movies are delivered on DVD in a wide-screen letterbox format that shows the
entire picture. These days this is often standardized to cinemascope or Panavision format,
which has an aspect ratio of 2.35:1. Adjusting the vertical zoom factor of the TV presents
a larger picture, but it sacrifices consistent scaling in X and Y. Figure 5-18 shows how these
formats are fitted onto a TV screen.
2.35:1 on 4:3 with letterbox cutout
2.35:1 on 16:9 with letterbox cutout
Figure 5-18 Panavision aspect ratio.