Image Processing Reference
Figure 34-15 Crop to remove data lines at the top.
the top of the picture and one at the bottom. This half line is required to adjust the timings
in the horizontal axis so that the interlacing works correctly. These half lines can be
cropped as well.
Figure 34-15 shows a snapshot of the top four lines of a captured frame of video.
After being scaled vertically by a factor of 10:1, the top line is blank and the second line
has some digital signaling superimposed. This must be cropped.
If you are creating some encoded footage for a very-low-resolution target platform
such as a mobile phone, then it is permissible to crop into the subject matter as closely as
Crop down to the safe area, which is a boundary that is approximately 10% of the screen
size around the border. This is important for content being viewed on a TV set because
it is designed to over-scan the picture in order to hide any nasty edges. Other devices
that show you the entire raster do not require this precautionary framing of the content.
Figure 34-16 shows where the safe areas are.
There are other safe-area designs, depending on who made the content and what
it was eventually intended for. Figure 34-17 shows a safe area graticule designed for
Action safe area
Title safe area
Figure 34-16 Safe areas.