- Tech know how online


The classic television standards work with interlaced scanning and two fields, which in the PAL television standard have only 312.5 lines each. For large-area displays and projections, this has a negative effect in that the relative speed of the projected light beam decreases with the size of the projection screen. In addition, the low line structure is disturbing because the dark intermediate lines of the respective other field are visible as black lines.

These limitations can be overcome by doubling the number of lines. The corresponding devices work with video processors and are called linedoublers or de-interlacers because they cancel the interlacing.

Linedoubler, Photo: Philips

Linedoubler, Photo: Philips

There are three technical approaches: Line Insert, Interpolation and Field Insert. With line insert, the line content of a line is repeated; the second line therefore has the same line content as the first. With interpolation, the video processor calculates the intermediate lines from the average value between two lines of a field. The interpolation technique is suitable for moving scenes.

For static video sequences without great motion dynamics, the field insert technique is used. In this technique, two fields are combined: the odd lines of the first field with the even lines of the following field. With all techniques, the number of lines doubles from 312.5 lines per field to 625 lines.

Informationen zum Artikel
Englisch: linedoubler
Updated at: 26.11.2008
#Words: 284