Interlaced Video Support - 1.0 English

AXI4-Stream Video IP and System Design Guide (UG934)

Document ID
UG934
Release Date
2022-11-16
Version
1.0 English

Interlaced video is a technique for doubling the perceived frame rate of a video display without consuming extra bandwidth. The interlaced signal contains two fields of a video frame captured at two different times. This enhances motion perception to the viewer, and reduces flicker by taking advantage of the phi phenomenon.

This effectively doubles the time resolution (also called temporal resolution) as compared to non-interlaced footage (for frame rates equal to field rates). Interlaced signals require a display that is natively capable of showing the individual fields in a sequential order. CRT displays and ALiS plasma displays are made for displaying interlaced signals.

Interlaced video standards have several differences over progressive standards:

Each field consists of a different set of lines. The set of odd lines is separated in time from the set of even lines.

The timing may vary on a per frame basis. Because there are usually an odd number of lines per frame, the number of total lines per field is different by one line. Moreover, this line difference may appear in the active period or in the blanking period depending on the particular line standard. This means that timing intervals may be different in odd frames and even frames.

There is a need to distinguish fields from each other. For progressive video, it is sufficient to mark video frames, because the timing and line composition of each frame is identical, however for interlace the two frames must be distinguished from each other, and the correct set of lines must be presented with frame timing for the picture to be displayed properly.