Sensor or film technique splitting frames into interleaved half-images — apparent higher frame rate without bandwidth cost. Legacy TV standard, rarely used today.
Post-war television faced a significant problem: the refresh rate needed to be high enough to avoid flicker, but available bandwidth was extremely limited. The solution was interlacing: each full frame was divided into two time-offset fields. The first field displayed the even lines, and the second displayed the odd lines. To the human eye, these 50 or 60 fields per second optically merged into a flicker-free image, even though the actual spatial resolution was significantly lower than a true full frame.
On set and in practice, interlacing was long the standard for PAL (50i) and NTSC (60i). The camera sensor or film camera had to capture two fields in rapid succession, which led to typical combing artifacts with fast motion. Anyone who has operated an old DV camera with 50i is familiar with this effect: fast pans or objects create jagged, doubled edges. In editing, deinterlacing was often a necessary evil – recalculating the fields back into a clean full frame, which cost quality.
Today, interlacing is practically obsolete. Modern sensors work with true full frames (progressive scan) – 24p, 25p, 50p, 60p – without the detour through fields. Streaming standards like H.264 and H.265 are optimized for progressive. Even with high-speed recordings on Red or Arri, we work with complete frames, not interlaced fields. The only places where you still encounter interlacing are when archiving old broadcast material or when working with legacy equipment – for example, during the restoration of archive footage. In such cases, you then need to deinterlace cleanly and convert to a modern format.
Anyone hearing about interlaced recording today usually means an archival matter or a mistake. For current productions, it has become irrelevant – and that's a good thing. The technical burden has been lifted, and quality has increased. Period.