interlacing

Interlacing is a technique used in video and image processing in which a frame is divided into two alternating fields that are captured or displayed at different moments. This approach aims to improve the perceived smoothness of motion without requiring additional bandwidth.

Historically, interlacing arose with analog television to conserve bandwidth while preserving motion clarity. It is standard in many broadcast systems such as NTSC, PAL, and SECAM. In digital video, interlaced formats such as 1080i and 576i are still used in some broadcasts, while progressive formats like 1080p and 720p are common for streaming and modern displays. Some content is converted between interlaced and progressive forms during processing or transmission.

Technical details: Each frame consists of two fields—one containing all the odd-numbered lines and the other containing all the even-numbered lines. The two fields are displayed in quick succession, creating the illusion of a full frame at the field rate, which is typically twice the frame rate. The order in which the fields are shown (top field first or bottom field first) is defined by the video standard and can affect how motion is perceived.

Deinterlacing and artifacts: When interlaced video is shown on a progressive display, a process called deinterlacing reconstructs full frames. Common methods include weaving (combining both fields when there is little motion) and bob deinterlacing (reconstructing full frames from each field). Artifacts such as combing during motion, flicker, or reduced effective resolution can occur if the deinterlacing method is not well matched to the content.

Other usages: The term also appears in image formats and data organization, where interlacing enables progressive rendering or interleaved data storage to improve loading times or access patterns.