A video display method that creates a full image by alternating scan lines, displaying odd and even lines in separate fields.
Interlace is a video scanning technique used to display images by dividing each frame into two separate fields. The first field contains the odd-numbered horizontal lines, while the second field contains the even-numbered lines. These fields are displayed in rapid succession, allowing the human eye to blend them together into what appears to be a complete image.
This method was originally developed to reduce bandwidth requirements while maintaining acceptable visual quality. By transmitting only half of the image lines at a time, interlaced video systems can deliver motion and detail using less data compared to progressive scanning. For example, a 1080i signal displays 540 lines per field, alternating at a high frequency, while a 480i signal displays 240 lines per field.
In commercial and industrial video systems, interlacing is commonly associated with legacy display technologies such as CRT monitors and certain broadcast formats. The timing between fields is critical, as the illusion of a complete image depends on precise synchronization. When properly aligned, static images appear stable because the eye integrates both fields into a single frame.
However, interlacing can introduce visual artifacts, particularly in scenes with motion. Since each field is captured or displayed at a slightly different time, fast-moving objects may appear distorted or create a comb-like effect. These artifacts occur when the two fields do not align perfectly to form a cohesive frame. This can be especially noticeable in video content with rapid movement or in conversions from film-based material.
Despite these limitations, interlacing remains an important concept in understanding video signal formats and system design. It highlights the trade-offs between bandwidth efficiency and image quality, and it continues to influence how video systems process and display motion.