In scanning, the technique of using more than one vertical scan to reproduce a complete image. In television, 2:1 interlace is used, giving two vertical scans(fields) per frame; one field scans odd lines, and one field scans the even lines of the frame.利用多次垂直扫描来重显一幅完整图象的扫描技术。电视中使用2：1的交错率，即每帧分两场，垂直扫描两次，一场扫描奇数行，另一场扫描偶数行。
