INTERLACED SCAN

Figure 1-3.-Inter1aced scan of a CRT. merge point. Two methods are used to increase the Interlaced scan CRTs are fine for television resolution of CRTs. These are interlaced scan and noninterlaced scan. INTERLACED SCAN.– Interlaced scanning makes it possible to double the number of horizontal lines in a picture. Figure 1-3 illustrates the principle of interlaced scanning in which two scans are required to display the full picture. The odd raster starts in the top left corner of the CRT, while the even raster starts in the top center of the CRT. The two complete scans paint the entire picture. By interlacing the odd and even lines of a picture, resolution can be increased without a noticeable flicker on the screen. Interlaced scanning is used with standard television and some computer monitors. It increases the maximum number of lines per frame to 525. Because of the vertical retrace time, the number of visible lines is 512. 1-4 transmissions and alphanumeric displays, but can cause a visible flicker when displaying fine digital graphics because of the abrupt changes in the levels of intensity required. To solve this problem, most computer monitors use noninterlaced scan. NONINTERLACED SCAN.– Noninterlaced scanning paints the entire frame of data from top to bottom. Figure 1-4 illustrates the noninterlaced scanning method of painting a single frame. To paint an entire frame without a noticeable flicker, the horizontal frequency is increased, which increases the number of lines per frame. The vertical frequency is also decreased from 60 Hz to 50 Hz in most monitors, which further increases the number of lines.