What is the difference between an interlaced and progressive image?
Now that we know there are 525 horizontal scanning lines stacked one atop the other, we should also be aware that only 480 of these lines form the visible image. The remaining 45 lines are in the background and form the vertical blanking interval (VBI). In an interlaced system, the very first type of television broadcast, the lines were painted in fields. One field painted all the odd lines 1,3,5,7 etc These lines were painted in 1/60 second. The second field, comprised of scanning lines 2,4,6,8 etc, is painted in the second 1/60-second. The two fields create a frame. Television images are shown 30 frames per second. Persistence of vision ensures we see a complete image as the inherent latency of the human eye makes it impossible to perceive visual changes that occur in less than 1/30-second. Computer monitors utilize a different method of display. Because in the early days of computers there was no need for motion in the images, the data could be painted (the refresh rate) at a higher
