- published: 26 Mar 2015
- views: 2503
Progressive scanning (alternatively referred to as noninterlaced scanning) is a way of displaying, storing, or transmitting moving images in which all the lines of each frame are drawn in sequence. This is in contrast to interlaced video used in traditional analog television systems where only the odd lines, then the even lines of each frame (each image called a video field) are drawn alternately.
The system was originally known as "sequential scanning" (a more technically correct description) when it was used in the Baird 240 line television transmissions from Alexandra Palace, United Kingdom in 1936. It was also used in Baird's experimental transmissions using 30 lines in the 1920s.
This rough animation compares progressive scan with interlace scan, also demonstrating the interline twitter effect associated with interlace. On the left are two progressive scan images. Center are two interlaced images. Right are two images with line doublers. Top are original resolution, bottom are with anti-aliasing. The interlaced images use half the bandwidth of the progressive ones. The images in the center column precisely duplicate the pixels of the ones to the left, but interlace causes details to twitter. Real interlaced video blurs such details to prevent twitter, but as seen on the bottom row, such softening (or anti-aliasing) comes at the cost of image clarity. A line doubler could not restore the previously interlaced image at bottom center to the full quality of the progressive image on the top left.