Progressive or noninterlaced scanning is a method for displaying, storing or transmitting moving images in which all the lines of each frame are drawn in sequence. This is in contrast to the interlacing used in traditional television systems where only the odd lines, then the even lines of each frame (each image now called a field) are drawn alternately. The system was originally known as "sequential scanning" when it was used in the Baird 240 line television transmissions from Alexandra Palace, England 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. The interlaced images use half the bandwidth of the progressive ones.

The left-center image precisely duplicates the pixels of the progressive one, but interlace causes details to twitter. Real interlaced video blurs such details to prevent twitter, but as seen on the right-center image, such softening (or anti-aliasing) comes at the cost of image clarity. A line doubler could not restore the previously interlaced image on the right to the full quality of the progressive image on the left.

(Note - Because the refresh rate has been greatly slowed down, and the resolution is much lower than that of typical interlaced video, the flicker in the simulated interlaced portions and also the visibility of the black lines in this image are exaggerated. Also, the images above are based on what it would look like on a monitor that does not support interlaced scan, such as a PC monitor, or an LCD or plasma-based television set, with the interlaced images displayed using the same mode as the progressive images.)

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