Progressive Scan

Better quality TV images

Progressive scanning is a method for representing moving images on a display screen, where every pixel is represented in each frame. This is in contrast to the interlacing used in traditional television systems (progressive-scanning devices are sometimes referred to as non-interlaced).

Progressive scan is used in computer monitors. Usually video monitors use a raster scan to order the placement of pixels of the frame of video from left to right and from top to bottom at a given frame rate (e.g. every 1/60 of a second).

In more detail, the visual example below shows what a standard television shows. The standard televisions are "interlaced", meaning each frame is drawn in two 'fields', each field consisting of half the lines in the image (odd lines first, then even lines).

First (odd) field:




Second (even) field:




Every 1/60th of a second, a new field is drawn. Because of a theory called persistence of vision, the human eye sees it as a smooth motion, not a series of half-images. However, there is an almost imperceptible flicker.

Progressive scan, on the other hand, draws a full frame in the same time it takes interlaced mode to draw a single field, like so:



Because progressive scan draws 60 full frames a second instead of 60 half-frames, the eye is able to see a much smoother motion. This motion therefore shows less flicker than interlaced scan, while also significantly reducing the visibility of the individual scan lines.

(Source: Wikipedia)

 

 

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