Progressive Scan
What is Progressive Scanning in HDTVs?
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.
Advantages of progressive scan
- Higher vertical resolution than interlaced video with the same frame rate.
- Absence of visual artifacts associated with interlaced video of the same line rate, such as interline twitter.
- No necessity in intentional blurring (sometimes referred to as anti-aliasing) of video to reduce interline twitter and eye strain.
- Offers much better results for scaling to higher resolutions than equivalent interlaced video, such as upconverting 480p to display on a 1080p HDTV.
- Frames have no interlace artifacts and can be used as still photos.
In the case of most media such as DVD movies and video games, the video is blurred during the authoring process itself to mask flicker artifacts when used on interlace displays. As a consequence, recovering the sharpness of the original video is impossible when the video is viewed progressively. An excellent, but rarely employed countermeasure to this is when display hardware and video games come equipped with options to blur the video at will, or to keep it at its original sharpness. This allows the viewer to achieve the desired image sharpness with both interlaced and progressive displays. An example of a video game with such a feature is Super Smash Bros Brawl, where a "Deflicker" option exists. Ideally it would be turned on when played on an interlaced display to reduce interline twitter, and off when played on a progressive display for maximum image clarity.
Scaling works well with full frames, therefore interlaced video must be deinterlaced before it is scaled. Deinterlacing can result in severe "combing" artifacts.
Disadvantages of progressive scan
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A disadvantage of progressive scan is that it requires higher bandwidth than interlaced video that has the same frame size and vertical refresh rate.
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