Deinterlacing: the conversion of a video signal from interlaced to progressive

Why deinterlace?
Modern pixel-based displays (LCD, DLP, LCOS, plasma,…) are progressive scan and require progressively scanned video sources, whereas many older video devices use the older interlaced scan technology.

Interlaced Scan: a complete image frame is encoded in two fields – one containing all the odd lines, and the next containing all the even lines. When displayed, the image is drawn with all the odd lines being scanned from top to bottom, followed by all the even lines top to bottom. Sixty separate fields are shown every second.

Examples of interlaced signals:

Standard Definition (480i): DVD, SD broadcast / cable, VCR, laserdisc,…

High Definition (1080i): HD broadcast / cable, DVHS, game consoles,…

Progressive Scan: a complete image frame contains all the lines of the picture, in order, from top to bottom. When displayed, each image frame is drawn in a single scan from top to bottom. Sixty complete frames are shown per second.

Examples of progressive signals:

Standard Definition (480p): progressive scan DVD players, progressive output from set top boxes

High Definition (720p): HD broadcast / cable, game consoles VESA (XGA@60HZ): Home Theater PC (HTPC), Laptop

The problems of Deinterlacing

There are a number of challenges in converting an interlaced video source into progressive scan format. Here are two of the main issues that a video deinterlacer has to deal with:

Motion Adaptive – allow for the movement of objects in the time between the two interlaced fields of a frame. Edges should be smoothed, but without losing detail. Our eyes are very good at detecting the slightest jagged edge, or hesitation in movement.

Film Source – detect original film source material that has been adapted for dvd and reverse that process (apply inverse 3:2 pulldown). Works on film are generally adapted to TV format by repeating every 3rd or 5th frame in order to bring it up to the right number of frames per second. When deinterlacing, it is important to allow for the duplicate frames to keep movement and edges smooth.

Not all Deinterlacers are created equal

Displays may have their own built-in deinterlacers, but these tend to be of inferior quality. Artifacts resulting from the slight time difference between interlaced fields can cause strange effects, and flickering may be a problem.

DVDO’s Precision Deinterlacing™ technology delivers the image quality demanded by today’s large-screen, high-resolution displays. It eliminates many of the artifacts found in common deinterlacers to produce a smooth image, free of artifacts such as jagged edges and combing.

Precision Deinterlacing features five-field motion-adaptive deinterlacing and edge-adaptive processing for video sources, along with advanced cadence detection for film and animation sources. All processing is performed at full 10-bit resolution to preserve all the detail and subtle nuances in the video source. Edge-adaptive processing uses an adaptive, continuous-angle detection algorithm to accurately identify and smooth image edges.

Unique, “any-cadence” processing automatically locks to the wide variety of film and animation cadences found in current video sources, including non-standard cadences, and will track right through many types of “bad edits” and cadence changes. The Precision Deinterlacing Card also features operating modes for special video applications, such as low-latency processing for video games, where timing is essential.