Motion picture films are recorded at 24 frames per second. When the movie is released for the home on DVD or a television broadcast, those 24 frames must be converted into 60 interlaced fields. Consider four frames of film: A, B, C, and D.

The first step is to convert these four frames into eight fields. This transforms 24 frames per second (fps) into 48 interlaced fields per second. Then, to account for the faster rate of the NTSC standard (roughly 30 frames per second or 60 interlaced fields per second), it is necessary to repeat certain fields. This is done by adding an extra field every other frame. That is, both fields of frame A are recorded (A-odd, A-even), but three fields of frame B are recorded (B-odd, B-even, B-odd). The cycle repeats with frames C and D. This is called a 2:3 cadence because two fields of one frame are shown followed by three fields of the next frame.

When this sequence is played back on a progressive-scan video display, it is possible to implement the same de-interlacing techniques described earlier (non-motion adaptive vs. motion adaptive, etc.). However, it is possible to perfectly reconstruct the original frames without losing any data. Unlike interlaced video, in which the two fields were recorded a fraction of a second apart, these fields were recorded at the same time in the same film frame and later separated into fields.

So, to display a video signal that originated as 24fps film, all a video processor needs to do is analyze the fields and determine that there is a regularly alternating pattern of two fields followed by three fields, etc. This recognition and reconstruction is called 3:2 pulldown, and it is found in all but the worst de-interlacers. Unfortunately, nothing is quite that simple.

Mixed Video and Film:
Sometimes, further editing and post-processing is done on film that has been converted to video. This includes titles, transitions, and other effects. As a result, simply reconstructing full frames results in combing artifacts because parts of the image are best processed using a standard de-interlacing approach, while other parts will look better by detecting the right cadence and reconstructing the original frames.

Like the various approaches to standard de-interlacing, there are many approaches to dealing with mixed video and film. If the processor interprets the material as film, feathering artifacts will appear around the video portion; if the processor interprets the material as video, the film portion will be displayed at half of its resolution. Some processors determine whether there is more film or more video content and choose the approach with the greatest benefit. Since this usually means film, the result is feathering artifacts. Other processors are designed with the idea that these artifacts should never be seen and use the video de-interlacing techniques in all cases, at the expense of as much as half the video resolution.

HQV Processing, on the other hand, uses per-pixel calculations for all of its processing. This means it is possible for the HQV processor to implement cadence-detection strategies for the pixels that represent film content while implementing pixel-based motion-adaptive de-interlacing for the video content that has been superimposed.

Other Cadences:
The HQV Processing advantage of true per-pixel de-interlacing becomes even more evident when dealing with other cadences. Although 24fps film and its associated 2:3 video cadence is the most common format, it isn’t the only cadence used today.

Sometimes, TV stations accelerate their film-based movies and TV shows by dropping every twelfth field to make room for more commercials. This speedup is usually too small to be noticed by the average viewer, but these “vari-speed broadcasts” end up having unusual cadences such as 3:2:3:2:2. If a de-interlacer is unable to detect this sequence, as with most of the competition,  half the resolution is lost.

The variety of cadences does not end there. Professional DVCAM camcorders are increasingly used in television and film production. In order to maximize the recording time, these camcorders use a 2:2:2:4 cadence or a 2:3:3:2 cadence to store the progressive source signal as 480i on the tape. Animation gets even more creative with cadences ranging from 5:5 to 6:4 or 8:7 for Japanese anime.

Most competitors’ processors compare the incoming fields and try to match them against known sequences such as 3:2 or 2:2 in order to select the right decoding. This works for the most part, but there can be a short delay before the processor is able to “lock on” and determine the right cadence. In addition, when the video processor encounters an unusual sequence such as animation or DVCAM, it may resort to discarding half the data if is a non-motion adaptive processor.

With HQV processing, there is never any confusion about cadence. Instead of trying to match the incoming video against known patterns, HQV processing simply identifies complete frames as they come in. HQV processing is able to identify all known cadences, no matter how uncommon, and it can also detect cadences that have not yet been invented.

No matter what type of video you’re watching or where it comes from, HQV processing will always provide the best reconstruction of the image.