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In 1997, Sony’s original DVP-S7000 helped launch the DVD-
Video format and was quickly acclaimed as the “Reference
Standard.” In 1998, the second-generation DVP-S7700 took
DVD playback to a new level of accuracy. Of course, both
players were designed to maximize performance with the huge
universe of televisions using 525-line interlace scanning.
In the mean time, TV stations have launched the era of Digital
Television (DTV) broadcasting. High Definition satellite
broadcasting has become a commercial reality. In response,
Sony and others have introduced a growing population of
televisions with higher scanning frequencies, capable of better
than 525-line interlace scanning.
Some of these new televisions offer progressive scan or 525P
inputs, which can accept 525P output from a DVD player. And
525P outputs have quickly been promoted as a must-have feature
in high-end DVD players. They promise reproduction that’s
even more detailed, more natural, more film-like.
However, there are important differences in how DVD players
process the 525P signal. Circuitry varies greatly in sophistica-
tion and cost. To appreciate the technology behind these
differences, readers need a firm understanding of progressive
versus interlace scanning, film versus video origination, 3-2
pulldown and 3-2 reverse conversion. This section reviews
these basic issues.
In video, what appears to be a continuously moving image is
actually a series of discrete still pictures, called frames. On the
typical direct-view television, each frame is created on the
picture tube by an electron beam that moves from the left edge of
the screen to the right, illuminating one scanning line at a time.
The American EIA television system uses 525 total scanning lines
per frame.
Due to bandwidth limitations from the early years of television,
the NTSC system was designed to capture 30 frames per second.
The natural way to display these images would be to show the
scanning lines in sequence, an approach called progressive
scanning. 525-line progressive scanning at 30 frames per
second is abbreviated 525/30P or simply 525P. Unfortunately,
525/30P creates flicker: the image visibly darkens between
frames. In addition, capturing images at 525/30P yields
unsatisfactory results in fast-paced action like live sports.
For these reasons, the early television engineers developed a
solution called interlace scanning. Instead of capturing and
displaying all 525 lines in their numerical sequence, the NTSC
system divides the image into two fields. The “A” field contains
the odd-numbered scanning lines (1, 3, 5, etc.) and lasts 1/60
second. The “B” field contains the even numbered lines and lasts 1/60
second. This system can be abbreviated 525/60i or simply 525i
(when discussing the line rate) or 60i (when discussing the picture
rate). The 525i solution is a compromise that doubles the picture rate
but halves the vertical resolution at any given instant. While it is a
compromise, the 525i system is highly effective, an elegant
engineering solution that has helped make television an essential part
of entertainment.
In the early days of television, when 12-inch diagonal screens were
commonly used in living rooms, halving the vertical resolution was
not a practical concern. But in today’s environment of 61-inch
diagonal projection systems, the illusion of a continuous picture on the
screen begins to fall apart, especially when you sit close to the screen.
Individual scanning lines become visible and the compromise in
vertical resolution becomes an annoyance. That’s why many of
today’s finest big screen televisions have the ability to input and
display 525P at 60 frames per second (525/60P). When carefully
executed, 525/60P can achieve fluid, lifelike fast motion, along with
breathtaking image detail. The 525/60P system is also superb for
resolving fine print on the screen — one reason why 525/60P is the
basis of the popular VGA computer display standard.
Movie film is conventionally shot and displayed at 24 frames per
second. In the camera, the entire frame of film is exposed at one
time. In the theater, the entire frame is projected at one time.
Unfortunately, projecting at the native film rate of 24 frames per
second creates flicker. That’s why movie projectors use a special
shutter to display each frame twice, creating the effect of 48
frames per second.
Theatrical release movies aren’t the only programs that are
originally captured at 24 frames per second on motion picture
film. The following is a snapshot of common industry practice:
Genre
Typical Origination
Theatrical release movies
24P film
Made for TV movies
24P film
Hour-long primetime dramas
24P film
Music videos
24P film
Network commercials
24P film
Sitcoms
Either
Documentaries
Either
Network news magazines
Either
Live concerts
60i video
Wildlife/natural history
60i video
Reality-based shows
60i video
Do-it-yourself series
60i video
Soap operas
60i video
News
60i video
Talk shows
60i video
Sports
60i video
Local Commercials
60i video
A Major New Opportunity
Film and Video Origination
Progressive and Interlace Scan
Fig. 1: Progressive scanning creates
the picture by illuminating each line
from top to bottom until all scanning
lines in the frame are completed.
Fig. 2: Interlace scanning divides the
frame into two “fields.” The first field
presents the odd-numbered scanning
lines (1, 3, 5, etc.). The second field
presents the even numbered lines.
