Electronic Media 

Published: 09-18-95 



OPTIONS FOR MORE TV DIGITAL DATA;IF FCC OPENS DOOR, HERE ARE 

SOME ROUTES YOU CAN TAKE    



Byline: Joe Fedele 



 Last month I sounded off about the Federal Communications

Commission politics that are keeping broadcasters from having

more leeway to insert digital data into their TV transmissions.

 This month I'd like to lay out the technical options for

inserting data into TV pictures.

 Putting digital data into a TV picture is nothing new. For

years, broadcasters have used the vertical blanking interval for

closed-captioning and the ghost canceling reference.

 Existing FCC rules permit these  services because they lie

within the first 21 lines of video. This ``hidden'' data in the

VBI is not viewable on consumer-grade TV sets.

 Another way to hide data involves  line 22, the first active

line of video immediately following the VBI.

 The FCC has already authorized line 22 to be used for the

electronic verification of broadcasts. This sets up time- and

date-stamps for commercials while checking the presence of audio

and video for commercial verification purposes.

 While this data lies just outside of the VBI it remains within

the ``overscan'' region of the video, which is the area used to

mask the narrow black border that surrounds the picture.

 Because overscanning provides a buffer zone that wraps

completely around the entire picture, it is possible to hide

data on the top, bottom, left and right margins of video.

 Another, more sophisticated method of hiding data, is called

``sub-video.'' This system conceals data by distributing it

throughout the visible picture. The amplitudes, or strength, of

the data is kept low enough that it is invisible to the viewer.

 However, if you attempt to strip out the data some video

degradation occurs. The cumulative effect of repeatedly deleting

data from video that is retransmitted could become noticeable

over several generations.

 This could spell trouble for sub-video proponents because the

FCC is insistent upon ensuring the highest quality video.

 The overscan method, on the other hand, inserts data at

specific places in the picture that are easily deleted by the

licensee without any picture degradation.

 The sub-video method also limits the ability of TV licensees to

easily control the ancillary communications, because the data is

not as easily extracted as in the case of the VBI method.

 That's a sticking point with the FCC, which maintains that

licensees ``must maintain control over all aspects of their

signal,'' including data transmissions within the video.

 The FCC takes the position that broadcasters should not be

allowed to  ``relinquish to the data or program supplier the

right to delete the data.''

 I tend to agree with the commission on this matter. If

broadcasters are to be held accountable for what they have on

the air, they must have the ability to control it.

 Data rates used by these insertion techniques range from

between 384 Kbps and 1.544 Mbps. With this kind of technology,

broadcasters need not wait for high-definition television to get

a head start on such interactive services as electronic TV

listings, promotional information and home shopping information.

 Of course, none of this will happen until the FCC gives

broadcasters the freedom to use what they are already licensed

for, namely, ``to serve the public interest.''