Digital TV Headaches: The Dreaded Postage Stamp


In the broadcasting business, its called "Postage Stamping," and it's one of those little "quirks" that consumers will start to become more aware of (and annoyed by) in the next few months.

Watching The Amazing Race last night was a perfect example. While watching on a 27" screen, the actual video was ony 15" in size, floating in a huge black frame. Why am I spending the money on a widescreen TV if the program playing is this tiny little picture surrounded by black?

The answer is that the local television station is screwing up the picture.

In the good old days of television, all TV's had the same aspect ratio. In other words the deminsions of the screen's width to its height, which was 4x3 (4 units wide, to 3 units high. The actual size may change in inches, but the ratio is always the same). When HDTV started showing up, the decision was made to switch to a wider aspect ratio to reflect most movie screen sizes, which are 16x9.

Most digital TV stations are either broadcasting in 4x3 or 16x9 and very few of them actually switch between the two.

Here is an explanation of what they are doing to make both of these formats work together:


If a television station normally broadcasts in 4x3 format and they play a program that was recorded in 16x9 format (like a movie), the broadcaster has to add black bars to the top and bottom of the image. This is known as "letterboxing."



If the television station normally broadcasts their programming in 16x9 format, like most are starting to do, and they play a program that was originally recorded in standard definition, 4x3 format, the black bars are added to the sides of the video. This is known as "pillarboxing."

Sometimes broadcasters "down-covert" this 16x9 HDTV signal to a standard definition 4x3 format so that it will play easier on older TVs.

Sometimes a local broadcaster will over-process a signal, as was the case with my CBS station last night. They down-converted a 16x9 image that was already downconverted, which results in the program being both letterboxed and pillarboxed simultaneously, or postage stamped.


In other words, fellas, "yer doin it wrong!"


Thankfully, until everything gets settled, viewers at home can circumvent the goofballs at the station by using the television's "zoom" function to expand the signal back to a more viewable size. Of course, this zooming is just processing a signal that has already been over-processed to begin with, so don't expect to see sharp, crystal clear looking images.

As more broadcasters start turning off their analog transmitters as part of the big digital switch that will take place next February, various little glitches like postage stamps will become more commonplace.

For more information about the digital TV switch taking place on Feb 17th, visit the FCC's website set up for consumers at www.dtv.gov/consumercorner.html

Images courtesy: FCC

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