Television: How blue-coloured screen works?

Hi, i had question on this from earlier this day. Whenever the signal from television cable cuts, the TV switches into a bluescreen automatically. That looks something like this: **broken link removed**

It does makes user getaway from a sort of annoying sound that no signal causes. It is called as blueback, if i'm right. Previously, like about 7-8 years ago, my old television had no such facility. It used display it like this:
**broken link removed**
But how that works? How does the TV switchover to Blueback when no signal is found?

TV sets are not what they used to be. They used to be all analog. The set displayed what it saw, (heard). No signal was noise.

When sets got several inputs, there was a small amount of smarts added. If an input did not have a signal then it would switch to another input. One of those inputs might be a test pattern. Also...When On Screen Display was added the set could put text and some patterns on top of the video. Now the set could overlay text and patterns over the noise, or switch to a pattern when there was no signal.

With 100% digital sets, the picture is de-compressed with a monster computer. (DSP) It can do whatever it is programmed to do when there is no signal. Black, Blue, flying logo…..whatever the programmers whant it to do.

Thank You, you gave me the idea behind it. The one i have is a CTV (CRT), i dont know whether it is digital/analog. (mostly digital because it is fairly new).

Again coming back, if there no input> then the display will be noise.
But, some of the TV commercials(TVcommercials) show the same noise like image (image with white black dots), but why wont the system switch to blueback then?

If DSP works for that, it should also work for TV commercial.

The "snow noise" during a commercial is part of the signal. Even though the commercial shows snow, there's still sync signals in there. The DSP only mutes the video if there is NO signal, or an incompatible signal.

Old analog sets had no way of detecting a "no-signal" condition so it would just give you snow. When microprocessors started being used in TVs, they could detect a no-signal condition and throw up a blue or black screen.

Wont you think using a DSP for this purpose is a costly affair?(Or DSP in TVs are used for anyother purposes in extra)
Does Blueback/Blackback save the power consumption of TV anyway?