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Odd effect?


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Old 24-09-2013, 16:42
Andy2
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Location: Vault 101, Cheshire
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I'm not sure where to post this, but here goes.

I've noticed that on 'police reality' shows, when peoples' faces are illuminated by the blue lights from police vehicles, the effect is not like it used to be.
The effect used to be a natural 'lit by blue light' effect, but now it looks like someone has painted the area with a thick bright blue paint, with no detail visible.

Good example here:

http://www.bbc.co.uk/iplayer/episode...thout_Warning/

starts at 45 mins in.

I've seen this many times on several TVs.
Is this something to do with digital TV or has camera tech changed recently?
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Old 25-09-2013, 14:10
nvingo
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...peoples' faces are illuminated by the blue lights from police vehicles, the effect is not like it used to be.
The effect used to be a natural 'lit by blue light' effect, but now it looks like someone has painted the area with a thick bright blue paint, with no detail visible...Is this something to do with digital TV...
Yes it is the result of video compression technology, that which allows five high-definition digital channels to be broadcast in the same bandwidth as a single standard-definition PAL analogue channel.
MPEG compression works by comparing a series of video frames, and coding only the data that changes between them. Most scenes don't change too rapidly for this to be an effective way to compress video data; ie. a static camera on a newsreader only the face will have inter-frame differences.
When the scene changes drastically, the detail has to be built up over several frames. This is why digital-friendly edits use transitions rather than cuts.
Rapidly-changing scenes such as when the lighting fluctuates cause a problem for the encoder as the bandwidth isn't there to code several full-frames in succession so the changing detail is lost.
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Old 25-09-2013, 16:04
Andy2
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A cracking explanation, thankyou. The effect is certainly disconcerting, almost cartoon-like.
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