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### Author Topic: How Can A TV Display 68 Billion Colours ?  (Read 3503 times)

#### neilep

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##### How Can A TV Display 68 Billion Colours ?
« on: 09/11/2007 23:44:29 »
A recent commercial I saw claimed that their latest Television can display something in the order of 68 Billion colours !!

Surely my eyes and yours can not perceive so many.....or can they ?....but I don't think so !!

....so....what advantage does a TV that displays so many colours really have  ?!!

Could I ask them to prove it to me ?...they claim it so...!!

When I get my credit card bill the only colour wifey makes me see is RED !!
« Last Edit: 10/11/2007 22:59:09 by neilep »

#### techmind

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##### Re: How Can A TV Display 68 Billion Colours ?
« Reply #1 on: 10/11/2007 11:43:21 »
He he. You're right to be cynical!
Was it a plasma TV?

Most computer- and TV displays and signals are based on 8-bit per channel (256 levels each of red, green, and blue) intensity-coding. That gives 256*256*256 = 16777216 - the familiar "16 million" colours.

But because human-perception of intensity is not linear, for efficiency the standard 0-255 intensity coding is also not linear. It is subject to a "gamma" function. This means that the actual brightness (as in number of photons) increases much more slowly at low grey-levels, and more quickly at high grey levels. Consequently although the perceptual "mid grey" is near code 128, it actually only has around 20% of the photon-count intensity of 255. The 50% photon-count happens near code 181.

Why am I telling you all this? Because the issue arises if your technology forces you (internally) to use a linear scale of brightness you find you need something like 4096 levels per R/G/B channel in order to get enough precision in the dark colours to not see banding. Plasma TVs inherently need linear-coding internally. The sales/marketing department then says "ohh 4096x4096x4096 = 68719476736  ... we got a 64 BILLION colour TV".
In reality of course the vast majority of the higher-brightness colours are indistinguishable. And in any case it's probably displaying a signal from an 8-bit (non-linear) source-signal anyway.

In short, you're not going to see any more colours, but compared to other plasma TVs you might find that dark colours are better reproduced, and you might find that you see less "speckle" in the picture overall.

LCDs usually work in 8-bit (non-linear) all the way through to the liquid crystal cell itself, so never have to go through a linear-coding stage. In fact many computer-monitor LCDs (certainly a couple of years ago) only drive the LCD cells at 6-bit (64-levels), but alternate the brightness slightly over several frames to fudge the in-between colours!
« Last Edit: 10/11/2007 11:53:50 by techmind »

#### neilep

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##### Re: How Can A TV Display 68 Billion Colours ?
« Reply #2 on: 10/11/2007 17:23:14 »
TECHMID IS GREAT !!

Fantastic Info.....yep !!..it's a PLasma alright !

THANK YOU for this wonderful detailed response. It's greatly appreciated.

#### neilep

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##### How Can A TV Display 68 Billion Colours ?
« Reply #3 on: 10/11/2007 23:00:01 »
Just saw the ad again...and TECHMID...you are spot on with your calculation it is in fact 68 Billion !!

#### The Naked Scientists Forum

##### How Can A TV Display 68 Billion Colours ?
« Reply #3 on: 10/11/2007 23:00:01 »