### Author Topic: tv lines  (Read 1802 times)

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#### abdullahseba

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##### tv lines
« on: February 25, 2015, 10:09:53 am »
If an LCD is full HD (1920x1080) does that mean that it has 1080 TV lines?
I am wondering because CCTV cameras usually have there resolution in TV lines (480tvl,700tvl etc.
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#### Psi

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##### Re: tv lines
« Reply #1 on: February 25, 2015, 10:24:16 am »
if its 1920x1080 then yes, it has 1080 lines of 1920 pixels each.

TV lines are pretty much what they sound like, 480 lines = 480 lines,
Its actually a bit more complex, but simply put <x>TVL is a measure of the number of vertical bands of different shading you can resolve across a horizontal line.

Keep in mind that there are "hidden" scan lines in a video signal that you don't see, that's where teletext info is encoded.
« Last Edit: February 25, 2015, 10:40:42 am by Psi »
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#### abdullahseba

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##### Re: tv lines
« Reply #2 on: February 25, 2015, 10:27:07 am »
so is there any way to work out how much resolution a camera has?
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#### Psi

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##### Re: tv lines
« Reply #3 on: February 25, 2015, 10:38:22 am »
Sorry, i got it wrong so edited my original post.

As far as i know the number of vertical scan lines is fixed for the TV standard your using, the TVL number refers to horizontal line detail in the analog video signal.

You can compare cameras by pointing them at a printout of alternating vertical lines and moving the distance between the camera and paper while watching the video signal on an oscilloscope. The higher resolution camera will keep the detail at a larger distance.
« Last Edit: February 25, 2015, 10:41:29 am by Psi »
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##### Re: tv lines
« Reply #4 on: February 25, 2015, 10:40:51 am »
I am wondering because CCTV cameras usually have there resolution in TV lines (480tvl,700tvl etc.

Its a hangover from the analogue days and it's almost always also completely fanciful. It was an indicator of the frequency response of the system but it was most often measured *at* the imager and what you got out of the BNC on the back was rarely within a bulls roar of what the spec sheet said you'd get, particularly when things went colour. After you shoved it down some cheap, badly matched coax that had been stretched by the grunt installing it and then put it into a third world sourced monitor or VCR any resemblance to the spec sheet resolution was at most purely coincidental.

On well made systems with excellent quality cabling and due care and attention paid to the installation and termination (read "an expensive install) you could often get over half the resolution the piece of paper said you would.

Having said that, IP cameras are no better. I tested some 16 megapixel units recently that produced less than half the rated real resolution at the recorder because the spec sheet lists the imager resolution and pays no attention to the mush the badly implemented compression algorithms make of what was likely a pretty nice image. It's a common problem across the industry and often leads to horiffic issues if the footage has to go to court because an expert (and these guys are as close as you'll get to one) points out that at the supplied resolution there is reasonable doubt as to the identity of the block of pixels accused of the crime.

Never, _ever_ believe a salesman, spec sheet or manufacturer data. If you can't test it yourself, get a professional to do it for you and if you think you can test it adequately yourself, you are probably wrong.

Welcome to the security industry, the last holdout of the theif and charlatan.

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##### Re: tv lines
« Reply #5 on: February 25, 2015, 10:41:19 am »
so is there any way to work out how much resolution a camera has?

Measure it. In god we trust, all others bring data.

Smf