TVL versus Effective Pixels

[Scruit 0]

I have seen cameras offered in may different configurations re: TV Lines and Effective Pixels...

 

It would seem to me that 480 TVL would mean that the camera generates an inamge that consists of 480 distinct pixels in height...

 

It would also seem to me that Effective Pixels would mean what the camera is capable of seeing, regardless of what it's able to send downt eh wire to the DVR.

 

And putting these together, it would seem sensible to me that a camera that offers a TVL rating higher than it's effective pixels height would be 'stretching' the image, whereas a camera that offers lower TVL than it's effective pixels would be 'shrinking' the image.

 

 

Of course, it can't be that simple.

 

So, please explain to me which of the following two cameras will generate the best image detail, *all other factors being equal*...

 

 

Camera A:

Image Device 1/3" color CCD

Picture Elements (H x V) 500 x 582 (doesn't sound right?)

Horizontal Resolution 330 TV Lines

 

 

Camera B:

480 TV lines & High Resolution

Effective pixels 768(H) x 494(V)

[lynndiwagon 0]

pixels and analog don't go together in my mind. It's like comparing apples to oranges.....

[SBTVideoman 0]

The number of effective pixels refers to just that - how many pixels on the CCD chip are physically collecting light. You will find that most 1/3" cameras today have approximately 440,000 pixels (approx 752 x 582 on a PAL camera). That number will be slightly different on a NTSC model.

 

However...you can have two cameras with an identical pixel count producing quite different TVL resolution.

 

The TVL resolution refers to the FINAL resolution of the camera...once you take into account all the post-CCD capture processing. This is where the overall design and build quality decides. That's why a full-body camera (for example a Bosch Dinion, a Siemens CCBC1337, a Panasonic SDIII or a Sanyo) will almost always produce a much cleaner, sharper image than a cheapie dome camera that uses nominally the same Sony CCD.

 

So....at the end of the day it's the quality of the overall electronics that's driving the CCD which will determine the final TVL resolution of a camera, not just the raw pixel count.

[CollinR 0]

You can also inverse that through post processing, his is basically like a "upconverting" DVD player. You have more TVL then you have effective pixels, this doesn't help picture quality narly as much.

[SBTVideoman 0]

Yes and no.

 

Resolution in TVL is a measure typically used in the "analog" world - in other words, taking the raw composite video signal and displaying it on an analog CCTV monitor while having the camera pointed at a standard test chart. The more TVL the higher the resolution and (theoretically) the better the image quality.

 

Pixel resolution is typically used when talking about the image displayed on a remote client connected to a DVR (ie when streaming video). This is not the same as TVL resolution...because even when the viewing window has an effective display area of 640x480 pixels (common for some IP cameras), this does not mean you have exactly that level or resolution -don't forget that the image has been digitally compressed (via Wavelet, JPEG2000, MPEG4, H.264 or other compression codecs) - hence some resolution is always lost. You may well end up with a number of the pixels in our 640x480 image being identical - this is the typical "blockiness" artefact you seen when playing back some DVD movies or movie trailers online.

 

My point is that the number of "effective pixels" on the CCD not always an indication of final image quality as seen either on an analog monitor on an a remote client streaming video off the DVR. In fact the latter case can be worse, as you're now depending on two things being done right

1) the camera electronics being good enough to generate a quality image

2) the DVR frame grabber and encoder being of sufficient quality to create a high enough quality image.

 

As an example - many PC-based (and some embedded DVR's) only record at CIF resolution (this is 320x288 in PAL). So - regardless of how many effective pixels the CCD has, or how many TVL the camera can produce, your final playback image will at best have 320x288 effective pixels, since that's the weakest link in the signal chain.

 

Hope that makes sense.

[rory 0]

For recording purposes, ignore the TVL and rely on the Image Pixels, thats what matters. There are many OEM cameras that claim they are 480TVL or 540TVL and yet if you check their specs (where available) their image pixels are only 512x492. Since we are talking about the camera's maximum quality, I wont mention any other situations which can ultimately effect the end result such as the viewing monitor, lighting conditions, recording compression and resolution; as those are not applicable to the OP's question.

 

To answer the OP's question, camera B, though that also depends on whether the specs are correct. Not every camera is made alike. Though I'd prefer the camera with 811x508 pixels myself. You get what you pay for.