resolution confusion

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baxterdmutt
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Joined: Tue Sep 16, 2008 3:47 am

resolution confusion

Post by baxterdmutt » Sat Sep 20, 2008 3:32 am

Hello all,
The manual for my Q-see camera says:
Picture element: 582(H) X 500(V): NTSC
Horizontal Resolution: 420 TVL Lines.

My question is what resolution should I be entering in the config box in ZM. I managed to get it to work with 240x200 but I just lucked into that number. I had tried 582x500 and 500x582, but I don't get an image with those. Is there a way to tell what my camera is generating for resolution. I am confused. Any help would be very much appreciated.
Thanks

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cordel
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Post by cordel » Sat Sep 20, 2008 5:23 am

What is described in CCTV cams as resolution does not reflect pixel resolution as in digital images but in spatial resolution to what the camera can distinguish by a certain pattern. The two are not the same.

In NTSC you have two upper limits as they translate into a digital image, the first is 320x240 which is the highest you can go without interlacing. The next limit is 640x480 which is an interlaced image and what is the standard for TV that's going to be phased out on February 2009 in favor of the ATSC standard.

Here are some links to explain the details:
http://en.wikipedia.org/wiki/Ntsc
http://en.wikipedia.org/wiki/Atsc
http://en.wikipedia.org/wiki/Interlace
http://en.wikipedia.org/wiki/Image_resolution

baxterdmutt
Posts: 25
Joined: Tue Sep 16, 2008 3:47 am

Post by baxterdmutt » Sat Sep 20, 2008 5:43 pm

I am still confused, how can I figure out what the pixel resolution is from the information they give. Is there no way? As I look at other cameras I see they all describe the pixels themselves the same way mine does. Is everyone left in that dark to guess at the resolution or is the information on the box useful for figuring this out?

Is it possible the resolution they give correct and I have a software setting problem? The size of the picture I see in xawtv is bigger than Zoneminder will let me go?
Thanks

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Lee Sharp
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Post by Lee Sharp » Sat Sep 20, 2008 6:15 pm

The Pixel resolution they give is NTSC which is 320x240 or 640x480 interlaced. Look at the links.

baxterdmutt
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Post by baxterdmutt » Sat Sep 20, 2008 10:35 pm

Lee Sharp wrote:The Pixel resolution they give is NTSC which is 320x240 or 640x480 interlaced. Look at the links.
OK, Problem solved. I think it was a shared memory thing. I couldn't enter the size of my camera, without getting a black screen.

I called Q-see and they told me the NTSC pixel resolution is as stated on the box. 568x500 NTSC. Regardless. I was getting a blank screen if I go anything above 200 in height.

I changed the shared memory to something ridiculously high (well above what I actually have in the machine). After restarting the system, the cameras are working. I still can't get past 500 x 520, but I only have 1gb of actual memory. I will increase that and see what happens.

Just for the record I did look at the link and did not see how you got 320x240NTSC out of 568x500 NTSC though.


Thanks.

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cordel
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Post by cordel » Sun Sep 21, 2008 12:59 am

Resolution for NTSC does not directly translate into pixel resolution it is Spatial.

baxterdmutt
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Post by baxterdmutt » Sun Sep 21, 2008 4:52 pm

cordel wrote:Resolution for NTSC does not directly translate into pixel resolution it is Spatial.
OK, so how does one figure out what the pixel resolution is. All the Mfgs give the NTSC resolution. There must be way to figure it out. I can set mine to almost anything, but I would prefer to know the true resolution. zmu, just gives the card settings and says nothing about the connected cameras.

Thanks again.

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Lee Sharp
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Post by Lee Sharp » Sun Sep 21, 2008 7:17 pm

NTSC is defined as 640x480i or 320x240. That is it. That is the definition in digital. You are looking at analog lines and over scan which do not apply. And the limitation is not the camera, but the A/D converter, usually a BT878 chip.

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