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Camera resolution
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Source：Internet Author：Unknow Pubdate：2010-06-24
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rulmismo (Electrical)
16 Jun 10 10:52
Hi,
I have a client that wants a CCTV recording system with 4CIF resolution for an on board aplication.
I have seen that CIF is thought for digitizing PAL field frames(352 × 288) (1 field giving 288 lines and each horizontal line sampled to 352 pixels)
4CIF (704 × 576) seems that might be used to digitize full PAL frames (2 consecutive fields giving 576 lines and horizontal line signal sampled to 704 pixels)
A supplier offers me a system with a PAL (analog output) camera that gets converted to a MPEG4 stream with a "converter".
My doubt is if the real digital resolution that I can really get from a PAL signal is (352 × 288) 1 field, or (704 × 576) (combined resolution of 2 fields).
some insight will be welcomed!
Thanks
rUL
IRstuff (Aerospace)
16 Jun 10 15:15
字串5
You seem to be a bit confused. PAL is an analog standard with a version with 576 visible lines of vertical resolution. The horizontal resolution can be adjusted as needed depending on the analog bandwidth available. TTFN
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rulmismo (Electrical)
17 Jun 10 17:53
Thank you IRStuff, I was cofused indeed.
So if I have my camera with PAL output and nice BW,
have I 704 × 576?
I suppose that the CCD+processig electronics of the camera should be able to get first that number of pixels and then have some nice electronics to generate a good BW PAL signal, isnt`t it?
Could be a clue the pixel count of the CCD to know if the PAL output signal will be near "equivalent" to 704 x 576?
My client wants 4CIF and I wouldn't like to give them 640x480 pixels converted to a blurry PAL signal 704 x 576 "equivalent", that gets converted again to MPEG4 to record it. 字串8
Regards and thanks for the reply!
IRstuff (Aerospace)
17 Jun 10 18:32
It's really hard to tell what you're actually winding up with. Much of it depends on waht "PAL" means to all concerned. As an example RS-170, in its original form, had a built-in bandwidth limiter that limited horizontal resolution. However, today, you can get "RS-170" compatible cameras with 1200 pixel horizontal resolution.
So, your supplier's camera may be outputting "PAL" video that matches the general timing and line format of the PAL standard, but can output the required horizontal resolution on the analog output. If that's the case, then a reasonably high performance frame grabber could acquire the video from this camera at its full resolution, at which point, the frame grabber could do whatever compression you ask it to do. TTFN
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字串8
rulmismo (Electrical)
18 Jun 10 1:54
Ok, I think that more o less understand it,
I found this:(http://tinyurl.com/382a25m)
Digitizing RS-170 video:
A typical digital image produced by video digitization would have a resolution of 512 (horizontal) X 480 (vertical) pixel resolution and would have individual pixels with a 5:6 aspect ratio. If you want square pixels, you have to digitize 646 pixels for each of the 485 lines. A fairly standard policy is to digitize 480 lines at 640 pixels per line (just leave out few scanlines and pixels from horizonal lines).
So for NTSC seems OK 640x480 camera sensor size, maybe need a little bit more for PAL (1 megapixel?) (because it has 576 vert. lines) in order to not losing information
IRstuff (Aerospace)
18 Jun 10 2:27
Standard PAL is still 4:3 aspect ratio, so 576*4/3 = 768, although most PAL systems have 720 horizontal resolution TTFN 字串9
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