Products distributed by:
BernClare Multimedia Inc.
Tel: 905-513-2722
e-mail: info@bernclare.com
Markham, Ontario, Canada |
How Clear an image
can your camera produce?
Depends on: CCD / CMOS resolution, lens focal length, object distance, brightness.
DVR-NVR recording resolution will also be a key factor for archived video.
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Video streaming and/or
Security Surveillance product for:
system integrators,
installers, dealers,
web designers, resellers,
IT personnels, users experienced in networks.
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This is a short document on how image quality of a cctv or IP camera would relate to the camera's ccd/cmos resolution, lens angle (focal length), object distance, brightness, DVR / NVR recording capability.
The relationship algorithm is based on simple trigonometry. If you want to find out how clear a face, or a license plate would get recorded by a camera on a DVR, you need to find out:
- Recording Resolution of the DVR. DVRs would record at CIF (352acrossx240 pixels), 2CIF(528x360), 4CIF (704x480). There are some new DVR that would take high definition, 1920x1080pixels. NVR recording resolution is higher, can be over 2560x1920pixels for 5M IP cameras@ 15fps, H.264
- Camera resolution, usually described in terms of horizontal pixels. Analog cameras usually have 420, 540, 600 pixels/lines of horizontal resolution. Some new Hi-def analog camera with DVI output can handle 1920x1080. IP cameras would cover as much as 2560x1920 pixels.
- Camera lens play a large part in the angle of coverage and the distance. In a general case for 1/3” CCD, a 3.5mm lens will generate a cone of view at 75º, 6mm at 48º, and 12mm at 25 º.
To simplify our discussion on how “clear” or how “blur” an image is, we would take two sample cases. To read a car license plate of about 1 ft across, you need at least 9 pixels across per character, 10 characters for the width of the plate, total 90pixels/ft of “pixel density”. This gives you a detail, clear picture. On the other hand, for a mediocre quality image of a person’s face of about 6 inches across, you need at least 12 pixels, giving you about 3~4 pixels per eye. This turns out to be 24pixels/ft of “pixel density”. This image is getting blurry and “loose”, and is at an acceptable but lower quality. Let us use the 90pixels/ft and 24 pixels/ft as our benchmark.
540 horizontal pixel cctv cameras with 3.5mm lens
From the lens point of view, the image view spreads out like a triangular cone, gets wider and wider as you move away from the lens. However, the CCD resolution is fixed, in this example, at 540 pixels. This 540 pixel is to cover the full width of the image. That means, the closer you are, the more dense will these 540pixels be. The further away you are, the wider is the coverage, and these 540 pixels will have to spread out more. To achieve 24pixels/ft “pixel density” that is for a “face”, the total image width can only cover 540/24 =22.5ft. across. If the pixel density is increased to 90pixels/ft. it can read a license plate, and this camera can only cover 540/90=6ft.across.
With a 3.5 mm lens on a cctv camera, the image view would be at ~75 degrees angle. An image of 6ft across @ 90pixels/ft density (license plate) has to be within 4 ft from the camera. An image of 22.5ft across @ 24pixels/ft density (blur face) has to be within 14.6 ft from the camera. If you go closer, the resolution is better, and if you move further away, the image “density” will be so diluted that you cannot recognize the face of a person.
1600 pixel IP camera with 3.5mm lens
With 1600pixels IP camera, @ 24pixels/ft, it can yield 1600/24 =66.6ft across for a mediocre quality, 1600/90=17.8ft. across for a license plate reading quality.
With a 3.5 mm lens, it will be at ~75 degrees angle. An image of 66.6ft across @ 24pixels/ft density (face) has to be within 43ft from the camera.
If you go closer, the resolution is better. An image of 17.8ft across @ 90pixels/ft density (license plate) has to be within 11.6ft from the camera.
540 pixel cctv cameras with 6mm lens
With a 6 mm lens on a normal cctv camera, it will be at ~48 degrees angle. An image of 22.5ft across @ 24pixels/ft density (face) has to be within 25 ft from the camera.
If you go closer, the resolution is better. An image of 6ft across @ 90pixels/ft density (license plate) has to be within 6.7 ft from the camera.
1600 pixel IP camera with 6mm lens
With a 6 mm lens, it will be at ~48 degrees angle. An image of 66.6ft across @ 24pixels/ft density (face) has to be within 75ft from the camera.
If you go closer, the resolution is better. An image of 17.8ft across @ 90pixels/ft density (license plate) has to be within 20ft from the camera.
540 pixel cctv cameras with 12mm lens
With a 12 mm lens on a normal cctv camera, it will be at ~25 degrees angle. An image of 22.5ft across @ 24pixels/ft density (face) has to be within 51 ft from the camera.
If you go closer, the resolution is better. An image of 6ft across @ 90pixels/ft density (license plate) has to be within 13.5 ft from the camera.
1600 pixel IP camera with 12mm lens
With a 12 mm lens, it will be at ~25 degrees angle. An image of 66.6ft across @ 24pixels/ft density (face) has to be within 150.2ft from the camera.
If you go closer, the resolution is better. An image of 17.8ft across @ 90pixels/ft density (license plate) has to be within 40.1ft from the camera.
From the above examples, you can compare the resulting image difference of cctv and IP cameras and select those that best fit your cost/quality ratio. Lens selection is as important, but be careful that IP cameras tend to be less light sensitive, and you need a higher quality IR panel to cover the image width and distance. IR panels are post on one of our web page.
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