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Learn about the resolution of CCTV cameras - image standards used in CCTV camera
The resolution of CCTV cameras - In digital systems, the image is made up of pixels (picture elements - pixels). The resolution of the camera output to the screen is measured by the number of pixels on the image sensor chip. Here are some common standards in determining the number of pixels.
1. What is Standard NTSC and PAL?
Although analog TV systems and video are widely used worldwide, but different countries to use different video standards. Most commonly it is NTSC and PAL.
NTSC (National Television System Committee) is the analog video standards prevalent in North America and Japan. And PAL (Phase Alternating Line) (PAL color TV system / Phase for each scan line of the image) is used more often in Europe. Both standards are derived from the television industry.
§ NTSC has a resolution of 480 TVL (480 single scan line), and use rate of 60 interlaced fields per second (or 30 image frames are transmitted per second).
§ PAL has a resolution of 576 TV lines (single scan line), and using the rate of 50 interlaced fields / sec (or 25 image frames / sec).
General information / sec is equal in both standards. When analog video is digitized, the largest number of pixels can be created is based on the number of TV lines can be digitized.
The typical setup for storage:
- D1 size digital image is 720 × 480 largest pixels for NTSC, the PAL, the size is 720 × 576 pixels.
- 4CIF (704 x 576 PAL / NTSC 704 × 480) resolution is the most frequently used
- Is 704 × 240 2CIF (NTSC) or 704 × 288 (PAL) pixels, which means dividing the number of horizontal lines by 2. In most cases, each horizontal scan lines represent double, also called "scan lines doubling ", when shown on a computer monitor to keep the correct ratios in the image. This is a way to solve the problem of motion blurred image in interlaced.
- Sometimes, a quarter of the CIF image is used, often referred to as QCIF (stands for Quarter CIF).
The resolution in the cctv
2. The difference between PAL and NTSC
The difference between PAL and NTSC started deeply systems that world energy use. In the United States, Japan, Korea, Taiwan, and some countries in the Americas to use the power system frequency of 60Hz, for technical reasons the strip processing information transmitted depends on the frequency of electric. So the signals are processed and transmitted in one second into 60 strips (usually known as a horizontal frequency 60Hz). We know most of the TV or video technology are using technology Interlace Scan (alternate line scanning technology) to create a complete picture. Because so fast scanning speed of this scanning range 2 people regarded it forms a frame. So with 60 bands are transmitted in seconds to form a 30 frames per second. That is also the reason to make up to 30 frames / s for NTSC.
PAL also, why? And we know in Europe, a number of Asian countries including Vietnam we use the power system frequency is 50Hz, by explaining similar to PAL frame number transmitted per second is 25 frames / s
Try comparing the two systems of image quality: Obviously with 576 scan lines and 480 scan lines for our PAL sharp picture than NTSC. But with 30 frames / s compared to 25 frames / s, the NTSC gives us a lot smoother image. One thing we should note is that when switching from NTSC to PAL image will be blurred images than the original view. By size photo frame launch will dilate, so the quality will be inferior. From PAL to NTSC transfer also can cause a jerky image, because the number of frames / s of less than NTSC PAL.
In addition there is a horizontal frequency vertical frequency, so make the frame size of the two systems is also different, so when we see a phenomenon often seen video aspect (not full screen) in some movie or some TV channels.
Here we have somewhat understand why in Vietnam you necessarily use that is not PAL NTSC, right. Not the cause of our equipment is due to decide that our grid !!!
3. Standard VGA
With the introduction of network cameras, 100% digital systems can be designed. This shows the limitations of NTSC and PAL standards unreasonable. Some resolutions derived from the computer industry have been introduced, providing greater flexibility, moreover, they are worldwide standards.
VGA (Video Graphics Array) is a graphics display system for PCs originally developed by IBM. This resolution is defined as 640 × 480 pixels, a very similar size to NTSC and PAL. Conventional VGA better suited to the network camera for video in most cases will be shown on a computer screen, with a resolution of VGA or VGA for many. Quarter VGA (QVGA - ¼ VGA) have a resolution of 320 × 240 pixels as well as a format in common use, very close to the CIF. QVGA is sometimes called SIF resolution (standard exchange format), easily confused with CIF.
The resolution is based on another XVGA VGA (1024 × 768 pixels) 1280 x 960 pixels and folding, 4 times VGA, gives megapixel standard.
MPEG always means one of the following resolutions:
- 704 × 576 pixels (TV PAL)
- 704 × 480 pixels (NTSC TV)
- 720 × 576 pixels (PAL or D1)
- 720 × 480 pixels (NTSC or D1)