DVR Resolutions

DVR Resolutions

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Resolution Overview The resolution of a DVR is an important factor in choosing your unit and should be considered carefully. The higher the resolution, the more information and detail an image holds. Resolution is based on pixels, or picture elements. A pixel is the smallest complete sample of an image. Contrary to popular belief, it is not necessarily a square or a dot, but rather an abstract sampling of the whole image. The more pixels in the image, the closer it will resemble the actual source. Generally, resolutions are defined by two numbers, indicating the width and the height of an image. Note that the numbers used to define resolutions indicate the maximum pixel ratio for that resolution. Therefore, it is possible for a smaller pixel ratio to be used in place of the maximum. The Four Basic Resolutions There are four basic recording resolutions associated with DVRs. They are CIF, 4CIF, Half D1 and D1. CIF, or Common Intermediate Format, is the lowest of the three resolutions at 352 x 240 pixels in NTSC (the video standard used in North America). A CIF is one quarter of the full resolution it is intended for, which is known as 4CIF. CIF is fine for events that occur close to the camera but distant events will be difficult to make out. 4CIF is defined as 704 x 480 pixels. While technically speaking a 4CIF image can produce a better image than CIF, this is not necessarily the case because of empty pixels. A CIF image at 352 x 240 means that 352 pixels will be filled with data across 240 lines. A 4CIF image at 704 x 480 pixels means that 704 pixels will be filled with data across 480 lines. But both images do not define the quality and/or amount of data that will be used. Pixels are filled with data which is referred to in terms of bits. Empty pixels contain no bits. A CIF image with more bits than a 4CIF image will produce a better picture. This can and does occur because of something called bitrate, which is the quantity of bits used over a specific amount of time. Thus, bitrate defines the detail in an image. D1 is the highest quality of all resolutions and was created by Sony. At up to 720 x 480 pixels, it delivers DVD quality video. In fact, the D1 VCR system, which was the first to introduce the resolution of the same name, and DVDs utilize the same sampling rate and are based on the same standard. As such, even distant objects will appear clearly at this resolution. Half D1 is exactly what its name implies, which is half of D1, or 360 x 480. It is suitable for home and small business use but is not of professional quality. The EV-4250N DVR by Nuvico.