There are lot of misunderstanding knowing about kind of video resolutions which are used in CCTV. This is my post to clarify and help others to more understand about it.
Resolution is the size of the image on the display. The most popular resolutions are D1 or 4CIF (720×480), and CIF (352×240). Nearly all DVRs will display in D1 or 4CIF but CIF is a more popular recording resolution. D1 and 4CIF are larger images, but to record the larger image takes up more hard drive space. In addition, most DVRs need to lower the frame rate dramatically when using these resolutions for recording. A DVR that records at 30 frames per second (real time) in CIF mode will usually only record around 7 frames per second in D1 or 4CIF. For a DVR to record at 30 frames per second in D1 or 4CIF mode requires special firmware which makes these units very expensive, however improvements in technology has now made these units more affordable. We now have a few models (QT518, QT5116, and QT528) that can record in D1 resolution at 30FPS (real time) at affordable prices.
CIF/SIF(525)___352 x 240
CIF/SIF(625)___352 × 288
4CIF/4SIF(525)_704 x 480
4CIF/4SIF(625)_704 × 576
D1(525)_______720 x 480
D1(625)_______720 x 576
* Sometimes 4SIF/4CIF is specified the same as VGA, which is 640 x 480 / 640 x 576 or is popular called as D1 also.
D1 (525) means 525 TVL 720 x 480 in NTSC
D1 (625) means 625 TVL 720 x 576 is in PAL
* There is also 1/2 frame or 2CIF, which is based on removing the odd or even fields and is usually specified as either 640 x 240 or thereabouts.
CIF (Common Intermediate Format), also known as FCIF (Full Common Intermediate Format), is a format used to standardize the horizontal and vertical resolutions in pixels ofYCbCr sequences in video signals, commonly used in video teleconferencing systems. It was first proposed in the H.261 standard.
CIF was designed to be easy to convert to PAL or NTSC standards. CIF defines a video sequence with a resolution of 352 × 288 like PAL Source Input Format, a framerate of 30000/1001 (roughly 29.97) frames like NTSC, with colour encoded using YCbCr 4:2:0.
QCIF means “Quarter CIF”. To have one fourth of the area, as “quarter” implies, the height and width of the frame are halved.
Terms also used are SQCIF (Sub Quarter CIF, sometimes subQCIF), 4CIF (4× CIF) and 16CIF (16× CIF). The resolutions for all of these formats are summarized in the table below.
|SQCIF||128 × 96|
|QCIF||176 × 144|
|SCIF||256 x 192|
|SIF(525)||352 x 240|
|CIF/SIF(625)||352 × 288|
|4SIF(525)||704 x 480|
|4CIF/4SIF(625)||704 × 576|
|16CIF||1408 × 1152|
|DCIF||528 × 384|
xCIF pixels are not square, instead having a native aspect ratio of ~1.222:1. On older television systems, a pixel aspect ratio of 1.2:1 was the standard for 525-line systems (seeCCIR 601). On square-pixel displays (computer screens, many modern televisions) xCIF rasters should be rescaled horizontally by ~109% to 4:3 in order to avoid a “stretched” look: CIF content expanded horizontally by ~109% results in a 4:3 raster of 384 × 288 square pixels.
The CIF “image sizes” were specifically chosen to be multiples of macroblocks (i.e. 16 × 16 pixels) because of the way that discrete cosine transform based video compression/decompression is handled. So, by example, a CIF-size image (352 × 288) corresponds to 22 × 18 macroblocks.
SIF (Source Input Format) is practically identical to CIF, but taken from MPEG-1 rather than ITU standards. SIF on 525-Line (“NTSC”) based systems is 352 × 240, and on 625-line (“PAL”) based systems, it is identical to CIF (352 × 288). SIF and 4SIF are commonly used in certain video conferencing systems.
DCIF means Double CIF, proposed as a compromise resolution between CIF and 4CIF that is more balanced (in terms of horizontal vs vertical resolution) and suited to common CCTV equipment (with 480+ scanlines but a maximum of about 560 TVL) than 2CIF (704×288). The pixel and therefore data rate is exactly double that of CIF , but the 1:1.375 image aspect ratio is a lot closer to standard 4:3, with essentially square pixels.