QVGA is sometimes called SIF (Standard Interchange Format) resolution, which can be easily confused with CIF. Other VGA-based resolutions are XVGA (1024x768 pixels) and 1280x960 pixels, 4 times VGA, providing megapixel resolution.
Day and Night Network Camera
The AXIS 221 Day & Night Network Camera offers progressive scan, Power over Ethernet (PoE) and built-in video motion detection. The AXIS 221produces color video when there is sufficient light and black-and-white video under dark conditions with simultaneous Motion JPEG and true MPEG-4 full frame rate video streams, The AXIS 221 uses a high performance Pentax lens and a progressive scan CCD image sensor that enables moving images to be presented without distortion or blur. Its PoE functionality is built according to the IEEE 802.3af standard, For more information, visit www.axis.com.
Network Video Compression Standards
Without the use of image compression, most local area networks (LANs) are incapable of managing or transporting video data. Digital video is always compressed in order to speed up transmission and to save space on hard disks. Selection and use of the right compression is critical.
- MPEG compression breaks down as follows:
- MPEG-1: 352 x 240 pixels; 30 fps
- MPEG-2: 720 x 480 pixels/ 1280 x 720; 60 fps TV quality.
- MPEG-4: Wavelet based files designed to transmit video over less bandwidth and can combine video with text, graphics and animation.
MPEG-1 was released in 1993 and intended for storing digital video.
MPEG-2 was approved in 1994 as a standard and was designed for high quality digital video (DVD), digital high-definition TV (HDTV), interactive storage media (ISM), digital broadcast video (DBV), and cable TV (CATV). The MPEG-2 project focused on extending the MPEG-1 compression technique to cover larger pictures and higher quality at the expense of a lower compression ratio and higher bit-rate. The frame rate is locked at 25 (PAL)/30 (NTSC) fps, just as in MPEG-1.
MPEG-4 is a major development from MPEG-2. There are many more tools in MPEG-4 to lower the bit-rate needed to achieve a certain image quality for a certain application or image scene.
Furthermore, the frame rate is not locked at 25/30 fps. However, most of the tools used to lower the bit-rate are today only relevant for non real-time applications. This is because some of the new tools require so much processing power that the total time for encoding and decoding (i.e. the latency) makes them impractical for applications other than studio movie encoding, animated movie encoding, and the like. In fact, most of the tools in MPEG-4 that can be used in a real-time application are the same tools that are available in MPEG-1 and MPEG-2.
There are two different approaches to compression standards: still image compression and video compression. All still image compression standards are focused only on one single picture at a time. The most well known and widespread standard is JPEG.
JPEG is short for Joint Photographic Experts Group International. It is a good and very popular standard for still images that is supported by many modern programs. With JPEG, decompression and viewing can be done from standard Web browsers.
JPEG compression can be done at different user-defined compression levels, which determine how much an image is to be compressed. The compression level selected is directly related to the image quality requested.
Motion-JPEG (M-JPEG) compresses individual jpeg images at 16 up to 30 images per second full motion video, depending on available bandwidth. (Individual image quality varies with bandwidth, but frame rate does not.)
Motion JPEG offers video as a sequence of JPEG images. Motion JPEG is the most commonly used standard in network video systems. A network camera, like a digital still picture camera, captures individual images and compresses them into JPEG format.
The network camera can capture and compress, for example, 30 such individual images per second (30 fps – frames per second), and then make them available as a continuous flow of images over a network to a viewing station. At a frame rate of about 16 fps and above, the viewer perceives full motion video.