Axis Communications 2120 Picture frequency for Networking Applications, Image Compression Ratios

30 Choosing Your Application AXIS 2120 User’s Manual

Picture frequency for Networking Applications

When used in a TCP/IP networking environment, the AXIS 2120 delivers up to 25/30 (PAL/NTSC) images/second; where the actual image frequency is typically limited by:

•your computer and browser

•the chosen image resolution and compression

•the lighting conditions at the point of installation

•available network bandwidth

•the complexity of detail and color variation within the image

Important!

60Hz and 50Hz variants of the AXIS 2120 are available to accommodate the different power supply fre- quencies found in the USA and Europe.

The 60Hz variant delivers a resolution of 525 lines at 60 half-frames per second and is suitable for use in the United States; whereas, the 50Hz variant delivers 625 lines at 50 half-frames per second and is appropriate for use in Europe.

Image Compression Ratios

Although the file size of a JPEG-compressed image depends upon the actual content of the image, images containing a lot of detail generally generate larger files. Image quality is largely controlled by the level of compression; where high compression yields small files, and low compression maintains higher image quality at the expense of larger files. The table below is derived from real-life tests, and defines the average file sizes for each supported image resolution:

60Hz (NTSC Countries)			50 Hz (PAL Countries)
Resolution	Filesize (kb)	Max fps*	Resolution	Filesize (kb)	Max fps*
4CIF (704 x 480) **	7 - 150	10	4CIF (704 x 576) **	8.5 - 180	8
CIF (352 x 240)	1.4 - 40	30	CIF (352 x 288)	1.7 - 50	25

*Maximum performance for a single viewing client.

**Interlaced image

Note: Using a modern computer will avoid introducing any unnecessary constraints on the imaging fre- quency.