Sony SNC-RZ25N - Network Camera Catalog - Page 5

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Image Processing Technologies

JPEG vs. MPEG-4

JPEG compression, which is conventionally used in

surveillance and monitoring systems is very good for

capturing high-quality still images. MPEG-4, on the other

hand, is ideal for image transfer over a network while

maintaining high-quality moving images. This is because

MPEG-4 requires a relatively small amount of network

bandwidth as a result of its structure as can be seen

below.

JPEG

MPEG-4

At 30 fps, 1 sec = 30 images

1 GOV ,1 sec. = 1 I-VOP and 29 P-VOPs

3 frames

Note: Each frame in MPEG-4 is referred to as a Video Object Plane (VOP).

A Group of VOPs (GOV) comprises of one second* of video. An I-VOP is the

first (Initial) "frame" of a GOV and is often referred to as an "anchor." The

I-VOP is similar to a JPEG image. P-VOPs are "Predictive" VOPs and only

"captures" movement relative to the previous VOP.

*The default GOV setting for Sony MPEG-4 cameras is one second.

The length of a GOV can be set between one and five seconds.

Rough Calculation of Data Size

JPEG

With JPEG at 30 fps, 1 sec = 30 images. Assuming each

JPEG image is 30 KB in size, then one second of video is

900 KB. At 8 bits per Byte, this translates to 7.2 Mb/s

MPEG-4

With MPEG-4, the I-VOP is approximately 30 KB in size.

Assuming there is little movement in the image, each

P-VOP is approximately 2 KB in size. This means that 1

second of data is approximately 88 KB. Again, using the

same calculations as above, this translates to

704 Kb/s. This is approximately 1/10th the size of

JPEG data.

I-VOP

VOPs

Activity Detection vs. Motion Detection

(SNC Series Cameras)

The following is a brief explanation outlining the

differences between Motion Detection and Activity

Detection: The general difference in concept between the

two detection methods is that Motion Detection utilizes

vector information associated with movement while

Activity Detection utilizes the difference in illumination

between frames. Activity Detection is available with JPEG

compression while Motion Detection is available with

MPEG-4 compression.

Activity Detection

Sony Activity Detection systems utilize hardware that

performs difference calculations in luminance between

frames. The absolute value of the difference in luminace

of each pixel is taken from one frame to the next. If the

sum of the difference is greater than a preset threshold,

then an alarm is triggered.

Motion Detection

Motion Detection systems utilize a Sony advanced

algorithm to determine whether or not there is actual

movement in the camera viewing area. This algorithm is

based on vector information available and inherent in

MPEG-4 compression. The vector information is

determined based on the amount of movement in 16 x 16

pixel-areas in the grid.

Motion Detection has an advantage over Activity

Detection because it can reduce the number of false

alarms caused by noise. Other advantages of Sony

systems that use Motion Detection are that up to four

distinct Motion Detection areas can be assigned, and real

time indicators are available to monitor sensitivity and

threshold levels.

Detection by average Change

in luminance of pixels

Detection by average Change

16 pixels

in luminance of pixels

16 pixels