Sensor Scan Modes - Vivotek IP Surveillance Overview

Chap.2 Lens and Image Sensor Technology
Megapixel
A megapixel network camera features a resolution at least three times larger than that of an analog CCTV camera.
A megapixel camera is mainly applied in occasions when accurate identification is needed such as vehicle license
plate recognition or facial recognition for it can provide images with exceptional details. Because of its high number
of pixels, a megapixel camera is also used in spacious areas such as parking lots or airports to provide images with
a wide view.
The megapixel sensor has contributed to a new breed of non-mechanical PTZ cameras, known as digital PTZ
cameras. The camera captures a megapixel image and delivers only a user-defined thumbnail to the monitor so
that users can view different images by selecting on the monitor instead of physically moving the camera.

2.2.3 Sensor Scan Modes

Image sensor scan modes include interlaced and progressive scan.
Interlaced Scan
Interlaced scan split a scene into even and odd fields that contain even and odd lines, respectively. When
rendering the entire scene, the even field is displayed first, followed by the odd field. The time interval between the
appearance of the two fields will lead to jagged edges, especially for a moving object.
Interlaced scan is mainly used in TV monitors with a lower refresh rate, which causes the screen to flicker easily.
Interlaced scan can reduce flickers because the field refresh rate of the interlaced scan seems two times faster
than the original frame rate.
Some monitors solve jagged edges by dropping odd field and replicate the even field as the odd field. However, the
vertical resolution will be cut by half.
Progressive Scan
Progressive scan renders the entire scene by displaying the even and odd lines of the frame sequentially instead of
by field. Since there is no time interval between each display, the problem of jagged edges when displaying moving
objects is eliminated.
Capture Display
Interlaced Scan
Odd Field Even Field 1 Frame
Progressive Scan
1 Frame
Interlaced Scan Progressive Scan
Figure 2.12 Progressive scan eliminates jagged edge artifacts of interlaced scan
13