Scanning method in tv and its type Horizontal & vertical scanning, flicker, interlaced scanning

 Scanning :-

Scanning is defined as scene or images are scanned rapidly both horizontal and vertical direction simultaneously to provide sufficient number of complete picture of frame per second to give Illusion of continuous motion for a video these method are used in camera tube in TV the frame reputation rate is 25 per second . 

There are two types of scanning method:- 

1. Horizontal Scanning. 

2.  Vertical Scanning.

Horizontal scanning:- 

This scanning process are defined as a scanning where a scanning are done by horizontally very fast so this is known as horizontal scanning.

In given figure a trace line started from left to right first line after that second line go back means right to left is known as retrace line ,by retrace line no scanning are done this process works very fast, rapid and continuously. 

Figure b shows linear rise in current from left to right scanning or trace in horizontal direction the peak is increasing when retrace are done graph is decreasing.

Vertical scanning:-This scanning process are defined as a scanning where a scanning are done by vertically very fast so this is known as vertical scanning.

Fig 1

In given figure 1 trace line started from top to bottom first line after that second line go back means bottom to top is known as retrace line ,by retrace line no scanning are done this process works very fast, rapid and continuously. 

Figure 2 shows linear rise in current from top to bottom scanning or trace in horizontal direction the peak is increasing when retrace are done graph is decreasing.

Fig 2

Flicker :- When the scanning rate of 25 frame per second in TV picture in tv picture are not enough to cause illussion of continuty. They are not rapid so one picture or frame are not mix with next frame then the screen is blanked, or this problem are known as flicker. 

How to eliminate the flicker?

The problem of flicker is solved by showing each picture twice time , to increase rapidly rate or illusion of continuity increases and decreases the blanked rate between two frame this process are known as interlaced scanning. 

Interlaced scanning:-

In TV picture particle scan it is 50 frame per second are utilised to reduce flicker this is achieved by increasing the downward rate of travelling the scanning electron beam ,so the every alternate line get scanned, when scanning beam reaches to the bottom of the picture it quickly return to the top of screen . This total number of scanning line are divided into two groups which are known as fields, there are two fields are used in interlaced scanning. In India 625 line system is used for successive interlaced scanning. Total 650 line is divided into set of 312.5 line and each set is scanned alternately.