An LED-backlit LCD is a flat panel display that uses LED backlighting instead of the cold cathode fluorescent (CCFL) backlighting used by most other LCDs. What is a Light-emitting diode (LED)?
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A light-emitting diode (LED)
An LED is more energy-efficient and a lot smaller than a CCFL, enabling a thinner television screen.
Raster and Random scan
There are 2 ways by which we can display an object on the screen
- Random scan
- Raster scan
Raster scan
A raster scan or raster scanning is the rectangular pattern of image capture. By analogy, the term is used for raster graphics. In a raster scan, the electron beam is swept across the screen, one row at a time from top to bottom. As the electron beam moves across each row, the beam intensity is turned on and off to create a pattern of illuminated spots. A raster image is a collection of dots called pixels.
Working of Raster Scan
Each screen point is referred to as a pixel or picture element. In raster scanning, the beam sweeps horizontally left to right at a steady rate. At the end of each scan line, the electron beam returns to the left side of the screen to begin displaying the next scan line.
As the electron beams move across each row, the beam intensity is turned on and off to create a pattern of illuminated spot. The return to the left of the screen, after refreshing each scan is called “horizontal retrace”. At the end of each frame, the electron beam return to the top left corner of the screen to begin the next frame, called “vertical retrace”.
Random scan
In this technique, the electron beam is directed only to the part of the screen where the picture is drawn rather than scanning from left to right and top to bottom as in a raster scan. Picture definition is stored as a set of line-drawing commands in an area of memory referred to as a refresh display file.
Vector scan displays are designed to draw all the components lines of the picture 30 to 60 times each second.
Difference between Vector Scan Vs Raster Scan
| Raster scan | Vector scan |
|---|---|
| Electron beam: the electron beam is swept across the screen, one row at a time, from top to bottom. | Electron beam: the electron beam is directly only to the parts of screen where the picture is to be drawn. |
| Resolution: it has poor resolution because it produces zig-zag lines that are plotted as discrete points sets. | Resolution: it has good resolution because it produces smooth lines because CRT beams directly follows the line paths. |
| Picture definition: it is stored as a set of intensity values for all screen points in refresh buffer area. | Picture definition: it is stored as a set of lines drawing instructions in a display files |
