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=Computer monitor vs TV=



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Interlaced vs progressive

I don't think we should start from the very begginning, explaining how a TV works by firing a stream of electrons onto a phosphor coated screen. Just remind you, that according to the American TV standard, called NTSC, the image is made of 525 scan lines (625 in European PAL standard).Every frame has an interlaced refresh rate of 30Hz (25Hz for PAL). The interlacing is an ingenious method, invented in 1927, of breaking every image into 2 fields: first - contains only odd lines, the second field - only even lines of the image. The interlacing allowes the picture refresh rate to be doubled to reduce annoying flicker, without increasing the bandwidth required for broadcasting. The computer has video memory to assemble an entire picture and send it to the screen progressively with higher frequency. It doesn't need to be compartible with old TV standards, which eliminates the need for interlacing and results in a more stable screen image. Modern LED TVs are a great example of this technology.

Resolution

Rather than dividing the screen into scan lines, a computer image is divided into dots or pixels. What kind of resolution is your monitor set for? Say it is 1024x768 pixels. How to compare it with a TV resolution? From 525 lines only 480 are visible, the rest are used for synchronization. So the vertical size of a TV image is 480 pixels. Knowing that the standard lenght/width ratio of TV screen is 4/3, the vertical size will be 640 pixels. This resolution is probably OK for 14" monitor, but on 27" monitor each pixel will have 4 time larger area!
However, don't forget about the distance you watch your TV from! A TV was not meant to be seen as close as a computer monitor.Your eyes are also part of the equation. It means that the difference in image quality between an HDTV (high-definition-television) and a regular analog TV can only be appreciated on big screens. For smaller screens the difference between a high-definition and an analog TV is hardly seen.
An HDTV monitor can display at least 720 image-carrying horizontal-scan lines in progressive mode, and at least 1080 lines in interlaced mode.

TV interface

Composite Video - also called CVBS (colour video baseband signal), contains luminance, chrominance and sync information in one signal. Look for "Video" RCA socket on the back of your TV.

S-Video - stands for separated video: luminance and chrominance signals are transferred separately, resulting in the greater image quality. The special S-video connector also carries left-and-right audio signals for stereo.

Component Video (YCbCr) - video signal is devided into 3 parts: Y - luminance signal (for compartibility with old monochrome TVs), Cb=0.564(B-Y), Cr=0.713(R-Y). Instead of transferring 3 chrominance signals (R,G,B ) it is easier to use just their difference (save bandwidth). Since Y is a combination of 3 major color signals, taken in the right proportion ( Y=0.587G+0.299R+0.114B), the third color component can be extracted from Y,Cb and Cr information. This method also provides high quality and eliminates cross-luminance and cross-color effects. The component video requires 3 RCA connectors.

RGB - are the 3 analog inputs for a regular CRT computer monitor. Hsync and Vsync are transferred separately.

DVI - digital video interface to transmit formatted graphics data to flat-panel displays. R,G,B signals are transferred in the digital format (8bit per signal) and accompanied by clock and control signals. Hsync and Vsync are sent over Blue channel during the inactive data portion or blanking periods.
 
 
References:
1.Harve Benoit, Digital TV,2002
2.B.Grob, Television and Video systems

 

 

 
 
 
   
 
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