S-Video, TV, VGA
I was interested to show PC picture in TV screen, or vice versa. For some odd reason on the market there is small LCD-screens with only TV input and large LCD screens with only VGA or DVI -interface in reasonable prices. I'm still looking for a solution for having a small screen that can be used for both worlds. So far the best solution is to get a LCD with VGA or DVI connection and a TV card to my PC.Another thing is that for example VIA Epia mainboard has three coutput connectors: VGA, S-video and Composite. I have not yet tested but VGA. It might be that those two other connectors give what I'm looking for.
S-Video or Super-Video is a technology for transmitting video signals over a cable by dividing the video information into two separate signals: one for color (chrominance), and the other for brightness (luminance). When sent to a television, this produces sharper images than composite video , where the video information is transmitted as a single signal over one wire. This is because televisions are designed to display separate Luminance (Y) and Chrominance (C) signals. (The terms Y/C video and S-Video are the same.)
The HSYNC rate of TV is 15625 Hz (for PAL and SECAM standards) or 15750 Hz (for NTSC standard). The VSYNC rate is 50 Hz (for PAL and SECAM) or 60 Hz (for NTSC). TV uses interlacing so that it shows 25 or 30 frames per seconds and shows those in to parts: one field includes all even number horizonal lines and other all odd numbered horizonal lines. Interlacing is the process of scanning 1 frame in two passes - the odd (or even) lines first and the even (or odd) lines second. This enables the low framerate of 25/29.97 to display without flickering as much on a system where the phosphors don't glow for long enough to get from top to bottom of a frame in one pass.
VGA monitor can only take RGB signals with separate sync signals (HSYNC, VSYNC). Original VGA used around 31 KHz HSYNC rate and 60-70 Hz frame rate. The whole picture is normally drawn at each screen update (no interlacing normally, can be used if wanted). The HSYNC rates and VSYNC rates have increased because of increased resolutions and need for faster screen refresh rates for less flickering. You can in real life see signal and monitor specifications in the ranges of an order HSYNC=30-65 kHz and VSYNC=50-120 Hz (those are not absolute maximums, but quite typical values graphics cards output and monitors can take).
Computer monitors, are designed for RGB signals. Most digital video devices, such as digital cameras and game machines, produce video in RGB format. The images look best, therefore, when output on a computer monitor.
If the picture looks better thru Composite than S-Video, it is because S-Video gives you such a sharp picture and excellent color definition, you can see all the "artifacts" that regular Composite was hiding up to now with its blurry picture. These include:
- Extensive Dithering
- Crude polygon construction
- Use of checkerboard pattern to provide transparent effect as opposed to a
true transparency
- Poor texture mapping
From the best to the worst:
VGA -Kind of version of RGB
RGBI -Red, Green, Blue and sync signals have their own lines
RGB -Red, Green and Blue signals have their own lines
S-Video -The signals are combined to two signals
Composite -The signals are combined to one signal.
R/F - The signals are combined and modulated to produce Radio Frequency signal
that can be fed to television thru the antenna connection.
S-video to composite video adapter
This simple adapter can be used to convert Y/C video (S-video) to a composite video. This adapter is useful in cases where your video output device has only S-video output but your signal source accepts only composite video input. This circuit works with both PAL and NTSC video standards.Y-ground-------------------+
+---------- RCA/composite ground
C-ground-------------------+
Y-Luminance----------------+
+--------- RCA/composite video
C-Chrominance------||------+
470pF | Female S-Video connector |
| 1 Y ground 2 C ground 3 Y (luminance+sync) 4 C (crominance) |
There seems to be two kinds of S-video connectors. Here is aouther:
S-video-connector, ver 2.
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VGA to TV, TV to VGA
There is no easy way to do it !Best information you can find from Toni Engdahls pages.
The only easy DIY solution is to make the VGA-adapter in your PC send TV-compatible
signal. Toni had on his pages this picture:
The circuit is rather simple, but it is only the beginning. The hard part is
the programs -There is only very limited selection ! ( I copied here one and another PAL-version to be used in DOS from Tonis page )
For Linux there is some possibilities, because you can edit the configuration files more easily than in M$Windows.
the TV.Another easy way is to go and buy a solution. There is boxes that make the conversion, but
remember that you will newer get as good picture as from your PC monitor, if
your TV monitor isn't done for it.
Commercial stuff
I don't give out the names or links of these devices and don't even recommend these. PC to S-Video or composite. The Laptop must have NTSC Output Capability. |  1600*1200 resolution , 640*480@120HZ. 117Hz for iMAC , Plug &Play Enjoy Internet , DVD Movie (Free Download) on TV & recording on VCR Personally I don't believe to these resolutions, except if you have some special HDTV device |
Links
VGA tp TV, TV to VGA I think you can find most of information needed from these pages.PTMUSTA at UTU.FI
