Introduction
There are several types of video connections that you can find on PC and CE products like TVs, DVD players and videoprojectors. Even though they all serve to the same purpose - connect video signal from one device to another - the video quality obtained by each type of connection is completely different. Since you probably want to get the best video quality from your equipments, we've written this tutorial to explain you the differences between each kind of connection and when to use each one of them, with many tips on how to improve the video quality from your equipment.
The connection types we'll cover are the following, listed from the worst video quality to the best:
- Radio Frequency (RF)
- Composite Video (RCA)
- Separated Video (S-Video)
- Component Video
- Red, Green and Blue (RGB)
- Video Graphics Adapter (VGA)
- Digital Video Interface (DVI)
- High-Definition Multimedia Interface (HDMI)
Radio Frequency (RF)
RF is the oldest way to transmit video signals. It is used on TVs and VCRs to connect these devices to both terrestrial (antennas) and cable transmitions. Since cable TVs are provided using this type of signal, unfortunetly you won't find anything better than this to connect your cable TV to your TV or VCR. This kind of connection can be used to connect your VCR to your TV, but since nowadays all TVs have composite video inputs (RCA), you should use composite video to connect your VCR to your TV, not RF, in order to get a better image quality. We'll talk more about this on the next page.
RF cables are found in two flavors: 75-ohm coaxial and 300-ohm parallel. This second type was used by old terrestrial broadcasting antennas, but even this kind of antenna use the 75-ohm coaxial cable nowadays. You can install a 300-ohm cable/connector into a 75-ohm connector by using an adaptor, as we show on Figure 6.
On Figure 1 you can see the RF input on a TV set. On this connector you should connect you cable TV or your antenna, if you still use terrestrial TV. Since this TV set has composite video inputs (“Video In”) you should not use this connector to connect your VCR. We’ll talk more about this on next page.
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Figure 1: RF input on a TV set.
On Figure 2 you can see RF input and output on a VCR. The input is used to connect the VCR to you cable TV (or decoder) or antenna, and the output can be used to connect the VCR to the TV, but like we said, this connection shouldn’t be done nowadays, since you can use composite video to connect your VCR to your TV, which provides a better image quality.
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Figure 2: RF input and output on a VCR.
On computers RF connectors are only used on video capture cards, to allow you to record live TV shows on your computer, connecting this connector to your cable TV system or a TV antenna. Don’t use this connector to hook a VCR to your PC, since you can use the composite video connection which provides a better image quality.
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Figure 3: RF inputs for TV antenna and FM antenna on a video capture board.
On Figure 4 you can see a typical RF cable and connector, and on Figure 5 another kind of connector that also can be used on RF connection. The difference between them is that the cable connector on Figure 4 is meant to be screwed to the female connector on your TV or VCR, while the second connector, on Figure 5, don’t need to be screwed, just push it towards the female connector and it will fit.
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Figure 4: Typical RF male connector and cable (screw type).
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Figure 5: Another kind of RF male connector.
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Figure 6: Adaptor to convert 300-ohm RF input (“old type”) into 75-ohm, which is more used nowadays.
Composite Video (RCA)
Composite vídeo is one of the most popular video connection types and uses a RCA connector (older videoprojectors can use a BNC connector for this connection). Composite video is used on the popular “video in” and “video out” connectors, found in VCRs, TVs, DVD players and video projectors. On PCs, some video cards can provide this output.
This is the best option to connect your VCR to your TV set, assuming that they don’t have a S-Video connector (usually newer TV sets have this connector, but VCRs usually don’t have S-Video output). But for other devices, like DVD players, videoprojectors and even PCs, you should not use this connection, because S-Video, Component Video and other standards offer better video quality and usually you can find at least S-Video on those devices.
On Figure 7 you can see the composite video input on a TV set and on Figure 8 on a VCR. Usually the female RCA connector used by composite video is yellow, in order to be differentiated from other commonly found RCA connectors, specially audio, where red indicates the right channel and white or black indicates the left channel. Pay attention that the TV set from Figure 7 also has S-video input, our next subject.
Since VCRs allow you to record videos, it has two composite connectors, one being an input and the other one being an output. You should connect the VCR output to the TV set input to make the proper connection. Its input should be used in the case you are willing to record something from another video source, like another VCR (for copying tapes) or even a PC with composite video output.
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Figure 7: Composite video on a TV set.
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Figure 8: Composite video on a VCR.
On Figure 9 you can see the outputs of a typical DVD player. Even though it has a composite video output, it shouldn’t be use to connect the player to your TV or videoprojector, since usually it has S-Video and/or video component outputs, which provide a better video quality. We only see two uses of the composite video output of a DVD player: if your TV set is very old or if you want to record on VHS tape the contents of a DVD.
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Figure 9: Outputs found on a typical DVD player.
Some video cards have a RCA connector, thus providing composite video. This output can be used to connect your PC to a TV (so you can use your TV as a video monitor) or to a VCR, to record images and videos on a VHS tape. The image quality of a TV set, however, is far below any video monitor. There are two reasons. First, the TV screen works at 640x480 resolution, lower than the most common screen resolutions nowadays. Secondly, TV sets work with interlaced scanning, while video monitors work with non-interlaced scanning (a.k.a. progressive scanning), which provides a far better video quality.
You can also connect your video card to your TV using S-Video, if both devices have this connector. Also, S-Video output from video cards can be transformed into composite video by the use of an adaptor, as we will explain on next page.
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Figure 10: A video card with composite video output.
Of course you will also find composite video on video capture cards, allowing you to connect your VCR on your computer in order to transform VHS tapes into computer video.
On Figure 11 we can see the famous RCA male connector used by composite video. The cable on the picture has two more connectors, for carrying audio (one cable for left channel and the other one for right channel). The composite video cable uses the yellow plug.
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Figure 11: Composite video cable.
Since RCA connectors are used for several different things (take a look on Figure 9), they are usually colored. In order to help you, here is a small list of the most used colors for RCA connectors and cables:
- Yellow: Composite video.
- Red: Right channel (audio).
- White or black: Left channel (audio).
- Orange: Digital audio (a.k.a. SPDIF).
- Green: Component video.
- Blue: Component video.
- Red: Component video.
Separated Video (S-Video)
S-Video provides a better image quality than composite video. On composite video there are only two wires, one carrying the video signal and the ground. On S-Video, three wires are used; one for carrying the image in black-and-white, one for carrying the color information signal and the third is the ground – hence the name of this standard, separated video.
All current TV sets and videoprojectors have this connector. You should connect your DVD player to your TV or videoprojector using an S-Video cable only if your DCD player and/or TV or videoprojector don't offer a better connection option, like component video, DVI or HDMI.
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Figure 12: S-Video connector on a TV set.
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Figure 13: S-Video connector on a DVD player.
Also, if you want to connect your computer to your TV to use it as a video monitor, this is one option, but should be used only if your TV doesn't provide any better connection option, like component video, VGA, DVI or HDMI (listed from the worst to the best).
Keep in mind that the image quality of CRT-based TV sets is far below any video monitor. There are two reasons. First, the TV screen works at 640x480 resolution (a.k.a. 480i or SDTV), lower than the most common screen resolutions nowadays. Secondly, TV sets work with interlaced scanning, while video monitors work with non-interlaced scanning (a.k.a. progressive scanning), which provides a far better video quality.You will only get good results if you use a HDTV set with progressive scanning as a video monitor and of course the higher the resolution of your HDTV, the better.
For connecting PCs to videoprojectors you should use the DVI or HDMI connectors, as we will explain you later (if your videoprjector doesn't feature any of these two connectors then the option is to use the VGA connection).
Nowadays, almost all video cards have S-Video output, as you can see on Figure 13. On video cards with video capture function (a.k.a. VIVO) or with component video output, this very same connector is also used by these functions. The standard S-Video connector has four pins. If the S-Video connector from your video card has more than four pins, that means your video card has component video or video capture functions. We’ll talk more about this on next page.
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Figure 14: S-Video connector on a video card.
On Figure 15 we see the standard S-Video connector and cable. S-Video signal can be transformed into composite video by using an adaptor (shown on Figures 16 and 17). This is useful to connect a video source that has S-Video output (like your PC) to a TV set that doesn’t have S-Video input.
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Figure 15: S-Video connector and cable.
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Figure 16: S-Video to composite video adaptor.
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Figure 17: This cable provides S-Video input and composite video output.
Component Video
Component video offers a far better quality than S-Video, being the preferred video connection to use between your DVD player or your cable/satellite converter and your TV set or videoprojector, in the case they have this kind of connection and they don't have a better connectivity option, like DVI or HDMI. It uses three cables, which should be connected as follows:
- Green connector: green input or input labeled as Y;
- Blue connector: blue input or input labeled as Pb or Cb or B-Y;
- Red connector: red input or input labeled as Pr or Cr or R-Y.
The Y connector transmits video information (black and white image) while the color information is transmitted on the other connectors.
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Figure 18: Component video connectors on a DVD player.
On the PC, some video cards have this kind of output, which should be used if you want to connect your PC to your TV set but your TV doesn't have a better kind of connection, i.e. VGA, DVI or HDMI.
The problem, however, is that is not so easy to recognize if a video card has or not this kind of output because it shares the same connector used by Separated Video (S-Video). Almost all video cards nowadays have one S-Video connector, but the majority doesn’t have component video output available on this connector.
One way to detect if your S-Video connector has component video output or not is looking at it. If it has only four pins, this means it has only S-Video output and doesn't have component video output. If it has more than four pins, this may mean that it has component video output. Check on Figure 19.
Figure 19: Identifying the S-Video connector used by your video card.
Pay attention that we said "may". This happens because there are some video cards – especially those with video capture (VIVO) function – that have more than four pins on their S-Video connector, but these extra pins are used by another feature, not by component video.
In summary: if the S-Video connector from your video card has four pins, it doesn't have component video output, if it has more than four pins, it may have component video output. To be sure, only reading the board manual and looking on its specs to see if it has this feature.
To use the component video output from your video card, you will need an adaptor. This adaptor usually comes with video cards that have component video output. So, if you video card came with a component video adaptor, this means it has component video output!
The aspect of this adaptor can vary; the two most common models we show on Figures 20 and 21.
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Figure 20: Component video adaptor.
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Figure 21: Another model of component video adaptor.
If your video card does not have component video output you can still convert the VGA or DVI output of your video card into component video using an adaptor. It is worth noticing that this connection is not just an electrical connection; you will need electronic components to make the conversion from the RGB standard to the YPbPr one used by the component video. That is why this adapter cannot be easily made at home. Be careful, because there is a USD 15 cable on the market that claims to convert the VGA output into component video, but this cable doesn't work correctly.
ATI manufactures this adapter for video cards that use this company's chip, which costs USD 30 (this adapter doesn't work in boards with chips from other manufacturers; this happens because boards with ATI chips already have support for the component video as a standard feature). For more information about the ATI adapter, visit http://ati.amd.com/products/hdtvadapter/.
Other manufacturers produce VGA or DVI converters for component video compatible with any video card, but their price is higher (up to USD 150, depending on the manufacturer and the functionalities). Be careful, for the cheapest converters may not generate a component video signal at the best resolution or quality that your TV may support. That's why that you have to check the resolutions and modes your TV supports and the resolutions and modes the adapter is capable of generating before buying it. The two most popular adapters among enthusiastic users are the Digital Key (model KD-VTCA3 - http://www.digitalconnection.com/Products/Video/kdvtca3.asp) and the Audio Authority (model 9A60 - http://www.digitalconnection.com/Products/Video/9a60.asp).
Red, Green and Blue (RGB)
RGB connection is an old standard used by workstation video monitors. It uses the same signals as VGA but instead of using a single cable carrying all the wires together and using a single connector with all signals, it uses a separated cable for each signal. With a separated cable, each signal has its own shielding, protecting it from interference, which does not occur on VGA cable. Because of that, RGB connection offers a better image quality.
At least in theory: since this standard can only be used with old video monitors that accept this kind of connection, the image quality is limited by the age of the video monitor (newer video monitors offer a far better image quality than older video monitors because the technology used) and the screen resolution. Also, most of these old RGB video monitors run at a different scanning frequency than VGA, making it impossible to connect older video monitors that use this standard directly to your video card.
So, we put this kind of connection here just as a reference, since you probably won’t see it around anymore. Anyway, if you are curious about this standard or happen to have an old RGB video monitor, take a look on this link, you will find it very useful: http://www.epanorama.net/documents/vga2rgb/.
Actually there are three different RGB cabling standards:
- RGB5: The one we mentioned on first paragraph; it uses five cables: red, green, blue, horizontal sync (Hsync) and vertical sync (Vsync).
- RGB4: Uses four cables: red, green, blue and composite sync (Csync).
- RGB3: Uses three cables: red, green + Csync and blue, also known as sync on green.
Each one of these cables use a BNC connector.
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Figure 22: Example of a RGB5 cable.
In summary, the RGB connection type is better than VGA, but because of the age, modern video monitors offer a far better image quality than these old RGB monitors.
Video Graphics Adapter (VGA)
VGA is the traditional connector used to connect your PC to video monitors. It is also one option to connect your PC to videoprojectors and HDTV sets. This connection offers a better video quality compared to component video, S-Video and composite video because it uses an independent wire for each video signal: red, green, blue, horizontal sync and vertical sync. It uses a 15-pin connector known as D-Sub, D-Shell or HD15. On this connection information is transmitted using analog signals, while on DVI and HDMI information is transmitted digitally, thus providing a better quality. So if your video monitor, videoprojector or HDTV set has a DVI or HDMI connector – which will be the case with current models available on the market – you should use one of them instead of the traditional VGA connector to connect your PC to your monitor, projector or HDTV.
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Figure 23: VGA connector on a video card.
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Figure 24: VGA cable of a video monitor.
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Figure 25: VGA connector on a HDTV set.
Digital Video Interface (DVI)
All connection types we’ve seen so far use analog signals. HDMI connection, which we will see on next page, uses digital signals. DVI, on the other hand, can carry both analog and digital signals. Here are the types of DVI connectors available:
- DVI-A: Analog connection.
- DVI-D: Digital connection. Usually when we say “DVI” we are referring to DVI-D.
- DVI-I: Cable or connector that can carry both DVI-A and DVI-D signals. DVI-A cables can carry only DVI-A signals and DVI-D cables can carry only DVI-D signals.
- Single Link: Allows screen resolutions up to 1920 x 1080 pixels at 60 frames per second.
- Dual Link: Allows screen resolutions up to 2048 x 1536 pixels at 60 frames per second.
On Figure 26 you can see the differences between these connectors.
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Figure 26: DVI connector types.
So, what is that all about? If you have a device that produces analog signal, it will have a DVI-A connector and you can only connect it to a display that has a DVI-A connector. You can use a DVI-A cable or a DVI-I cable to make this connection. The same idea goes for digital devices: if your device has a DVI-D connector you can only connect it to a display that has also a DVI-D connector. You will have to use a DVI-D or DVI-I cable to do such connection. You cannot connect a DVI-A device to a DVI-D display and vice-versa.
If your device has a DVI-I connector – which is the case of video cards – this means that it produces both analog and digital signals. You should use a cable (DVI-A or DVI-D) according to the kind of connection your display supports, analog or digital.
Of course using digital connection is the best, but you are limited to what kind of connection your product offers. But you should not worry so much about these several different kinds of connections available. Today almost all consumer electronics products feature digital connection, so you will find either a DVI-D or a DVI-I connector and you will probably be using a DVI-D or DVI-I cable, which fit both connectors, so you have nothing to worry about – just see the examples below.
Since computers, digital cable/satellite converters and DVD, Blu-Ray and HD-DVD players are digital equipments, when transmitting video signals using an analog media like the VGA or component video outputs they must first convert the signals from digital to analog. On the other end of the cable, the LCD monitor, HDTV set or videoprojector must convert the analog signal back to digital, since these devices are also digital. There is image quality drop in this process of converting the signal from digital to analog and then back to digital.
So the advantage of using DVI-D or HDMI connection is that you skip these digital/analog/digital conversions, thus improving image quality.
All PC video cards nowadays offer at least one DVI output (usually a dual-link DVI-I connector, allowing you to connect displays with analog or digital connection), as you can see on Figure 27. You can also find DVI connectors (usually a DVI-D connector) on LCD monitors, digital cable/satellite converters, HDTV sets, videoprojectors and some DVD players. If they don’t have a DVI connector they will have a HDMI connector, which is even better.
DVI-D and DVI-I connectors can be easily converted into HDMI, as HDMI is fully compatible with DVI-D, and that’s why you probably won’t find products with these two connections available at the same time. We will talk more about this on next page.
So to connect your PC to your video monitor, videoprojector or HDTV you should use DVI connection instead of the traditional VGA connector, as it will provide the best image quality possible. If your HDTV has a HDMI connector you can connect your PC to it using a DVI-to-HDMI converter or cable, as we will show on next page. The same idea is valid to consumer electronics products: to connect your digital cable/satellite converter to your HDTV set use this connection (as mentioned, if your HDTV set has a HDMI connector instead of a DVI one you can use an adapter or cable to convert the DVI connector into HDMI).
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Figure 27: DVI output (DVI-I dual link connector) on a video card.
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Figure 28: DVI output (DVI-D dual link connector) on a digital cable TV converter.
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Figure 29: DVI input (DVI-D single link connector) on a HDTV set.
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Figure 30: DVI-D single link cable.
We posted a tutorial on how to connect your PC to your HDTV panel. On this tutorial you will find a lot of useful information on how to use this connection. Please read it if you want to connect your PC to a HDTV panel or any other device with DVI input.
It is very interesting to note that DVI-I outputs can be transformed into VGA outputs by the use of an adaptor that usually comes with the video card (see Figure 28), if the DVI-I connector has analog signals (DVI-A) present – which is the case with all video cards. Thus you can transform the DVI-I connector of your video card on a second VGA output, allowing you to connect two video monitors to your computer. This connection, however, will be analog, not digital, since the VGA connection uses analog signals and you are using the DVI-A signals from the connector to generate this output.
Connecting two DVI devices to your PC, however, is only possible if you have a video card with dual DVI outputs, since converting a VGA output to DVI is not possible as VGA output uses analog signals and video monitors featuring a DVI input usually require digital signals (i.e. a DVI-D connector).
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Figure 31: Two DVI to VGA adaptors.
High-Definition Multimedia Interface (HDMI)
HDMI is today the most high-end kind of video connection available and you should use it if the parts you are connecting support this connection. You will find this connection on the latest DVD players, Blu-Ray players, HD-DVD players, HDTV sets and probably on the latest digital cable/satellite converters.
This connection works 100% in digital mode, is capable of transferring higher resolutions than DVI – including resolutions not commercially released yet –, features a copy-protection mechanism called HDCP (High Bandwidth Digital Copy Protection) and transfers digital audio signal on the same cable, eliminating the need of an extra cable for connecting audio – if your devices support this feature.
We have already written a tutorial explaining in-depth how HDMI works, so you may want to read it if you are interested on HDMI.
On the pictures below you can see some examples of HDMI use.
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Figure 32: HDMI output on a DVD player.
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Figure 33: HDMI inputs on a HDTV set.
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Figure 34: HDMI cable.
As we mentioned you can easily convert DVI-D and DVI-I to HDMI thru a cable or adapter. If you want to connect your PC to your HDTV set you will need to use this kind of cable or adapter, see Figures 35 and 36.
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Figure 35: DVI-to-HDMI cable.
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Figure 36: Two DVI-to-HDMI adapters.
Originally at http://www.hardwaresecrets.com/article/157
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