Hooking Up A PC to A HDTV

The question of hooking up a PC to a HDTV comes up often and the subject has many twists and turns depending on the video card in the computer, the type connection, DVI, VGA, component, etc., and the type HDTV and its associated video connections.   This essay is intended to be a starter for those that wish to make the PC to HDTV connection.

Also for you strictly technical guys out there, I do take a little poetic license to try and simplify the subject somewhat.

Introduction
Some HDTVs are PC ready and some are not.  Most HDTVs are just that, TVs and are not intended to be connected to a computer, but most all HDTVs can be connected to a computer with varying success. CRT based HDTVs are probably the least desirable HDTVs to hook to a computer because of the overscan associated with these type TVs.  The fixed pixel type TVs generally will be the best type HDTVs for connection to a PC and many of them are equipped with a VGA port for connection of a PC.  These units generally will only require the use of a VGA cable and the setting of the PC video card to match the recommended resolution of the HDTV.

Overscan
Overscan has been a part of TV since the beginning. Basically TVs are set to display a smaller area of the picture than what is received in order to insure there will not be any black borders around the picture. The overscan is due to the TV settings not the devices sending the signal to the TV.

The reason the TV manufacturers do this is twofold. First it was determined that people want to have the entire area of the picture filled. We have seen many posts about getting rid of the black or grey bars on the 16:9 sets when 4:3 images are displayed on this forum. Fact is most people would rather watch a stretched or zoomed picture as opposed to the black or grey bars. Second is the precision of the TVs themselves. Early models in particular could not produce a straight line at the edges of the picture. Over the years the technology has improved in CRTs to where this is the case with computer monitors are set with a small black border around the picture. This is required in order to be able to see the entire computer frame. For some reason people will accept this setting for a computer monitor, but will not for watching TV.

Fixed pixel monitors have eliminated this issue, but because the television programming producers still produce images targeted for the "sweet spot" many plasmas and flat panels only display the overscaned picture instead of the entire picture. If they displayed the entire picture received, you would get black surrounds or video noise in the surround areas on many programs.

Due to the overscan issue, it caused a problem when you try to use the HDTV as a computer monitor in that some of the desktop is not displayed on the TV screen. The amout of the desktop that is cut off will vary between 5% and 15% according to what I have read.

Here are two screen captures of my desktop:

Fig. 1 - Screen that shows on my computer monitor


Fig. 2 - Overscanned screen that shows on my HDTV.

As can be seen in Fig. 2, there is a whole row of icons across the top and an entire column on the left that is not shown on the overscaned TV screen. Additionally the Start button and the bottom row of windows is off the screen.

The resolution for the images shown is set at 1380×720p and the clarity of the HDTV picture is very good and quite useable except for the overscan. The connection to my 50" HDTV is through the component cables using a Key Digital KD-VTCA3 VGA to component converter. This converter allows me to have both my VGA monitor and my HDTV connected at the same time.

The video card I am using is an ATI 7500 pci Radeon that has both a DVI and a VGA output connector, so I’m able to connect my 40" HDTV in my living room via the DVI connection and the overscan is about the same. The overscan is somewhat better at 1920×1080i, but the overall picture is worse when displaying computer screens.

Using DVI or HDMI
The reason many TV manufacturers include a DVI connection in addition to component video was not to allow the connection of a computer. The main reason was to allow the exchange of video information in a digital format rather than analog. The DVI interface came into being due to the LCD and plasma flat panel computer monitors and projectors, and later DLP and LCOS (D-ILA) displays and
projectors. Since these are fixed pixel devices an interface that would present a digital value for each pixel rather than an analog signal level made sense.

The DVI interface answered the question of, "Why start out with a digital array of pixel values then convert them to an analog signal to send to a monitor only to have the analog signal reconverted back to digital?" With the DVI interface the possibility of the signal remaining all digital is possible.

The DVI interface was also given interaction capabilities between the video card and the monitor. This allowed the computer to inquire of the monitor what the resolution and timing that it supported and then via software in the computer set the video output accordingly. This capability is actually the essence of the DVI interface, the ability to tell the source what signals the monitor will display. The earliest DVI-I interfaces were actually just VGA analog signals with the digital link to allow the information to be exchanged between the computer and the monitor. There is a cable available to convert a DVI-I output from a video card to a VGA input on a monitor.

The DVI connection that is most desirable for fixed pixel devices is the DVI-D, dual link connection. This is the connection that most HDTV manufacturers use primarily for compatibility reasons.

Adoption of DVI for HDTV Signals
Since the computer was able to ask the monitor to supply information concerning its signal capabilities, as well as other information, the consumer electronics industry saw this interface (and later the HDMI) as a possible answer to the copy protection issue that had prevented HD movies from being made available for broadcast in HDTV. The entertainment industries were concerned with copy protection and insisted on a method of preventing cloning of their movies. The HDCP protocol was developed and the DVI became the first interface to have HDPC implemented. This allowed the broadcasters to "raise the HDCP flag" that would prevent a recording device connected to the DVI output from recording by shutting off the output. As long as a monitor only device was connected the output was enabled.

Computer Output Compatibility
Many people think that because there is a DVI connection on their HDTV that it should be a matter of connecting a DVI cable between the two and presto! We have computer video on our HDTV screen. Well I’m sorry to say this is not the always the case, in fact rarely.

There are exceptions to this, primarily plasma, LCD displays and projectors. These are generally higher cost display units that are built with the connection of a computer in mind, but most HDTVs are not built with the connection of a computer. Computer monitors today will accept a vast range of video signals. Refresh rates from 50Hz to 120Hz are typical for most computer monitors, whereas most HDTVs will only handle 59 to 61Hz refresh rates. Horizontal scan ranges are also reduced compared to a computer
monitor. Here is my HDTV information returned by MonInfo, a utility that can be downloaded and run to get information from your HDTV via the DVI connection:

Quote:
Monitor
Windows description……… Plug and Play Monitor
Manufacturer description…. R40W46
Manufacturer……………. LG Electronics
————————————————————————————
Plug and Play ID………… GSM0101
Serial number…………… (n/a)
————————————————————————————
Manufacture date………… 2003
EDID revision…………… 1.3
Display type and signal….. Digital
Sync input support………. (n/a)
Screen size…………….. 710 x 400 mm (~34")
Power management………… Not supported
Color characteristics
Display gamma…………… 2.20
Red chromaticity………… Rx 0.640 - Ry 0.340
Green chromaticity………. Gx 0.300 - Gy 0.690
Blue chromaticity……….. Bx 0.138 - By 0.038
White point (default)……. Wx 0.270 - Wy 0.365
Timing characteristics
VESA GTF support………… Not supported
Horizontal scan range……. 31-45kHz
Vertical scan range……… 59-60Hz
Video bandwidth…………. 80MHz
Timing recommendation #1…. 1920×1080 at 30Hz
Modeline……………. "1920×1080" 74.250 1920 2008 2052
2200 1080 1084 1094 1124 interlace +hsync +vsync
Timing recommendation #2…. 720×480 at 60Hz
Modeline……………. "720×480" 27.000 720 736 798 858
480 489 495 525 -hsync -vsync
Standard timings supported
720 x 480 at 60Hz - LG Electronics
1920 x 1080 at 30Hz - LG Electronics

Note that the 30Hz indicates these are interlaced timings.

The reason HDTVs have such narrow response is a cost issue. Most people who buy an HDTV do not want to pay the extra $2k or so required to expand the response to allow the computer timings.

What Is Possible
But there are many reasons to connect your computer to your HDTV, even though it will not be a big screen duplicate of your computer monitor. Slide shows of digital photos, DVD viewing and group web surfing are just some of the possibilities, but I find it will not replace my computer monitor.

To find out what is possible for your HDTV the first step, after the connection of the appropriate DVI cable, would be to download and run MonInfo.
This utility will tell you what resolutions your TV will display. I have found that this is not the only resolutions, but the recommended by the manufacturer. For example my LG will also display 1920×540 at 60Hz which is the progressive scan counterpart to the 1920×1080 at 30Hz. It is probably not recommended by LG due to the aspect ratio issues.

It is important to know what is possible for your particular HDTV because serious damage can be done to your HDTV if non viewable signals are sent to your TV. If while trying out different resolutions and timings you hear a high pitched noise from your TV, remove the signal or turn off the TV immediately.

Recommended Steps To Get Started
First of all you will need to have a computer monitor connected as well as your HDTV. Since the majority of resolutions that can be displayed on your monitor will not be displayable on your HDTV, you would be operating blind and that just will not work. Some video cards have both a VGA output and a DVI output and if yours is this type, then you can hook up your monitor to the VGA output. If your computer monitor is a DVI unit then you will need a DVI distribution box, like the DTronics
DD-12P
, for example.

Start by setting your computer to 640×480 and get a stable picture. This should be no problem. Most likely the 16:9 resolutions of 720×480 and 1920×1080 will not be listed with the standard video drivers. In order to be able to set custom resolutions it will be necessary to download a program called powerstrip, which is available here: PowerStrip - English and the home page to read up on the software is here: http://entechtaiwan.net/util/ps.shtm
A really good guide to using powerstrip is located here:

Powerstrip
101 How to use it to Connect your PC to your HDTV

Most likely without the powerstrip software you will go no further. Some video cards have some HDTV drivers for their latest and greatest cards, but if you have an older card - 6 months old even - you will need powerstrip. In the end, you may need to get a newer card anyway. Even if you get a newer card that supports HDTV resolutions, you may still need powerstrip to tweak the display to reduce the overscan. 

This is a fairly complex issue to get your computer connected to your HDTV successfully, but with some persistence it can be done.

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