ATI and NVIDIA: Quick Look at HDTV Overscan Compensation
by Andrew Ku on August 25, 2004 12:00 PM EST- Posted in
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NVIDIA - Underscan
We kind of went over NVIDIA's overscan compensation method, called "overscan shift", in our eVGA GeForce FX 5700 Personal Cinema review, but hopefully, this gives you a clearer sense of what is going on. We used the ForceWare 56.72 drivers, which is why we simply followed the instructions for the ForceWare 56.72 drivers to set up NVIDIA's overscan compensation method in the release notes under "configuring HDTV".
1280 x 720 desktop resolution@720p output
Click to enlarge.
As we mentioned in a previous review, overscan (as seen in the above) seems to be limited to only three sides of the signal: left, right, and bottom. The upper portion of the image seems to encounter no degree of overscanning.
There are technically two overscan compensation methods that NVIDIA implements. The first is underscanning, where NVIDIA outputs the picture at a lower resolution so that the TV displays everything. The problem with underscanning is that you can get a lot of wasted space.
Click to enlarge.
It is a fairly simple process, as you just move the track slider on the "change resolution" page of NVIDIA's display control panel. In this case, we are outputting 1088 x 612 in a 720p environment, which runs natively at 1280 x 720. Basically, you are looking at a 1088 x 612 image on a 1280 x 720 screen.
Click to enlarge.
As you notice, this accomplishes the goal of having zero underscanning, but in many cases, there is going to be a significant portion of screen that isn't being utilized by the computer's HDTV output, which brings us to overscan shift...
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AndrewKu - Wednesday, August 25, 2004 - link
#2 - True. Hopefully, their will be more convergence in the spec.aw - Wednesday, August 25, 2004 - link
Keep in mind that for HDTV gaming, consoles are actually ahead of computers. A lot of games on the Xbox and a few on PS2 come in 480p/720p/1080i flavors, so they look great on the HDTV without any screwing around. Hopefully, computer game makers will start offering standard HDTV resolutions soon in all games...I have no idea how practical that is but if consoles can do it I assume they can too...Questar - Wednesday, August 25, 2004 - link
"It is implemented deliberately on TV sets because of the different video input formats: composite, s-video, etc., all of which the TV needs for which to provide support. If overscan was not implemented as a factor of these different formats, there would likely be underscanning of different degrees on different TV sets. This is due to the different protocols and inherently different signals that the TV needs to handle."Where do you come up with this crap?
Overscanning is to eliminate the black bars around the picture. This was done long, long before there was s-video, component inputs, etc.
The type of input has nothing to do with overscan.