Jem (![[info]](http://l-stat.livejournal.com/img/userinfo.gif){kind=small} gothgems) wrote,@ 2008-03-30 23:02:00 |
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HDTV output from an ATI HD graphics adapter
We had a little accident about a week ago. The TV got damaged. Destroyed actually. I replaced it with a new 40" 1080p Samsung LE40M86BD HDTV. When I plugged in my PC to this super TV I got some strange anomalies.
Using the VGA socket, the 1920x1080 image was pin-sharp. Using a DVI-HDMI adapter, the image was blurred although it was filling the screen. When displaying a test image that consisted of alternate lines of red and white, the HDMI display had obvious horizontal red banding while the VGA display looked a uniform pink.
VGA Image
HDMI Image
It looked like some kind of scaling issue, but there was absolutely no reason for the TV or the PC to be scaling the image as it was matched to the TV's 1080p resolution.
I found several settings in my ATI Catalyst driver software related to under/overscan and GPU image scaling, but nothing I did with these settings made any significant difference. It was still showing banding on the test image and blurring of screen fonts.
I discussed the strange effects with some technophile friends, and I have to give my thanks to Steve Roberts of Doctor Who Restoration Team fame, who gave me the clue I needed to solve the problem.
Steve pointed out a setting on the TV menu that I hadn't seen. Under the "Picture" menu there was a setting for "Just Scan", while the default was "16:9". When I switched to "Just Scan" there was no noticable difference, but then I started to play around with the driver settings.
Switching "GPU Scaling" mode to "Centered Timings" resulted in an image that had black borders around it, even though it was a 1920x1080 desktop. It was obvious that the underscanning was reducing the size of the image now. I set underscan to 0% and switched off GPU Image Scaling. Result: a perfect image.
I'd already worked out it was something to do with the scaling and scanning but it was the "Just Scan" setting on the TV that was missing. Without that, the TV was compensating for everything I did on the PC graphics driver and displaying a distorted image at full screen resolution.
If anyone else is struggling with an ATI Catalyst driver and a 1080p TV, I hope this saves you some effort!
We had a little accident about a week ago. The TV got damaged. Destroyed actually. I replaced it with a new 40" 1080p Samsung LE40M86BD HDTV. When I plugged in my PC to this super TV I got some strange anomalies.
Using the VGA socket, the 1920x1080 image was pin-sharp. Using a DVI-HDMI adapter, the image was blurred although it was filling the screen. When displaying a test image that consisted of alternate lines of red and white, the HDMI display had obvious horizontal red banding while the VGA display looked a uniform pink.
VGA Image
HDMI Image
It looked like some kind of scaling issue, but there was absolutely no reason for the TV or the PC to be scaling the image as it was matched to the TV's 1080p resolution.
I found several settings in my ATI Catalyst driver software related to under/overscan and GPU image scaling, but nothing I did with these settings made any significant difference. It was still showing banding on the test image and blurring of screen fonts.
I discussed the strange effects with some technophile friends, and I have to give my thanks to Steve Roberts of Doctor Who Restoration Team fame, who gave me the clue I needed to solve the problem.
Steve pointed out a setting on the TV menu that I hadn't seen. Under the "Picture" menu there was a setting for "Just Scan", while the default was "16:9". When I switched to "Just Scan" there was no noticable difference, but then I started to play around with the driver settings.
Switching "GPU Scaling" mode to "Centered Timings" resulted in an image that had black borders around it, even though it was a 1920x1080 desktop. It was obvious that the underscanning was reducing the size of the image now. I set underscan to 0% and switched off GPU Image Scaling. Result: a perfect image.
I'd already worked out it was something to do with the scaling and scanning but it was the "Just Scan" setting on the TV that was missing. Without that, the TV was compensating for everything I did on the PC graphics driver and displaying a distorted image at full screen resolution.
If anyone else is struggling with an ATI Catalyst driver and a 1080p TV, I hope this saves you some effort!
