Incorrect screen resolution

[Kasper Dupont]

I'm using an Elysion U1 computer together with a BenQ projector. Ubuntu reports that the monitor is not detected and defaults to a screen resolution of 1280x800 pixels.

When I use the monitor preferences to change the resolution to 1024x768 (which is the correct resolution for this projector), the image gets even more blurry than when the incorrect resolution is used.

xdpyinfo claims the resolution has been changed to 1024x768 pixels, but the actual output being sent on the DVI port is still 1280x800 pixels.

It appears Ubuntu has configured the graphics chip to scale the 1024x768 image to 1280x800 pixels which the projector then needs to scale back to 1024x768 pixels, which results in a blurry output, which is almost unreadable.

The bug exists in both the preinstalled Ubuntu 9.04 as well as in the Ubuntu 10.04, that I just installed from the official Ubuntu DVD image.

ProblemType: Bug
DistroRelease: Ubuntu 11.04
Package: gnome-control-center 1:2.32.1-0ubuntu15
ProcVersionSignature: Ubuntu 2.6.38-8.42-generic 2.6.38.2
Uname: Linux 2.6.38-8-generic i686
NonfreeKernelModules: nvidia
Architecture: i386
Date: Mon Mar 19 15:30:44 2012
EcryptfsInUse: Yes
InstallationMedia: Ubuntu 11.04 "Natty Narwhal" - Release i386 (20110427.1)
ProcEnviron:
 LANGUAGE=en_US:en
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: gnome-control-center
UpgradeStatus: No upgrade log present (probably fresh install)

[Kasper Dupont (ubuntu-launchpad-feb)]

I tested the 1024x768 resolution with all the possible refresh rates that gnome-display-properties permits for this resolution. It makes no difference which of the refresh rates from 52 to 56 Hz I choose, the output always ends up being 1280x800 at 59Hz.

[Kasper Dupont (ubuntu-launchpad-feb)]

I finally found a way to get the correct screen resolution on the output. In the nvidia-settings utility there is a section called DFP-0 where there is a "Flat Panel Scaling" box. In that box I disabled "Force Full GPU Scaling"

The "Flat Panel Information" claims the native resolution of my projector is 1280x800 (which is incorrect). So something autodetects the resolution as 1280x800 and set the GPU to do the scaling such that the projector doesn't have to do it.

This should help narrow down the location of the bug. But disabling "Force Full GPU Scaling" is a suitable workaround. Now I just need to figure out how to make the change permanent.

[Kasper Dupont (ubuntu-launchpad-feb)]

The bug is still present in 12.04. The workaround of disabling GPU scaling through the nvidia-settings utility still works. But that still leaves the login screen with an incorrect resolution. Additionally guest sessions will always start with an incorrect setting, so after starting a guest session you have to start the nvidia settings utility, then disable GPU scaling, then manually set the correct resolution. That makes the workaround way too cumbersome to be acceptable, especially for the guest account which is expected to be used by less experienced users.

[dino99 (9d9)]

This version is no more supported and is not a 'security' problem; so does not expect a backport