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Garrett
06-02-2011, 04:34 PM
Hi, Our lab just got a new Samsung 2233 monitor, which we're using to run some simple opengl applications. I'm running into a problem where I draw a white circle moving across a light grey background: for some reason as the circle moves, it's followed by a short discolored trail.

The application is double-buffered, and I've checked the framebuffers: the circles appear to be drawn correctly. So I think the ghost artifact we're running into has something to do with the display (we don't run into this problem when using a different monitor).

If you've run into a similar problem before, or have suggestions on how to go about debugging this problem, I'd love to hear back from you.

Thanks!

~Garrett

Alfonse Reinheart
06-02-2011, 05:05 PM
It almost certainly has nothing to do with OpenGL. The best way to verify that is to grab a window and drag it around; if you see ghosting in that window, it isn't OpenGL's fault.

It is entirely possible that your monitor is just not a good monitor. Poor LCD monitors will exhibit ghosting. I did a search on Amazon for "Samsung 2233" and found this (http://www.amazon.com/Samsung-2233SW-21-5-Inch-Widescreen-Monitor/dp/B001QVLD8A/ref=sr_1_1?ie=UTF8&qid=1307059310&sr=8-1). If that's your monitor, then it seems pretty reasonable.

Assuming that your monitor is reasonably decent, I would suggest playing with monitor settings. I had a ghosting problem with my monitor for several months. In a fit of pique, I just started poking around and eventually, something I did made it go away, and the monitor has been pretty good ever since. So break out the instruction manual and poke at stuff.

ZbuffeR
06-03-2011, 12:06 AM
Indeed this is a too common flaw of modern screens :(

This feature is sometimes called "overdrive", and the aim is to reduce time needed by liquid crystals to switch between very distinct colors.
More often than not, this overdrive is tuned by butchers, to make (artifically measured) response time reviews look good.
2 ms response time for black to white transition ! Great for gaming ! But totally destroying movement on subtle colors ! Yay !

Play the videos from this post (sorry it is in french but some google translate should make it almost understandable) :
http://www.lesnumeriques.com/legrandforu...03_1.htm#t62856 (http://www.lesnumeriques.com/legrandforum/avis/Ecrans-TV-Videoprojecteurs/ecran/remanence-b2409hds-etoile-sujet_6303_1.htm#t62856)
I ended up exchanging the iiyama B2409HDS I had bought with an Asus VK266H just because the iiyama did not have adjustable overdrive, whereas the Asus had this setting...

Apparently your model does not have an adjustable "overdrive" setting, too bad because this is the only good way to solve the problem.
These guys "solved" it for your model by pushing hard the monitor contrast setting :
http://www.quakeworld.nu/forum/viewtopic.php?id=4103

Keep a good old CRT around to check for "the real stuff" :D

Garrett
06-06-2011, 02:15 PM
Hi, Thanks for the quick responses! Looks like it's most likely a display issue rather than an OpenGL one, the 'overdrive' feature sounds like it could be the culprit. Apparently this has been an issue on other displays too: Viewsonic VX2265wm and Viewsonic VX2268wm.

I tried playing around with the contrast and some other settings, to no avail. I think I'm going to use a different colour scheme, where the effect is less noticeable, or switch back to a CRT monitor, which didn't produce the same ill-effect.

Thanks again!

Ilian Dinev
06-06-2011, 02:34 PM
If the display applies a high-pass filter, pre-apply a lowpass filter :D . (old-style motion-blur, with accumulation buffer or whatever).
I've seen a Samsung 223BW in person, and its overdrive is really nasty. By simply hiding a window or menu, you can immediately see the overdrive. So, maybe the 223x line is cursed like that. (while other Samsung models are perfectly fine).