Green flickering pixels that move with black images

Question

Strange question... Occasionally, on my LCD screen, pixels that should be black flicker rapidly and constantly between black and green, about 4 flickers a second.

The crazy part is, unlike dead/stuck pixels, they are relative to content on the screen and move with it.

For example, I might be looking at a web page with a picture that has lots of black. There might be a couple of green flashing pixels in that black that shouldn't be there. I scroll the page, and the green flickering pixels move with the image. It seems that everyphysical pixel is fine, but somehow something interprets part of the image in a way that causes flickering green...

It's not just in a web browser. My first thought was to blame a trolling blogger cunningly uploading an animated gif that simulates a failing pixel... but it happens in a wide range of applications. It seems to occur randomly, other than that it seems to only occur in areas of pure black, and it's always pure 100% green.

It happens rarely enough that it's not a big deal, but it's such a strange problem it bugs me. I can't find any info on anything like this. I'm not even sure if it's hardware or software.

Any ideas? (windows 7 laptop connected to LCD by DVI to HDMI cable)

Answer 1

TLDR: My fix was using a much shorter and better quality cable.

I managed to find a solution to this not that long ago on a brand new monitor that required me to buy a cheap 5m DVI to HDMI cable (I couldn't get anything else quickly).

Like you the problem was highly dependant on what was on screen and seemed more prevalent with darker images. When moving windows around they seemed to "push" the flickering pixels around which I found aggravating.

I tried a number of things including changing screen resolution, refresh rate, colour space (sRGB/CMYK as my graphics card supported both) and nothing at all would stop the flickering pixels.

Eventually in frustration I purchased a simple DVI to HDMI adaptor and combined with a 1.5m HDMI cable and appeared to fix the problem for me. I can only assume that due to the age of my graphics card and the questionable nature of the long cable that data signals for darker areas were somehow corrupted, perhaps something about weak signals and the 8/10b encoding. I'm not completely sure why, but this completely got rid of my flickering pixels.

-=EDIT=-

I've tried to look into what might have been causing this issue for me and so here's my disclaimer for the next bit: Here be dragons and wild guesses as to what is failing.

DVI (and HDMI) use TMDS. TDMS, according to wikipedia, uses "current mode logic (CML), DC coupled and terminated to 3.3 Volts" The effective signal path between transmitter and receiver looks something like this:

My wild guess is that due to the DC coupling at the destination the source must effectively "sink" the current out of the wire in order to produce a valid "0" on the line. A longer (and lower quality) cable will have a higer resistance and thus mean that the source must work marginally harder to pull the line low.

This is where my "weak graphics card" hypothesis comes into play. If the source is unable to completely and consistantly sink the current in the wire then by the time the destination is reading the bit pattern it may be that it reads a 1 where there should be a 0, causing a bit error. Too many bit errors lead to a pixel error and thus the pixel gets the wrong value and appears to be the wrong colour. Now the kicker is that these errors will not be completely consistant due to the source sometimes managing the job and sometimes failing.

I have a suspicion that the somewhat non-random nature of the problem is somehow also related to the 8/10b encoding which tries to achieve DC balance in the signalling protocol. My flickering was worse in particular areas, with there seeming to be some correlation between a group of dark and light mixtures making a "flicker" more likely to happen. I do not understand enough about it to form a firm idea of why it might cause the problem.

Of course, it could have just been a dodgy connector in the cable (I tried both graphics card outputs so nada there...)

Answer 2

Late to the party, but it may prove useful: ( http://www.overclock.net/t/692956/just-got-rid-of-green-dots-on-screen )

The problem is simply because ATI drivers set 2D clocks too low (157Mhz Core,300Mhz memory). At higher resolutions like 1680x1050 these clocks are not sufficient and causes this problem so you need to up them to get rid of these green dots randomly appearing on the screen.

I found this post in AMD official forums. Follow the instructions, it's very simple:

Code: Hey guys,

I did the same and it helped a little bit but there were some green pixels left so I created a CCC-Profile and modified the xml-profile file via the editor and changed the idle clock from 157/300 to 300/500. Now there are no green pixels left and I think I can live with this solution.

To modify the CCC profile you have to do as follows:

1. Open CCC
2. Unlock and Enable Overdrive if they aren’t already.
3. Go to Options/Profiles/Profiles Manager. Create a new profile. Under composition make sure “ATI Overdrive” is checked. Save and Close, DO NOT ACTIVATE.
4. In windows go to: C:\\Users\\{yourusername}\\AppData\\Local\\ATI\\ACE\\Prof iles (you will need to have “show hidden files” turned on for this)
5. Open the xml document with the name of the profile you just created (notepad is fine)

6. Change the values of the Clock and Memory speeds to look like this (these specific values are what worked for me and my card, use judgment) EDIT ONLY THE BOLD VALUES.

   Feature name="CoreClockTarget_0"
   
   Property name="Want_0" value="30000"
   
   Property name="Want_1" value="60000"
   
   Property name="Want_2" value="85000"
   
   Feature
   Feature name="MemoryClockTarget_0"
   
   Property name="Want_0" value="50000"
   
   Property name="Want_1" value="90000"
   
   Property name="Want_2" value="120000"
   

7. Save and close. Go back to CCC and activate the profile you just created.

This will make the card idle at 300core, 500memory. (2D clocks are the "Want_0" values) http://forums.amd.com/game/messagevi...VIEWTMP=Linear

If the green pixels still occur just try some higher clocks.

I hope this will help some of you to fix this problem :-).

Answer 3

Could it be a loose connection? (especially if you're using an adapter for DVI to HDMI)

Otherwise make sure your graphics drivers are up to date.

To figure out if it's hardware or software, see if you can test your laptop with a different screen. Also do the same with your current LCD screen. Test it with a friend's laptop using a different cable.

Answer 4

What fixed it for me was to re-plug the video cable tightly (really tightly!) in the video card socket, and make sure it is not bend the first several centimeters - so there is no strain on the socket. Simple solution, perhaps it will help someone too :)

Answer 5

I had a very similar problem. Flickering red and green pixels in dark areas of the screen (and by putting my nose on the wall i project at, I noticed that the white areas had faint yellow pixels). I think it only seems the pixels move with the image, when really the black image makes the underlying errounous pixel pattern visible.

I fixed it by changing the "color pixel format" option in my graphic cards control center; that option has values like "YCbCr 4:4:4".

Answer 6

I fixed this problem by setting my GAMMA to high on my TV (I am using as a monitor). It was hidden under advanced settings, but for some reason, putting GAMMA to high totally removed all the green areas that were appearing in the dark areas of the screen, that showed up especially strong with dark movies.

Answer 7

I had the same problem using an older HP laptop with HDMI output to an HP monitor with extended desktop. Same photographic desktop image on both, but only the monitor had the green pixels. I moved the HDMI cable around, and if seated properly in the HDMI port, the pixels would disappear. Definitely not a monitor problem, rather a connection/port/cable issue for me.

Answer 8

I had this issue on my third screen hooked up to an AMD 270x via DVI. It runs at 1920x1200, which is a little higher than most panels, and apparently supports refresh up to 75 Hz.

I solved flickering and dancing green & yellow pixels by opening Catalyst Control Center => My Digital Flat-Panels => Properties => selecting the display at the top of the pane (ASUS VW266H for me) => and checking both "Reduce DVI frequency on high-resolution displays" and "Alternate DVI operational mode".

Finally fixed!