Monday, January 11, 2016

Ghost in the machine: faint remanence of screen contents across reboots in a Macbook pro retina

As was noted a few times before, I happen to own a Macbook Pro Retina laptop I mostly use under Linux. I had noticed from time to time weird mixes between two screens, i.e. I would be looking at a website, but, in some areas with uniform colors, I would see faint traces of other windows currently opened on another screen. These faint traces would not show up in a screenshot. It never really bothered me, and I attributed that to a weird specificity of the mac hardware (they often do that) that was not well handled by the nouveau driver, so I had simply dismissed that. Until, one day, I switch off the computer, switch back on, boot to MacOS and see this as a boot screen:
Here is a close-up view of the top-left corner of the screen:
If you look carefully, you can still see the contents of the page I was browsing just before switching off the computer ! So this problem is not Linux-specific, it also affects MacOS... To be honest, I don't have a clue about what's happening here, but it has to be a serious hardware malfunction. How can two video memory regions be composed upon display without the computer asking explicitly for it ? Why does that problem survives a reboot ? I mean, someone switches on my computer and can see the last thing I did on it ? I could actually read the address line without difficulty, although you'll have to take my word for it, since the picture does not show it that well. That's scary...

19 comments:

Steven C. said...

lightdm with nouveau on Debian wheezy would (I presume) fail to load the background, and instead show a collage of pixmaps or blocks of rendered text from the previous boot. You're maybe seeing the same bug on a Mac, where alpha-blended grey was supposed to be composed over some buffer that was not initialised?

Obviously it raises serious concerns about the security of NVidia graphics chipsets, *and* the nouveau driver; that this malfunction was even possible suggests flaws an attacker could exploit deliberately (and probably see a lot more). I absolutely don't trust either these cards or this driver any more.

lverns said...

What pops into my head when seeing an issue like this is, "The screen itself is bad." I've seen this occur in a Dell LCD monitor (produced in the early 2000's), but the ghosting wouldn't last more than 30 seconds. I've also seen this on a "big" (somewhere between 40 and 60 inch) LG TV. It was one of those "smart" TVs, probably produced some time after 2010.

Anyway, just my thought.

Vincent Fourmond said...

@lverns What I realize I forgot to mention is that it can't be just physical screen remanence, since inbetween the two images, a lot of things have happened on the screen: the detailed power off log, and then the EFI display (that wasn't showing this as far as I remember).

@Steven C. Unfortunately, I'm stuck with both the hardware and the driver as of now... I'm unsure nouveau is to blame, though. Maybe it should blank the video memory before powering off, but, shouldn't it be the hardware's job to do that ?

Ruben said...

Try this, connect an external monito to your pc, if the external screen shows those faint pixels, you have 2 possibilities, its a hardware problem, or software problem, if not, it's a screen problem.

Unknown said...

It's not the memory or the software, it is the display itself. This was a known problem on some Macbook units in that generation (including my own) depending on which of two manufacturers made the panel in your system.

The effect is tied to how long an image was on the screen, so lots of stuff flashing by transiently wouldn't necessarily clear the ghost of something that sat for a while.

If you bring it in to an Apple Store and show them, they'll run a standardized ghosting test, and replace the monitor for free (as the original is accepted as defective) if it's bad enough. This is what I did for mine.

Vincent Fourmond said...

@Unknown Thanks, I will have to try contacting them. Do you have any publicly available source for that ?

Anonymous said...

It's a common effect on some displays. It's not at all specific to Apple. See https://en.wikipedia.org/wiki/Image_persistence

Steven C. said...

Similar to what @Ruben said, perhaps you could rule out the display by leaving it switched off while you launch something (perhaps over VNC) and then shut down. Then reboot and switch the on the display afterward to see if it shows this.

Vincent Fourmond said...

Wow, I'll have to test all this... When I can ! I hadn't realized the remanence could be a physical property of the screen (especially of such an expensive screen), but I'll have to test that.

Noel said...

I had Apple replace the screens on two retina macbook pros last summer, one personal and one for work. This was a big problem with the first generation ones. So far no problems on the latest one I have or the two replaced ones. I had to send the laptops in but in like 2 days they where back and fixed.

Samuel Hall said...

I have the same problem using 2013 iMac 27". When editing a file in Photoshop app, I noticed some very fainted desktop icons in my screen which is interesting. I am using the latest OS X.

Scott said...

This looks a lot like what's called "screen burn in" or "screen burn" which is a permanent discoloration of areas caused by cumulative usage of the same pixels in the same part of the screen (wikipedia). Is that an image of a web page you look at frequently?

Vincent Fourmond said...

I had the opportunity to check with an external screen, and the phenomenon is not visible on the external screen. Faint ghost images can appear with as little as ten seconds of display. I wasn't really aware that screen burn-in also affected LCD screens, because I had never seen that on any display before. I wasn't expecting that on something that is branded as the highest quality display on the market. I'm getting Apple to replace the screen.

franciskim said...

I'll keep this in mind and check next time I reboot. Right now I have too many tabs/things open.

Vincent Fourmond said...

Just got the computer back, with a fresh new screen (and no damaged pixels), with no way to test the ghosting problem at the moment (tonight).

Monty said...

Yea! Glad you got this fixed. Before I headed to the comments I was thinking "This happened to me and he can get it repaired, for free, by Apple". Anyway, enjoy.

Gregory Fleischman said...

How much did this repair cost? My Retina MBP, mid 2012, recently started doing this...

Vincent Fourmond said...

Free, but the laptop was still under warranty. Had to change my charger today, though.

Gregory Fleischman said...

Dang. I'm no longer under warranty. I bought my retina MBP the day it came out. I read about apples lawsuit about this screen and was hoping something came from it but I don't see anything. My battery is going out too. Seems when it gets to 30% it just shuts off.

I ended up buying a new MBP with more storage and want to get the battery and screen problems fixed on old one.