# Hidden dithering or broken synchronization in graphics stack that causes eye strain?



## kammerer (Sep 5, 2019)

Hi All, my question could look strange, but actually I can't use any modern FreeBSD/Linux distribution
cause of eye strain that i got on any graphic card (nvidia, ati, intel) regardless of used driver.
I'm using Ubuntu 14 now without any problem but on attempt
to switch to any newer OS on same hardware (and same monitor: Dell U2711 with CCFL backlight)
I got problem with eyes (seems problem starts with overstressed eye muscles).
Looks like that problem could be linked with software changes but It's not clear which ones.

So maybe you could suggest what is the root of problem.
Is it some hidden system dithering? Or some problem with video data synchronization?
Or smth  else that could affect pixel rendering/representation/transfering that affects eye focusing
(in my case it's not linked with font rendering cause I got same problem just looking at any picture)?

xrandr output on both system is quite similar:

FreeBSD 12
`2560x1440 (0x49) 241.500MHz +HSync -VSync +preferred
        h: width  2560 start 2608 end 2640 total 2720 skew    0 clock  88.79KHz
        v: height 1440 start 1443 end 1448 total 1481           clock  59.95Hz
  1920x1200 (0x4a) 154.000MHz +HSync -VSync *current
        h: width  1920 start 1968 end 2000 total 2080 skew    0 clock  74.04KHz
        v: height 1200 start 1203 end 1209 total 1235           clock  59.95Hz`

Ubuntu 14.04
`2560x1440 (0x57)  241.5MHz +HSync -VSync +preferred
        h: width  2560 start 2608 end 2640 total 2720 skew    0 clock   88.8KHz
        v: height 1440 start 1443 end 1448 total 1481           clock   60.0Hz
  1920x1200 (0x58)  154.0MHz +HSync -VSync *current
        h: width  1920 start 1968 end 2000 total 2080 skew    0 clock   74.0KHz
        v: height 1200 start 1203 end 1209 total 1235           clock   60.0Hz`

Some additional context:

Maybe you now about ledstrain.org society that unites different peoples with one common problem:
they can't use monitors with led backlight. They have year-proven old hardware with CCFL backlighted monitor
but on attempt to swap it with LED backlighted one they got different problems: noursea, eye-burning, headaches and so on.
With time many of them also starts notice that they have similar eye/brain related problems with newer OS (Linux, Windows)  on same year proven hardware.

NB: There was a post on forum 4 year ago "Eye strain from certain video modes/drivers" 
where foster found solution for himself with disabling hardware acceleration:

"I just realized the "working" modes that I marked green in my first post have something in common. 
They don't use hardware acceleration. Do you know of any differences in the video signals when hardware acceleration is used? 
Even the smallest difference might matter, so please reply if you know something."









						Eye strain from certain video modes/drivers
					

Hello,  I get eye strain from some graphic cards and certain video modes. Maybe you have more technical knowledge than I do, and you can help me find the cause. I already tried other operating systems and know which ones I can use without problems, but if it is possible to fix the eye strain I...




					forums.freebsd.org


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