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LG 27GK750F-B - 240Hz, 27" 1ms Blur reduction, Freesync

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Re: LG 27GK750F-B - 240Hz, 27" 1ms Blur reduction

Postby k2viper » 31 Jan 2018, 12:23

Chief Blur Buster wrote:260Hz works? Neat. Mind if you briefly try 280Hz with Reduced Blanking?


280Hz/reduced timings works the same way the 250 and 260: displayed out of range message, it disappears if I go to main OSD or select DP as input via joystick, but after some seconds error message appears again :(
Strobing didnt work at 250, 260, 280Hz either.
So these overclocks renders unusable. At least if we'll not find a way to get to service menu (i found no methods for LG monitors with joysticks, having no dedicated "menu" button).
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Re: LG 27GK750F-B - 240Hz, 27" 1ms Blur reduction

Postby Chief Blur Buster » 31 Jan 2018, 12:29

Fascinating. 280 Hz overclock, as I predicted.

If you're feeling adventurous, mind if you take a picture?

1. Reduce the brightness of the screen to force your smartphone to take longer camera exposure.
2. Take a photograph of http://www.testufo.com/frameskipping in Chrome while it says a green "READY"
(may need to all other browser tabs and applications to make browser run stable).
3. Post the photograph (or few).

Preferably one (or more) photo of 40+ squares exposed. If only ~20 squares exposed, post 4 (or more) photographs since the 1-in-40 frameskip found on certain other 240Hz monitors, may be missed.

Some other forum members do firmware hacking and might be able to force the "OUT OF SYNC" to go away. I'm simply interested if the 280Hz overclock is otherwise successful (no frameskipping). This can then warrant whether it's a worthwhile effort for someone to try hacking the "OUT OF SYNC" message away, or petition LG to release a firmware that enables dismiss of the message.
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Re: LG 27GK750F-B - 240Hz, 27" 1ms Blur reduction

Postby k2viper » 31 Jan 2018, 12:33

Tried 242Hz with reduced timings: works, strobing works too and - looks like crosstalk is massively reduced!
Unfortunately, as I see, my browser massively stutters at 242hz. I gonna experiment further with reduced timings.

upd: no browser problems, looks like switching to reduced timings shortened strobe length (screen becomes dimmer), and strobing gone out of sync with refresh (strobes 240 while refreshing 242), and that was the massive stutter/unsmoothness cause.
Last edited by k2viper on 31 Jan 2018, 12:42, edited 2 times in total.
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Re: LG 27GK750F-B - 240Hz, 27" 1ms Blur reduction

Postby k2viper » 31 Jan 2018, 12:37

Chief Blur Buster wrote:If you're feeling adventurous, mind if you take a picture?


I'm feeling adventurous, but I just do not have much time to try. Sure I will take a photo of 280Hz, maybe in a few days.
Gonna try 250/reduced now.
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Re: LG 27GK750F-B - 240Hz, 27" 1ms Blur reduction

Postby k2viper » 31 Jan 2018, 13:11

250hz shows out of range with reduced too.
Played some more with front-back porch and sync numbers at 240hz/strobed. Havent found anything interesting, actually I havent seen a difference in crosstalk.
Turned back to "default" 240hz + VT 1304. With it, crosstalk at center is acceptable, so looks like strobe phase (area) is fine. Maybe, strobe length could be adjusted via service menu, or LG will make update to their firmware.
Going to stick with 240/MBR/1304VT for now.
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Re: LG 27GK750F-B - 240Hz, 27" 1ms Blur reduction

Postby Chief Blur Buster » 31 Jan 2018, 14:15

Great to hear.

This is the first 240Hz monitor that I've seen that supports a large vertical total at full 240Hz -- I'll need to see if this is the new gold standard for 240Hz strobing -- and obtain a unit for upcoming 240Hz versus tests.
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Re: LG 27GK750F-B - 240Hz, 27" 1ms Blur reduction

Postby k2viper » 01 Feb 2018, 03:24

Hope that with more users buying this display, we'll find a way to finetune full 240hz mode for clean strobing.

Overdrive looks fine (better then VG278H at lightboost 10% mode), scrolling text shows some minor smearing, but still is very readable.

Eventually, as a competitve Overwatch player I'm satisfied with this monitor, its crosstalk dont look awful in actual game. Also I didnt feel difference in responsiveness (input lag) when enabling MBR.

Sticked with 240Hz, MBR and VT1304 (pixelclock 638mhz) for now.
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Re: LG 27GK750F-B - 240Hz, 27" 1ms Blur reduction

Postby k2viper » 01 Feb 2018, 13:15

VT 1336 is an absolute maximum I can reach at 240Hz. Reduced horizontal total, to keep pixelclock in range.

Image
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Re: LG 27GK750F-B - 240Hz, 27" 1ms Blur reduction

Postby Chief Blur Buster » 01 Feb 2018, 15:48

VT1336 at 240Hz!

That's fantastic for 240Hz motion blur reduction.
That is equal to ((1336-1080)/1336) * (1/240) = 0.8ms vertical blanking interval

Not much time for the 1ms TN LCD GtG, so top/bottom edges will have tons of strobe crosstalk, but should certainly make the screen centre zone little bit clearer. Most VBI at 240Hz is only 0.1ms or 0.2ms by default, so you've pretty much massively enlarged your VBI to create more time for LCD pixel transitions between strobe backlight flashes.
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Re: LG 27GK750F-B - 240Hz, 27" 1ms Blur reduction

Postby k2viper » 02 Feb 2018, 02:50

Chief Blur Buster wrote:VT1336 at 240Hz!

That's fantastic for 240Hz motion blur reduction.
That is equal to ((1336-1080)/1336) * (1/240) = 0.8ms vertical blanking interval

Not much time for the 1ms TN LCD GtG, so top/bottom edges will have tons of strobe crosstalk, but should certainly make the screen centre zone little bit clearer. Most VBI at 240Hz is only 0.1ms or 0.2ms by default, so you've pretty much massively enlarged your VBI to create more time for LCD pixel transitions between strobe backlight flashes.


Boldened quote is exactly the case at 240hz. Crosstalk at center is quite acceptable at 1300+ VT, but at top and bottom crosstalk become more obvious. It's obvious, but I'd not call it "tons", at least for 240hz mode, which is an optimal mode since we're buying 240hz monitors to take advantage of 240hz, right? :)

Chief, a bit later I found that when reducing Horizontal Total under 2040 to keep pixelclock in <640Mhz range (when lifting VT over 1306-1308) - screen becomes a bit stuttery/unsmooth BUT what is more interesting, that unsmooth picture shows way less crosstalk then smooth as butter sync picture.
Same happens when I tried 242hz with reduced timings and strobing.
Looks like reducing HT made image out-of-sync with strobing.

HT 2040 (default) - perfectly smooth as butter picture. VT 1306-1308 at max.
HT 2020 - picture smooth, but stutters every 2-3 secs. VT ~1320 at max.
HT 2000 - picture still smooth but stutters every 0,5secs, VT 1330 at max.
HT 1990 (working minimum) - picture unsmooth, constantly microstuttering, VT 1336-1338 absolute max. Unusable, due to microstuttering/unsmoothness.

I havent tried this without strobing yet, maybe this unsmoothness is strobing-related.
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