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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 » 06 Feb 2018, 09:14

Chief Blur Buster wrote:From the pictures I am seeing, your monitor is indeed frameskipping. (at 280 Hz overclocked)


It is not G-SYNC! Its freesync one.
It frameskips at > 240hz overclocked modes, so they are anyways "not guaranteed".

Or, you mean, that 240hz picture frameskips too?
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Re: LG 27GK750F-B - 240Hz, 27" 1ms Blur reduction, Freesync

Postby Chief Blur Buster » 06 Feb 2018, 11:35

Ooops! Edited my original message.

No, your monitor is indeed fine at 240Hz (as far as I can see -- albiet longer camera exposure is better, to capture more contiguous squares -- to be absolutely sure, because some early 240Hz FreeSync monitors frameskipped 1-in-40)

So, too bad that 280Hz overclocked does not work correctly.

But the great news is Large Vertical Totals successfully helps your strobe crosstalk at both 120Hz and 240Hz! This is a generic strobe crosstalk reduction technique and I'm glad to see it working with LG strobing too. Is the crosstalk zone much thicker at top or at bottom, or fairly equally balanced? Inverting Front/Back Porch can move the crosstalk thicknesses around.
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Re: LG 27GK750F-B - 240Hz, 27" 1ms Blur reduction, Freesync

Postby k2viper » 07 Feb 2018, 02:01

Chief Blur Buster wrote:No, your monitor is indeed fine at 240Hz (as far as I can see -- albiet longer camera exposure is better, to capture more contiguous squares -- to be absolutely sure, because some early 240Hz FreeSync monitors frameskipped 1-in-40)


I did some more frameskipping tests yesterday with longer exposure (took 6-7 shots with continuous square sequences) - no frameskips at 240hz so far.

Chief Blur Buster wrote:Is the crosstalk zone much thicker at top or at bottom, or fairly equally balanced? Inverting Front/Back Porch can move the crosstalk thicknesses around.


Crosstalk at center is thin and fairly acceptable, thicker at top, and at bottom its a bit thinner then top but still obvious. Actually I'm fine with current strobe "area" that display provide, middle of screen looks better. What I would like to have a chance to adjust, is the strobe length. I feel it is excessively long. Tweaking brightness/contrast, as I can see, do not change crosstalk at all, so I suppose brightness changes strobe height, not width.

I tried to do these front-back porch tricks, and it doesnt work or I'm just not doing it correctly to see the difference.
E.g. default 240hz mode look like this:

Image

What exact numbers for front and back porch I should try?
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Re: LG 27GK750F-B - 240Hz, 27" 1ms Blur reduction, Freesync

Postby Chief Blur Buster » 07 Feb 2018, 10:33

Front/Back porch are inexact. The name of the game for every 1 you subtract from Front Porch, you add 1 to Back Porch.

On certain displays (not sure which sync signal the LG strobe phase syncs to), this can shift crosstalk zone vertically by 1 pixel. Sometimes there's no effect.

Start with your working VT1302 or VT1336 timings.

Special Note: For specific custom resolution utilities (GPU vendors), if Back Porch is missing, just add/subtract from Front Porch while keeping Vertical Total unmodified. The missing value is derived from the Total minus all the other numbers.

If there is no effect, then not worth doing. Try large numbers in one of the Porches, then swap the numbers (Front vs Back) to see if the crosstalk band zone moves upwards/downwards by approximately 200 pixels.

It is only a workaround when there is no "Strobe Phase" adjustment.
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Re: LG 27GK750F-B - 240Hz, 27" 1ms Blur reduction, Freesync

Postby k2viper » 07 Feb 2018, 12:09

Just to clarify, I need to modify horizontal "pixels", or vertical "lines" numbers in Front/Back porch strings?
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Re: LG 27GK750F-B - 240Hz, 27" 1ms Blur reduction, Freesync

Postby k2viper » 09 Feb 2018, 14:13

Image Image Image

Other camera. Tried to pursuit with hand.
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Re: LG 27GK750F-B - 240Hz, 27" 1ms Blur reduction, Freesync

Postby Chief Blur Buster » 09 Feb 2018, 14:19

k2viper wrote:Image Image Image
Other camera. Tried to pursuit with hand.

Better, but for strobe crosstalk testing (instead of blur testing), static photography actually can produce better results than hand-pursuited photos. I'd rather have stationary-camera fast-shutter close-ups of the top edge and bottom edge.

What I am seeing seems to look pretty good/impressive.
That's 240Hz strobed, right?

Pretty clear and crosstalk-free for screen center, I'm impressed.
I'll say it does look better than 240Hz BenQ strobing.

Can you take stationary-camera super-sharp-focus closeups of top/center/bottom?
1. Verify your camera is a fast shutter (1/240sec or faster). You can try to brighten your screen or use a camera app that lets you adjust exposure (many camera apps)
2. Pause the pattern (or display a different computer screen)
3. Lock your camera focus (fix focus it by tap-and-hold). Focus works better with stationary screen.
4. Resume the pattern (un-minimize TestUFO)
5. Now take macro photo
6. Photo should look ultra-sharp when zoomed.

Unless you have a camera rail or need to test non-strobed motion blur, strobe crosstalk photography tests works well with stationary cameras too, since you're simply determining if one strobe flash shows two refresh cycles (e.g. panel not finished refreshing when it strobes).
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Re: LG 27GK750F-B - 240Hz, 27" 1ms Blur reduction, Freesync

Postby k2viper » 09 Feb 2018, 16:41

Chief Blur Buster wrote:What I am seeing seems to look pretty good/impressive.
That's 240Hz strobed, right?

Pretty clear and crosstalk-free for screen center, I'm impressed.
I'll say it does look better than 240Hz BenQ strobing.


Yes, that's 240hz strobed, with VT 1306.
Center really looks pretty clean, crosstalk is faint and acceptable. Hopefully I will be able to get better focused pics.
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Re: LG 27GK750F-B - 240Hz, 27" 1ms Blur reduction, Freesync

Postby k2viper » 10 Feb 2018, 09:16

What is also interesting, is the non-strobed performance of this display.
I found its blur is really low non-strobed in 240hz (same VT1306 mode, just turned off strobing). Overdrive is also nearly perfect.

Even for me, used to strobing, its playable without MBR.
In Overwatch, tracking targets dont make them feel like smeary spots, e.g. I've played on Benq 2411 144hz and it was very smeary to me.

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

Postby Chief Blur Buster » 10 Feb 2018, 19:30

Thanks, yes that's relatively good for 240Hz. I'd have to look really closely.

That's a hand-propelled mid-air pursuit photograph? (Wave camera, following motion, snap a 4-refresh-cycle (1/60sec) exposure at 240Hz?). That's an excellent job for a forum reader -- the ladder track is very well formed for a non-rail pursuit, just like you would see with human eye at www.testufo.com/ghosting

I'd still love to see the strobe crosstalk very-close-up photos too -- this time, pursuit is not necessary for strobe crosstalk photography provided you capture only one refresh cycle (1/240sec camera shutter).
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