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

[GammaLyrae]

I posted some of my impressions about this monitor in the thread I made asking for buying advice, here. But since much of my opinion was directly comparing the monitor to two others I have in my house, I figured I'd avoid cluttering this thread with paragraphs of info.

[k2viper]

For 120-144hz modes maximum working VT is 1580-1582, looks like a firmware limitation even it haves dotclock headroom. Stil better then default, though.
Btw, same maximum VT is mentioned in Benq XL2540 topic as max VT for 180-182hz mode. That also poitns that Benqs and LG uses the same Mstar display controller.
LG though have 640mhz dotclock headroom at 240hz.

[Chief Blur Buster]

For 120-144hz modes maximum working VT is 1580-1582, looks like a firmware limitation even it haves dotclock headroom. Stil better then default, though.
Btw, same maximum VT is mentioned in Benq XL2540 topic as max VT for 180-182hz mode. That also poitns that Benqs and LG uses the same Mstar display controller.
LG though have 640mhz dotclock headroom at 240hz.

Interesting, thanks for letting me know!

Are you able to enable/disable strobing during VT1580-1582?

Yes, LG is unique in its ability to accept pixels at 640Mpixels/second delivery rate over the cable -- if only they didn't frameskip at 280Hz -- but at least 240Hz refresh cycles are arriving almost 0.8ms more quickly. I'm still impressed they managed 0.8ms VBI at 240Hz for better-looking 240Hz strobing. While not perfect, LG has come a long way from the LG24GM77 that was all 100% bad strobe-crosstalky.

[GammaLyrae]

For 120-144hz modes maximum working VT is 1580-1582, looks like a firmware limitation even it haves dotclock headroom. Stil better then default, though.
Btw, same maximum VT is mentioned in Benq XL2540 topic as max VT for 180-182hz mode. That also poitns that Benqs and LG uses the same Mstar display controller.
LG though have 640mhz dotclock headroom at 240hz.

Interesting, i wonder if controls for strobe length and phase might be exposed, then. If it's the same scaler as an xl2540, the capability exists, it's just a matter of finding out whether or not LG locked it down, and then the address for it - I doubt it shares the address with the Ben q model, even if it is the same scaler.

And you may try VT tweaked timings I use:

This is really good info btw. Stutter free 240hz mode with slightly increased vertical total. I had my own settings going for a bit, but I started to notice some microstuttering. These settings (and the default settings detected after running reset-all) were the only ones that got rid of it.

I'm starting to notice that red / green and blue start to have poorer interactions at higher intensities. I first noticed it in explorer, where some things that had more of a reddish-yellow tone started pushing more towards blue or green. Starting to think about grabbing a colorimeter to help clean some of that up, lol. The ICC profile available as part of the monitor driver did not really help with this.

[k2viper]

Are you able to enable/disable strobing during VT1580-1582?

Yes, in 120-144hz. An other LG's limitation comparing to Benqs, is that looks like it only strobes at 120-144-240hz, not 180hz, not 200hz I tried.

[k2viper]

Interesting, i wonder if controls for strobe length and phase might be exposed, then. If it's the same scaler as an xl2540, the capability exists, it's just a matter of finding out whether or not LG locked it down, and then the address for it - I doubt it shares the address with the Ben q model, even if it is the same scaler.

I tried some findings here, but unfortunately atm I havent find a working way to adjust strobing.
MCCS controls at 4D, 4E, 4F LG expose as valid control codes, but they do not accept values other then defaults (return error if I SetControl a value other then default). Or these controls are firmware-locked and not changeable, or maybe I havent tried an appropriate values to set. I also tried to read values from common 40, 41, 42 VCP's but they seem not valid (all return 0000).

Maybe you have ideas how to "hack" these controls further and are able to do some tests/research using SoftMCCS.exe.

[giubox360]

Are you able to enable/disable strobing during VT1580-1582?

Yes, in 120-144hz. An other LG's limitation comparing to Benqs, is that looks like it only strobes at 120-144-240hz, not 180hz, not 200hz I tried.

Just a question mate, do you think is possible to raise more VT over 1304 @240hz if we create a lower custom resolution? like 1280x720 or something like that?

[GammaLyrae]

The more I use this monitor, the more noticeable it is that the green channel in particular is way overblown. It kinda gives a sickly hue to everything.

I was able to (mostly) fix it with some tweaking, but I had to move a lot of levers, so to speak, to get there.


On gamer profile 1 (the only one that is fully adjustable), I use 20 brightness, 60 contrast, 50 sharpness, Gamma mode 4, Color temp: Custom (with RGB set to 50 across the board), and DFC off. I also installed the ICC profile supplied by LG. Then I went into the windows calibration tool to make further adjustments to each individual color channel and subtracted green until there was a slight red push on the grey colors. (You could probably accomplish the same effect by reducing the G channel in the monitor OSD, which would help correct sources that don't expose fine color control to you like PCs do.)

The intensity of red and blue sharply drops off at higher levels of saturation, while green sharply rises. This is confirmed by hardware.info's review. The average gamma curve sounds good on paper (it's a fairly decent adherence to a 2.2 curve, on average), but due to the very sharp changes at the higher ends in particular, colors can look very, very wrong - most notably, anything involving the green subpixel. The fixes I've applied are imperfect - less saturated colors have a stronger red or blue push, but I find this less noticeable than brighter colors having a green push. The net effect of the changes I've made is to take the sharp deviation from a proper gamma curve, and average it out over 0-100% intensity rather than letting it all sit at 90-100%. A colorimeter could probably fix this more cleanly, possibly by reducing overall color saturation (so the problematic elements of the curve don't come into play), reducing contrast ratio, introducing dithering, or some combination of those.

It may have been a placebo, but I also wanna say the color response felt a little bit better when sticking with the default resolution options, without modifying the vertical totals. I think some additional crosstalk is a sacrifice I'm willing to make if it means the monitor will look better for regular use with freesync.

[k2viper]

Just a question mate, do you think is possible to raise more VT over 1304 @240hz if we create a lower custom resolution? like 1280x720 or something like that?

Probably yes, we should be able to raise VT up to 1580-1582 just like at 180hz-144hz-120hz if we will have dotclock headroom at 240hz by lowering the resolution. I havent tried it though, atm I'm not interested in resolutions lower then native.

[GammaLyrae]

Anyway, once I dialed in the colors and settings to something I find agreeable to look at, I now notice some pixel inversion artifacts. It seems more apparent whenever a bright color suddenly overlaps a darker color, and is primarily visible as vertical interlacing. Upon digging around to see how common this is... Apparently it's common enough that it gets mentioned in reviews for other high refresh LCD panels, including all-stars of the previous generation like the Viewsonic XG2401. Some degree of it is probably normal. I hadn't seen it before on my CFG70, but it honestly wouldn't surprise me if the pixel transitions on that panel were slow enough to hide it completely.

I don't know that I'd describe the extent to which I experience it a defect, but perhaps I'm just less sensitive to it than others.