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CHG70 - Overdrive, ghosting and Freesync

PostPosted: 11 Jan 2019, 07:02
by foresterr
Hello knowledgeable people,
Would you say this level of inverse ghosting / overshoot is insane, or I'll learn to live with it eventually? ;)
Image

This is CHG70 (27 inch version) running at static 60Hz. That's also exactly what happens when Freesync falls into lower FPS. It makes it damn near unusable if a game in question happens to have any darker scenes.

I still have a hard time believing this monitor does not even have appropriate overdrive level for each static refresh rate it supports, though. It's really a pity, as I quite like everything else about it (well, except the stand :lol:).

Re: CHG70 - Overdrive, ghosting and Freesync

PostPosted: 13 Jan 2019, 03:11
by Chief Blur Buster
VA panels often has pretty ghosty colors in dark shades, which can be quite noticeable for many. This seems average, possibly above average, for a VA panel, actually -- Samsung does it well -- I've seen way worse. Although a non-pursuit-photograph, I'm able to deduce the amount of ghosting from those.

VA has unusually asymmetric pixel response speeds (10x slower for dark shades than bright shades).

VA is also more temperature sensitive than other panels, so having the VA panel warm-up for 30 minutes can really help it. However, there are limits to that too.

The best solution is to try to keep your framerates really high, as that does help VA well.

Also, emulators and console ports may look somewhat better running at 60fps@120Hz, since the two-pass refresh cycles cleans up VA artifacts faster. This is not as applicable to TN or IPS. though.

Re: CHG70 - Overdrive, ghosting and Freesync

PostPosted: 13 Jan 2019, 06:35
by Q83Ia7ta
Chief Blur Buster wrote:VA has unusually asymmetric pixel response speeds (10x slower for dark shades than bright shades).

Nice fact. What are fastest/slowest shades for TN?

Re: CHG70 - Overdrive, ghosting and Freesync

PostPosted: 17 Jan 2019, 04:15
by foresterr
Thanks for taking a look! I've tried to do a proper pursuit photograph, but with just hand stabilization and my phone camera I can't achieve anything remotely approaching quality.

At some point I also recorded how it looks in-game:
phpBB [video]


Those are the kind of colors where it's looking the worst - darker objects on dark background leaving light trails when moving (which obviously aligns with what you've said about VA pixel response times)

At this point I'm mostly wondering what the firmware updates changed for this monitor (in my case it had newest firmware out of the box, so I can't make my own impression ;) ). Initial batch of reviews (almost 2 years ago) typically mention it's ghosting above 100 Hz, but none say anything about this inverse ghosting at lower frequencies. Now, at the newest firmware, I can't notice any ghosting at 144 Hz (maybe if I reeeeally squint...), so it looks like overdrive was re-tuned to look good at 144 Hz, while throwing anything lower under the bus.

Re: CHG70 - Overdrive, ghosting and Freesync

PostPosted: 19 Jan 2019, 01:34
by Chief Blur Buster
BTW, for embedding videos, make sure it's enabled to play on other websites:
Image
That said, I went straight to YouTube and played it:

From what I am seeing, VA ghosting at 60-70Hz is really par for the course. It's really, really hard to tune VA ghosting for dark colors -- very few monitor manufacturers manage to get it right. There's just an unusual amount of pixel-response asymmetry between bright color versus dim colors in VA panels.

Hopefully further improvements occur in firmware updates but I've seen much worse for VA ghosting of dark color shades, and rarely anything much better than that (for the dark colors).

All in all, Samsung has done a fairly good job with their VA panels -- it's just an extremely difficult task to tune VA pixel response.

Re: CHG70 - Overdrive, ghosting and Freesync

PostPosted: 19 Jan 2019, 01:36
by Chief Blur Buster
Q83Ia7ta wrote:
Chief Blur Buster wrote:VA has unusually asymmetric pixel response speeds (10x slower for dark shades than bright shades).

Nice fact. What are fastest/slowest shades for TN?

They can get much more symmetric, with a bit of differences at near fullwhites/fullblacks (because of lack of ovedrive overshoot room). On good LightBoost monitors, the GtG is almost a symmetric 1ms for all shades with no hotspots of "slow GtG" in the GtG graphing.

TN panels:
GtG90% can be less than a 50% difference between the best GtG and worst GtG on some TN panels (e.g. 0.8ms versus 1.1ms)

VA panels:
GtG90% can be a 1,000% difference between the best GtG color pair and worst GtG color pair (e.g. 3ms versus 30ms)

Manufacturers often come up with an average, though. GtG90% = the time it takes from pixel transition to reach from 10% transition to 90% transition, the industry standard measurement cutoffs for GtG.

Re: CHG70 - Overdrive, ghosting and Freesync

PostPosted: 20 Jan 2019, 05:39
by foresterr
Chief Blur Buster wrote:BTW, for embedding videos, make sure it's enabled to play on other websites:
That said, I went straight to YouTube and played it

Argh, figures I'd do something wrong. First time uploading anything to Youtube.

Thank you very much for your explanations (and patience).

Re: CHG70 - Overdrive, ghosting and Freesync

PostPosted: 23 Jan 2019, 03:31
by lexebidar
Seems like VA monitors are not the best idea for dark souls games and bloodborne :lol:

Re: CHG70 - Overdrive, ghosting and Freesync

PostPosted: 23 Jan 2019, 16:19
by RealNC
lexebidar wrote:Seems like VA monitors are not the best idea for dark souls games and bloodborne :lol:

Weirdly, they are and aren't. VA panels are really good at black levels. So they're best for this kind of game. On the other hand, you get the pixel response issue in dark scenes, making them less suitable...

Depends on your priorities, I guess. Although in defense of VA panels, in dark scenes, bad pixel response is harder to notice :mrgreen:

Re: CHG70 - Overdrive, ghosting and Freesync

PostPosted: 24 Jan 2019, 23:13
by Chief Blur Buster
I suppose it depends on the amount of motion you need from your game. Stationary dark images look really good on VA but ghosting can be a mess when in motion. Those arts games with static backgrounds really look good on VA monitors, though more games have full screen motion nowadays.