LG OLED CX 120Hz BFI

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GameLifter
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LG OLED CX 120Hz BFI

Post by GameLifter » 11 Feb 2020, 23:54

The new LG OLED TV's set to release this year are going to get a 120Hz BFI mode and I've seen people on other forums who are really looking forward to this feature. I've been wondering how this method of eliminating motion blur might compare to the others out there and if it could be viable for both 60Hz and 120Hz content.

alapsu
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Re: LG OLED CX 120Hz BFI

Post by alapsu » 17 Feb 2020, 12:00

Disclaimer -- I think this is correct, but if anyone reading this notices an error, please reply with a correction.

The 120 Hz black frame insertion won't work with 120 Hz content because the way it works is that it converts every other frame to pure black. Frametime at 60 Hz is ~16.67 milliseconds and frametime at 120 Hz is ~8.3 milliseconds.

Normally, when displaying 60 Hz content on a 60 Hz screen without BFI, each frame is displayed for 16.67 milliseconds. With BFI, each frame is displayed for 8.3 milliseconds, followed by 8.3 milliseconds of pure black. So over the course of one second, you'll see a total of 60 frames regardless of whether you're viewing the content at native 60 Hz or 120 Hz with BFI. The difference is that with BFI, each frame is displayed for half the time it would be displayed in the other case.

This reduces motion blur because your brain 'fills in' the gaps, creating the appearance of clearer motion.

BFI is especially useful/desirable on OLED displays because these displays feature exceptionally fast pixel response times and virtually-perfect blacks. So inserting black frames achieves the same thing other MBR displays achieve via backlight strobing (and due to the response times + black levels, BFI should be superior to backlight strobing).

For BFI to work well with 120 Hz content, the display would need to be capable of refreshing at 240 Hz.

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GameLifter
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Re: LG OLED CX 120Hz BFI

Post by GameLifter » 17 Feb 2020, 12:57

alapsu wrote:
17 Feb 2020, 12:00
Disclaimer -- I think this is correct, but if anyone reading this notices an error, please reply with a correction.

The 120 Hz black frame insertion won't work with 120 Hz content because the way it works is that it converts every other frame to pure black. Frametime at 60 Hz is ~16.67 milliseconds and frametime at 120 Hz is ~8.3 milliseconds.

Normally, when displaying 60 Hz content on a 60 Hz screen without BFI, each frame is displayed for 16.67 milliseconds. With BFI, each frame is displayed for 8.3 milliseconds, followed by 8.3 milliseconds of pure black. So over the course of one second, you'll see a total of 60 frames regardless of whether you're viewing the content at native 60 Hz or 120 Hz with BFI. The difference is that with BFI, each frame is displayed for half the time it would be displayed in the other case.

This reduces motion blur because your brain 'fills in' the gaps, creating the appearance of clearer motion.

BFI is especially useful/desirable on OLED displays because these displays feature exceptionally fast pixel response times and virtually-perfect blacks. So inserting black frames achieves the same thing other MBR displays achieve via backlight strobing (and due to the response times + black levels, BFI should be superior to backlight strobing).

For BFI to work well with 120 Hz content, the display would need to be capable of refreshing at 240 Hz.
Interesting, the 2019 OLEDs have a 60Hz BFI mode. So, going by your explanation the 2019 OLED panels may actually be refreshing at 120Hz in BFI mode to show all 60 frames and the new 2020 OLEDs could be refreshing at 240Hz to show all 120 frames?

AddictFPS
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Re: LG OLED CX 120Hz BFI

Post by AddictFPS » 17 Feb 2020, 15:10

About OLED response time:

Rtings.com review of OLED LG C9 2019 show that maximun GtG 100% response time is 8.8ms, current IPS 240Hz like Viewsonic XG270 have a panel with 8.9ms maximun.

From black to others colors, unfortunately OLED is slow like LCD :( Due to this, even with 240Hz refresh, 8.33ms frame + 8.33ms blackframe, the frame not get the target color from start, is changing the color during all the frame duration (blurring), so in continuous movement, color and contrast is much lower that in static image.

From colors to black 100% GtG time is 0.2ms, this make a good work eliminating motion blur, no ghosting, no overshot artifacts like LCD.

But the main issue of OLED is the burn-in, user need to take it in account several use tips to avoid fast wear.

Also, LG OLED TV C9 has automatic brightness control, so user do not have full control over brightness like in monitors. But if people do not set to much bright, i think TV not automatic reduce bright. Moreover low bright is good for slow burn-in.

Also note, input lag of LG OLED C9 is much more that high end gaming monitor, even with TV in game mode.

alapsu
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Re: LG OLED CX 120Hz BFI

Post by alapsu » 17 Feb 2020, 19:34

GameLifter wrote:
17 Feb 2020, 12:57
Interesting, the 2019 OLEDs have a 60Hz BFI mode. So, going by your explanation the 2019 OLED panels may actually be refreshing at 120Hz in BFI mode to show all 60 frames and the new 2020 OLEDs could be refreshing at 240Hz to show all 120 frames?
My previous post in this thread is wrong, so I'll give it another shot. (see this RTings page: https://www.rtings.com/tv/tests/motion/image-flicker)

That page contains two charts showing examples of backlight brightness over time for 60 Hz content as well as 120 Hz content.

60 Hz graph:

https://www.rtings.com/images/reviews/t ... -large.jpg

120 Hz graph:

http://i.rtings.com/images/reviews/tv/s ... -large.jpg

For 60 Hz, a new frame appears every 16.67 ms and for 120 Hz, a new frame appears every 8.33 ms. In my previous post, I assumed that 120 Hz BFI essentially referred to displaying each frame of 60 Hz content for one 8.33 ms frame followed by a black frame for 8.33 ms, followed by the next frame, etc. This would necessarily imply that the amount of time black frames are displayed equals the amount of time lit frames are displayed. This is not the case.

It seems BFI actually refers to simply displaying a black screen for a portion of each refresh cycle. The duration of the black screen need not equal the duration the actual frame is displayed. For example, in the 60 Hz graph, we see that each cycle consists of ~2 ms lit frame followed by ~14.67 ms of black screen. In the other graph, we see that each cycle consists of ~1.67 ms lit frame followed by ~6.67 ms of black. Therefore, it would not be the case that watching 60Hz content with BFI requires a refresh rate of 120 Hz.

AddictFPS corrected me about OLED response times. What I make of this is basically that the pixels on an OLED screen can change to black very quickly (~0.2 ms), but require much more time to change from black to something else.

So if it takes 10 ms for the screen to change all its pixels from black to something else to display a frame, and at 120 Hz a new frame is shown every 8.33 ms, that's a problem for 120 Hz BFI. I think the problem is essentially that the duration of the black frame is limited so that a new frame can be displayed at the start of the next cycle, a.k.a. you end up with high persistence. The lower the persistence, less perceived motion blur, meaning essentially that you want a relatively high ratio of black screen to lit screen.

(again, please correct me)

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Re: LG OLED CX 120Hz BFI

Post by Chief Blur Buster » 17 Feb 2020, 21:29

GameLifter wrote:
11 Feb 2020, 23:54
The new LG OLED TV's set to release this year are going to get a 120Hz BFI mode and I've seen people on other forums who are really looking forward to this feature. I've been wondering how this method of eliminating motion blur might compare to the others out there and if it could be viable for both 60Hz and 120Hz content.
OLED BFI is excellent, the question is how big the pulse width is.
alapsu wrote:
17 Feb 2020, 19:34
So if it takes 10 ms for the screen to change all its pixels from black to something else to display a frame, and at 120 Hz a new frame is shown every 8.33 ms, that's a problem for 120 Hz BFI. I think the problem is essentially that the duration of the black frame is limited so that a new frame can be displayed at the start of the next cycle, a.k.a. you end up with high persistence. The lower the persistence, less perceived motion blur, meaning essentially that you want a relatively high ratio of black screen to lit screen.

(again, please correct me)
Giving you a correction. :D

It doesn't work exactly like that.

Those familiar with high speed videos of LCD / OLED refresh, www.blurbusters.com/scanout -- will better understand this reply, so once you've seen those high speed videos, you'll better understand the below:

Black frame insertion (BFI) doesn't have to be monolithic when using an independent OFF scanout pass at a custom temporal offset.

For example, it can be:

Image

Or it could be:

Image

The Sony TriMaster used BFI at a 7.5ms:16.7ms ratio, in a rolling-window scan.
There are scan patterns that can be engineered.

Also, it's possible to have a higher refresh rate with a slowscan, e.g. 120Hz refresh rate out of 60Hz-velocity scanout, if you use two different scanwindows:

Image

Lessons:
- Not all pixels refresh simultaneously. They 'scan' from top to bottom on most display panels
- BFI doesn't have to be integer divisors (in other words, custom BFI pulse ratios are possible)
- Refresh rate doesn't have to determine scanout velocity (if using creative engineering)
- It's possible to concurrently-scan if the panel is designed as such (but should use anti-sawtooth-artifact technique)

Related thread:
OLED Rolling Scan Patterns
Including a possible scan-pattern path to doing 960 Hz refresh on an OLED.

Image

It may just be better to refresh 8-pixel-rows simultaneously in blocks at a time (ultra-fast scanout), but either way, that's a microwire engineering nightmare at this stage.

The point is, you can create really insane refresh rates out of really low scan velocities taking longer than a refresh cycle, via an advanced concurrent-scan algorithm (and eliminate sawtooth artifacts by permanently assigning one unbroken framebuffer per separate unique scanout sweep, which will require framebuffering 8 refresh cycles off the wire (DisplayPort), to do an 8-concurrent scanout)

Somebody needs to point a 960fps camera at the LG 120Hz OLED displaying www.testufo.com/scanout and post it on YouTube or here for us. I can easily tell you how its BFI works simply by staring at these high speed videos.
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GameLifter
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Re: LG OLED CX 120Hz BFI

Post by GameLifter » 19 Feb 2020, 00:13

Chief Blur Buster wrote:
17 Feb 2020, 21:29
(fantastic illustrated post about OLED scanouts)
Very informative post! Now I have a better understanding of how rolling scans work. Before I was the least familiar with them out of all the blur reduction methods.

AddictFPS
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Re: LG OLED CX 120Hz BFI

Post by AddictFPS » 19 Feb 2020, 05:29

alapsu, Rtings.com BFI images you linked is only a example of BFI, using a TV LCD Sony X850D with "fullscreen" mode backlight strobe, but each TV has different BFI settings, and OLED not use backlight, light comes directly from pixels, and strobe with "rolling scan" mode, the new LG OLED CX 48" has a menu to config BFI with four different settings, i suppose is for adjust "Scan Window" size, named "OLED Motion Pro"

phpBB [video]


This is LG OLED C9 BFI behavior, 8.33 ms frame 8.33 black frame

Image

Official input lag of LG OLED CX is around ~11ms, one of the best in TV, but far compared with a good gaming monitor that is less 1ms. Bad for competitive gaming, enough good for fun gaming.

I think the price is the most serious issue of LG OLED CX for most of us :lol:

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Re: LG OLED CX 120Hz BFI

Post by Chief Blur Buster » 27 Feb 2020, 00:02

GameLifter wrote:
19 Feb 2020, 00:13
Chief Blur Buster wrote:
17 Feb 2020, 21:29
(fantastic illustrated post about OLED scanouts)
Very informative post! Now I have a better understanding of how rolling scans work. Before I was the least familiar with them out of all the blur reduction methods.
Yep! Motion Blur Math is super simple, thanks to Blur Busters Law.

Motion Blur = Pixel Visibility Time

1ms of pixel visibility time = 1 pixel of motion blur per 1000 pixels/sec

For sample-and-hold, pixel visibility time equals frame time.
For strobed, pixel visibility time equals backlight strobe flash length.
For rolling scan, pixel visibility time is the time from pixel-ON to pixel-OFF.

Image

Image

More information can be found in my articles, found as Blur Busters Law: The Amazing Journey To Future 1000Hz Displays, as well as GtG versus MPRT articles. When I was at CES checking out the TestUFO demo I created for CES 2020 for NVIDIA / ASUS -- it was ASUS who actually told me these Blur Busters articles helped them decide to roadmap 1000Hz. We're certainly influencing the industry, bit by bit, I have been micdropping 30fps-vs-60fps debates since 1993. Cheers!
Head of Blur Busters - BlurBusters.com | TestUFO.com | Follow @BlurBusters on Twitter

       To support Blur Busters:
       • Official List of Best Gaming Monitors
       • List of G-SYNC Monitors
       • List of FreeSync Monitors
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Malinkadink
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Re: LG OLED CX 120Hz BFI

Post by Malinkadink » 01 Mar 2020, 22:37

AddictFPS wrote:
19 Feb 2020, 05:29
alapsu, Rtings.com BFI images you linked is only a example of BFI, using a TV LCD Sony X850D with "fullscreen" mode backlight strobe, but each TV has different BFI settings, and OLED not use backlight, light comes directly from pixels, and strobe with "rolling scan" mode, the new LG OLED CX 48" has a menu to config BFI with four different settings, i suppose is for adjust "Scan Window" size, named "OLED Motion Pro"

This is LG OLED C9 BFI behavior, 8.33 ms frame 8.33 black frame


Official input lag of LG OLED CX is around ~11ms, one of the best in TV, but far compared with a good gaming monitor that is less 1ms. Bad for competitive gaming, enough good for fun gaming.

I think the price is the most serious issue of LG OLED CX for most of us :lol:
11ms is the total delay of the display on 60hz content, it's competitive with the best 60hz monitors that range in the 8-10ms range. Typically 144hz monitors at 60hz will have a total delay of 10-12ms and 240hz unfortunately can be as high as 14-16ms. At 120hz the OLED has a delay of around 6ms which again is in line with monitors if running them at 120hz. The only displays that will truly be faster are the 240hz ones that are in the realm of 2-4ms, but you're paying a price for those monitors, they look like crap next to OLED, or even IPS lol.

The C9 rtings tests shows it getting 6-7ms delay at 120hz, and 13-14ms at 60hz. If the CX can improve the 60hz down to 10-11ms that's great, and i expect the 120hz performance to stay the same around 6ms.

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