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post #1 of 18 Old 01-15-2020, 02:47 PM - Thread Starter
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Do you use a Samsung 4K TV as a PC monitor?

I'm hoping for a little help with an experiment.

In a nutshell, what I'm trying to do is determine whether there are any exceptions to what I've determined about the dithering Samsung TVs implement. I have identified two types, and have put together test images which make it easy to identify the presence of either without having to closely scrutinize pixels. But the truth is that I only own a single Samsung TV myself, and even though I've spotted the same dithering on Samsung TVs in brick & mortar stores, there's nothing to guarantee that every 4K Samsung TV made exhibits the same dithering patterns.

The first dithering type seems to be permanently on at all times, non-defeatably. It is a pattern where every other horizontal line is visibly somewhat darker, giving a look not dissimilar to CRT scanlines in e.g. a retro video game. It seems to affect blues and oranges the most. This is the test image for identifying the "scanline" dithering.

The second dithering type is a crosshatch pattern—every other pixel, on both x and y axes, exhibits a pattern of alternating brightness and/or hue. This pattern can be disabled in theory, but the reality is there's a 99% chance you're staring at it right now. To explain: On my Samsung model (Q70R), in order to force the pattern to go away and not return, I must: 1) Label the HDMI port as "PC". 2) Use only 29, 30, 59 or 60 Hz refresh rates—no movie-compliant 24 Hz allowed. 3) When first turning the TV on, briefly swap the refresh rate to 59 Hz and back to 60 Hz. The latter step is required because my TV will "forget" to leave the crosshatch dithering off whenever it is freshly turned on. This is the test image for identifying the crosshatch dithering. The file format of the image is .MNG, which is animated .PNG, and the only viewer I know of which will view it correctly is IrfanView. The reason it must be animated is that the crosshatch dithering is something the Samsung TV will occasionally only turn on under certain circumstances (after which it won't turn it back off), and my test image has been developed to trigger those circumstances, thus ensuring no anomalous behavior from the TV.

As noted in the images themselves, both images must be viewed at "100% zoom", which is to say not fullscreen but instead in a window with no resizing. IrfanView will do this by default. It might also be helpful to make certain you're using 4:4:4 color, which can be tested with this image by JoelArt, as found in this post.

Prediction:

What I anticipate is that everyone will see evidence of dithering from both test images. If crosshatch dithering is not in evidence, it might be worthwhile to try turning the TV off for a minute, and then turning it back on to see if crosshatch dithering has returned, as it will have in the case of my Q70R. As previously noted, it should be possible to make the crosshatch dithering go away by swapping refresh rates (60->59->60). But I do not believe the "scanline" dithering can be defeated.

One thing I hope people will confirm for themselves is that the crosshatch dithering will always return at 24 Hz, which is the particular issue I have with my own TV—if I want to watch movies at their intended framerate, I have to stare at crosshatch dithering and lose some detail. I generally just watch movies at 60Hz because of this.

Discussion:

Why is dithering a problem? Aside from the perhaps obvious point that the TV is proving unable to accurately reproduce the video it is fed, resulting in somewhat inaccurate colors, the perhaps more important issue is that dithering of these types lowers the effective resolution of the TV. Not just the color resolution—the entire screen resolution. You are not getting 4K. The actual effective resolution is not easy to quantify, and is in fact dynamic, because the dithering itself tends to depend on what colors are being displayed, but for example take a look at this image from FlatPanelsHD:



The crosshatch dithering is readily visible in the Q90R specimen. When sitting from a typical viewing distance, the crosshatch pattern likely diminishes, but what doesn't diminish is the loss of fine detail. This picture of an eye is meant to have a certain amount of detail, which the Sony AF9 reproduces faithfully, but which the Q90R effectively crushes due to its dithering. It is no longer 4K.

Rtings discusses dithering briefly in their What Is The Resolution article. They accurately note that crosshatch dithering on the Q90R can be disabled in "PC" mode. What they fail to note, however, is that one still needs to jump through hoops to ensure it's gone, and the user still cannot watch movies at their native 24 Hz because the crosshatch dithering will simply come right back. They also fail to account for the "scanline" dithering which is ever-present.

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post #2 of 18 Old 01-15-2020, 03:58 PM
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what exactly is supposed to be the difference in those 2 pics between AF9 and Q90R ?
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post #3 of 18 Old 01-15-2020, 04:10 PM
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what exactly is supposed to be the difference in those 2 pics between AF9 and Q90R ?
Indeed only horizontal on the q90 while I see crosshatch on the af9.

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post #4 of 18 Old 01-15-2020, 04:14 PM - Thread Starter
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Originally Posted by UltimateDisplay View Post
what exactly is supposed to be the difference in those 2 pics between AF9 and Q90R ?
You're unlikely to notice any difference if viewing this thread on a mobile device. But apart from what I already underscored in the OP, you can read more about the dithering and its consequences in the aforementioned FlatPanelsHD article.
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post #5 of 18 Old 01-15-2020, 04:16 PM - Thread Starter
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Indeed only horizontal on the q90 while I see crosshatch on the af9.
If you don't have the ability to view images at their native resolution on your mobile device, you may need to wait until you can read this thread on a 4K monitor. This thread was only ever intended for those using a Samsung 4K TV. That said, if you're convinced FlatPanelsHD has it backwards, you might consider reaching out to them to offer your correction.
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post #6 of 18 Old 01-15-2020, 04:18 PM
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i am reading at home on a 27" 2560x1440p monitor
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post #7 of 18 Old 01-15-2020, 04:31 PM
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The "Eye test" samples have different patterns. Are both supposed to be a example of dither effects on different TV's?


As I can see it the Samsung Macro-shot has a X-pattern to the pixels while the AF9 has a vertical ||||||| pattern to the intensity of the brightness of pixels. Both look bad if I may say so.



Sure the AF9 looks more detailed but it also is clearly apparent on having the vertical lines for every row of pixels. Samsung manages to hide the X-patterns but also makes the image softer as a effect loosing detail like there is some blur effect being set upon the image as a whole.

One might add there is a hint of === Horizontal "scan lines" on the samsung but I would say the Vertical |||| on the AF9 is more obvious.


EDIT:
I have the Q8DN. I would say with 4:4:4 RGB 8 bit in PC Mode the results would be comparable to the x900f example
The Q90r with it's "blur filter" example seems to show proper pixel rendition but the effect of the "blur" is horrible for accuracy. All pixels look 2x the width they actually are because of the Ultra viewing angle.
I can see why resolution takes a loss now. You don't want Ultra vieving angle blur effect for PC use.

Last edited by Nighthog; 01-15-2020 at 05:19 PM.
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post #8 of 18 Old 01-15-2020, 05:26 PM
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Quote:
Originally Posted by Colmino View Post
If you don't have the ability to view images at their native resolution on your mobile device, you may need to wait until you can read this thread on a 4K monitor. This thread was only ever intended for those using a Samsung 4K TV. That said, if you're convinced FlatPanelsHD has it backwards, you might consider reaching out to them to offer your correction.
I was replying to another poster and described what O could see on my device. My apologies for intruding...

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post #9 of 18 Old 01-15-2020, 06:01 PM
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is this Samsung dithering thing only present on models with Ultra Wide viewing angle ?

to use2019 examples :
- Q80R & Q90R have Ultra Wide viewing angle - so they have dithering
- Q60R and Q70R do not have Ultra viewing angle - so are they free from this dithering and detail loss or not ?





this is especially important for 2020, cause 2020 QLEDs may get HDMI 2.1 (excellent for PC use) and as far as i know it was confirmed that Q90T will have UWVA, but Q80T will not have it ..
so it may make sense to actually get the cheaper Q80T if you sit dead center, since both sets are FALD, but Q80T will lack potential issues associated with UWVA ...
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post #10 of 18 Old 01-15-2020, 06:11 PM
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Quote:
Originally Posted by UltimateDisplay View Post
is this Samsung dithering thing only present on models with Ultra Wide viewing angle ?

Ultra viewing angle is the cause of the BLUR /resolution loss, any eventual dither is another matter.



Any dither depends on your input mode and Motion Interpolation or other settings enabled. Basically processing done on the TV end where ultra viewing angle can't be adjusted at all, it's a actual physical filter.
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post #11 of 18 Old 01-15-2020, 06:19 PM - Thread Starter
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As I can see it the Samsung Macro-shot has a X-pattern to the pixels
The X-pattern is crosshatch dithering, and manifests because of alternating brightness/color from pixel to pixel, both vertically and horizontally. It is the fact that half of the pixels are displayed wrongly that leads to the reduced effective resolution

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while the AF9 has a vertical ||||||| pattern to the intensity of the brightness of pixels. Both look bad if I may say so.
[...]
One might add there is a hint of === Horizontal "scan lines" on the samsung but I would say the Vertical |||| on the AF9 is more obvious.
The vertical pattern you identify with the AF9 is the result of two things: The shape of the subpixels (R, G, B), and the way the image was picked up by the camera. The Q90R photograph exhibits a similar phenomenon, manifesting instead as horizontal lines, as you note—also mostly the fault of the camera. These phenomena do not have any bearing on the accuracy of individual whole pixels. These are close-up photographs showing more detail than the user is expected to see in day-to-day use, and they are intended in this case to reveal with clarity the dithering being implemented by the Q90R, which they do. Unlike the RGB subpixels, the dithering pattern affects entire pixels in a grid pattern, and this phenomenon is discernible at any viewing distance that reveals detail of >1080p to the viewer.

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I have the Q8DN. I would say with 4:4:4 RGB 8 bit in PC Mode the results would be comparable to the x900f example
The Q90r with it's "blur filter" example seems to show proper pixel rendition but the effect of the "blur" is horrible for accuracy. All pixels look 2x the width they actually are because of the Ultra viewing angle.
I can see why resolution takes a loss now. You don't want Ultra vieving angle blur effect for PC use.
The blur effect implemented by the Q90R (and, I think, the Q80R) has an effect at the subpixel level, which is to say the individual red, green and blue elements. A single whole pixel is one square comprising of one each of R, G and B. The dithering described by both myself and FlatPanelsHD and others is something which occurs on the scale of whole pixels, not subpixels. Therefore the blurring technique implemented by the Q90R is irrelevant, the dithering is still a problem, and my test images will reveal dithering on that model as well. I will add that since the Q90R's blurring is only discernible on the subpixel scale, it shouldn't have any meaningful impact for PC use.
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post #12 of 18 Old 01-15-2020, 06:36 PM
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Originally Posted by Colmino View Post
The blur effect implemented by the Q90R (and, I think, the Q80R) has an effect at the subpixel level, which is to say the individual red, green and blue elements. A single whole pixel is one square comprising of one each of R, G and B. The dithering described by both myself and FlatPanelsHD and others is something which occurs on the scale of whole pixels, not subpixels. Therefore the blurring technique implemented by the Q90R is irrelevant, the dithering is still a problem, and my test images will reveal dithering on that model as well. I will add that since the Q90R's blurring is only discernible on the subpixel scale, it shouldn't have any meaningful impact for PC use.

It for sure has a obvious effect in my opinion. The 4:4:4 RGB PC MODE Q90r looks like 4:2:2/4:2:0 Chroma with the dim /blurred edges to text with the ultra viewing angle on rtings sample images on my Q8DN with no such filter.

It has a significant effect on detail concerning PC use!
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post #13 of 18 Old 01-15-2020, 06:42 PM - Thread Starter
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is this Samsung dithering thing only present on models with Ultra Wide viewing angle ?
No. It is present in all Samsung models, until somebody can show me a photo of their TV at 24 Hz with my test images proving dithering is absent. You are getting conflicting replies. I made the test images in order to make it easy for people to see for themselves.

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this is especially important for 2020, cause 2020 QLEDs may get HDMI 2.1 (excellent for PC use) and as far as i know it was confirmed that Q90T will have UWVA, but Q80T will not have it ..
so it may make sense to actually get the cheaper Q80T if you sit dead center, since both sets are FALD, but Q80T will lack potential issues associated with UWVA ...
Irrelevant. Samsung seems to have used dithering for every 4K TV they've made, and while some publications will make note of the issue (and FlatPanelsHD will even point out that it lowers effective resolution), none seem ready to give negative marks for it, even though it is without question an issue. But I need to stress that in spite of everything I've discovered about this phenomenon, I did not return my Q70R. Why? Three reasons.

1: The "scanline" dithering is relatively subtle. It only pops out at you when there are certain colors like sky blue or fire orange. I can live with this for the ~2 years I expect to keep this TV before selling.

2: The crosshatch dithering can be worked around for the most part, as I previously described. Yes, if you use a Samsung for anything but "PC", you're going to get the dithering. Yes, it will still come back in you try using 23, 24, 25 or 50 Hz. And yes, I still have to "jumpstart" the TV every time I turn it on (swapping refresh rate 60->59->60). But, again, I can live with this for the time being.

3: As long as crosshatch dithering is off, and I have turned off "PC Global Dimming" in the service menu, the most infamous dealbreaker with Samsung TVs, global dimming, is defeated.

There's nothing stopping Samsung from making these things defeatable, but it's important to understand that Samsung has developed a habit of implementing things like this as a balancing act. Non-defeatable global dimming is a huge issue... but it's how Samsung hides clouding and blooming, and that's the reason they give their customers no real way of turning it off. Dithering is a way of hiding color reproduction shortcomings. And lately, Samsung has started forcing their flagship TVs—again, non-defeatably—to display movies too bright (see video), in a bid to make their TVs stand out on the showroom floor. My recommendation would be to find a way to test their 2020 models before buying.

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post #14 of 18 Old 01-15-2020, 06:44 PM - Thread Starter
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It for sure has a obvious effect in my opinion. The 4:4:4 RGB PC MODE Q90r looks like 4:2:2/4:2:0 Chroma with the dim /blurred edges to text with the ultra viewing angle on rtings sample images on my Q8DN with no such filter.

It has a significant effect on detail concerning PC use!
That is interesting. It is plain to see that despite the blurring effect on the individual subpixels, each whole pixel remains a distinct square. I'd be interested to know what result you get from JoelArt's 4:4:4 test image.
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post #15 of 18 Old 01-16-2020, 04:39 AM
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That is interesting. It is plain to see that despite the blurring effect on the individual subpixels, each whole pixel remains a distinct square. I'd be interested to know what result you get from JoelArt's 4:4:4 test image.

There is no issue when using 4:4:4 RGB in PC MODE with the JoelArt's test image @ 4K 60/59/30/29hz... 50/25/24/23hz get only 4:2:2 Chroma in any mode. [4:4:4 -> 4:2:2 & 4:2:2 -> 4:2:0??? anyway much worse, double conversion basically]
Anyway firmware 1290.4 in PC Mode @ 50/25/24/23hz has issues with "fit to screen" not working causing HDMI Overscan issues so you don't want to use that mode for those resolutions anyway.

Though I have to note sending a YCbCr 4:2:0 Chroma signal is "better than" the RGB/YCbCr 4:4:4->4:2:2 conversion even though you might get some slight banding issues. The TV handles 4:2:0 differently and "corrects" the Chroma errors in many test images but text can still be blurry like with if you picked 4:2:2 Chroma directly. For example the JoelArt's test image looks like you had 4:4:4 chroma functional. Same with scan-line dithering test image, it no longer has differing fields.

It's not without faults as the blurry effect from chroma subsampling is present but it corrects the "faults" one would notice looking at these particular test images. One can still see that Chroma is less than 4:4:4 or 4:2:2 if one takes a look at the partcular Chroma444 test pattern with text [the quick brown fox .... the lazy dog] for example.

I find this test pattern the best to see all kinds of faults. This is the only one where I can for sure see 4:4:4 RGB is actually working when all text is sharp and clean.
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post #16 of 18 Old 01-16-2020, 07:45 AM - Thread Starter
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Originally Posted by Nighthog View Post
There is no issue when using 4:4:4 RGB in PC MODE with the JoelArt's test image @ 4K 60/59/30/29hz... 50/25/24/23hz get only 4:2:2 Chroma in any mode. [4:4:4 -> 4:2:2 & 4:2:2 -> 4:2:0??? anyway much worse, double conversion basically]
Hmm. I don't have any issues with chroma at the trouble framerates, though of course since it's in crosshatch dither mode, things are fuzzier than they should be. I definitely still get 4:4:4.

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Anyway firmware 1290.4 in PC Mode @ 50/25/24/23hz has issues with "fit to screen" not working causing HDMI Overscan issues so you don't want to use that mode for those resolutions anyway.
I found a way to permanently fix this. (Otherwise I would definitely have had to return the TV.) YMMV. I labeled the TV as "Game Console". This fixed the issue. Then I changed the label back to "PC". The fix stayed. Yes, it was a gigantic dealbreaker until I found the solution. I spent a lot of time plugging away at Samsung's customer support chat over the issue. They were no help; I had to discover it myself. That it can be fixed at all is, of course, a totally random miracle, because it's certain that Samsung doesn't care and won't be fixing it themselves in any capacity more proactive than accidentally. And I also acknowledge that probably nobody else even knows it can be fixed, despite the latest firmware.

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Same with scan-line dithering test image, it no longer has differing fields.
I doubt I need to point out that "passing" test images by interpolating resolution is a far cry from actually displaying fully 4:4:4 color. If I were concerned people would misinterpret what they're seeing in that fashion, I could just as easily have produced a more robust test image.

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I find this test pattern the best to see all kinds of faults.
Most test patterns arguably have their uses. I just happen to prefer patterns that have no ambiguity. I'm sure you can easily imagine many people looking at the "quick brown fox" image with 4:2:2 chroma and unironically asking just exactly what they're supposed to be seeing. It's not so easy to be able to say you can't tell whether box A looks like box B or box C—it's yes or no. JoelArt's does a fine job of this. The traditional Belle-Nuit chart is perfectly revealing but still requires a bit of interpretation.
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post #17 of 18 Old 01-16-2020, 08:07 AM
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Hmm. I don't have any issues with chroma at the trouble framerates, though of course since it's in crosshatch dither mode, things are fuzzier than they should be. I definitely still get 4:4:4.
Can be a difference between the 2018 & 2019 sets there. I for sure can't get 4:4:4 chroma to display at all for 23/24/25/50hz @ 4K. It gets downsampled to as best 4:2:2 chroma even if you send 4:4:4.

But I can't tell yet about Cross-hatch issue. I've not noticed it myself yet on mine display, I've seen the examples but not seen it present itself in content or images on my own display the way it's presented.




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I doubt I need to point out that "passing" test images by interpolating resolution is a far cry from actually displaying fully 4:4:4 color. If I were concerned people would misinterpret what they're seeing in that fashion, I could just as easily have produced a more robust test image.


Most test patterns arguably have their uses. I just happen to prefer patterns that have no ambiguity. I'm sure you can easily imagine many people looking at the "quick brown fox" image with 4:2:2 chroma and unironically asking just exactly what they're supposed to be seeing. It's not so easy to be able to say you can't tell whether box A looks like box B or box C—it's yes or no. JoelArt's does a fine job of this. The traditional Belle-Nuit chart is perfectly revealing but still requires a bit of interpretation.

The problem with the JoelArt's & scan-line test pattern is YCbCr 4:2:0 looks to make a pass and shows no apparent faults. The only hint you get is that the edges might be a little blurred for the squares top and bottom. rather than 1 pixel row you might get 2 rows of pixels every other row moving the image. It looks like 4:4:4 RGB otherwise.

Here the [quick brown fox] test pattern quickly and apparently shows the red and blue text are blurry /smudged. They aren't sharp as in proper 4:4:4 chroma situation. Magenta is a little blurred as well.



Would need further thought and inspection but it's obviously handled different when sending 4:2.0 versus 4:4:4 when it's sampled down to 4:2:2 or sending direct 4:2:2 which looks horrible & 23/24/25/50hz video modes.
4:2:0 looks best using the test patterns but there are some other drawbacks in other aspects.
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post #18 of 18 Old 01-16-2020, 03:10 PM - Thread Starter
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Can be a difference between the 2018 & 2019 sets there. I for sure can't get 4:4:4 chroma to display at all for 23/24/25/50hz @ 4K. It gets downsampled to as best 4:2:2 chroma even if you send 4:4:4.
This much is at least new information. If Samsung were willing to fix 4:4:4 color at certain refresh rates, they might be open to fixing the issues that remain in their 2019 models. But then again, the fact that those refresh rates are the very same ones for which crosshatch dithering remains non-defeatable can't be a coincidence.

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But I can't tell yet about Cross-hatch issue. I've not noticed it myself yet on mine display, I've seen the examples but not seen it present itself in content or images on my own display the way it's presented.
It's one of those things you can't un-see once you've noticed it. It's probably better just to check the second test image and note which pattern is being shown in the large box at the top.

One thing I neglected to mention about the dithering is that it adds noticeable input lag, doubtless because of its nature as post-processing. The (excellent) input lag results seen on the likes of Rtings cannot be achieved when it is on, and as I've made a point of underscoring, it is in fact on for almost everyone.

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The problem with the JoelArt's & scan-line test pattern is YCbCr 4:2:0 looks to make a pass and shows no apparent faults.
That is really inexplicable. If I output 4:2:0, as I am doing right now, the pattern corresponds to the samples indicated at the bottom, as intended.

You might have better luck with the aforementioned Belle-Nuit test chart. The thing to watch for is visible disagreements in color between the individual sections of red/cyan near the "1" or "2". You'll see what I mean when you swap between 4:4:4 and other chroma modes.
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