[BenQ EX240] Hand-held pursuit photo validation and artifact

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EternalCoconut
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[BenQ EX240] Hand-held pursuit photo validation and artifact

Post by EternalCoconut » 27 Nov 2022, 18:59

Hello, I took a few images of what I would consider the ideal settings for the BenQ EX240 just for comparison with another monitor, but since I haven't really done this before other than that one time recently (of the AOC 25G3ZM https://forum.pcmonitors.info/topic/aoc ... post-69846), I'm not sure that they're good enough and would like help determining whether they are, and if they are, which ones (single one) to use out of each set of multiples (for 60 and 120Hz). I used a hand-held phone with no guide rail, so I realise that the perspective is a bit wonky, stability is so-so and so on, but they don't need to be perfect as long as they're at least usable.

The UFO images:
https://mega.nz/folder/s1YkybaI#XqyCKLJrnyJqprgP3p5a0w

Artifact
Also, running the testufo page on BenQ EX240 for just a little while produced these peculiar artifacts. It never happens otherwise, even leaving a windows explorer window open (mostly solid white) doesn't leave a mark, but this test does within a few minutes. They do go away after a while. In addition to the guide track dots, if you look at 60Hz photo #4 and 120Hz #3, you might be able to see an effect left by the UFOs themselves, in their path, as well. Some sort of ghostly impression reminiscent of very faint overdrive artifacts, perhaps the very aether itself being disturbed by the locomotive technology utilized by the expulsion-less craft and its little green inhabitant.

Is it something to be worried about, and should I contact BenQ about it?

Image

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Re: [BenQ EX240] Hand-held pursuit photo validation and artifact

Post by Chief Blur Buster » 29 Nov 2022, 14:59

This is image retention from flicker patterns --
viewtopic.php?f=7&t=7539
These are static electricity buildup in pixels.

Use the monitor normally to cause these to disappear.
Chief Blur Buster wrote:
22 Sep 2020, 21:38
Crossposting here.
Joel D wrote:
19 Sep 2020, 13:26
Dang. Thats the weirdest thing ever. I've had the same static image on the screen for hours at a time, never had a issue. Wow, I'm amazed this happened in such a short time. Furthermore, omg that retention in general is loud and bold ! Most bold IR I've ever seen. How high do you have your brightness ? IMO 99% of people use their monitors way too bright, in which could be culprit to image retention quicker. It is also why they see outrageous screen bloom and backlight bleed.
Image Retention ("Temporary Burn-In")
From Temporary Static Electricity Buildup In Pixels


Flicker patterns such as:
- Emulator black-frame insertion
- 3D-glasses software
- Certain motion tests (including but not just TestUFO's Sync Track)
- Anything that does exactly a half-Hz or quarter-Hz flicker with no dropped frames for a sustained period

Can create temporary LCD image retention. It's a static-electricity behavior when a flicker goes in sync with the positive-negative voltage inversion algorithm, and creates this inversion-related image retention.

This is temporary and you just display video full-screen, or some other thing that really exercise the whole screen -- e.g.
This gets rid of the per-pixel static electricity buildups.

You also get the same problem in anything that flickers pixels in-phase with the positive-negative voltages of the LCD inversion algorithm.

https://www.google.com/search?q=techmind+LCD+inversion

Voltages inverts to try to balance the electricity buildup in the panel, but flicker patterns that go in sync with this, can cause a voltage unbalance = static electricity build up, as an LCD pixels can accidentally behave as capacitors.

The layered nature of an LCD unfortunately creates unavoidable capacitance effects that interfere with operation.

Image

Modern LCDs try to avoid this by using spatial and temporal alternating voltage (positive voltage, then negative voltage, then positive voltage, then negative voltage, and so on)

Image

It's often in a chessboard pattern spatially, which sometimes produces an inversion artifact. Normally this is invisible when the positive voltages are perfectly balanced with negative voltages. But the voltage balancing is not always perfect, so you see this:

Image

However, this is also done temporally -- the voltages swap (like an inverted chessboard) at the next refresh cycle.

Now, if you flicker perfectly (at half Hz), then pixels that gets the "higher voltage" (different brightnesses = different voltages) are always getting negative voltages or always getting positive voltages = static electricity buildup = image retention.
  • The chessboard artifact is the quirk from spatial component of the inversion algorithm.
  • The image retention is the quirk from temporal component of the inversion algorithm.
Not all screens use the same inversion pattern / inversion algorithm, so some LCDs don't get image retention easily, while others do. In an ideal world, we would be now using error-diffusion temporal dithering or some randomized dithered inversion algorithm, to be fully immune to all material. But in the real world, the panel makers don't do that, and just settle for simple patterned inversion algorithms which are easier to do at high refresh rates (complex invisible inversion processing can be costly). Historically, this is why inversion patterns often have showed up more commonly on high-Hz monitors -- for example, the early ASUS VG278HE (one of the first-ever 27 inch 144Hz monitors) was particularly known for its chessboard artifact during 3D glasses operation.

Thusly, I am not surprised that the world's first panels of a specific refresh rate has some "inversion-related quirks". Every single 240Hz 1ms IPS panel currently has this pixel-as-capacitors quirk at the moment, that only shows up with sustained exact-Hz flicker patterns. As time passes, I'm sure this will improve, with improved inversion algorithms.

Since the pixels have inadvertently behaved like capacitors because of the layered nature of an LCD worked against proper pixel operation. Now you got to drain the charge -- the built-up static electricity stored in the pixel.

Draining the pixel static electricity charge is best done by playing highly active video material. If you want to erase image retention faster, use full screen random-color flashing (fully randomized colors).

HOW TO FIX FIX: Play highly active fullscreen video or animation.
Play pixel fixer software https://www.youtube.com/watch?v=39HUG7QrQi8 (play at 2X speed, it's too slow)
Or simulated analog TV noise https://www.shadertoy.com/view/tdXXRM -- this usually erases image retention faster.
I prefer simulated analog TV noise as a quick burn-in eraser.
Make sure to click the full screen button

While a technology quirk, it is not an RMA defect at all.

Emulator/RetroArch BFI: Use an odd divisible Hz such as 180 Hz or 300 Hz

Doing this techniques is 100% immune to these problems.

If you want to keep using emulator BFI, use the new 180Hz BFI feature now found in some emulators, a 3-cycle flicker pattern never produces image retention on majority of monitors -- RetroArch is building this feature in now.

NOTE: Some old LCDs had inversion-algorithms bugs (firmware bugs or hardware bugs) that caused burn-in even with stationary images, especially at certain picture settings. Also, certain manoevers such as overclocking an LCD may cause inversion algorithms to fail, creating a more image-retention-sensitive LCD. You will immediately know if image retention occurs with stationary images instaed of moving images.
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Discorz
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Re: [BenQ EX240] Hand-held pursuit photo validation and artifact

Post by Discorz » 30 Nov 2022, 07:18

EternalCoconut wrote:
27 Nov 2022, 18:59
Hello, I took a few images of what I would consider the ideal settings for the BenQ EX240 just for comparison with another monitor, but since I haven't really done this before other than that one time recently (of the AOC 25G3ZM https://forum.pcmonitors.info/topic/aoc ... post-69846), I'm not sure that they're good enough and would like help determining whether they are, and if they are, which ones (single one) to use out of each set of multiples (for 60 and 120Hz). I used a hand-held phone with no guide rail, so I realise that the perspective is a bit wonky, stability is so-so and so on, but they don't need to be perfect as long as they're at least usable.

The UFO images:
https://mega.nz/folder/s1YkybaI#XqyCKLJrnyJqprgP3p5a0w
Good job!

Good enough demonstration of motion performance. There are few thing u could try to improve tracking accuracy but it would result in small differences.

When tick marks in Sync Track vertically overlap or separate this indicates unwanted vertical camera movement. When tick marks are not vertically aligned this means ufo speed and horizontal camera speed are not perfectly synchronized. You want both correct - 4 tick marks will look like vertically flat line. Other camera settings like shutter, focus, iso look good on your images imo.

Image Image ✖ Affected result

Image Image ✔ Perfect enough

Regarding ideal settings, it's a personal preference thing. People choose best for their use case. It's usually clearest and least distracting option.
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Re: [BenQ EX240] Hand-held pursuit photo validation and artifact

Post by Chief Blur Buster » 12 Dec 2022, 16:20

Discorz wrote:
30 Nov 2022, 07:18
Image Image ✖ Affected result
Depends on your required error margin. For some rough tests (especially the left edge), this can be adequate, especially since this is a tiny fraction of 60Hz blur.

But for strobed or ultra-high-Hz, your accuracy needs to be as outstanding as possible.

A common rule of thumb is the misalignments should be less than 1/10th the horizontal thickness of a tickmark.

Image

This one is still horizontally within roughly 95% of WYSIWYG, because the total combined tracking error appear to be visually only 5% of the tickmark width. It's VERY tough to accurately track a camera for 1/15sec at 60Hz sample and hold, so a bit more error is tolerable there;

However, the perfectionist in me hates this image; it's not a pretty-publish. But if you're doing hundreds of tests and specify your error margin to be within 10% of WYSIWIG blur, one is just tempted to move along, because 60Hz pursuit camera tests are just plain unfun; so who cares if you add 0.5 pixel of motion blur to 16 pixels of motion blur for plain 60Hz tests. It's like comparing 60Hz versus 57Hz -- hard to see blur apart.

Human eyes sees geometric blur differences, e.g. 1/120sec blur versus 1/360sec blur is easier to tell apart (whether be SLR camera shutter photograph, or framerate=Hz sample and hold motion blur), which is also why I tell users to upgrade in big 2x-4x Hz increments, with framerates to match.

But if you're a reviewer who needs to publish images, including the sync track, definitely go for the beauty. Experienced users will give accolade for including a beautiful sync track in published reviewer photos.
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Re: [BenQ EX240] Hand-held pursuit photo validation and artifact

Post by Discorz » 13 Dec 2022, 08:24

That makes sense, lower the persistence the more accurate our tracking needs to be. Small inaccuracies can hide inside 16.7ms of blur but not as much in 1ms. However isn't vertical accuracy just as important? In fact its the opposite with vertical tracking, at high persistence it adds more blur than at low persistence.
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Re: [BenQ EX240] Hand-held pursuit photo validation and artifact

Post by Chief Blur Buster » 18 Dec 2022, 21:34

Discorz wrote:
13 Dec 2022, 08:24
That makes sense, lower the persistence the more accurate our tracking needs to be. Small inaccuracies can hide inside 16.7ms of blur but not as much in 1ms. However isn't vertical accuracy just as important? In fact its the opposite with vertical tracking, at high persistence it adds more blur than at low persistence.
Accuracy that is perpendicular to the motion vector is quite important too, but shorter camera exposures reduces vertical error margin, e.g. 1/60sec camera exposure at 240Hz has less vertical hand-shake blur than 1/15sec camera exposure at 60Hz.

But the large amount of horizontal blur kind of masks the vertical error margin partially, you're less likely to see 1/4th pixel vertical handshake blur if there's just a massive 16+ pixels of horizontal motion blur.

Continual steady motion on a screen is fundamentally two dimensional, a single motion vector, so you're prioritizing measurement along one axis (the motion axis: horizontal axis). That will be the axis of dominant blur, especially in sample and hold operation, and horizontal will dominate verticals. As long as you're not blurring a full pixelheight, even oftentimes a half pixelheight of vertical blur is tolerable when measuring 60Hz blur -- at least when you're hobbyisting through this rather than as a monitor reviewer.

Now, whereas, with strobed low persistence, multiple-image-effects are more noticeable, so you need to pursuit more accurately. But strobing usually mainly occurs at higher refresh rates than lower, and with strobing you can make do with just about two refresh cycle exposures (basically just a confirmation of accurate tracking speed from one refresh cycle to the next), for measuring motion blurs of different strobe pulse widths. So overlaying only two strobes rather than multiple strobes is easier, especially when pursuiting low strobe Hz.

And now, if you're doing ultra high frame rate low persistence, the low horizontal blur may make the vertical error more noticeable, but the shortcut of using short exposures easily done with ultra high frame rates (still looks similar to 1/30sec human integration time, simply because of how sample-and-hold displays work) -- minimizes the opportunity of vertical blurring.

The errors of horizontals and verticals are more-or-less going up and down with each other -- longer exposures means more errors in both horizontals and verticals. In the vast majority of times, the errors build up in both axes, but most of the error will always be the horizontal. It's just much harder to see 1/2 pixel of error in 16 pixels of horizontal motion blur, than 1/2 pixel of error in verticals because there's supposed to be no vertical motion in the camera relative to the moving object. You can even run into a situation where you've got unnoticed 2 pixels of motion blur in a 60Hz unstrobed pursuit, while really noticing the 1/4 pixel of vertical blur... It's very hard with the gigantic amounts of horizontal motion blur along the horizontal motion on a 60Hz display to handwave steadily at 1/15sec.

In my experience, the TestUFO track is reasonably accurate from 2 refresh cycle exposures through 7 refresh cycle exposures. Less than 2 and you can't determine if tickmarks start/end accurately (since a leading edge may be a trailing edge, or vice versa, in an interrupted tickmark blur). More than 7 and you no longer accurately know how well all the bright tickmarks may properly overlap each other;

Image

That being said it's theoretically possible, with a camera of excellent dynamic range, and known refresh rate, and excellent spatial resolution, to try and triple-stack the tickmarks and gain ability to do 8 through 11 refresh cycle exposures. That may be possible on OLEDs, which makes the sync track fairly bright (because of fast OLED GtG near instantly to white), but I wouldn't trust most users to understand how well triple-overlapped tickmarks are.

I'm finally working on TestUFO now again (because I'm adding HDR to it), so I'm going to investigate adding other features, including subpixel speeds (scaled/blended motion) and possibly adjustable count of sync track tickmarks.
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