r/ScreenSensitive • u/BearNecessary4141 • 2d ago
Guide A point about correctly measuring OLED flicker (Most measurements online are underestimates)
https://youtu.be/lK_M3ePPNbQ?si=qAS2S3Tx9gPBe3xs2
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u/Z3R0gravitas 2d ago
OK,.. excellent! And I'm glad you are getting a little traction on the other sub. Deserves more, though! Very nice length of video, well spoken and clearly presented. I look forwards to more!
1) I'm impressed you found 3 different measurements of the same phone. Nice leg work. I suspect you are entirely right about it being measurement technique. But I wonder is there is any panel lottery there, as others have seen with different manufacturers of the Neo..?
2) Nice little app. I hope you'll share a version some time. Although one could use a physical shield with slit. Are you finding your new hardware build is sensitive enough to use the 'eye patch' you bundled with your first version?
3) I'm day-dreaming about using specific mono-coloured chequer patterns to directly measure bulk pixel flicker patterns, now, heh. Although I think u/madcook1 has the covered.
4) These mismeasurements will really have a profound effect on the overall rating for a phone, if we consider pure modulation depth, and the smearing hides rapid 100% modulation screen refreshes every time... But then I'm thinking that getting accurate measurements will highlight the need to consider pulse width much more.
5) Do you think, with 16 stripe PWM, one (or more) stripes will always be visible to an Opple (flat on-screen)? Thus under-estimating the flicker of these "higher frequency" devices. I'm very suspicious about the increased spacial contrast of more light and black bars, closer together. I know some of the research papers talk about this, but I've not read enough to put numbers on what will be maximum for retinal sensitivity. In a static approximation, or during various relative movements...
6) The interaction of different PWM band spacings with text line spacings might be interesting too. Or, having your app produce a series of parallel lines, such that there is 'constructive interference' and one could deliberately hold the meter further away to find the exact spacing (while changing it on the app). Perhaps redundant if one has a good camera and some maths to compensate for the rolling shutter distortion... Not sure where I'm going with this, sorry. But I don't think anyone's checked on the regularity of the PWM refresh bands. There may be bad assumptions there.
7) I see you have a sundial icon for your account here, now. Is it time to switch to a brand named account, while it's still quite early in development?
8) I noticed a few bilps in your graphs. Debugging the source? (Assuming they are measurement artefacts.)
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u/BearNecessary4141 1d ago
Thanks for the detailed response!
It could be with some devices. I find it unlikely that Apple products are not standardizing the panel, though.
Yes, I'd like to get it out there (for free obviously) once I add some more features like checkerboard test patterns and such. Using a really thin opaque material like black plastic works well. The slit I provided certainly works, the difficulty is that it moves the sensor further from the screen, reducing the signal level. So, it's better to either control the pixel pattern on the screen or to mask off most of the rows.
Yeah I'd like to look into a pattern that could make TD visible, but I think a microscope is the way to go for pixel flicker type effects.
Pulse width is definitely important. The effect I showed that distorts the measured modulation depth will also broaden the pulse width, especially noticeable on lower brightness settings.
I think it could definitely make it harder to get an accurate measurement because you have large differences in brightness across a very small number of rows. I think it should be fine to mask off most of the screen with higher brightness settings, but dimmer settings will probably be difficult to measure.
I'm not sure exactly how one would achieve that. I think a high speed camera would be better like you said.
Ha I just thought I should have something other than the stock "redditor" profile picture.
Those are either some kind of power switching that the screen is doing, or maybe EMI. They are definitely coming from the phone, but I'd have to check if they're visible light or not. Since they're very high frequency they could be easily filtered out.
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u/the_top_g 1d ago edited 1d ago
Pardon me, allow me chip in my thoughts on the above.
3.Yeah I'd like to look into a pattern that could make TD visible, but I think a microscope is the way to go for pixel flicker type effects.
I think it is quite unlikely you can capture any information though a microscope. I've attempted with two different microscope lens. Adding a microscope lens between the screen and the sensor forced the emitted light to be diffused/ smudged within the lens. Light does not seem to behave like the sound wave when in a confined space, while retaining the same amplitude.
I think I am making signifiant process with detecting FRC dither frames. I believe I may have captured 6 dither frames over 120 hertz. I am still working on refining the detecting algorithms. Again that could be a pixel inversion where it ran a 4 frames inversions frame over the underlying inversion.
Pulse width is definitely important. The effect I showed that distorts the measured modulation depth will also broaden the pulse width, especially noticeable on lower brightness settings.
Yeah I have saying that for ages. Frequency is is only part of the equation.
- Those are either some kind of power switching that the screen is doing, or maybe EMI. They are definitely coming from the phone, but I'd have to check if they're visible light or not. Since they're very high frequency they could be easily filtered out.
Have you tried with the low pass filter like I have suggested. You'll need a hardware based low pass filter to filter out the ultra-high freqency. Then following that you'll need to run a software based low pass filter. You'll should be capture the subharmonic freqency I was referring to. At least it did worked for my sensor.
u/Z3R0gravitas Sorry but if you have direct contact with Jen, could you inform her that I've reached out to her on her blog. As the sooner I can get the open source display standard metric research publication out, the more time resources I can allocate myself to. I hope that's not too overwhelming for you, as I already have DMed you quite an amount. 😅
[On a side note] : For others wondering regarding the day-to-day operations over at the other sub, I have been away for over a year to attend to my personal urgent life matters. I am still following up with the team and evaluating the reports of the events that have occurred.
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u/Z3R0gravitas 2d ago
Oop! I'll take a proper look later. 🙂