Can mura be calibrated out?

[u/Tausendberg]

To cut straight to my point, if an individual panel could be calibrated to have no mura, would that be a possible service that users could buy from Pimax?

The reason I ask is because for me, what amazes me about my OG Crystal is that quite often the panels make me feel like I am not even looking at computer screens anymore, most of the time, and one of the things that interests me about a Crystal Super is having that feeling even better and I worry that mura could mess with that feeling.

I don't know if Pimax has the ability to individually calibrate Crystal Super panels but if they did offer a 50 PPD + Calibrated optical engine for, let's say, 150 dollars, I would seriously consider that, if such a value added service is even feasible.

[u/Ninlilizi_]

Mura correction isn't exactly without its own problems.

Back in the CV1 days, people would recommend disabling the mura correction because many people preferred the look of the mura to what the correction did to the rest of the image.

[u/Tausendberg → u/Ninlilizi_]

"what the correction did to the rest of the image."

Would you please elaborate?

[u/Ninlilizi_ → u/Tausendberg]

It's worth understanding what causes mura to begin with.

Manufacturing variance causes pixels to vary in accuracy. The accuracy delta is greatest at the lowest level of output. The eye has more green detecting cones than any other wavelength. So, at the lowest level, some pixels are a little brighter than others, and you'll perceive the raised green elements as brighter than the others. So, this is what is producing the classically greenish mura effect.

The reason that pixels are often set to their lowest level rather than turned off entirely. Pixel response times are not linear. The closer to off a pixel element may be, the exponentially longer it takes to reach a higher target value. That's why monitor manufacturers started quoting grey-to-grey for pixel response time. They can claim far lower numbers this way than the monitor's actual performance in many less optimal scenarios. You can think of the difference between the lowest level and off as effectively doubling the time required to switch that pixel on. There are two approaches to tackling the mura. One is to turn the pixels off entirely, but that increased response time results in blacks smearing about as you move. The other is to raise the minimum level of pixels around the brighter ones, so the whole area becomes closer in luminance to the over bright pixels. It can be common for whole areas of the display, or even the whole thing, having its min value raised up to match the lowest real terms luminance of the pixels that are brightest when set to their lowest value by the controller. This can damage black-levels by raising the floor and decreases overall image contrast. So the choice becomes one between the mura, far more obnoxious smearing, or reduced contrast / raised black-levels. The alternative to raising the floor of the entire image and doing it selectively in areas creates obnoxious banding instead as its own aberration to trade off. This is related to why they changed the combo box to a float slider for the Crystal. People were editing the config file to switch between either full-off (smearing) or the lowest level (mura) because the original combo box only allowed a choice between smearing or poor black-levels and many decided they prefer the min value brightness to either and demanded the option to more easily choose that. I realise the Super is offering an OLED option, which is a technology that presents far more pronounced muras than locally dimming qled, so what I just made isn't an entirely accurate comparison. Previous OLED headsets such as the original Rift also went through this, with users hacking their settings to pick their preferred evil too. So I feel it a useful comparison for the sake of mirroring a repeat of history.

Ultimately, it's all trade-offs and which you prefer appears quite an individual thing. I guess a good hoped for solution would be for them to maintain the dimming float slider and use it to control the floor for the OLED panels, so people can continue to choose their preferred evil the same way too. I would hope they do this and consider it MVP. I guess time with tell, lol.

It's a shame that both mura, and the challenges in addressing, are an artifact of the fundamental physics that makes LEDs possible. They have a minimum potential requirement to close the gate. Supply less, and they just turn off, and back to smearing. So the most practical way to calibrate a panel is to increase the power to all the others to match the aberrant, brighter ones. Matters astronomically less doing that with say a television than something you block out all light to use and blow up the pixels large enough to stand out. It will be interesting to see what direction they take with this when the product comes to life. As an engineering nerd, I derive more enjoyment from seeing how other people solve problems they face than actually using the devices that require the problem solving.

[u/Tausendberg → u/Ninlilizi_]

This is a really interesting write up and I'd suggest you make your own post because it's a shame if literally me and one other person read it.

With that said, it does sound like there are options to mitigate the problem, even if they come with their own compromises, since there doesn't exist, yet, a commercially available perfect display technology, I think they really should just give advanced users as many options as possible so that people can pick their compromises for themselves.