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I wonder, why black-white pixels pattern as seen on this page http://www.lagom.nl/lcd-test/clock_phase.php is displayed wrongly by UHD LCDs (on all i tried). Please note, that it must be displayed 1:1 (no browser / windows zooming).

On some monitors, that pattern is immediately seen as very green, usually on top it's most green, in lower parts there is not so much green. On some it's not so obvious, but to spot it, it's e.g. enough to lower contract from 75-80 to e.g. 50-60.

Even more, if pattern is present on screen more time, with certain offset, then screen becomes purple. See this foto, it's from lenovo y32p-30 display: https://rt.sk/~jmi/uhd_issue/lenovo_foto.jpg

This is the screenshot, so you can try yourself: https://rt.sk/~jmi/uhd_issue/lenovo.png (view 1:1 with no scaling)

On dell S2722qc it's same issue (better visible if contrast is lowered to 50-60) with green and purple.

Video demonstration: https://rt.sk/~jmi/uhd_issue/PXL_20231226_221917539.TS.mp4

Important: when i open OSD menu, then on lines where OSD is located are less green than without OSD. Hence visible "border line" between two areas appears, where y-possition is top and bottom of OSD menu. See photos for better understanding: https://rt.sk/~jmi/uhd_issue/PXL_20231226_222856271.MP.jpg https://rt.sk/~jmi/uhd_issue/PXL_20231227_111708420.MP.jpg

What is reason of such behavior?

Now i'm testing asus proart PA279CRV. Here things are little different. From dell xps over both hdmi and usbc pattern was greenish as usually. But on desktop PC it's greenish only for fraction of second and then it corrects itself. Why does it fix itself?

And i spotted new problem, e.g. when having dark bookmark tab on side and switch back to tab such pattern, for fraction of second a bookmark tab contains lots of lines accross. While experimenting more, i found also cases, when problem is persistent (not just flicker) and is best visible on artificial image (again must be observed without any zooming/scaling): https://rt.sk/~jmi/uhd_issue/asus_issue_1.png

Result is similar on asus and dell S2722QC (don't have lenovo anymore and any other to test more): https://rt.sk/~jmi/uhd_issue/PXL_20240110_112757340.MP.jpg zoomed links will be posted to comment as i cannot use more links as newbe user.

Can someone explain this? Is it caused by my PC (input signal quality) or by monitor? Is it common issue, or was i just unlucky on selecting affected monitor models?

I tried several UHD monitors, combined with several PCs connected over different cables (HDMI/DP/usbC). Issue with greenish picture was present in all combinations. Doesn't matter if pattern is displayed from browser or image viewer.

Note: some monitors allow to not use full signal range (0-255), but only e.g. 16-254 or 16-235. Make sure to use full range, as in my tests, some of them "worked" fine if full range was not used.

thank you

best regards

saliem12

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Monitors are made up of red green and blue components those components have different visibility from different angles and distances. This can effect how we perceive the image on the monitor.

This can can be seen in the linked images as the color shifts from green at the edges towards gray in the center. You can get virtually any monitor to exhibit this behavior. Camera's make the issue even more apparent, especially if the image is taken at an angle.

Why green? Our eyes are more sensitive to colors at around 550nm in day light which we perceive as green. Our eye's are also sensitive to blue's (450nm) blue+green is purple. Finally our eye's are least sensitive to red, around 700nm.

So if you cover an entire screen with a gray color that sets all the red,blue, and green components to the same brightness small shifts in brightness resulting from viewing angle of those components will cause us to perceive the color differently, and the most likely colors we will see are greens followed by blues. Which gives the effect listed in the question.

On both of my monitors when viewed straight on with the monitors at eye level the images look like I expect. But if I change my viewing angle just by moving my seated position I can get them to shift towards green, although on both of my monitors the effect is much less pronounced then in the linked images.

I should add the hardware plays a role here, and small difference in brightness caused by the technical details of how a monitor works also cause some of this effect.

This exemplifies how setting up monitors correctly effects viewing.

Finally, I find myself wondering what my cat see's when viewing this effect.

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