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Comment by pygy_ | Hacker News Reader

Could someone explain why this image is flickering on my MacBook Air screen?

http://thume.ca/assets/postassets/doubleVision/out.png

Especially "ze first" image as seen in FF and Chrome.

I suppose it is related to how monitors use temporal dithering to fake 24 bit colors when they really have 18 bits per pixel, but why is it more apparent on this kind of picture?

Is it a perceptual issue or a technical one?

It is also apparent when using Windows XP under virtualization. Some windows have checkerboard patterns that flicker.

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Here's a page with a test and a potential explanation http://www.lagom.nl/lcd-test/inversion.php

More detailed explanations:

http://www.mvkonnik.info/2009/04/brief-note-about-lcd-displa...

http://www.solomon-systech.com/files/ck/files/Application%20...

tl;dr: the liquid crystals in LCDs need to be driven with AC voltage to prevent electrolysis degradation. This is known as "inversion" and there are different patterns used. If the magnitude of the + voltage is different from the - voltage, i.e. the "common" voltage Vcom is not exactly in the middle, the subpixels change brightness slightly on each cycle and this causes flicker. The flickering becomes much more noticeable if the pattern displayed in the image matches the inversion pattern.

Neither of my (nearly 10 years old now... but still working well) LCD monitors flicker on all the images, so this is something that shouldn't be occurring on a good monitor. I suppose manufacturers now are relaxing the tolerances to save cost, justifying it by the fact that flickering is not observable on "most" (debatable) content.

Yah this happens because the image is based on a grid. You can see it on any monitor if you open it up in an image viewer and zoom in an out.

As another commenter mentioned these effects are called Moiré patterns: https://en.wikipedia.org/wiki/Moir%C3%A9_pattern

They may be more or less apparent depending on the scaling on the image and the scaling algorithm being applied. Some scaling algorithms apply filters that can make the effect even more weird than normal.

It's not Moiré. If it's displayed 1:1 as the image is designed to be, there won't be any, and even if it isn't and the patterns appear, those patterns shouldn't flicker on a properly adjusted monitor.

I expect this is due to a Moiré pattern between your monitor's pixel grid and the "dots" in the image.

Thanks everyone for the details. I don't think it's a moire pattern because the image is displayed at native resolution. So it is a low level calibration issue. Disappointing to see this on a Mac.

I've wondered if it's a DisplayPort bandwidth thing.

Also happening in Firefox on Arch Linux.

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