Pixel Inversion

Pixel inversion is the process of alternating the polarity of the electrical current of the pixels in LCD screens, similar to how alternating current works in your home's electrical wiring. If you're curious about what's happening at the microscopic level, here's a zoomed-in, slow motion video showing the flicker from pixel inversion.

Pixels fluctuate in brightness when the polarity of the electrical current is reversed. If all pixels changed from negative to positive polarity at the same time, the flickering would be noticeable. So LCD/LED screens use a pattern where half the pixels switch from negative to positive and the other half switch from positive to negative. The pixel inversion tests on this site block out half the pixels in the pattern in order to make the flickering visible.

Why do we need another pixel inversion test?

This is a necessary modernization of the work done by Lagom and Techmind. This test covers everything in those two tests, plus:

  1. Support for modern screens where you cannot set the screen to its true native resolution. It accomplishes this by zooming the image to match the actual resolution.
  2. Support for more layouts (Lagom does not have the vertical line layouts and Techmind does not have vertical line or 4x2 layouts).
  3. Support for more colors (screens vary regarding which colors will produce flicker).
  4. Usability enhancements.
This is not a criticism of Lagom or Techmind; this site would not be possible without the work they did. But the tests on this site are more comprehensive and will produce more accurate results.

Why I care

My interest in pixel inversion is in its potential to cause headaches. Viewing flickering screens caused by pixel inversion will give me a splitting headache. That said, these are extreme examples and are not necessarily representative of what happens with everyday use. I am highly sensitive to screen backlights that use Pulse Width Modulation (PWM) and I avoid screens with PWM. But there are screens without PWM that still cause headaches for me, and my goal is to determine whether pixel inversion is at least partly to blame.

My goal for this site is to prove (or disprove) two things:

  1. The flickering from pixel inversion can cause headaches in everyday use, not just in these extreme examples.
  2. Some screens are less likely than others to cause headaches. This could be due to any number of reasons. Perhaps some LCD screens:
    • have pixel inversion layouts that are not likely to be encountered in everyday use
    • flicker in a way that is less headache-inducing
    • don't have any flicker caused by pixel inversion
If we can prove these two things, then these tests could be used as a way to find screens that don't cause headaches. I say "we" because I don't have all the answers. I've very intentionally put upvote/downvote buttons on each image so we can crowdsource the images that flicker the most. And I've very intentionally put a discussion section at the bottom. I welcome your comments, questions, criticisms and findings.

My findings

My findings thus far are promising but not conclusive. I've tested about a dozen screens, but only five that don't have PWM and that I have extensive experience with.

Screens that I can use without headaches

  1. Asus VW228: has very little flickering, which is uncommon. This finding supports my hypothesis.
  2. Dell 5567 laptop #1: has typical flickering. Brighter green pixels (such as #009F00 and #9F9F9F) flicker with a 4x2 pattern. This finding does not support my hypothesis unless the condition for brighter green pixels in a 4x2 pattern doesn't happen frequently during normal use.

Screens that immediately give me headaches

  1. Dell 5567 laptop #2: has strong flickering. Green, red and blue pixels with a wide range of brightness flicker with a 2x4 pattern. This finding supports my hypothesis.
  2. Benq GW2780: has strong flickering. Green and red pixels with a wide range of brightness flicker with a 2x4 pattern. This finding supports my hypothesis.

Screens that give me headaches if I use them long enough

  1. ViewSonic VX3276: has typical flickering. Fully bright green pixels (such as #00FF00 and #FFFFFF) flicker with a 2x2 pattern. This finding supports my hypothesis.


Copyright 2003 Greg Atkinson