Dotted Overlay Creates Monitor Flicker

Question

There was a recent question discussing dotted overlays/dithering patterns on images, and I wanted to explore the method. I set it up so it was one black pixel, one blank, one black, etc. After duplicating it to cover the page, I found that it created what I can best describe as monitor flicker, or maybe banding? Something's happening on my screen. Here's a screenshot; see if it does the same to you!

What causes this, and how can I minimize it? I found that using other colors helped, but I'd much rather understand why than pick colors and hope it works. I know that monitors are very different from each other, so I'd like to know that if I get it right on my screen, it'll be right on other screens.

Answer 1

Try adjusting the dot—gap ratio to 1:1.5+ so that the dots and gaps are not the same size. I believe it's has to do with screen drawing/movement and moire/strobe effect.

Try the gap thing. You may need to make it 1:1.75 or even 2 to make it not flicker. Also, if you have not, define a pattern and fill, that will make testing faster. Thinking about it, if it's 1 pixel dot and a 1 pixel offset, then you may need to have at least 1:2 ratio.

As one set of dots cover and the other set (of equal size/distance) uncover the strobing effect is produced, this becomes apparent as you start to scroll and the computer de-draws the graphic, hence the larger gap between pixels. You might be able to enlarge the dot and spacing to 2 or 3 pixels, but may still face the flickering. Cheers and good luck!

Note: if you zoom into the page and scroll you'll notice that the flickering doesn't happen... it's one of the issues of using a 1 pixel screen (pattern).