36

Below is the new Sonos logo.

When you scroll up and down with the image on screen, it looks like sound waves are pulsing outward.

What causes this effect to occur?

enter image description here

  • For way too much information, check out Nyquist-Shannon Sampling aka the Shannon frequency: to reproduce a signal one needs to have about 1.5-2x the samples of the frequency. This is the reason why digital audio is approx. 44kHz (human hearing has about 22Khz bandwidth) and images for print are 300dpi (150 line screen). The "second grid" overlaid on the image (as spoken of below) is the "sampler" in this case, and the grids are too similar in scale. – Yorik Feb 19 '15 at 15:25
33

It's called a Moiré pattern.

It forms when two 'grid' patterns (loose term that could apply to geometric lines, dots, etc.) are overlaid with each other and moved.

In this case, the two 'grid patterns' are the image, itself (which is geometric lines) and the pixel based screen-refresh of your screen.

A similar effect is when newscasters would wear tightly striped patterns on TV: https://www.youtube.com/watch?v=jXEgnRWRJfg

  • 2
    And it's strongly tied to certain resolutions. Zooming in on that image on my iPad, the effect rapidly diminishes and then disappears. – usr2564301 Feb 17 '15 at 21:09
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    This effect is also known as "OW OW OW MY EYES DAMMIT MAKE IT STOP," although that's industry jargon. – Lauren Ipsum Feb 17 '15 at 21:10
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    @Jongware Unfortunately I can't reproduce your results. Even when zoomed in further than screen filling it won't lose it's effect. It would make a good follow-up question. – Mast Feb 18 '15 at 2:48
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    (singing) When the lines on the screen make more lines in-between, that's a Moiré... – Jeff Bowman Feb 18 '15 at 23:32
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    @JeffBowman well played, sir, well played. – DA01 Feb 19 '15 at 0:38
23

Moiré of the pattern overlaying itself

The pattern of the logo creates a surprising visual appearence of motion when it is shown on an LCD* and the view is scrolled by small fractions of the pattern size.

The effect seen when scrolling the image up and down is a Moiré pattern.
This kind of pattern appears when two regular line patterns overlay.
The two patterns, in this case, are both from the same image:

It's the current screen image over the afterimage of the previous screen state in the brain of the viewer.

The pattern in the logo image is called "Siemens star":

Siemens star cropped

(From forum.luminous-landscape.com)

Now, let's see how it looks when adding a 50% transparent layer with the same image, and shifting it down by some pixels:

Shifted down by 3 pixels:

Shifted down by 3 pixels

Shifted down by 10 pixels:

Shifted down by 10 pixels


Why pulsating?

Notice how the moire pattern has a different size - it gets larger for more offset. This explains the pulsating effect you can see while scrolling: The scrolling is not using equal steps, so the offset varies a little.


* The effect does not depend on using an LCD. It should occurr very similar on any display based on a physical pixel matrix. On CRT displays, the effect may be harder to observe. One reason is that the artifacts of the CRT display concept are such that they may interfere easily here. Also, an important difference between CRT and LCD is that a CRT represents a pixel usually a little too unsharp, compared to an ideal image, while an LCD typically shows pixels too sharp (!) - sharper than they should ideally be. As the Siemens star pattern is making explicit use of the upper limits of the display resolution, the difference has a strong influence.

  • It may be worth noting that different monitors and refresh rates may cause the effect to be more or less pronounced. On CRT screens where scrolling is synchronized to the refresh rate, the effect may be mild or even non-existent compared with many LCD screens. – supercat Feb 19 '15 at 0:21
  • @supercat Right - I somehow assumed LCD without stating it; On a CRT, "tearing" could cause one part of the pulsation-"pulse" to be smaler or larger. Interlacing would have a pretty strong effect, I guess. – Volker Siegel Feb 19 '15 at 2:36
  • On a CRT, visual artifacts from the top-bottom scanning will only be an issue if objects move a substantial portion of the screen size per frame. Interlacing will be an issue unless the number of pixels moved vertically per frame is a consistent multiple of four (i.e. two pixels per field). I wish high-refresh-rate LCD monitors would add an option to alternate visible and black frames; it would cut the maximum brightness in half, but frame-synchronized motion may look better showing image for 1/120 sec and black for 1/120 than showing images for 1/60sec each. – supercat Feb 19 '15 at 3:36
3

The moire effect and similar visual effects are a, likely big, part of the story. However, with LCDs you have an extra twist that depends on the LCD model:

The reponse time (time for a pixel to change state to what is needed) depends on the grey levels (begin and end).

http://www.lagom.nl/lcd-test/response_time.php#response_time_gif

The lines, especially thin ones, present a multitude of greylevels to the monitor and they are not distributed evenly, thus adding actual physical shifts to the ones perceived anyway. Use the test obove as an indicator how much your LCD falls victim to this effect.

1

The Moiré pattern is part of the cause, but another factor (since it's more noticeable when you scroll) is the refresh rate of the screen, and the fact that not all lines update at once. It usually updates line by line horizontally, and this distortion combined with the Moiré makes the pulsating effect.

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    The refresh rate is actually what causes the moire pattern. It's acting as the second 'grid' overlay. – DA01 Feb 18 '15 at 5:05

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