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I've recently found the following image:

enter image description here

I can easily see the "17" in the image if I'm scrolling and (much less easy) when I move my eyes and don't look directly on it. Why is that the case?

In case you don't see it:

enter image description here

Martin Thoma
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    As an aside, I can see the 17 clearly when I (a) zoom out to make the image smaller, or (b) move my eyes away from the image. – Jeromy Anglim Nov 28 '16 at 05:30
  • Intersting! When I step away from my monitor, I can see it MUCH clearer! – Martin Thoma Nov 28 '16 at 06:14
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    In this case I suppose it is simply because the stripes are extremely high contrast which simply kicks out every other information from picture. So if you apply dithering (or move image) or defocus the eye, you reduce this contrast, and the number is better seen. – Mikhail V Nov 28 '16 at 08:59
  • @Mikhail: so if this is true, making the black stripes white avoid make the 17 clearly visible, right? – Martin Thoma Nov 28 '16 at 09:05
  • @MartinThoma Not quite understood your formulating, but removing the black stripes of course will make 17 clearly seen. So it is opposite to your statement, or? – Mikhail V Nov 28 '16 at 09:11
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    Sorry, that was autocorrect. "Avoid" should be "should" – Martin Thoma Nov 28 '16 at 09:15
  • Also as an aside, I can see it extremely clearly and easily on my phone, but hardly, if at all, on my computer – Ebbinghaus Nov 30 '16 at 06:23
  • @MikhailV Seems you are right: http://imgur.com/a/vxVaf (although it is not completely clear to see, it is certainly much easier) - do you want to make it an answer? – Martin Thoma Nov 30 '16 at 07:48
  • @MartinThoma it is true that I can filter out the number with Photoshop, it would not however tell exactly why is it easier to see when you move the image, so there must be something more fancy to explain it, but probably I'll try sometime ;) – Mikhail V Nov 30 '16 at 09:44

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You can see the number better when you move the image or your eyes, because with this action you reduce the overall contrast of the image. The "image" in brain is a composition of many images which are acquired in small time periods, and the result can be approximately described as an average of many still images. So they are kind of blurred together. When scrolling it can also help to reduce contrast, because in short time periods the LCD pixels cannot reach the full contrast, so it appears in lowered contrast.

The contrast of stripes in your initial image is very high. Actually contrast is the synonym for information. So the underlying number 17 is simply lost in dominant information.

To demonstrate it better, one can play with different image filters which can reproduce the movement effect. A good one is Photoshop's "Motion blur" filter, here is the result for Motion blur at 45 degrees:

enter image description here

Mikhail V
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