<p>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.  </p>

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

<p>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:   </p>

<p><a href="https://i.sstatic.net/GWM1j.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/GWM1j.jpg" alt="enter image description here"></a></p>

CC BY-SA 3.0
2016-12-01T22:54:58.883Z
Why does moving the image reduce the images contrast?
Martin Thoma
CC BY-SA 3.0
2016-12-01T23:30:52.523Z
@MartinThoma added some more info
Mikhail V
CC BY-SA 3.0
2016-12-01T22:29:34.083Z
2016-12-01T23:30:14.690Z
2016-12-01T23:30:14.690Z
Mikhail V
<p>I've recently found the following image:</p>

<p><a href="https://i.sstatic.net/eZpKy.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/eZpKy.png" alt="enter image description here"></a></p>

<p>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?</p>

<p>In case you don't see it:</p>

<p><a href="https://i.sstatic.net/Skz1m.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/Skz1m.png" alt="enter image description here"></a></p>

CC BY-SA 3.0
2016-11-28T05:30:35.160Z
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
CC BY-SA 3.0
2016-11-28T06:14:15.093Z
Intersting! When I step away from my monitor, I can see it MUCH clearer!
Martin Thoma
CC BY-SA 3.0
2016-11-28T08:59:15.687Z
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
CC BY-SA 3.0
2016-11-28T09:05:53.290Z
@Mikhail: so if this is true, making the black stripes white avoid make the 17 clearly visible, right?
Martin Thoma
CC BY-SA 3.0
2016-11-28T09:11:40.347Z
@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
CC BY-SA 3.0
2016-11-28T09:15:25.087Z
Sorry, that was autocorrect. "Avoid" should be "should"
Martin Thoma
CC BY-SA 3.0
2016-11-30T06:23:11.713Z
Also as an aside, I can see it extremely clearly and easily on my phone, but hardly, if at all, on my computer
Ebbinghaus
CC BY-SA 3.0
2016-11-30T07:48:18.857Z
@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
CC BY-SA 3.0
2016-11-30T09:44:39.637Z
@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
<optical-illusion>
Why can I see the number only when I don't look directly at it?
Martin Thoma
# Why can I see the number only when I don't look directly at it?

(Asked by: username_0 on 2016-11-27)

I've recently found the following image:

[![enter image description here](https://i.sstatic.net/eZpKy.png)](https://i.sstatic.net/eZpKy.png)

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](https://i.sstatic.net/Skz1m.png)](https://i.sstatic.net/Skz1m.png)

**Tags:** optical-illusion

> **Comments:**
> **username_1**: 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.  
> **username_0**: Intersting! When I step away from my monitor, I can see it MUCH clearer!  
> **username_2**: 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.  
> **username_0**: @Mikhail: so if this is true, making the black stripes white avoid make the 17 clearly visible, right?  
> **username_2**: @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?  
> **username_0**: Sorry, that was autocorrect. "Avoid" should be "should"  
> **username_3**: Also as an aside, I can see it extremely clearly and easily on my phone, but hardly, if at all, on my computer  
> **username_0**: @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?  
> **username_2**: @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 ;)  

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## 1 answers

### Answer by username_2 on 2016-12-01. Score: 1

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](https://i.sstatic.net/GWM1j.jpg)](https://i.sstatic.net/GWM1j.jpg)

> **Comments:**
> **username_0**: Why does moving the image reduce the images contrast?  
> **username_2**: @MartinThoma added some more info  

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