# Frequencies that trick the eye

Discussion in 'Physics' started by Thevenin's Planet, Apr 5, 2010.

1. ### Thevenin's Planet Thread Starter Active Member

Nov 14, 2008
183
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Cloudy and drizling rain today

I would like someone to explain the difference between light frequency and
sound frequency? This is an article I would like someone to analyze. It speaks
about frequenncies of light.Also , I am wondering do the analogy televisions would be processing light frequencies or just voltages of light waves? Aude Oliva is a professor or scientist at MIT.She has been doing reseach on Cognition.HTTP://WWW.interestingillusions.com/en/creators/aude-oliva

Last edited: Apr 5, 2010
2. ### jpanhalt AAC Fanatic!

Jan 18, 2008
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833
Which article do you want us to look at? Aude lists a few, only one is from 2009.

Sound is a pressure wave in a medium. Audible sound to me is up to a few KHz (I'm old).

Light is an electromagnetic wave. It is in the terahertz range. Not only is it of a different nature, but it is >10E9 time greater in frequency.

Aude is kinda cute and probably very bright. I suspect she is non-tenured, so she may be moving to a place nearer you soon.

John

3. ### Thevenin's Planet Thread Starter Active Member

Nov 14, 2008
183
1
Hello

I notice you did not read the article to understand what the picture are showing.If you look at the each picture at difference disances the faces become another different image.More as a superimpose image.The Professor/Scientist speaks about low frequences and high frequencies.(For some reason beyound my finite knowlege regarding such things) ,The professor seems to be saying that the human eyes register certain frequencies at different distances. These people have manage to superimpose these different frequencies, that is high and low, on a plane surface.Also, I anticipates that this could be the method that is being use in movies when a character face would transform into another person face.I have seem this result used also by Televisions advertisements.
Terahertz is a very large amount of cycles,so would the lines of the images become lignt or bold imprints accordingly to its frquencies?And you did not give a feedback on the question about the television handling these frquencies in someway; I suggested voltage,asumming this is what the analog television would use.

4. ### jpanhalt AAC Fanatic!

Jan 18, 2008
5,538
833
I did not and still cannot find any scientific "article" associated with the images.

That is a well know effect in visual perception. The description that appears upon clicking on the image is not what I consider an article.

I think you need to read up a bit more about frequencies and be a bit more careful as to how you use the term, particularly as related to light. For example, the frequency of a red light (say 670 nm) is about 4.5E14 Hz (if my math is correct). If that light flashes at 100 Hz, and you use the term "frequency," you need to be clear as to whether you are referring to the fundamental frequency of the light or its flashing. The radio signals that your TV receives are only in the mega- to gigahertz range; nevertheless, they provide information that can be converted to the visual (i.e., light) images you perceive. The light that you perceive is not the radio signal, but rather it is the much higher light frequency. You also need to read about visual perception and the chemical changes that occur in the retina. The visual pigments do in fact respond to light of the correct frequency. The configuration changes are slower than the frequency of light perceived, and the neural impulses to your brain are nowhere near that frequency.

If you want a simple example of another visual phenomenon, consider a rapidly flashing LED. Look straight at it and adjust the frequency of flashing (NOT the frequency of the light) until it just appears to be solid "on." Then observe the light from the corner of your eye. You should notice that it still appears to be flashing. In other words, your perception of flickering is better from the corner of your eye than from straight on. Can you think of any reason for that? Why would that difference be preserved during evolution?

As for your hypothesis about voltage, I have no idea what you mean.

John

5. ### AlexR Well-Known Member

Jan 16, 2008
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The frequencies in this case have nothing to do with the actual frequency of light but rather refer to optical resolution (modulation transfer function) of the image elements. It is measured in line pairs per mm.

6. ### rjenkins AAC Fanatic!

Nov 6, 2005
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I get the impression that the effect uses a combination of sharp, fine detail for one image overlayed with a slightly out-of-focus image.

Close up, you see the detail.

At some distance, the fine detail is too small to see clearly but the out of focus details are spread over such a small visual angle the fuzziness no longer detracts from the other image.

I'm short sighted; without my glasses, the image 'changeover' happens at about 15", with them it's about a yard.

Nov 14, 2008
183
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8. ### Thevenin's Planet Thread Starter Active Member

Nov 14, 2008
183
1
In a magzine called, "Wired", The article stated that low frequencies and high frquencies was used to produce the image (which was on paper). Are there low range and high range within the band?Do the various ranges are hue affiliated ? And lastly,how can such frequencies be measured in order to know what is high or low range ?

9. ### redlight000 Member

Feb 26, 2010
66
2
Hi Thevin planet,

Just asking did you get my Private msg that I sent you?

cheers
redlight000

10. ### Thevenin's Planet Thread Starter Active Member

Nov 14, 2008
183
1
what private message? How do I find that I have private massages.I am not as much knowledgeable about this system as I should be. Ok I discovered it and sent a reply.I guess it was done correctly.

Last edited: Apr 8, 2010
11. ### redlight000 Member

Feb 26, 2010
66
2
Hi,
Yup I did get, cool..
When you first login, look at the very Top right of your screen... and it lists there, if you have any messages.. or not.... and another handy link is the quick Links) on the system menu bar...
HTH
cheers
redlight

12. ### Thevenin's Planet Thread Starter Active Member

Nov 14, 2008
183
1
The modulation transfer function seems to me to be the way the lens is adjusted.That control details from object to the produced image on the lens.Is it safe to consider that lens is the only major controler of these IR frequencies?

13. ### Wendy Moderator

Mar 24, 2008
20,735
2,499
Actually there is no control of the IR frequencies. You are drastically misusing the term, you don't really understand the concepts.

14. ### retched AAC Fanatic!

Dec 5, 2009
5,201
312
Spatial Frequency and the frequency of reflected light are two very different things.

The way the eye combines details in relation to others "tricks" the brain, not really the eye.

I am having a problem understanding EXACTLY what you are trying to figure out.. Could you link to the WIRED article?

15. ### Thevenin's Planet Thread Starter Active Member

Nov 14, 2008
183
1
http://www.wired.com/medtech/health/magazine/17-05/st_Alphageek.
Accordingly to the information I received Modulation Transfer is a the measure of the transfer of contrast or modulationfrom the subject to the image.It is regarded as how faithfully the lens reproduces or (transfers)
details from the object to the image produced by the lens.It seems as though this transfer function has the concepts of transistors or filters transfer function idea.But to continue,if the lens is manipulating the object(s) light rays, the next premise of mine is that its shaping the or bending the rays or light frequencies,IR or the 380 or 400nm to about 760 or 780nm.

16. ### Wendy Moderator

Mar 24, 2008
20,735
2,499
Like I said, it doesn't work that way. You can bend light waves with lenses and prisms, but you don't change frequencies like that. The camera doesn't record wavelengths very well anyhow, especially in the infrared region. When you refer to wavelengths of light, you are referring to color. In the infrared region it doesn't resolve colors, just intensities.

You can move frequencies around with careful designing, florescence is such a case, but it doesn't happen casually, and not in the context you are referring to.

17. ### Thevenin's Planet Thread Starter Active Member

Nov 14, 2008
183
1
The web sit that I had given Retched,but for some reason, when I uploaded, it left out data where the three (...) are located . Go to,"Wired Magazine,Aude Oliva,'Double vision: Parsing Images that trick the brain,".
She is associateing High spatial frquencies as sharp lines and low ones as blurred shapes.Is this relating frequencies with focus?

18. ### Thevenin's Planet Thread Starter Active Member

Nov 14, 2008
183
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This is the problem,how can I achieve this effect?

19. ### retched AAC Fanatic!

Dec 5, 2009
5,201
312
Well mathematically, I don't know. Artistically you can use GIMP or Photoshop and blend two images. using opacity settings, bring the top image barely into sight. Then use Gaussian blur to work with the difference. that will adjust the spatial frequency.

You should try with the same image first. You will start to see when they break plane.

20. ### Thevenin's Planet Thread Starter Active Member

Nov 14, 2008
183
1
That's ah 10-4 good buddy.