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In computers science, the main idea behind blurring a photo is to set the RGB value of every pixel to the average of all the values of its neighbours.

For more details on what I mean by "blur":

Basic Concept
More in detail

I'm wondering if there is a mathematical relation between eye power and blurriness in pixels - this is because I am trying to create a web app where users can in real time experience the vision of a myopic eye

I'm sorry if this is the wrong stack exchange site, just direct me to the right one! and also feel free to add the right tags cuz this site is new for me and I have a tough time deciding tags.

Thanks!

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CSS filter function This is what I'm going to be using and it says something about Gaussian that I don't really understand. Would be great if you can explain and not just throw an equation in the answer section thanks

Tilak Madichetti
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    Please make clear what you do not understand so we can address it in answers. I'll throw an equation in: $1+1=2$. Myopic eyes are caused by the focal length of the lens not matching the distance to the retina. Given the focal length and actual distance, you can compute the circle of confusion, the size of the circle on the retina that a point at a given distance creates. It sounds like you need to understand more about vision before you worry about the details of a blurring algorithm. – Ross Millikan Jul 04 '20 at 15:16
  • @RossMillikan okay so i mean if someone has an eye power of -2.75 then they basically see everything blurred right ? I need to know what is the radius of distortion from the clear image that such a person experiences. – Tilak Madichetti Jul 04 '20 at 15:40
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    When you say they need a -2.75 diopter lens that means their eye has too strong a lens. When it tries to focus at infinity it it really focused at $\frac 1{2.75}$ meters. It can focus somewhat closer than this, for a young person probably +4 more diopters so without glasses they can see clearly from $\frac 1{6.75}$ meters to $\frac 1{2.75}$. The lens makes this $\frac 14$ to infinity. If you find the typical dimensions of an eye you can find what the focal length should be and what it is. The blur circle will be that error in distance times the f/ number of the eye. – Ross Millikan Jul 04 '20 at 15:48

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One idea would be to take your input as visual acuity, the numbers like $20/20$ that come from a test. You could look up the size of the characters in the $20/20$ line. I would estimate that it takes about eight vertical pixels to resolve the letters, which gives you the angular size of the blur circle in a standard eye. Somebody who tests at $20/40$ needs the letters twice as large, so their blur circle is twice as large. I don't know if there is a standard conversion between lens power and acuity. It clearly depends on how bright the light is, because with brighter light the pupil will narrow and the blur circle will get smaller as the lens is operating at a smaller aperture.

Ross Millikan
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