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or even better, is there software available which can do it?
–new detail
to people that is saying that it’s impossible, I remember that at college, staring into the projector, the analogic focus could be changed so I could se a clear image without the glasses.
Sadly, no. The problem with myopia is that the light coming into the eye is not focused correctly upon the retina. No matter what you do to an image, that image will come in unfocused. Unfocusing the image in any way will just mean that the viewer will have a blurrier image of a blurry object.
The crazy part of this answer: this could be possible if you had a monitor that, for each pixel, could potentially shine at different intensities/colors at different emission angles. If you had that setup, and had an image that supported it, and you knew the exact amount to adjust by, and could get the person to sit in exactly the right spot, you could potentially adjust it to be focused. However, this is more of a conceptual pipe dream than feasible reality.
EDIT: Tom asked me to respond to this:
I’ll assume that you had either an overhead/film/lcd projector or something similar…I’m guessing it doesn’t make a difference. They have manual focus features that can be used to bring the image in or out of focus…this is used to allow the image to focus correctly at different wall/screen distances. I’m not sure exactly what you mean by “stirring in the projector”…but I’m going to assume you mean “staring into the projector”.
I haven’t tried this (and since I don’t need glasses, I can’t), but I suspect that this would work. But what you’re doing is essentially the same thing as wearing glasses…you’re looking at an image, and adjusting the focus to compensate for your myopia. The lens is inside the machine rather than in a pair of frames on your face, but the concept is otherwise very similar.
However, it doesn’t mean that you can take an image on a screen and blur it and have it render correctly.
Without a diagram, it’s difficult to explain why, but a simplified explanation about why they’re not identical cases could be made like this…in the case of the projector/glasses, you’re starting with a perfect image that isn’t being focused correctly by a set of lenses, and then adjusting the lenses (adding glasses or changing focus on the projector) to correctly bring it into focus…and this is the critical part: you are not degrading the image in any way. You’re just using refraction to change the angles at which the light is traveling.
On the other hand, if you have an image on a monitor, and you blur it in some way, you are changing and degrading the image itself. No matter how good the receptor viewing it is, the best it can do is the blurred image that is being displayed.
Okay, that’s not satisfying probably, so I’m going to try to make a few pictures:
P will be our source point. It emits photons from it in every direction. Some of these photons go into our eye. If our eye is perfect, the lens focuses all of those rays onto a single point on the retina.
For simplicity, I’ve drawn only three photons being emitted from the source point, but in reality there would be a large number of them, at many different angles. The point is that all of them should be focused by the lens onto a single spot on the retina.
But in a myopic eye, the focal point is before the retina, and so the rays cross over and do not hit at the same point on the retina.
This is what causes blurring by myopia…each source point is seen a tiny bit in a few spots, rather than exactly one.
This also shows how glasses and staring into a projector can help…we’re adding a second lens into the mix to compensate slightly for the not-perfect one. (Image slightly expanded)
Notice the path of the light bends outwards slightly by the glasses…this is how they compensate for the lens in your eye.
Now is there anything can can be done by blurring the original image to compensate for this? Unfortunately, no. If we try to do this, we end up with something like this, with the source point now blurred into two locations that we’ll call Q and R. If things work perfectly the blurred P (now Q and R) should reconstitute themselves correctly back into P:
(I’m expanding the picture a bit for clarity…though it’s still not great.)
First, we’ll look at an ideal eye:
We get exactly what we expect from the ideal eye…a perfect replica of the original (blurred) image. (It’s reversed, but that’s okay; the focusing of the eye always does that…the brain flips it around so it looks correct.)
So what happens when we try the blurred image with the myopic eye?
As you can see, our image has just gotten worse. Instead of recombining Q and R back into P, it’s blurred them even more. We’ve taken a blurry image, and just made it more blurry.
I know the pictures aren’t great, but I hope this makes things a bit clearer (no pun intended.)
Another Edit:
Just as an aside, because I’m sure this will be brought up…the majority of the focusing power of the eye is not actually done by the “lens” of the eye, but rather by the cornea…or more specifically, light passing through the aqueous humor contained by the cornea. This is why laser surgery that reshapes the cornea can be used to correct eye focus problems. However, since “lens” is more familiar and makes semantic sense here, I’m sticking with that.