| From: Steven | 12/10/99
11:55:48 |
| Subject: Out of focus photo. | post id:
43633 |
| If you had the right corrective
lenses, could you clearly see an out of focus
photo? | |
| From: Dan B. | 12/10/99
12:11:02 |
| Subject: re: Out of focus photo. | post id:
43642 |
| No, it is impossible to sharpen
an off focus print. A lens (glasses) alter the focal point of a sharp
image that would normally be blurred. You can only go one
way. Dan. | |
| From: Andrew | 12/10/99
12:24:13 |
| Subject: re: Out of focus photo. | post id:
43645 |
|
Dan, using a computer you can apply mathematical algorithms which can produce something that looks more in focus (I realise it isn't what you would have got if it had been in focus in the first place). The susccess of this technique depends on the subject matter of the photo and the degree of blurring. Steven, try scanning it and playing with Photoshop or take it to a lab that can do digital processing, they might be able to produce something acceptable. | |
| From: Steven | 12/10/99
12:30:33 |
| Subject: re: Out of focus photo. | post id:
43648 |
| That's a bit hard as it's a
theoretical photo. | |
| From: Dan B. | 12/10/99
13:14:53 |
| Subject: re: Out of focus photo. | post id:
43658 |
| Eve in Photoshop, if you grab a
photo, blur it, then sharpen it, you do not return the image to the
original. It can however be done with time and skill (after-touching) but
the result, as you said, will not be as good as a sharp
original. Dan. | |
| From: Dr. Ed G (Avatar) | 12/10/99
23:50:46 |
| Subject: re: Out of focus photo. | post id:
43840 |
| As soon as you create a 2-D image
from a real 3-D image, you destroy information from the original image. If
we consider only a black and white photograph, there are effectively two
types of information in the light rays that define a real 3-D
image (i) where the light rays are coming from - the "positional information", and (ii) the direction of the light rays - the "angular information". Now, when you form a 2-D image from a 3-D image, you have to destroy some of this information, and in order to get a correctly focused image you have to destroy the angular information. One way you can do this is by passing the rays through a tiny pin-hole, so that the light rays coming from a given point can only go through the pin-hole in the one direction (at the same angle). This is how a pin-hole camera works. Another way of getting a correctly focused 2-D image is by bending the rays with a lens, so that, in a certain plane from the lens, called the image plane, all the rays that left a single point in the image (at different angles) arrive at a single point in the image plane (again at different angles) - forming an image on any film you put in this plane that contains only "positional information". So if I'm talking a picture of a building, all the rays that enter the lens at different angles from a point at the top of the building, will be focused to one point in the image plane (corresponding to the same point at the top of the building in the actual image). Similarly, all the rays that enter the lens at different angles from a point at the bottom of the building, will be focused at a different point in the image plane (corresponding to the same point at the bottom of the building in the actual image). Thus a correctly focused 2-D picture can be formed. Now, at a different distance away from the lens than the image plane there is another plane, called the diffraction plane, that destroys not the "angular information" but all the "positional information" - all the rays that land at a given point in the diffraction plane left the original image at the same angle. So, all the rays that enter the lens from all parts of the image at the same angle will all arrive at a single point, and all the rays that arrive from the image at a different angle will arrive at a different point. [Note: this would all be a lot easier to explain with a picture] So, if you form your image by placing your film in the image plane of your lens, you conserve all the positional information, but lose all the angular information, resulting in a perfectly focused image. However, if you form your image image with your film in the diffraction plane, you will conserve all the angular information, but lose all the position information, resulting in an entirely unfocused image. If you form you image somewhere other than the image plane or the diffraction plane, you will both conserve and lose some fraction of both. So, if you form an image anywhere other than the image plane of your lens you will lose anywhere between some (slightly out of focus) and all (entirely out of focus, in thediffraction plane) of the "positional information" of the image, and this information is totally unretrievable no matter how hard you try, so there is nothing you can do to truly correct the focus of your image. That is for a 2-D image, however. For a hologram, the situation is entirely different. A hologram conserves both the positional, and angular information of an image, which is what allows it to form a 3-D image. If you managed to bungle you laser optics in a way that effectively created an out of focus hologram, it could be possible that you could correct it with the right sort of lens - because in a hologram all the information is still there, whereas in a normal photograph it isn't. Soupie twist, Ed G.  | |