Deconvolution Vs. Unsharp Mask
In the past, Unsharp Mask was seen as the best way to sharpen photographs which were a little blurred. It increases the contrast of the edges of an image to make it look sharper. There are many programs which have Unsharp Mask (or Sharpen) included, and there are even some dedicated Unsharp Mask programs. The mathematics is quite simple (see How Unsharp Mask Works), and it runs quite fast. Focus Magic however doesn't use the Unsharp Mask principle to sharpen an image. It uses advanced deconvolution to reverse the way in which the image got out of focus to restore the original "in focus" image as much as possible. On this page we compare Unsharp Mask with Deconvolution (as implemented in Focus Magic) for various degrees of blur, starting with a slightly blurred image and finishing with a very blurred image.
The blur width parameter in Focus Magic is equivalent to the diameter of a circle and is in each of the following examples set to twice the Unsharp Mask Radius. The Amount is in all cases set to 100%. For Unsharp Mask the Threshold is set to zero. For Focus Magic the Noise Reduction is set to Auto and the Image Source is set to "Conventional Camera" (except for example 2 which was taken with a digital camera). Feel free to experiment with different Unsharp Mask settings if you want to.
Example 1 - Slightly Blurred Image
This image of an old historic building is only a little bit blurred. Unsharp Mask makes the image grainy and doesn't sharpen the brickwork silhouetted against the clouds very well. Focus Magic sharpens the brickwork a lot better and doesn't make the image grainy.
Example 2 - Fairly Blurred Image
(taken again in focus)
This image of a fridge magnet was taken firstly "out of focus" and then "in focus" with a Fuji digital camera. The photo's were taken with the camera on a tripod, and only the focus setting was changed between the two shots. Although Focus Magic could not restore the image completely back to what it should have been, it did take it back a long way. Unsharp Mask made the image grainy, didn't sharpen the image much (or at all), didn't recover any of the detail in the eye and has a more severe "halo" effect.
With the naked eye we would not have been able to see from the original that the eye consisted of a black dot on a white background. It looks more like some kind of a plastic bobble. Focus Magic is able to restore the eye mostly back to what it should have been. The ability to recover detail that is not normally visible makes Focus Magic invaluable for forensic scientists.
There is unfortunately a limit to how much Focus Magic can restore detail. The limiting factor in restoring an image is not in the power of the focusing algorithm used by Focus Magic, but it is in the quality (or accuracy) of the input image. Under laboratory conditions, images which are de-focused with software, saved as 48 bit images, and then re-focused can be re-focused a lot better than real world images.
Example 3 - Very Blurred Image
This image which shows part of a mans face has a blur width of about 20. When an image gets out of focus, point sources of light (from small shiny objects) become circles. With Focus Magic the circles become smaller concentrations of light, which is what you would expect when sharpening an image. With Unsharp Mask the circles stay the same size and get brighter which is not correct for sharpening an image. The iris in his eye now has well defined edges and has the circular shape we expect.