Deconvolution vs. Smart Sharpen
In the past, Smart Sharpen (previously known as 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 Smart Sharpen (or Sharpen) included, and there are even some dedicated Smart Sharpen programs.
The mathematics is quite simple (see How Smart Sharpen Works), and it runs quite fast. Focus Magic however doesn’t use the Smart Sharpen 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 Smart Sharpen 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.
Testing Method
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 Smart Sharpen Radius. The Amount is in all cases set to 100%. For Smart Sharpen, 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 Smart Sharpen settings if you want to.
Example 1 - Slightly Blurred Image
This image of an old historic building is only a little bit blurred. Smart Sharpen 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
This image of a fridge magnet was firstly taken “out of focus” and then “in focus” with a Fuji digital camera. The photos 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. Smart Sharpen 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 sharpened a lot better than real world images.
Example 3 - Very Blurred Image
This image which shows part of a man’s face has a blur width of about 20 pixels. 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 Smart Sharpen, 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 would expect.
