How Images Get Blurred
Whether you scan, shoot, print or develop a photo, a little bit of blur is added at each stage. As a result, nearly all photographs can be sharpened with Focus Magic. This may come as a surprise to many people. The real question is not "can the photo be sharpened?" but rather "how much can the photo be sharpened?". Some photo's can only be sharpened a tiny bit, while others can be sharpened quite significantly.
The most common ways that an image gets blurred are:-
- Camera is Out of Focus
A single pixel expands out to a circle of pixels. The blur is an equal amount in all directions.
- Motion Blur
The camera or subject move while the picture is taken. The blur is only in one direction.
- The Digitizing Process of Digital Cameras
Continuous gradations of color are transformed into points on a regular sampling grid. Detail finer than the sampling frequency get averaged into a single pixel producing a softening effect.
- Developing a Film
When a film is developed a negative is projected onto photographic paper. The equipment can again be out of focus. This is more of an issue for old photographs which were manually developed (and manually focused), but even modern machines add a little bit of blur.
- Scanning an Image
This can add quite a substantial amount of blur especially if a cheap or old scanner is used. Lots of scanners interpolate pixels to give a higher ppi (points per inch) than what they can actually scan. One scanner we have produces very blurry images.
- Printing an Image
Inkjets and color laser printers use dither patterns. Magazines and newspapers, make "half tone" plates where the image is made into millions of tiny dots (see the despeckle filter). It is often beneficial to slightly over-sharpen an image if it is to be printed on one of these media.