What do I need to know and do to restore damaged photos -- Part Three

In thinking about my last post, I realized that I had mentioned that all digital editing is destructive. That issue needs to be explained further especially to anyone involved in restoring scanned
images of old photographs.

Before taking even the first step in restoring old photos, you should understand what happens when an image is scanned or otherwise digitized. The
digitization process involves creating a numerical representation of the
information contained in the original photograph. In both photographic
and digitized images a major concern is the clarity or resolution of the
image. In photographs, the discrete grains of the photographic
chemicals are so small that absent microscopic examination, the grains
are not usually visible to the unaided eye. However, if a photograph is
is greatly enlarged, you can often detect a graininess to the image. The
resolution of the image depends not only on the ultimate size of the
film grains but also on the camera and lens system. You cannot get high
resolution images out of a bad lens. The measure of resolution in a
photograph and of a camera lens is measured in terms of the how closely
printed black parallel lines can be resolved. The number of lines per
inch (or other measure) is called the image's spatial resolution. There are standard resolution test
documents that determine the actual physical resolution of a camera
system and of a photograph produced by the camera and lens combination.
One of those is the 1951
U.S. Air Force resolution test target. Various other systems of
testing the resolution of camera lenses have also been developed, click
here for another type of chart.
Read more...