Photo enhancement

What's really there?

Digitally manipulated images surround us. On television, faces in a razor blade commercial morph into one another. In newspapers and magazines, the photographs of long-missing fugitives are aged to show us what they might look like today. And in the movies, some actors find themselves in scenes with dead presidents while others are hunted down by carnivorous dinosaurs. As with many things, the increasing power of the computer has turned the amazing into the commonplace. What is not commonplace, however, is an understanding of how these advances can be used to solve more prosaic problems.

Taking measurements from videotaped objects; reading a sign or a label in a dark corner of a photograph; finding scratches, bends, chips, and paint marks to match up actual objects with those shown in photographs--these are the sorts of "image processing" chores that come up on a daily basis when investigating and reconstructing accidents. And while they can be performed using rulers and traditional darkroom techniques, they can be done with greater speed and accuracy when done digitally.

Many photographs contain information that is obscured in light or dark areas. For example, the left photograph below presents a typical problem. The photographer, knowing that the size of the part would be of some importance, has put a ruler in the scene. Unfortunately, much of the ruler and bolt are obscured in the washer's shadow.

If the negative is available, you might be able to reprint the photograph lighter to see more detail in the shadow. Of course, that might also make other parts of the image so light that their detail is lost. Then a more sophisticated darkroom technique called "dodging and burning" would be needed. There's a fair amount of trial and error involved in these procedures, and they all take time--even when the people involved are skilled. If the negative is not available, the process described above must be preceded by taking a photograph of the print.

To accomplish the same thing digitally, you simply scan the photograph (either a negative or a print will do, although you generally get better results with a negative) into your computer, select the dark areas of the image, and adjust the brightness and contrast of the ruler and bolt until you get what you want. A skilled operator can do the whole thing in very short order. The results are shown in the right photograph above. In addition to bringing out detail in the ruler, the enhancement has revealed thread damage, shown between the added red arrows.

To be sure, there can be just as much trial and error in the digital procedure as in the traditional one. But on a computer, each trial takes seconds rather than minutes, and the whole process is greatly compressed.

Is a digitally manipulated image still an accurate representation of the photographed object? If the purpose of the manipulation is to reveal information that is contained in the original photograph, and if the new image is presented to its audience as an enhancement rather than as an original, then there is no misrepresentation.

If you have any questions regarding image manipulation or photo enhancement, feel free to call Unified Engineering and ask for David Dix or Mark Lawrence. We'll be happy to help.