Global Quality Services, Inc.

The Science of Scanning

High-Resolution film scanning is a science. It is a critical step in the creation of a highly accurate digital mapping product. Any problems introduce in this phase are the most costly to repair as they are carried through the entire process and are possibly enhanced during the production of the final product. In the past the main concern was the accuracy of the digital scan, now however, the concerns have grown to encompass both the graphic quality and the metric quality of the imagery. This puts even more pressure on the production of a quality scan before introduction into the orthophoto or other follow-on processes. Many companies have spent thousands of dollars correcting a radiometric error introduced during scanning; the prevention of these types of problems and the production of quality imagery is the science of scanning.

The most vital thing to know about converting film to digital imagery is that if data is lost during scanning then no amount of post processing will bring that data back. This includes over-saturation, where building roofs and beaches are pure white, and under-saturation, where shadow detail is close to black. Previously, the imagery detail was considered to be sacred by photogrammetrists, but the demand in the industry for prettier pictures in a mapping product has made imagery detail take a second seat. The only way to do both is to always work with the most image information possible and only introduce the finishing touches to the final product. Starting with a good scan this process is not as hard as it sounds.

The following information is presented to show what goes into getting what is seen from a plane to what is seen on the computer monitor. There are issues and problems at each step that can cause the imagery to look less than perfect. We will briefly discuss some of the issues at filming and developing as they each can change the look and feel of the final product, but we will concentrate most of our efforts on the actual scanning process and steps to ensure the best quality digital output.