Optical scanning of a surface is a common operation performed in a variety of contexts. For example, there is often a need to create electronic data based on the appearance of a surface; optical scanning is a often crucial tool for fulfilling this need. One example of such scanning is reading of bar codes.
Numerous methods exist for reading bar codes. In various of these methods, it is necessary to control the speed with which a bar code is scanned. However, this can require complicated mechanisms (e.g., rotating mirrors), thereby increasing cost. If scanning speed is not controlled, it may be necessary to assume that a bar code is scanned at a constant rate. In such case, however, a bar coding scheme must be tolerant of variations in scanning rate (e.g., when scanned by a handheld scanner). In view of these and other issues, there remains a need for improvements in systems which can be used to scan a bar code.
Imaging is another area in which there is also need for improvements in scanning systems. One technique for creating images of a surface (e.g., a page of text or other information being scanned for digitization) requires moving an array of photosensitive elements relative to that surface. At multiple times during that movement, images are generated for portions of the surface from which the array can receive light. These portions (or “frames”) can then be combined to create an image of a larger area of the scanned surface. However, this combination requires knowing the proper relative positions of frames relative to preceding and/or succeeding frames. In many existing systems, this is achieved by correlating surface features common to overlapping portions of adjacent frames. When such surface features are absent or hard to detect, however, problems can occur.