Image Difference Extraction Technology

Comparing revised drawings with the older versions to quickly and accurately extract and identify changes is crucial in the checking process for drawings revised in the design and development work involved in manufacturing and construction. It takes much time for people to manually check revised drawings. There is also the risk of a checker possibly misreading or overlooking changes. Thus, a technology and a system that can automatically extract such differences have been in demand.

To address such challenges on customer worksites or at the management level, Fuji Xerox has developed image difference extraction technology (InkLifting® technology) that enables the extraction of differences in, for example, two hard-copy drawings scanned through multifunction devices.

When scanned images are simply compared before and after revision, positional shifts (e.g., shifts in parallel direction, rotation, magnification, reduction in size) occur in the images, and upon scanning some parts of the images become distorted by being stretched or shrunk. This often results in changes being mistakenly detected in an area where no changes were made. In order to prevent such image shifts, reference points are set within the images to be compared so that the amount of shift or skew can be calculated and corrected based on these points. The use of two images with such shift or skew correction enables the accurate extraction of any differences in the images.

Regarding reference points, there is also a way to add alignment marks to an original image for use in correcting any shifts. However, adding alignment marks to an original later is often difficult in many cases. Therefore, our technology incorporates a process that automatically extracts multiple reference points from images to be compared, in order to correct skew and positional shifts.

Fig. 1: Conventional Check of Drawings

Fig. 2: Image Difference Extraction System

The required time shown in Fig. 2 is based on our research. The required time refers to the total time taken by the checking process, including the time taken by customers to check the extraction result. The required time (5 to 10 minutes) is the sum of the time taken for image difference extraction and the time taken by the customer to check the result.