About Exception List
During image processing, PPP might find an error. Some of these errors are fatal, while some of them are just warnings. They all are called exceptions in PPP. An exception occurs if the processing parameters are ambiguous or wrong, or if there is a problem with the image being processed.
The image processor does not stop on each exception. It just adds the exceptions to a list called the Exception List. After all the image files are processed, you can investigate the errors in the Exception List. You cannot say that the job is finished until the Exception List is empty. Items in the Exception List mean that something went wrong that should be fixed.
The best case would be if you never met the Exception List. Unfortunately, it is unavoidable. If PPP was a super intelligent person, it would solve all kinds of errors alone. But PPP is a computer program, therefore it sometimes requires human help.
It might sound strange at first, but it's true -- if the Exception List is empty after processing hundreds of files, it means an error. The bad result is wrong. The good result is fine. But the flawless, excellent result is too good, which is also bad. If the Exception List is empty, the image processor did not find any problems, did not even suspect some images. This is because the quality checking is too loose. This is very dangerous, because bad images might also pass the loosely configured quality check. It is usually better to get one or two false alarms than letting bad images pass the quality check. The cost of the false alarm is usually much less than the missed alarm.
In this chapter, we will discuss the details of the Exception List. We will also suggest some methods to fix the problems.
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