What Are Jobs?
Jobs are very important in PPP. All document processing revolves around the job concept. Therefore you should understand what jobs are and how they work.
Consider the following situation. You have scanned a lot of images from a book, and you wish to process them with PPP. This is a job. PPP uses a job file to save everything about your job: the image files to be processed, the margins, the cleanup options, and other important parameters. A job file always reflects the current state of your job. First you will have an empty job. Then you will add your images to the Image Selection List. This list contains all the images that you want to process in the current job. Next, you set up the processing parameters. They are all part of the job file.
Chapter 4, Processing Jobs, gives you a good understanding of the operation of the image processor. For the time being, you only need to understand that there are several parameters, settings, and a list of images that are part of your job.
When you set up all the parameters, you will be ready to start processing your job. PPP will go through all the images and process them image by image. When all images are processed, you will get into the next phase in your job. It is possible that PPP will find some erroneous images that could not be processed. These errors are also a part of the job file. You can investigate the output images to decide if they meet the requirements. The information that PPP needs to display and investigate these images is also a part of the job.
PPP will automatically take care of the job handling for you. You must save the current job before you exit. This way you ensure that PPP will continue the job where you exited.
A job consists of adherent images; for example, images scanned from the same book. All images will use the same processing parameters. In this version of PPP, you cannot assign different processing options to the different images in the same job. However, odd and even images can be processed using slightly different parameters. But the set of the processing parameters always apply to the whole job, to all of the images in your job. If some of your images needs special handling, you must place them in a different job.
JOB and LOG File Generation
Job files have an extension of .JOB. Though they are simple text files, we discourage you to edit their contents on your own. A job file contains a lot of numbers and special codes generated by PPP. Changing these numbers might damage your job file, PPP, or even crash your operating system. Use PPP to save and load these JOB files.
The JOB files are usually not alone on your hard disk. Along with your JOB files you will also find LOG files. Though LOG files are separate files, they are also part of the jobs. LOG files are much easier to read than JOB files. LOG files are automatically generated when you process images. LOG files are like log books -- they contain a log entry for every single operation. PPP saves the date and time of the processing, the parameters, the image file name, and other data, from which other programs can extract a lot of information and make statistics.
A JOB file only contains the current state of the job. When you load a job, you load the JOB file. On the contrary, LOG files cannot be loaded by PPP. The LOG files contain almost everything about the life cycle of your job, including all the previous states of the job. Each state is time-stamped, so the date and time information can easily be extracted from the LOG file. LOG files are not for user editing either. You can read LOG files if you want to extract information from them, but it's not a good idea to edit the LOG files.
JOB and LOG files should be kept together. If you copy or move a JOB file, you should copy or move the LOG file as well. Though a JOB file contains all the necessary information alone, we do not recommend that you delete the LOG files. If you delete the LOG file, you will not be able to extract statistical data about your job, and you will not be able to check the previous states of your job.
Each JOB file is accompanied by two special files with an extension of .$c$ and .$i$. They are thumbnail image cache files that belong to the job. The purpose of the cache is to speed up the thumbnail image display. We are going to discuss thumb nails later in this manual. Right now you do not have to understand the thumbnail cache concept of PPP. It is enough to know that those two special files belong to the job. It is good to know that those files are not vital at all. It does not matter if you accidentally lose them. You do not have to backup .$c$ or .$i$ files. The .$c$ files might be extremely huge in some cases. If you run out of disk space, feel free to delete them. PPP is always able to regenerate both of these files, but it might take a lot of time.
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