From the Data Format and Mime Types main window, click the New button: 
The New Data Format dialog box appears.
Enter the name of the new format in the Data Format field.
Select the class of the item type from the Class list.
Select the Compression level. This is the level of compression to be used when getting item revisions that are assigned this data format. Choose between:
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No Compression.
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Fast Compression —This performs the compression quickly and using less memory but is the least compressed.
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Normal Compression—a normal degree of compression. This is a happy medium between Fast and Best.
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Best Compression—This is the slowest but gives the best compression.
data format.
Enter a valid MIME type in the MIME Type field.
Optionally, enter a description of the format in the Description field.
Click OK.