TNL is an obsolete image format storing thumbnail images. It is considered rare and probably difficult to open using regular image viewers. Conversion to more popular formats might be the best way to access TNL files.
The quick and simple way to handle your files is to get a quality piece of software, such as reaConverter. This software is extremely efficient in managing a wide range of batch conversions. As you will soon realize, reaConverter will help you avoid spending countless hours trying to figure out how to convert multiple TNL files as once.
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