SYN is an old and obsolete image format also known as Synthetic Universe. It is similar in size and features with the SYNU format, and might be equally difficult to open via regular image viewers. In case you found or were sent such a file, it's probably best to convert it to a more accessible format before trying to open it.
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 SYN files as once.
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