An ST4 file represents a RAW image taken with an SBIG CCD camera. SBIG is a producer of astronomical instruments and ST4s most likely contain images related to some type of scientific or industrial application. They are considered rare and are probably difficult to open using regular image viewers.
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 ST4 files as once.
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