XnConvert is a powerful and free cross-platform batch image processing software. Using the batch processing module of XnViewMP, it supports batch conversion, folder imports, filters, resizing, and several other advanced options. It is free to use.
With XnConvert, you can change over any of around 500 image formats to your decision of around 80 others. That means, it can probably convert the rare image format that you cannot open.
Check the complete list of supported formats: XnConvert Formats.
XnConvert is compatible with from Windows 2000 to Windows 10. It can also work with Mac and Linux operating system. On the download page, you can even get the protable option for windows 32-bit and 64-bit versions.
– Supports 500+ input formats & 80+ output formats
– Converts multiple images at once
– Customizable settings
– Compatible with Windows, Linux and macOS
– Portable option is available