Several Apple apps including the basic Preview from Mac OS X can access icons from ICNS package and export the individual icons as normal images. Just make sure you export the icon of the file size you want and save it as EXR file.
Home > Search converters: icns to exr
Conversion of icns file format to exr file format beta
Search for icns to exr converter or software able to handle these file types.
Convert Apple icon graphic format to OpenEXR Image Format.
We have found one software suitable in our database for this conversion.
Articles and other information relating to icns into exr conversion:
How to get png or jpg icon from an app on Mac - Export icons from ICNS file format to PNG or JPG images on your Mac by using Finder and default OS X Preview app.
Apple macOS / Mac OS X software 
- convert icns to exr on OS X
Preview
Apple Preview is document and graphic viewer that is integral part of Mac OS X operating system. It can view and also export/convert the most common bitmap picture formats.
File extension | Convert | Open | Save | Edit | Create | Import | Export | Extract |
|---|---|---|---|---|---|---|---|---|
Convert from icns file | Yes, Preview supports icns file conversion as a source file type. | Yes | No | No | No | No | Yes | No |
to exr file | Yes, Preview supports exr file conversion as a target file type. | Yes | No | No | No | No | Yes | No |
The table with program actions contains information about what each program is capable of doing with their files. This may be a good pointer for further searches for certain file conversions and help you find the converter you are looking for if our search result is insufficient for you. However, it is far from perfect and may sometimes show results which are not really usable because of the nature of the software handles the files. So a conversion that appears as possible, just because of matched actions, may in fact not be possible.
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