This is a V-Ray application that is common across all V-Ray installations.
The VRImg to OpenEXR converter is both a command-line utility and a simple GUI application that can be used to convert .vrimg image files to .exr files in OpenEXR format. The .vrimg file format is a special format used by the V-Ray VFB to store the rendered image incrementally while rendering, in full floating-point format, with all available render elements. The V-Ray Image to EXR Converter converts .vrimg files to EXR format so the render elements may be loaded into compositing software, where they can be used for Back-to-Beauty compositing or for other adjustments and fine-tuning at the render element level.
This tool comes with the V-Ray for Houdini installation. You can start it from the shortcut in Windows Start > All Programs > Chaos Group > ..... or manually running it from its executable in the V-Ray bin folder in the Chaos Group folder where your applications are installed:
Windows: start the vrimg2exr executable from 
Linux: start the vrimg2exr executable from
Mac OS X: start the vrimg2exr executable from