GRO and GRB are image formats associated with a brand of calculators released by HP during the 1990s for advanced mathematical operations. The HP 48 and the HP 49 were both programmable and very popular among science professionals. At the moment, such files are considered uncommon and obsolete, so in case you found an old one on your computer it's probably best to convert it to a more popular extension.
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 GRO files as once.
JPEG JPG PNG GIF TIFF TIF BMP ICO EMF WMF AI PDF EPS PS EPI WEBP WEBPLL JP2 PCX TGA DWG DWF DXF DGN WMZ CGM DRW SHP GBR PCT MIF PLT PCL SVG WPG CIN DCX DIS HRU MTV PRC RAD PIC RLA QRT SGI XBM XPM SWF CAL FAX FITS PSD PGM JXR BPG APNG DDS SVGZ CG4 FLIF AVIF