Convert bmp to gbr Online: bmp2gbr
You can use Tom's Editor to easily convert images from
Microsoft Windows bitmap .BMP to GIMP Brush
Tom's Editor is a free, online image manipulation and converter program.
Go to Tom's Editor
Format created by Microsoft for their Windows and OS/2 operating systems. Images can be compressed or not.
GBR are images that can be used as brushes in GIMP image editor.